Film Critique of the Lower Extremity - Part 2


Anatomy and radiographic critique of the femur, knee, tibia, and fibula.

Author: Nicholas Joseph Jr. RT(R)(CT) B.S. M.S

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Instructions:

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Objectives

Upon completion, the reader should be able to:

  • Identify required anatomy of the femur, knee joint, tibia, and fibula on radiographs.
  • Discuss the anatomy of soft tissue structures of the knee, including the menisci, collateral ligaments, and cruciate ligaments.
  • Describe the structure of a diarthrodial joint, for example the knee joint.
  • State the proper positioning of the femur, knee, or leg for the AP, lateral, and other named radiographic projections.
  • Describe the use of the anode-heel effect when imaging the femur and tibia.
  • State why both joints are demonstrated when the femur or tibia/fibula is radiographed.
  • Tell why and how a proximal or distal joint is presented when the distal femur or proximal tibia is imaged.
  • Discuss why a grid is used when imaging the femur and knee and is not used when imaging the tibia/fibula and ankle.
  • Discuss what structures are in profile on various projections of the knee.
  • Discuss what structures are demonstrated on the various projections of the femur, knee, and tibia/fibula.
  • Discuss how to properly reposition the patient when radiographs of the femur, knee, or leg do not meet the diagnostic criteria.
  • State what adjustments are needed (e.g. kilovoltage, mAs, or use of grid) and what structures are demonstrated by a properly chosen exposure technique for the femur, knee, or leg.
  • Discuss the importance of including knee and ankle joints on the AP and lateral views of the leg.
  • Discuss the proper application of the anode-heel-effect when imaging the entire tibia/fibula.


Article Navigation:

Introduction

Anatomy of the Femur and Knee

Diagnostic Criteria for the AP and Lateral Knee Radiographs

Diagnostic Criteria Medial and Lateral Oblique Projections

Diagnostic Criteria for the Holmbald Projection

Diagnostic Criteria for the Merchant Projection

Diagnostic Criteria for Imaging the Tibia/Fibula-AP and Lateral Views

Summary Points

References

Test



Radiographic Film Critique of the Lower Extremity:

Part 2: Femur, Knee, and Tibia/Fibula

Written by Nicholas Joseph Jr. RT(R)(CT) B.S. M.S

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  • Film Critique is a visual learning tool that allows the radiographer to understand the diagnostic criteria for each view in a radiographic series. Film critique is where professional imaging standards move beyond the classroom and into the real life practice of radiographic imaging.
  • This is a reverse learning session. You will see poorly made radiographs and then learn what can be done to make better images in many difficult situations.
  • Before beginning this lesson you should be familiar with the anatomy of the lower extremity, the effects of radiographic exposure techniques (mA, kVp), and patient positioning.
  • The imaging professional must decide if a film is truly useful as a diagnostic tool before it reaches the watchful eye of the radiologist who will use it for interpretation. Knowing the diagnostic standard for each film is of paramount importance where the goal is the presentation of useful images.
Lower Extremity Film Critique
The purpose of this critique is to raise the technologist’s awareness of what radiologists and orthopedic physicians require when diagnosing and treating injury and disease involving the lower extremity. It is hoped that your examination of this treatise will result in your production of better radiographs.

  • This lesson is organized so that images are presented and then critiqued so as to promote effective learning. Each subject matter should take about 10 minutes.
  • Upon completion, you may take brief exam which presents questions on a sampling of images.
Glossary of terms:
  • Overexposure (too much mAs)
  • Underexposure (too little mAs)
  • Overpenetrated (too much kVp)
  • Underpenetrated (too little kVp)
  • Positioning error (patient position)
  • Tube error (improper tube angle)

Introduction

The femur is the longest and strongest bone in the body. Its main function is to transmit weight-bearing forces from the pelvis to the leg, then to the foot where it is disseminated to the ground. Strong muscles on its anterior and posterior surfaces move the extremity and afford mobility. The femur articulates with the pelvis proximally and with the tibia distally. Although it is a strong bone, it is frequently fractured at the hip, and also at the knee. Annually more than 352,000 hip fractures occur in the United States, 90% result from fall injuries. By year 2050 it is estimated that we will see some 650,000 hip fractures annually. Women over the age of 50 years are 2 to 3 times more likely to suffer hip fractures than men.

It is fairly common for the hip and knee joints to suffer chronic degeneration due to osteoarthritis. Annually in the United States about 5 million orthopedic visits occur for knee problems that range from bone injury to ligament injury. Therapeutic treatment including physical therapy and exercise is used to reduce morbidity. For many, prosthetic hip and knee replacements procedures are performed worldwide. The incidence (annual) of total hip replacement in the United States is 120,000 individuals (NIAMS). This gives an incidence rate of approximately 1 in 2,266 or 0.04% of the United States population. Total arthroplasty offers relief for many suffers of joint disease or pain; however, there is a significant incidence of morbidity associated with these procedures. For example, 25 percent of hip fracture patients make a full recovery, while 40 percent require nursing home care. Half of hip fracture patients require a walker or cane for long-term mobility support. Being over age 50 at the time of hip fracture carries a high morbidity and mortality; nearly 24 percent will die within 12 months. Because of complications and lengthy recovery associated with hip fracture the cost per incident averages about $27,000 per patient. In addition, about 5 million orthopedic visits occur in the United States annually because of knee problems. Of these nearly 1.4 million are due to emergency room visits alone. In 1994 hospitals reported about 50,000 repairs of the anterior or cruciate ligaments. Unequivocally, more total knee replacements are performed than replacement of any other joint.

Radiographic imaging of the hip is performed both before and after hip surgery. The standard radiographic examination of the femur consists of an AP and lateral view. Standard radiographic views of the knee include the AP and lateral views. Less frequently both medial and lateral oblique projections, the axial projection of the patella, and tibia plateau projection is requested. Most injuries of the knee are ligamentous and may require magnetic resonance imaging to diagnose; however, with good radiographic plain film imaging even subtle injury can be demonstrated. Soft tissue is very important to diagnosing injuries on plain films. For example, an anteriorly distended knee joint capsule with displacement of the patella may indicate hemarthrosis. Unilateral widening of the knee joint space could indicate an unstable ligament injury. A small avulsion fracture could indicate ligament damage and the need for further imaging. So our goal is to discuss the diagnostic criteria for imaging the femur and knee so that accurate diagnosis is possible.

Anatomy of the Femur and Knee

The femur extends from the hip joint to the knee joint. The femoral head fits snugly into the acetabulum forming the hip joint, and its massive condyles articulate with the tibia distally. It contains two extremities (ends), and the shaft, or body. The proximal portion of the femur has the expanded head, neck, and greater and lesser trochanters. These structures have been previously described with the hip joint. The distal femur, which we will discuss shortly, articulates with the tibia and patella to form joints of the knee. The hip joint is a diarthroses, or synovial joint. It is normally capable of flexion, extension, abduction, adduction, circumduction, and internal and external rotation.

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These two CT 3-D volume rendered images of the femur show it from the anterior view (Ant) and posterior aspects (Post). The proximal portion of the femur was discussed in part 1. The shaft (A), distal femur (D) and the femoral artery (B) are also labeled.

We will only discuss briefly the proximal femur since it was discussed in part 1 in association with the hip joint. Briefly, the proximal femur has a large expanded head that fits into the deep socket of the hip bone called the acetabulum. A shallow pit, called the fovea capitis femoris is located in the lower center of the femoral head. The fovea capitis femoris is the point of attachment for the ligamentum teres, which attaches the femur to the acetabulum. The head is connected to the shaft by a short stretch of bone called the neck that joins the head and body at an angle of about 125 degrees. The neck of the femur terminates laterally at the greater trochanter. The femoral neck is an important anatomical and radiographic structure because it is frequently fractured, especially in older persons. The greater trochanter is a large lateral prominence that lies close to the surface and can be palpated. Its superior portion is at the level of the hip joint; locating it is an alternative way to find and position the hip joint. The lesser trochanter bulges slightly from the posteromedial aspect of the proximal femur. It serves as an attachment for the psoas muscle seen in the abdominal cavity. A prominent ridge of bone called the intertrochanteric crest connects the greater and lesser trochanters posteriorly. The femur has several structures that serve as attachments for muscles.


These two CT images demonstrate the proximal femur as seen from the anterior (Ant) and posterior (Post) aspects. Labeled are the head of the femur (A), greater trochanter (B), lesser trochanter (C), intertrochanteric crest (D), and femoral neck (E).

The knee is composed of four bones, the femur, tibia, fibula, and patella. The knee joint is a hinge-type joint, which is capable of flexion and extension motions. Flexion and extension are not the only motions of the knee, in the last 50 years it has been discovered that the knee performs slight rotational movement. It is this rotational component that accounts for the frequency of knee injuries. The distal femur articulates with the tibia and the patella. The distal femur is broadly adapted for articulation with the tibia. The articulation with the tibia is through its large prominent condyles that project posteriorly. A large intercondylar notch seen posteriorly separates the medial and lateral condyles of the femur. On the anterior surface the condyles are separated by a slight groove called the patellar surface over which the patella (kneecap) glides during flexion and extension of the knee joint. The patella is a sesamoid bone developed within the tendon of the quadriceps femoris tendon. The patella is triangular shaped having a broad base and an inferiorly pointed apex. The articular surfaces on the posterior aspect of the patella articulate with the medial and lateral condyles of the femur. The two primary functions of the patella are to strengthen the tendon of the quadriceps femoris muscle, and to protect the knee joint. The patella strengthens the quadriceps muscle by increasing its leverage as it extends (straightens) the knee joint. Essentially, the role of the patella is to aid in changing the direction of forces from the quadriceps muscle as they pass through the knee joint and are applied to the tibia.

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These anterior views of the distal femur show the patella (E) in its anatomical position over the patellar surface (G). The patellar surface is located between the condyles on the anterior surface. The base of the patella is superiorly directed and the apex directed inferiorly. Just above the condydyles are the medial epicondyle (A), and lateral epicondyle (B). The medial condyle (C) and lateral condyle (D) are located on the medial and lateral surface of the distal femur, respectively. A portion of the shaft of the femur (F) is shown. A concave patellar surface on the distal femur (G) articulates with the patella. The shaft is slightly bowed medially to bring the knee in line with the body’s center of gravity.
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The patella is the largest sesamoid bone in the body. Its posterior surface presents medial and lateral articular surfaces that articulate with the medial and lateral condyles of the femur. The apex (A) is directed downward and the patellar base (B) is directed upward. The anterior surface is scored with openings for blood vessels and nerves to penetrate and supply nutrients. The patella is sometimes fractured by direct blow and only rarely does it fragment. It more often dislocates than fracture and can present as a congenital dislocation due to underdevelopment of the lateral condyle of the femur.
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These views of the distal femur show the major bone structures on the posterior aspect. Demonstrated on the 3D CT image on the left) are the popliteal surface (A), lateral epicondyle (B), medial epicondyle (C), lateral condyle (D), medial condyle (E), and intercondylar notch (In). The radiograph on the right also shows these structures; however, only the lateral epicondyle (B), medial epicondyle (C), medial condyle (E), and intercondylar notch (In) are labeled.

Proximal Tibia and Fibula

The tibia (shinbone) receives the weight of the body through its articulation at the knee joint with the femur. At its distal end it articulates with the talus to distribute weight to the ankle and foot. The proximal tibia has two concave surfaces, the medial and lateral condyles, which articulate with the femoral condyles. Between the condyles is an upward projection called the intercondylar eminence. On the proximoanterior portion of the shaft is the patellar ligament, which is the tendon of the quadriceps femoris tendon, and attaches the patella to the tibial tuberosity.

An important feature of the proximal tibia is its bone composition. For example, the bone structure of the tibial plateau is cancellous bone, as opposed to the bone structure of the tibial shaft, which is cortical bone. What this means to its structure when injured is that cancellous bone often becomes compressed and remains depressed. Compression of the tibial plateau often results from high impact injury, like a motor vehicle crash in younger persons. Older individuals can suffer tibial plateau injury from low impact trauma such as a fall from a short height, or even from a standing position because the bone may be softer (osteoporosis) in this population.

The fibula is a long, relatively slender bone that provides attachment for muscles of the knee. It does not have a weight-bearing role at the knee joint. The proximal tibia has on its lateral end just below the lateral epicondyle, a flattened smooth surface called the fibular articular facet where the head of the fibula articulates. The proximal fibula has a complimentary facet for articulating with the tibia, called the tibial articular facet. The neck of the fibula is just distal to the head and articular facet.

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This 3D volume rendered CT image shows the femur removed from the knee articulation to show the superior surface of the tibia. The lateral tibial condyle (A) presents the lateral tibial plateau (B), the medial intercondylar eminence (C), lateral tibial plateau (D), and tibial tuberosity (F) are demonstrated. Other structures shown in their anatomical relationship are the patella (E) and the femoral artery (G). The composition of the proximal tibia, the plateau, is cancellous bone. Trabecular cancellous bone can be seen in this image as darker composition against the cortical bone just inferior to it.

Injury to the knee is not limited to bone only, soft tissues can also be injured, and structures within the knee joint too. Soft tissue injury can manifest as swelling about the knee, inability to bear weight, loss of function such as bending or straightening of the joint, or other clinical indicators. Radiographically, soft tissue surrounding the knee must be demonstrated when imaging for trauma. Fractures that involve the upper fourth of the tibia, may or may not involve the knee joint, and may be limited to ligaments supporting the joint. Fractures that enter the knee joint often render the joint defective and the once smooth joint surface made irregular. Additionally, fractures resulting in improper limb alignment may contribute to long-term morbidity like arthritis, instability, and functional loss of motion. Consider that the knee joint is the largest weight-bearing joint of the body. For many years anatomist classified it as a simple hinge joint however, its motions are more complex occurring in several planes. Complex motions of the knee joint render the stability of the joint dependent on soft tissues (muscles and ligaments), and on the alignment of the joint surfaces that oppose each other. The proximal fibula also contributes to lateral stability of the knee joint by providing supportive attachment for the lateral collateral ligament of the knee. Ligaments within the knee joint also support the knee. These ligaments may be injured with trauma sparing bone. Therefore, it is important that the radiographer understand the basic soft tissues of the knee and their relationships to knee stability.

The stabilizing ligaments of the knee include the medial collateral ligament (MCL) and lateral collateral ligament (LCL), and are located outside the knee joint proper; the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are stabilizer ligaments located within the knee joint. The patellar ligament is located outside the knee joint; it also provides support for the knee by shielding it, and strengthening the actions of the quadriceps femoris muscle. Because the patella is integrated into the extensor knee apparatus it contains both passive and active elements. The patellar ligament is one of the passive elements of the knee. It originates at the apex of the patella and extends to the tibial tuberosity. The role of the patellar ligament is to limit proximal patellar ascent.

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This schematic drawing of the knee in a slightly bent position demonstrates some of the soft tissue structures of the knee joint. The patella (B) is shown suspended in the tendon of the quadriceps femoris muscle (A) and attached to the tibial tuberosity by the patellar ligament (C). The articular surface of the femoral condyle (D) will articulate on the tibia through shock absorbing cushions called the meniscus. The knee joint is stabilized by internal ligaments like the anterior cruciate (E) and externally by the lateral collateral ligament (F), and other structures not labeled on this drawing.

The space between the condyles of the femur and the tibial plateaus is small. This space contains the menisci, articular cartilage, and the anterior and posterior cruciate ligaments. The bent knee drawing above is exaggerated to demonstrate these important structures within this space. The knee contains two semi-lunar C-shaped menisci composed of fibrocartilage. The two menisci lie on the tibial plateaus along the lateral peripheries of the joint. The function of the meniscus is to provide shock absorption to the knee during the stress of weight-bearing and movement. The youthful healthy meniscus is only partially supplied with blood and is stronger than older cartilage. With age the meniscus deteriorates and can easily tear. A damaged torn meniscus can seed torn pieces into the joint (meniscal fragment) causing pain, swelling, and loss of function. The reason meniscal fragments are released is that the majority of the meniscus has no blood supply and does not properly heal when damaged. Instead, deteriorated portions of the meniscus tend to tear off and enter the joint space between the bones. A surgical procedure called arthroscopic surgery may be indicated to remove some types meniscal fragments or flaps.

Other soft tissue structures that are critical to proper knee function include the medial collateral ligament (MCL), lateral collateral ligament (LCL), anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), articular cartilage, joint capsule and synovial fluid, and bursa. The collateral ligaments resist widening of the knee joint. The cruciate ligaments, which are within the knee joint proper, resist hyperflexion and hyper extension and also slight rotational movements of the knee. Articular cartilage is bathed by synovial fluid that lubricates the knee joint.

There are two collateral ligaments of the knee, the medial collateral ligament (MCL) and lateral collateral ligament (LCL). The MCL spans from the medial femoral condyle to the top of the lateral tibia (shin bone) and had multidirectional fibers on the inside of the knee joint too. The medial collateral ligament resists medial widening of the joint that would “open-up” the knee. The LCL spans from the lateral condyle of the femur to the lateral portions of the fibula. Its main function is to resist lateral widening of the knee joint.

The anterior and posterior cruciate ligaments are located within the center of the knee joint. The PCL originates in a fan-shaped fashion from the anterolateral aspect of the medial femoral condyle near the intercondylar notch. It courses posteroinferomedially to insert on the backside of the tibial plateau. It functions to reduce internal rotational movements of the knee, and to prevent the tibia from sliding backwards on the femur. In other words, the PCL prevents hyperflexion of the knee joint. The ACL arises from the posterior part of the medial surface of the lateral condyle and courses anteroinferiorly and medially to the anterior plateau just posterior to a rather prominent synovial fold. It then inserts in a fossa in front of and lateral to the anterior intercondylar eminence of the tibia. It should be noted that the ACL lies within an intra-articular compartment of the knee joint, but is extrasynovial. The functions of the anterior cruciate ligament are to resist rotational motion of the knee and prevent the femur from translating backwards on the tibia. In other words, it limits hyperflexion of the knee joint. The most common mechanism of ACL injury is internal rotation of the femur when the knee is in full extension. A damaged ACL or PCL will result in instability of the knee when the foot is planted causing the knee to give way or to buckle.

Synovial joints are found where there is extensive movement of bone on bone such as the femur and tibia of the knee. Synovial joints are also classified as diarthroses, or freely movable joints. At the point of bone articulation there is a thin covering of hyaline cartilage covering the ends of bone called articular cartilage. This cartilage is maintained in apposition by ligaments of the knee and the surrounding joint capsule. Articular cartilage of the knee is found on the articular surfaces of the femur, tibia, and underside of the patella. Articular cartilage is void of blood vessels (avascular) and depends on diffusion of nutrients from synovial fluid that bathes it. The capsule of the knee joint is a sac that encloses the joint cavity. It is perhaps better thought of as a cavity rather a simple membrane. It completely surrounds the knee joint having compartments that surround the patella and the knee joint. The capsule is firmly attached to bone and is composed of a tough fibrous outer membrane and an inner synovial membrane. It is the inner layer of the synovial membrane that produces synovial fluid that bathes structures within the knee joint proper. Four bursa are found in the knee are found near tendons to provide smoothening of motions of their muscles. Like all bursa those of the knee are also subject to inflammation (bursitis) and to inflammatory reaction from trauma.

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These two drawings demonstrate the soft tissue cartilage and tendons of the internal knee joint. The lateral collateral ligament (A) is located outside of the knee joint proper. Within the knee joint is the lateral meniscus (B), and medial meniscus (F), which act as a shock absorbers for the knee joint during weight-bearing. The anterior cruciate ligament (C) and posterior cruciate ligament (D) cross in the center of the knee joint. Their functions include stabilizing the rotational motions of the knee joint and limiting hyperflexion and hyperextension of the knee.
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This MRI image shows important details of the structure of the knee. Although all parts are not labeled the articular cartilage (A), lateral meniscus (B), and medial meniscus (C), are labeled. These structures are not seen on plain films of the knee; however, bone alignment and opened femorotibial joints are a must see on plain films. Information about the cruciate ligaments and meniscus can sometimes be inferred from accurately positioned plain film x-rays.
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This coronal thick slab MRI image shows a portion of the knee through the menisci. The right and left menisci (arrows) are shown magnified to give a better look at their structure. The meniscus serves as a shock absorber type cushion between the femoral condyles and the tibial plateau. Notice the oblique linear tear in the posterior horn of the medial meniscus (R). A thick articular cartilage covers the condyles of the femurs and tibia.
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This sagittal thick slab section through the knee shows the posterior horn of the meniscus. Notice the meniscal tear of the posterior horn extending to the junction with the body of the meniscus. This oblique linear meniscal tear extends inferiorly to the articular surface as well.
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This sagittal MRI image shows the patella (A), patella ligament and infrapatellar fat pad (B), epiphysis (C), articular cartilage of femur (E), synovial fluid in synovial capsule (D), and the lateral meniscus (arrow). While these soft tissues are not seen on plain films of the knee, demonstrating soft tissue can indicate injury to these tissues when the radiographic exposure technique is optimal.
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These two reformatted sagittal CT views of the knee demonstrate the anterior cruciate ligament (white arrow) and posterior cruciate ligament (blue arrow). The cruciate ligaments are better seen with MRI; however CT can be useful for those patients who cannot undergo MRI. To adequately demonstrate ligaments within the knee joint with CT, a double contrast arthrogram is performed. Radiopaque contrast material is seen within the patellofemoral joint compartment on this sagittal image. Administering single or double contrast agents into the joint capsule allows us to see it on an x-ray.
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This sagittal MRI image demonstrates the relationships of various structures of the knee. The distal femur (F), proximal tibia (T), and patella (P) form the knee joint. Ligaments support and stabilize the knee joint, which has a relatively weak bone structure. The MRI image on the right magnifies the area showing the cruciate ligaments. Seen on the magnified image is the anterior cruciate ligament (yellow arrow) and posterior cruciate ligament (blue arrow), which are within the knee joint proper. Notice their crossing pattern from which they get the name cruciate.
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These three CT arthrogram images demonstrate the synovial capsule of the knee. Left is the sagittal image that shows the extensive architecture of the capsule, especially the patellofemoral compartment. The middle axial image also shows the patellar femoral compartment. The right image shows the distal femur near the articular surface that is enclosed by the capsule. Although the capsule like other soft tissue structures of the knee are not fully appreciated on plain films these images are presented to help the radiographer appreciate the complexity of the knee. Many inferences can be made from plain films when properly positioned and the correct radiographic exposure made.

Plain Film Imaging of the Femur and Knee

Now that we have discussed the anatomy of the femur and knee we should turn our attention to radiographic imaging of these structures. The knee is probably more commonly injured than any other joint in the body. It is highly susceptible to injury considering its design and ubiquity of athletic sporting. The injury dilemma is that sometimes a normal appearing radiographic examination does not exclude ligament injury. Likewise, there may be extensive soft tissue swelling that does not include clear radiographic sign of an underlying injury. Therefore, it is imperative that good radiographs are presented for diagnosis because these dilemmas exist. Proper anatomical positioning of the part and radiographic exposure criteria must always be met.

The entire femur is often requested when trauma has occurred and mid-shaft injury or fracture is suspected. A minimum of two radiographs at ninety-degrees to each other are always taken of the femur. The standard radiographic views of the knee may include the anteroposterior, lateral, medial oblique, and lateral oblique. Often when only the proximal femur is the subject of interest the affected hip is requested. Likewise, when the distal femur is the subject of interest the affected knee is requested. When either the proximal or distal femur is the subject the adjacent joint must be entirely included. For example, if the proximal femur is the subject of examination, then the hip joint must be entirely included.


Diagnostic Criteria for imaging the distal Femur-AP Projection
  • When a request for a femur is made the entire femur including both the hip joint and knee joint must be included on the radiograph. If the femur cannot be demonstrated on a single film then two projections with overlapping parts should be taken. Always include all soft tissues of the thigh when the femur is being imaged. This means the skin line of soft tissues should be seen.
  • Proper positioning of the femur for the AP projection involves placing the condyles of the femur parallel to the image receptor. The lateral should place the superimposed femoral condyles perpendicular to the image receptor.
  • The proximal femur should display the greater trochanter in profile laterally, the lesser trochanter medially, and the femoral neck in profile without foreshortening.
  • The distal femur should display symmetry of the epicondyles with the femoral condyles in profile. The intercondylar eminence of the tibia is seen within the intercondylar fossa of the femur. The medial and lateral femoraltibial joint is demonstrated open with good spacing between the femur and tibia.
  • Optimal exposure to penetrate the femur when a grid or reciprocating bucky is used is between 70-80 kVp for film-screen imaging, and 75-85 kVp for digital radiography. It is also recommended that the knee be placed over the anode and the hip over the cathode to take advantage of the anode-heel effect. Good penetration of bone yet maintaining soft tissue detail is the goal when selecting radiographic exposure.


Diagnostic Criteria for imaging the distal Femur-Lateral Projection
  • When a request for the femur is made the entire femur including both the hip joint and knee joint must be included on the lateral view. If the femur cannot be demonstrated on a single film then two projections with overlapping parts should be taken. Always include all soft tissues of the thigh including the skin on the lateral view.
  • Proper positioning of the femur for the lateral projection involves superimposing the condyles and aligning them perpendicular to the image receptor. The femur is rotated onto the lateral side routinely; however, a horizontal beam lateral technique is used when a fracture is suspected.
  • The anterior and posterior surfaces of the femoral condyles are superimposed and aligned, and the fibula is slightly superimposed by the posterior tibia.
  • The distal femur should display symmetry of the epicondyles with the femoral condyles in profile. The intercondylar eminence of the tibia is seen within the intercondylar fossa of the femur. The medial and lateral femorotibial joint is demonstrated open with good spacing between the femur and tibia.
  • Optimal exposure to penetrate the femur when a grid or reciprocating bucky is used is between 70-80 kVp for film-screen imaging, and 75-85 kVp for digital radiography. It is also recommended that the knee be placed over the anode and the hip over the cathode to take advantage of the anode-heel effect. Aligning the long axis of the femur with the long axis of the image receptor will allow for good collimation of the field. Good penetration of bone yet maintaining soft tissue detail is the goal when selecting radiographic exposure.

Positioning of the knee for the AP projection is obtained with the patient supine or erect, so that the knee is extended and the leg internally rotated. A point for point line passing through the femoral condyles placing them equidistant from the tabletop eliminates rotation. Also, the central ray should pass through the knee just inferior to the apex of the patella to demonstrate the medial and lateral compartments of the femorotibial joint space without rotation. The tibial plateau, medial and lateral intercondylar eminences, and intercondylar notch are all clearly demonstrated. The AP projection poorly demonstrates the patella superimposed on the femur; however, including the lateral and tangential views when needed makes up for this. An “open-joint” view, sometimes called the “tunnel view,” may be requested when optimum visualization of the intercondylar eminences and intercondylar notch is needed. Additional imaging procedures may be indicated following plain film imaging that may include CT and MRI of the knee. By properly limiting the field of view when imaging the femur or knee, the patient dose can be reduced, which is in keeping with the as-low-as-reasonably-achievable (ALARA) mandate.


Diagnostic Criteria for the AP Knee Projection
  • The supine view is good for identifying fractures/dislocations. Standing views may be requested for pre-prosthetic evaluation, or to evaluate functional loss due to arthritic joint erosion.
  • For the AP view the condyles of the femur are parallel to the image receptor. The CR should pass through the knee joint just below the patellar apex at an angle of about 5 degrees cephalic. The CR should enter the part parallel with the tibial plateau to demonstrate the femorotibial joint space open and the anterior and posterior margins of the tibial condyles superimposed. The fibular head is seen about 1 cm (0.5 inch) distal to the tibial plateau. On a well-positioned AP view the femorotibial joint is centered on the radiograph; it can be found about 2 cm below the palpable medial epicondyle, or at the apex of the patella.
  • The AP view demonstrates about one-fourth of the distal femur and one-fourth of the proximal tibia, and all surrounding soft tissue within in a well-collimated field. When properly positioned the AP view will demonstrate the epicondyles in profile and the intercondylar eminence of the tibia centered within the intercondylar fossa of the femur. The proximal tibia will slightly superimpose the proximal fibula, and the patella seen slightly above the patellar fossa and slightly lateral to midline. When imaging a prosthetic device, such as knee prosthesis, the entire device must be seen on a single radiograph of each view. The joint space between adjacent components of the prosthesis must be demonstrated just as with bone anatomy.
  • The knee can be optimally penetrated using 60-70 kVp without a grid. However, a grid should be used if the knee measures 14 or more centimeters in the AP direction. When using a grid, 70-80 kVp is recommended. Sufficient exposure will penetrate the bones of the knee with good visualize soft tissue in and around the femorotibial joint, and the patella through the distal femur.

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This radiograph demonstrates the structures seen on the AP knee radiograph when properly positioned and the correct exposure technique used. Structures labeled on are: the femur (A), patella (K), lateral epicondyle (B), femorotibial joint (C), fibular head (D), fibular neck (E), tibia (F), lateral intercondylar eminence (G), medial intercondylar eminence and medial tibia plateau (H), medial femoral condyle (I), medial femoral epicondyle (J), patellar surface of femur (arrow). Notice that the femorotibial joint is open and the intercondylar eminence of the tibia is seen between the femoral condyles.

Before performing the lateral projection the technologist should evaluate the patient to determine the correct method for accomplishing this projection. The lateral projection of the knee is routinely taken with the patient in the recumbent lateral position and the x-ray beam directed vertically. When the patient history includes trauma with swelling of the knee or pain suggestive of a fracture the patient is positioned supine and the beam directed horizontal to the long axis of the femur and tibia. It is important in either case that the knee is in a true lateral with the condyles of the femur superimposed and not rotated. Proper positioning of the knee for the lateral projection is very important in order for pathological relationships to be differentiated. For example, significant joint effusion causes the patella to be displaced anteriorly and canted inferiorly as the joint capsule distends. Joint effusion can manifest itself as a slight displacement of the patella. In order to appreciate the extent of a joint effusion the knee should be positioned in a true lateral. Equally important is using an optimal radiographic exposure technique. Good bone penetration is necessary to identify the character of fractures. Soft tissue visualization is also important in that signs of injury are often seen in these tissues. For example, a pneumohemarthrosis may show air in the joint with the right radiographic exposure. Air-fluid level follows the contour of blood within the joint due to air being lucent. Air-fluid level can be seen with the horizontal beam lateral view when present. An avulsion type fracture of the tibial spine or femoral condyles or tibial tuberosity may indicate ligamentous injury. Although most injuries of the knee are ligamentous and radiological findings absent or subtle even when present, radiographs are essential.

Keep in mind that injuries such as fracture or dislocation of the knee joint are orthopedic emergencies and require optimal radiographic imaging. Consider that anterior dislocation of the knee causes popliteal artery injury in approximately 40% of these patients. Peroneal nerve injury is seen in about one-third of patients with anterior dislocation of the knee. This is usually manifested by foot-drop or weakness on dorsiflexion of the foot, an observation that mandates performing the horizontal beam lateral knee projection. Longitudinal traction is often applied to the lower limb to reduce the dislocation. In such case it is advisable to perform the AP and lateral views in traction unless the orthopedic physician is available to remove traction during radiological imaging. So, let’s review what should be demonstrated on the lateral view of the knee and how we know when the lateral view meets the diagnostic criteria.

The lateral view should include the distal one-fourth of the femur and proximal one-forth of the tibia/fibula. All surrounding soft tissue must be entirely demonstrated. Keep in mind that joint effusion is best diagnosed when the knee is flexed no more than 20 degrees. This is because flexing the knee more than 20-degrees causes tightening of the muscles/tendons across the knee joint and patella resulting in the patella to obscure the fat pads. The anterior and posterior suprapatellar fat pads must be visualized to evaluate joint effusion. Positioning the knee in a true lateral by aligning the tibia on the same plane parallel with the tabletop is crucial. Angling the central ray 5 to 7 degrees cephalic will project the medial condyle proximally and slightly anterior in alignment with the lateral condyle. This angle is reduced for tall thin patients having a long femur. The medial condyle is further from the image receptor for the mediolateral knee projection, which causes it to be shifted more than the lateral condyle with cephalic angulation. The radiographic exposure should demonstrate good bone penetration, yet good soft tissue detail seen. The fibula should be seen through the superimposed tibia. A grid should be used if the knee measures more than 5 cm in the mediolateral plane. Close collimation to enhance detail should be applied; however, all soft tissue of the knee should be demonstrated.


Diagnostic Criteria for the Lateral Knee Projection
  • For the lateral view the condyles are superimposed by placing the tibia on the same plane as the femur. The condyles of the femur are placed perpendicular to the tabletop as an imaginary line is drawn through the epicondyles. The knee is flexed 20-30 degrees unless a patella fracture is suspected. Decrease the amount of knee flexion to no more than 20 degrees when joint effusion is suspected. The patellofemoral and knee joints should be seen with a space between their articulations.
  • On an accurately positioned radiograph the femorotibial joint is centered and well collimated. All soft tissues surrounding the bones and joints must be demonstrated. If a prosthetic device is present the entire device must be seen on the lateral view. The joint spaces must be demonstrated opened as with bone anatomy.
  • Radiographic technique should allow for visualization of soft tissue structures such as blood effusion or air within the joint or its capsule. A grid should be used for the lateral projection if the mediolateral diameter measures 5 cm or more.

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This lateral view of the right knee displays optimal positioning and exposure for visualizing bone and soft tissues. The femoral condyles are superimposed as are the tibial condyles. There is no rotation of the part so that the anterior and posterior borders are superimposed. The patella is demonstrated in a true lateral with the knee slightly flexed. The exposure technique demonstrated excellent bone penetration while preserving contrast in the soft tissues. The patellar ligament is well defined as is the fluid capsule surrounding the knee.
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This radiograph demonstrates the importance of radiographic exposure technique. Notice the good bone penetration throughout the distal femur and tibia. Soft tissues of the knee are demonstrated in good contrast to bone and air is seen in the joint capsule. Labeled on the radiograph on the right is the apex of the patella (A), which is distal and the tibial tuberosity on the anterior surface of the tibia (B).

Now let’s review some images of the distal femur and knee for critique.

Radiograph #60

image060 This is a follow-up radiograph of the lower femur to check postoperative bone alignment and fixation. Consider that this radiograph was taken with a mobile x-ray machine in the recovery room. Patient history: “post-surgical evaluation of ORIF and alignment of bone fragments.” Does this radiograph meet the diagnostic criteria for imaging the distal femur?

Critique of Radiograph #60

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    The anatomy in question is not entirely demonstrated on this radiograph. Although the entire femur is not required, the entire fixation apparatus must be demonstrated. Including the entire area under evaluation, proper positioning of the part and good exposure technique are critical factor for diagnosis. The presentation of the anatomy seen here is acceptable under the circumstances; however, it should be mentioned that the femoral condyles are not superimposed. They are obviously rotated, specifically; the medial condyle is posterior to the lateral condyle. To correct rotation seen here the patella should be rotated away from the image receptor to align the condyles. Also, the femur is grossly underpenetrated. The patella and soft tissues are “burned out” indicating mAs is too high. Several slits in the fixation device are under-penetrated. To correct the displayed exposure, increase the kVp and decrease the mAs using the 50/15 rule. This projection should be repeated correcting the exposure and properly aligning the distal femoral condyles.

Radiograph #61

image061 This radiograph was taken on a patient who presented to the emergency room by ambulance with suspected fracture of the femur. This is part of a two-film series that imaged the entire femur. Consider the proximal femur was properly demonstrated. Under what stipulation does this radiograph meet the diagnostic criteria for the AP projection of the femur?

Critique of Radiograph #61

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    This is a good radiograph of the distal femur that meets the diagnostic criteria for the AP projection. The stipulation is that this is an acceptable view when the proximal femur view provides anatomical overlap. It is recommend that a full 14 X 17 cassette be used since it will give you enough room to include all soft tissues of the thigh. Because a 7 X 17 cassette was used the identification blocker near the proximal femur obscures soft tissue. Remember, all soft tissue out to the skin line must be seen because in some cases foreign bodies or indications of an open fracture are seen. As for the radiographic exposure technique, this radiograph demonstrates good bone penetration; however, bone detail is diminished because of motion artifact. Using sand bags to stabilize the leg, or taping the part along with using a shorter exposure time will reduce the likelihood of patient motion. This radiograph does not need to be repeated.

Radiograph #62

image062 Consider this radiograph of a patient who presented to the radiology department with a clinical history of chronic mid-shaft pain. The orthopedic physician requested an evaluation of the entire femur. Does this single radiograph meet the diagnostic criteria for the lateral projection of the femur?

Critique of Radiograph #62

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    There is considerable motion artifact seen on this radiograph, which has degraded subject detail. The amount of motion artifact is significant enough to warrant repeating of this film. To properly demonstrate the femur two-views is needed, one of the proximal femur and a second overlapping view to include the distal femur. Careful positioning of each extremity of the femur is a must when two images of the same projection are needed. Slight rotation of the knee is seen so that the knee is not shown in a true lateral. To get a true lateral, slightly flex the knee joint and make sure that an imaginary line connecting the epicondyles is perpendicular to the tabletop. This will align the anterior and posterior surfaces of the femoral condyles. It will also present the correct amount of space between the patella and the femur to demonstrate the patellofemoral joint.

Radiograph #63

image063 Consider this radiograph of a patient who presented to a local emergency room by ambulance. Chief complaint is extreme pain after a motor vehicle/pedestrian accident. The orthopedic physician requested an evaluation of the entire femur. Does this radiograph meet the diagnostic criteria for the lateral projection of the femur?

Critique of Radiograph #63

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    This radiograph does not meet the diagnostic criteria for imaging the femur. The main reason this radiograph must be repeated is that neither the proximal nor distal joints of the femur are demonstrated. This is an example of what not to do when imaging the femur. When imaging the femur and it cannot be entirely demonstrated on a 14 X 17 inch cassette, then you must include at least one joint of either bone extremity. Making a radiograph of the femur demonstrating the shaft without an extremity is a cardinal imaging “no, no.” This view must be repeated to include at least one joint either proximally or distally. A second film to include the remote joint must also be made. It is important that both radiographs include the entire fracture site and partial overlap of anatomy. This will assure accurate anatomical referencing.

Radiograph #64

image064 Give your critique of this AP knee radiograph taken on a patient 32 years age that presented with a clinical history of “knee pain” and no history of trauma.

Critique of Radiograph #64

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    This is a good AP view of the knee. The joint space of the knee is not presented opened. Because the fibular head is more than 1 cm below the tibial plateau and proper overlapped by the tibia the closed joint space is due primarily to the angle of the CR used. The correct amount of cephalic angulation is 5-7 degrees. Another cause of a closed joint is that the femur and tibia are not on the same plane. Placing a towel or sponge under the heel will extend the knee and place the leg and femur on the same plane. This is also an alternative method of positioning so that no tube angle is required.

Radiograph #65

image065 This radiograph was taken 1 week following surgical reduction with internal fixation of the distal femur. The reason for the exam is to “evaluate bone alignment.” Does this radiograph meet the diagnostic criteria for the AP knee or distal femur projection?

Critique of Radiograph #65

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    As required by the diagnostic criteria the entire metallic internal fixation device and the distal femur are demonstrated. The condyles are nearly parallel to the film placing the knee in a relatively true AP position. However, the fibular head is completely superimposed by the tibia indicating the leg is externally (laterally) rotated. Notice that the comminuted fragments of the distal femur extend into the intercondylar notch. Therefore, demonstrating an open femorotibial joint space is essential. Because the fibular head is less than 1 cm distal to the tibial plateau it indicates the tube angle is too caudal. The radiographic exposure technique is optimal for bone and soft tissue detail. Unfortunately, this radiograph should be repeated. The CR must be parallel with the tibial plateaus so that the knee joint is open, and the leg internally rotated to reflect a true AP view.

Radiograph #66

image066 This radiograph was taken for follow up on a patient 4 months post surgical fixation of a mid-shaft femur fracture. The patient’s chief complaint was chronic knee pain when walking. Does this radiograph meet the diagnostic criteria, and did the technologist use the right exposure technique for this radiograph?

Critique of Radiograph #66

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    This radiograph is presented so we can discuss our professional role in patient imaging. The technologist should always take a good patient history that includes asking about postoperative trauma, past surgery of the affected knee, and what is the chief complaint. These inquires would have revealed that the purpose for imaging the knee is to determine if there are loose screws in the fixation apparatus near the knee, or inflammatory changes indicating risk for osteomyelitis, and the like. Notwithstanding, the positioning seen here is adequate. The radiographic exposure technique is adequate to evaluate soft tissue and bone. However, an optimal radiograph will demonstrate good bone detail and an especially a well-penetrated look at the fixation apparatus. Notice that motion artifact obscures visualization of the threads of the screws essential to diagnosis. Therefore, this radiograph must be repeated without motion artifact and good detail of the fixation screws.

Radiograph #67

image067 This AP knee projection was taken on a patient who suffered severe trauma during a sporting event. Does this radiograph meet the diagnostic criteria for the AP knee projection?

Critique of Radiograph #67

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    This is a good radiograph that meets the diagnostic criteria. Notice that the epicondyles are profiled, the condyles near equal in size and are parallel with the tabletop. The joint space is opened and the intercondylar eminences are easily seen. The fibular head is partially obstructed by the tibia and there is good bone penetration showing the patellar shadow. The radiographic exposure technique displays good bone detail and sharp edge differentiation of cortical bone. Soft tissues of the knee are well displayed showing good contrast with bone. The midsagittal plane of the leg is straight; however, the cassette was not aligned with the long axis of the femur and tibia. Aligning the long axis of the film with the part permits easier evaluation for unilateral widening of the joint space indicative of ligamentous injury. Overall, the anatomical positioning of the knee is very good.

Radiograph #68

image068 This patient had an open reduction with internal fixation of the distal femur 20 weeks prior to this radiograph. He now presents for upright knee radiographs to evaluate stability of the healing femur. Does this radiograph meet the diagnostic criteria for the AP knee or distal femur projection?

Critique of Radiograph #68

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    This is a good film in terms of positioning of the part and collimation. The radiographic technique is adequate for bone and soft tissue. Detail about the fixation and the screws in it can be seen on this radiograph. Loosening of the screws or signs of infection in the bone can also be evaluated. It bears mentioning that the entire internal fixation apparatus should be seen on both the AP and lateral views. If the fixation goes above mid-shaft, then the femur should be ordered to demonstrate the entire surgical fixation. This is a follow-up radiograph taken in the upright position to demonstrate weight-bearing and structural stability of the healing femur. This radiograph overall shows great positioning and radiographic contrast. I recommend repeating this radiographic projection to demonstrate the entire fixation. No other factors need to be changed to make this an optimal radiograph. Compare the detail seen in the fixation screws with that seen in radiograph #66.

Radiograph #69

image069 Patient history stated “hemiarthroplasty six months ago, follow up evaluation.” Does this radiograph meet the diagnostic criteria for the AP projection of the knee?

Critique of Radiograph #69

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    As stated, this radiograph was taken to evaluate knee joint six months post hemiarthroplasty. The entire unilateral prosthesis is entirely seen. Soft tissue shadows are also important because they can indicate a slow smoldering infection that could represent osteomyelitis. The medial joint space is opened; however, the lateral joint space is obscured. The primary cause is that the anterior and posterior cortical margins of the tibia are not superimposed (arrows). Failure to open the femorotibial joint is the reason this radiograph should be repeated. To open the joint space the CR should enter the knee perpendicular to the tibial plateaus. This will superimpose the anterior and posterior tibial condylar margins. The radiographic exposure technique shows good contrast between the prosthesis, bone, and soft tissues.

Radiograph #70

image070 This patient’s chief complaint was “that her knees always hurt.“ Standing bilateral AP and lateral views of the knees were ordered. Does this radiograph meet the diagnostic criteria for the AP projection?

Critique of Radiograph #70

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    This is a good radiograph of bilateral standing knees. This projection is often requested to evaluate joint space degeneration due to arthritic erosion. Notice each knee is positioned correctly by internally rotating the leg. Even though both knees are being radiograph together you must position each one separately to achieve this quality in your imaging. Radiographic technique is adequate for imaging both knees. Good bone penetration is seen, and the bone trabeculae as well as soft tissues are all well demonstrated on this film.

Radiograph #71

image071 This radiograph was taken in the recovery room following hemiarthroplasty of the knee. The orthopedic surgeon specified that the brace was to remain on during imaging. Does this radiograph meet the diagnostic criteria for the AP projection?

Critique of Radiograph #71

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    This is a well positioned AP knee radiograph that meets the diagnostic criteria. Comparing the lateral joint space to the right hemiarthroplasty joint space will confirm accuracy of positioning. Notice the anterior and posterior condylar margins of the lateral tibia are superimposed and the lateral joint space is open. Also notice that the medial joint prosthesis is aligned along its anterior and posterior condylar borders, and the medial joint open. The intercondylar eminence is clearly seen between the femoral condyles. Superimposed anterior and posterior condylar borders, and opened femorotibial joints is the standard for imaging knee joint prosthesis. The reason this is such a great radiograph is that the CR is parallel to the tibial plateau. The radiographic technique adequately demonstrates bone and soft tissue detail.

Radiograph #72

image072 This radiograph was taken in the recovery room following ORIF of the proximal tibia. The orthopedic surgeon specified, “Postoperative evaluation of ORIF alignment and fixation placement.” Does this radiograph meet the diagnostic criteria for the AP projection?

Critique of Radiograph #72

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    This is a post surgical radiograph in which the surgeon specified, “proximal tibia internal fixation” evaluation. When imaging post operative cases it is important to clearly understand what surgical procedure was performed. You can get some of the information you need from the radiologic technologist who operated the C-arm during the case. Certainly, knowing the length of the fixation will lessen the likelihood of repeating the radiograph, which is in keeping with ALARA. It is important to include the entire prosthesis, which is not demonstrated on this view. Therefore, this radiograph must be repeated to include the proximal tibia, entire prosthesis, and the knee joint. Radiographic exposure technique demonstrates bone, soft tissue, and metal very nicely with good contrast.

Radiograph #73

image073 This AP projection was taken several months after having prosthetic knee replacement. The patient was doing fine; however, there was a complaint of mild knee weakness when walking. The orthopedic physician requested this radiograph to evaluate the prosthesis and bone for signs of infection. Does this radiograph meet the diagnostic criteria for the AP knee projection?

Critique of Radiograph #73

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    This radiograph does meet the diagnostic criteria for the AP knee projection. Specifically, the positioning of the knee is optimal for demonstrating the prosthesis and joint space. Notice that the femoral condyles are not rotated. This is important when demonstrating the distal femur for prosthesis evaluation. Also notice that the fibulotibial joint space is opened, and the anterior margin of the tibial prosthesis is aligned with the posterior margin. This is excellent positioning, and I might add that this is the presentation orthopedic surgeons want for the AP knee prosthesis image. The radiographic exposure is very good too. It shows good contrast between metal, bone and soft tissues, and can show infection if it exists.

Radiograph #74

image074 This patient was brought to a local emergency room by ambulance after suffering a tremendous fall. There was high suspicion for a fracture of the knee. Does this radiograph meet the diagnostic criteria for the AP knee projection, why or why not?

Critique of Radiograph #74

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This radiograph would normally be considered adequate for demonstrating the required anatomy for the knee. The proximal third of the tibia is demonstrated; however, the dilemma is that there is a fracture that extends distal to the area covered on this radiograph. It would be a bit unfair to say that the radiographer did not meet the diagnostic criteria when the positioning of the part is optimal. Notice that the joint space is opened, the tibial plateau is well demonstrated, the condyles are symmetrical, and the fibula is within 1 inch distal to the tibial plateau. So I would consider this a good radiograph. Here’s what I would recommend. Consult with the ordering physician and ask them to order the entire tibia/fibula. This pattern of injury seen is similar to a Maisonneuve fracture so the ankle too may need to be evaluated. Consulting with the ordering physician is the best option to determine the full extent of the fractured tibia. The radiographic exposure is very good showing excellent bone and soft tissue detail.

Radiograph #75

image075 This radiograph is taken a few days post surgery to evaluate healing of this comminuted fracture aligned by internal fixation. Does this radiograph meet the diagnostic criteria for the AP knee projection, why or why not?

Critique of Radiograph #75

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    The radiographic exposure technique selected is optimal. Notice that all fragments of this comminuted fracture is well penetrated. The quality of this radiograph allows the physician to look for signs of malunion, nonunion, osteomyelitis, and early signs of infection. It is also important that the physician can evaluate all screws in the fixation device to determine if they are loosening over time. Therefore, it is without exception that the entire fixation device be demonstrated. The identification blocker obscuring part of the fixation device has resulted in this radiograph needing to be repeated. Be careful not to use a half cassette (7 X 17) when taking post-operative radiographs. Repeating a view because of poor positioning or in this case I.D. marker artifact is not in keeping with ALARA.

Radiograph #76

image076 Give your critique of this knee radiograph taken in the recovery room following prosthetic knee replacement surgery. Discuss the importance of demonstrating open joints on the lateral view, and tell why this radiograph does not, or does meet the diagnostic criteria.

Critique of Radiograph #76

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The sponge under the knee indicates that this is a horizontal beam lateral projection. It is note worthy that the medial and lateral margins of the tibial prosthesis are aligned and the knee is in a true lateral position. When imaging the knee in the lateral position it is important to demonstrate an open fibulotibial and patellofemoral joints. If you do not demonstrate these joints open and the prosthesis aligned for either the AP or lateral view, then you must repeat that projection. The technologist did a great job in demonstrating these joints. The radiographic exposure technique adequately penetrates bone structures without burnout of the soft tissues. This is an excellent radiograph of the knee for post surgical prosthesis evaluation. Take a good look at this radiograph because it meets the diagnostic criteria orthopedic surgeons want for post-surgical evaluation of the lateral knee view.

Radiograph #77

image077 This weight-bearing radiograph of the knee was taken to evaluate the femorotibial joint space as part of an evaluation for possible knee replacement surgery. Does this radiograph meet the diagnostic criteria for the lateral knee projection?

Critique of Radiograph #77

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Weight-bearing views of the knee are commonly taken to evaluate the knee joint. It is important that the joint space be demonstrated on both the AP and lateral projection. This is a mediolateral projection, which should demonstrate the medial femoral condyle posterior and distal to the lateral condyle. If the patient were in a lateral recumbent the central ray would be angled 5 degrees cephalic to achieve the proper projection. However, this is an upright patient position with a horizontal beam. The femoral condyles must be aligned parallel to the floor. Keep in mind that the femoral shaft inclines medially 10-15 degrees when positioning the knee. The lesser amount of inclination is seen in those with a narrow pelvis and long femur. The patellofemoral space can be demonstrated by rolling the knee a quarter inch towards the image receptor from the true lateral position. The radiographic exposure technique seen is adequate for bone and soft tissue detail.

Radiograph #78

image078 Discuss why this upright lateral radiograph of the knee taken to evaluate the femorotibial joint space is positioned more accurately than what is seen on radiograph #77. Does this radiograph meet the diagnostic criteria for the lateral knee projection?

Critique of Radiograph #78

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This time we see a much better positioned upright knee than the one presented on radiograph #78. The patellofemoral joint is opened; the femoral condyles are nearly superimposed displaying an opened femorotibial joint. What is different is that the knee is slightly externally rotated, that is, the patella is rotated towards the image receptor about a quarter (0.25) inch to open the patellofemoral joint space. The patient is slightly off the vertical plane so that the medial condyle is aligned with the lateral femoral condyle. This is an excellently positioned patient. The radiographic exposure technique demonstrates good soft tissue detail and excellent bone penetration and detail.

Radiograph #79

image079 Discuss why or why this radiograph does not meet the diagnostic criteria for the lateral knee projection. Consider that this is a post surgical radiograph to evaluate the new prosthesis.

Critique of Radiograph #79

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What is good about this radiograph is that the femorotibial joint is opened and the exposure technique demonstrates good contrast and detail between bone and soft tissue structures. However, this radiograph must be repeated because it does not demonstrate an opened femoropatellar joint. The condyles of the femur are not aligned, which diminishes the value of this radiograph. Alignment is very important here and the knee must be positioned to demonstrate true anatomical relationships. Orthopedic surgeons demand that both joints of the knee be demonstrated open and that the medial and lateral edges of the femoral and tibial prosthesis be aligned and superimposed.

Radiograph #80

image080 This radiograph was taken on a patient who complained of excruciating pain related to a sports injury. The technologist put a sponge under the knee and took a horizontal beam lateral to reduce the risk of injuring the knee. Does this radiograph meet the diagnostic criteria for the lateral knee projection?

Critique of Radiograph #80

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    This radiograph does meet the diagnostic standards for the lateral knee. The sponge shadow under the knee indicates this is a horizontal beam lateral. There is minimal rotation of the femoral condyles; however, the patella slightly superimposes the patellar surface of the femur. This results in the suprapatellar fat pads being obscured. This positioning error must be corrected and this radiograph repeated. Decreasing the cephalic angle to about 5 degrees caudal will open the patellofemoral joint. The medial femoral condyle is anterior and slightly proximal to the lateral condyle, and the fibula is not free of the tibia. A slight rotation of the knee away from the image receptor will better superimpose the femoral condyles. The radiographic exposure technique demonstrates good bone and soft tissue detail.

Radiograph #81

image081 This patient presents to the radiology department with a clinical history of distal femur fracture s/p 26 weeks prior, now with chronic pain on weight bearing. The orthopedic surgeon requested, “knee and distal femur AP and lateral views upright.” Does this radiograph meet the diagnostic criteria for the AP knee or distal femur projection?

Critique of Radiograph #81

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This standing lateral knee radiograph shows the entire internal fixation, distal femur, and the knee joint. The positioning is excellent in that the femoral condyles are nearly superimposed. The patellofemoral joint space is not projected opened, which commonly happens when positioning the upright patient. Getting the femoral condyles superimposed and the patellofemoral joint space opened can be challenging, especially when the extremity is imaged in the upright position. To open the patellofemoral joint and knee joint one must superimpose the femoral condyles and get them parallel with the floor. Since the x-ray beam is horizontal for the upright projection you must align the femur and tibia with each other and parallel with the image receptor. Also, flexing the knee more than 20 degrees brings the patella closer to the patellar surface of the femur projecting the patellofemoral joint space closed.

Radiograph #82

image082 This radiograph was taken in the recovery room. The ordering physician specified, “AP and lateral views of the knee to evaluate prosthesis.” Does this radiograph meet the diagnostic criteria for the AP knee or distal femur projection?

Critique of Radiograph #82

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Patient positioning is good as the femoral condyles are superimposed, and both the patellofemoral and knee joints are opened. The space between the femur and tibial prosthetic articulations are opened, which must be demonstrated on both the AP and lateral views of the knee. The exposure technique is superbly demonstrates a delicate balance between bone penetration, and soft tissue detail. This is a very good radiograph, and I might mention that it was taken as a crosstable lateral projection.

Radiograph #83

image083 Give your critique of this radiograph taken of a patient presenting to the emergency room with a history of hard fall, swollen painful knee, and a history of knee replacement surgery 9 months prior to this injury?

Critique of Radiograph #83

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    The knee is properly positioned for this radiograph. The entire prosthesis is demonstrated and there is good contrast between bone and soft tissue. The physician wanted to evaluate the bone and joint for fracture or displacement of the prosthesis. This radiograph adequately answers these concerns. The technologist elected to take the image as a horizontal beam lateral so comparisons could be made with films taken months earlier. The image shows no disruptions of the joint spaces, or dislocation. Being able to make radiographs of this quality using a horizontal beam is truly an art. The visualization of soft tissue and bone are balanced nicely on this radiograph. Notice there is no air in the joint, and the soft tissue detail shows the architecture of the artificial meniscus in the joint space. This is truly an A+ film.

Radiograph #84

image084 This patient presented to the emergency with trauma related knee pain. Does this recumbent mediolateral projection meet the diagnostic criteria?

Critique of Radiograph #84

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This is a fairly good radiograph that by most standards would not be repeated. It gets an “A” for radiographic exposure technique. Good bone penetration, bone detail and soft tissue are displayed. What is good about the positioning seen here is that the anterior and posterior suprapatellar fat pads are demonstrated. Also the knee is not flexed more than 20 degrees. Demonstrating the suprapatellar fat pads and the knee in slight flexion enables the radiologist to accurately diagnose joint effusion. To correct the projection of the medial femoral condyle, which is seen posterior the lateral condyle, simply rotate the patella 0.25 inch closer to the cassette.

Summary: AP and Lateral knee Views

  • For the AP view the condyles of the femur are parallel to the image receptor:
    1. CR should pass through the knee joint just below the patellar apex. On a well positioned AP view the femorotibial joint is centered on the radiograph; it can be found about 2 cm below the palpable medial epicondyle, or at the apex of the patella.
    2. At least ¼ of the distal femur and ¼ of the proximal tibia and all surrounding soft tissues should be included on the radiograph. The medial and lateral epicondyles profiled, and the intercondylar eminences of the tibia demonstrated in an opened femorotibial joint.
    3. Supine view is good for identifying fractures/dislocations. Standing views may be requested for pre-prosthetic evaluation, or to evaluate functional loss due to arthritic joint erosion.
  • For the mediolateral view the condyles must be superimposed. This is accomplished by placing the tibia on the same plane as the femur, and the femoral condyles perpendicular to the image receptor:
    1. Knee is flexed no more than 30 degrees unless a patella fracture is suspected. The patellofemoral and knee joint spaces should be demonstrated with their articulations opened. Decrease the amount of knee flexion to no more than 20 degrees when joint effusion is suspected.
    2. On an accurately positioned radiograph the femorotibial joint is centered and well collimated. All soft tissues surrounding the bones and joints must be demonstrated. Both the femorotibial and patellofemoral joint spaces are projected opened.
    3. Radiographic technique should demonstrate good bone penetration; good bone detail, and allow for visualization of blood effusion or air soft tissues or joint capsule.
  • When imaging a prosthetic device, such as knee prosthesis, the entire device must be seen on a single radiograph of each view. The joint space between adjacent components of the prosthesis must be demonstrated just as with bone anatomy.
Diagnostic Criteria Medial and Lateral Oblique Projections

There are three additional views of the knee commonly requested along with the AP and lateral views. These are the medial and/or lateral oblique, tunnel (Holmbald), and the sunrise (Merchant) projections.


Diagnostic Criteria for the Medial and Lateral Oblique Projections
  • For the medial or lateral oblique projections of the knee the condyles of the femur are rotated to a position of 45 degrees with the tabletop. When rotated too much the condyles will show slight superimposition. An over rotated lateral projection will show superimposition of the femoral condyles and the fibular head slightly free or along the posterior edge of the tibia.
  • When properly positioned the oblique view demonstrates the femorotibial joint space opened, the anterior and posterior margins of the tibial condyles superimposed, and the fibular head slightly below the level of the tibial plateau.
  • The medial oblique should demonstrate the fibular head without superimposition on the tibia. The lateral condyle is seen in profile with a portion of the joint space distal to it opened.
  • The lateral oblique should demonstrate the fibula and tibia superimposed, and the medial condyle profiled.

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This medial oblique (MO) of the knee demonstrates the proper positioning of the knee. Notice that the femorotibial joint is opened, the intercondylar eminences clearly seen, and the superior surfaces of the tibia are seen without superimposition by the distal femur. The patella is partially free of the femur, but mostly seen through the femur. The fibula head is demonstrated free of the tibia and the lateral femoral condyle seen in profile. Structures that are labeled are: distal femur (A), lateral femoral condyle (B), lateral femorotibial joint (C), neck of fibula (D), patella (E), medial femoral condyle (F), medial tibial plateau (G), and proximal tibia (H).
image260
This lateral oblique (LO) of the knee demonstrates the proper positioning of the knee. Notice that the femorotibial joint is opened, the intercondylar eminences clearly seen, and the superior surfaces of the tibia are seen without superimposition by the distal femur. The patella is partially free of the femur, but mostly seen through the femur. The fibula head is demonstrated free of the tibia and the medial femoral condyle seen in profile. Some labeled structures are: medial femoral condyle (A), medial tibial condyle (B), proximal tibia (C), patella seen through femur (D), and lateral tibial condyle (E). The arrow points to the closed epiphysis that is barely seen as a thing line through the proximal tibia.
Diagnostic Criteria for the Holmbald Projection

The purpose of the Holmbald (tunnel) projection is to demonstrate the medial, lateral, and proximal portions of the intercondylar fossa. The tunnel view specifically demonstrates the posterior femoral condyles, intercondylar eminence, and plateau of the tibia. There are several named methods of demonstrating these structures, for example, the Holmbald method, Camp Coventry method, and the AP axial projection, which is used when trauma or fracture is suspected. I would suggest you review these projections, which can be found in any standard radiographic technology textbook such as “Radiographic Positioning and Related Anatomy by Kenneth Bontrager.”

The importance of the tunnel view for evaluating osteoarthritis is well documented. Diminution of the femorotibial joint space typically affects the medial joint more than the lateral joint. Routine knee radiographs (AP and lateral views only) are limited in assessing the degree of cartilage destruction. The tunnel view, especially weight bearing, better demonstrates severe interosseous joint space loss or obliteration of the joint space. This is because the tunnel view better demonstrates the posterior portion of the condyles and congruity of the articular surfaces. Furthermore, joint alignment is maintained by muscle action during weight bearing, which furthers aids in unilateral joint compartment evaluation. Because the joint space is well defined by the tunnel view intra-articular loose bodies are clearly seen, for example bony avulsion characteristic of a cruciate ligament tear.


Diagnostic Criteria for the Holmbald Projection
  • When properly positioned the Tunnel view should demonstrate the femoral and tibial condyles, the eipcondyles of the femur in profiled, and the intercondylar eminences within an opened femorotibial joint. The patella should not be projected inferiorly so that it obstructs the femorotibial joint space.
  • Optimum exposure should visualize soft tissues surrounding the knee joint and within the knee joint. The patella is visualized through a well-penetrated distal femur, and trabecular markings of the femoral condyles and proximal tibia are clearly demonstrated.

image261
This radiograph demonstrates the anatomy seen on a properly positioned PA/AP axial projection (Holmbald Method). The purpose for this view is to demonstrate the intercondylar notch and intercondylar eminences in profile. Demonstrated and labeled are: (A) lateral epicondyle (A), lateral femoral condyle (B), intercondylar eminence (C), medial femorotibial joint space (white arrow, and intercondylar notch (yellow arrow).
image262
These two radiographs of the tunnel view demonstrate standing views (left) and recumbent view (right). Notice that the recumbent view demonstrates the intercondylar notch (arrow) better because the femur makes a 70-degree angle with the tibia. The upright view is made with the knee bent approximately 45 degrees.

Diagnostic Criteria for the Merchant Projection

Fractures of the patella often occur as a result of direct blow or by indirect forces transmitted by strong forced contraction of the quadriceps tendon. Most fractures of the patella are transverse; however, about 30% are comminuted and about 15% are vertical. Generally an AP and lateral view is needed at 90-degrees to each other are to evaluate a fracture or dislocation. Often the patella is poorly demonstrated on the AP view because it is seen through a superimposed femur. When visualization of the patella is of concern the axial patella projection is requested. This view demonstrates the shape of the patella in its articulation with the trochlear groove and the femoral condyles. Sometimes the axial view is taken at various degrees of knee flexion, for example, 30, 45, and 90 degrees to assess patellar travel, angle of congruity, trochlear angle, and the patellofemoral angle. Therefore, it is important that we review the diagnostic criteria for the Merchant view since this projection is commonly requested. Keep in mind that there are many names for the Merchant view, for example, sunrise, Hougston, and others. You should refer to an atlas of radiographic positions for specifics of these views.


Diagnostic Criteria for the Merchant Projection
  • The Merchant projection is taken to demonstrate the patellofemoral joint, subluxation, and difficult to see vertical fracture of the patella. There are as many methods of taking this projection, as there are names for it. A dislocated patella will be demonstrated laterally on the Merchant projection. The intercondylar sulci (trochlear groove) must remain positioned superiorly in order to distinguish patellar dislocation from a rotated knee projection.
  • The Merchant view is used to accurately demonstrate the relationship of the patella to the patellar surface of the femur. This is a preferred projection to demonstrate dislocation of the patella and an open femoropatellar joint space. Often poor positioning can make this view ambiguous. A properly positioned Merchant projection will demonstrated the anterior femoral condyles and intercondylar sulci superiorly, and the lateral femoral condyle is often projected slightly higher than the medial condyle.
  • Key point! Acute flexion of the knee should not be performed until a fractured patella has been ruled out by other projections, such as the lateral knee view.

image263
This lateral view of the knee shows an acute patella fracture (arrow). Before positioning the knee in extreme flexion to demonstrate the open patellofemoral joint be sure a fracture of the patella is not present. When performing the axial view of the patella various degree angles of knee flexion can be used to achieve the proper view. Various degrees of knee flexion is sometimes requested when making the sunrise view to assess patellar travel, angle of congruity, trochlear angle, and the patellofemoral angle
image264
The labeled parts of the Merchant view are the: patella (A), patellofemoral joint (B), lateral femoral condyle (C), medial femoral condyle (D), and the intercondylar sulci (arrows) along the patellar surface of the femur.
image265
These two radiographs demonstrate proper positioning and anatomy to be demonstrated on the axial view of the patella. The radiograph on the left demonstrates bilateral patellae. Each patellofemoral joints is open and with the patella properly aligned over the intercondylar sulcus. On the right the axial view demonstrated the patellofemoral joint following total knee replacement. Notice the positioning of the knee in this view also demonstrates an open patellofemoral joint and the patella in profile. An asterisk marks the lead apron used to protect the gonads when the tube is angled cephalic.
Radiograph #85

image085 This radiograph was taken on a patient who suffered a hyperflexion knee injury. State what ligament of the knee resists hyperflexion, and give reasons for why this radiograph does or does not meet the diagnostic criteria for the medial knee view.

Critique of Radiograph #85

image085

    The positioning seen here is adequate, but is not optimal. The patella is projected almost free of the femur, whereas it should be superimposed on the femur. When over rotated the femoral condyles become superimposed approaching a lateral position. We can see the femorotibial joint space and intercondylar eminence. The joint space between the head of the fibula and the inferior surface of the lateral condyle of the tibia is also projected free of superimposition. A good radiograph exposure technique has been selected as it shows good bone and soft tissue detail. The knee is well-penetrated allowing for visualization of the bony architecture. Incidentally, the anterior cruciate ligament is responsible for resisting hyperflexion of the knee joint.

Radiograph #86

image086 Does this medial oblique knee radiograph meet the diagnostic criteria? History for the exam is “chronic knee pain; evaluate for chronic osteoarthritis.”

Critique of Radiograph #86

image086

    When a history of osteoarthritis is given it is especially important to demonstrate an open femorotibial joint space. Sometimes there is no joint space due to pathological erosion of the joint. However, in this example erosion is not excessive and the joint space should have been demonstrated. Sometimes pain makes it more difficult to achieve proper rotation and flexion of the knee. Aligning the femur and tibia on the same plane can open the joint. Place a sponge or towel under the leg to get the femur and tibia on the same plane. This will also help manage pain while rotating the lower extremity. If the knee is still slightly flexed, angle the tube 5 degrees cephalic so the CR enters the knee parallel to the tibial plateau. The radiographic exposure technique is adequate for bone and soft tissue detail. Air in medial joint compartment is seen, which could indicate acute injury. Repeat this radiograph taking measures to open the medial and lateral joint space.

Radiograph #87

image087 This patient complained of knee pain following a fall. Being an elder woman the physician was highly suspect for knee fracture. The AP, lateral, and medial oblique views were taken. Does this medial oblique view meet the diagnostic criteria?

Critique of Radiograph #87

image087

Demonstrating an opened femorotibial joint, the tibial plateaus, and the intercondylar eminence is required. This is sometimes difficult because the knee is either excessively rotated or is slightly flexed. Clearly, the femoral condyles are projected onto the tibial condyles causing the femorotibial joint to appear closed. Sometimes placing a rolled towel under the ankle will reduce knee flexion and place the femur and tibia on the same plane. Or, you may wish to use a slight cephalic tube angle. The key point is that the central ray must be perpendicular to the tibia, and parallel to the tibial plateaus to project the joint space opened. The amount of internal rotation should be no greater than 45 degrees so that the patella is not projected free of the femur. The radiographic exposure technique is adequate for bone and soft tissue detail. Always support the knee so motion artifact does not degrade image detail.

Radiograph #88

image088 This medial oblique knee radiograph was taken for trauma as part of a three projection series (AP, lateral, and oblique). Does this radiograph meet the diagnostic criteria for the medial oblique knee projection?

Critique of Radiograph #88

image088

This radiograph demonstrates the required anatomy for evaluation of the knee in the medial oblique position. The fibular head is projected free of the tibia and the patella only slightly free of the femur. The joint space is not fully appreciated; however, it is not poorly presented. Keep in mind that the joint space must be demonstrated opened. This is the problematic criterion for the oblique knee radiograph. When the CR is parallel to the tibial plateau the joint space will be open. Paying close attention to the angle of the CR is key to getting this view right. The radiographic exposure technique shows good penetration of the femur and tibia. The surrounding soft tissues are well demonstrated. This radiograph should only be repeated if the joint space is not demonstrated on the AP and lateral view. This is a pediatric patient (epiphyseal plates are seen) so practice ALARA in deciding whether or not to repeat this view.

Radiograph #89

image089 Does this radiograph meet the diagnostic criteria for the oblique knee projection? Tell what should be done to correct it if it does not.

Critique of Radiograph #89

image089

The reason this radiograph does not meet the diagnostic criteria is that the femorotibial joint space is only partially opened, and the intercondylar eminences are not projected free of superimposition within the joint space. The fibular head is shown in profile and completely free of the tibia. Notice the femoral condyles are partially superimposed obscuring part of the lateral condyle. The patella is nearly free of the femur indicating the knee is rotated more than 45 degrees. To correct these positioning errors be sure that an imaginary line through the femoral condyles is no more than 45 degrees with the tabletop. You can feel the medial edge of the patella to make sure that it is not rotated beyond the medial edge of the femur. What is good about this radiographic is the exposure shows good bone penetration and soft tissue detail. This radiograph should be repeated correcting the positioning concerns stated.

Radiograph #90

image090 There was a question about a subtle fracture involving the intercondylar eminence and tibial plateau. Does this radiograph meet the diagnostic criteria for the Holmblad (tunnel) view?

Critique of Radiograph #90

image090

The purpose for the Holmbald projection is to demonstrate the intercondylar fossa in profile, the femoral and tibial condyles, intercondylar eminence, and articular facets of the femur and tibia. All of these structures are anatomically demonstrated on this radiograph. The femorotibial joint space open, and the intercondylar fossa is free of superimposition by the patella. There is symmetry in the appearance of the distal posterior femoral condyles and the fibula is properly aligned with the tibia. This radiograph does not meet the diagnostic criterion for exposure technique. A proper exposure will demonstrate the patella through a well-penetrated femur. This is a high contrast image, which is displays poor detail in the distal femur. Increase the kVp and decrease the mAs to demonstrate better bone detail in the distal femur when repeating this projection.

Radiograph #91

image091 The AP, lateral, and medial oblique views of the knee did not adequately demonstrate the intercondylar eminences and tibial plateau. It was requested that the technologist take a “tunnel projection” to demonstrate the area of interest. This radiograph was taken with the patient supine and CR directed AP. Does this radiograph meet the diagnostic criteria for the Holmblad method?

Critique of Radiograph #91

image091

The AP projection is a modification of the standard Holmbald view, which is taken with the patient prone. This projection is preferred when a fracture of the distal femur or proximal tibia is suspected. There will usually be mild distortion the anatomy unless the proper tube angle is used. The problem with demonstrating the intercondylar fossa with the AP projection is distortion due to improper tube angle or cassette placement. Increased part-cassette distance is the usual cause for increased distortion. This radiograph shows distortion of the tibia and a closed femorotibial joint. CR is not perpendicular to the tibia evidenced by the femoral and tibial condyles overlapping. To open the joint space the CR must enter the knee perpendicular to the tibia. This assures the CR is parallel to the tibial plateau when the knee is bent 40 to 45 degrees. Motion artifact has also contributed to loss of subject detail. Use sandbags or tape to immobilize the leg. As for radiographic exposure, there appears to be good bone penetration as the patella is seen through the femur. This radiograph should be repeated.

Radiograph #92

image092 Does this radiograph meet the diagnostic criteria for the tangential (skyline/sunrise) projection of the knee? In your critique state the purpose for the tangential projection.

Critique of Radiograph #92

image092

The tangential view used to demonstrate the intercondylar sulcus of the femur, an opened patellofemoral joint, and show clearly defined bony margins of the condyles and patella. Therefore, proper positioning is especially important because this view can demonstrate subluxation or a subtle vertical patellar fracture. The diagnostic criteria for the sunrise view have been achieved on this radiograph. The exposure technique displays good bone and soft tissue detail. The clothing artifact seen does not obstruct the image in a way that necessitates repeating the radiograph. However, you should be aware that when clothing is worn it is possible to have artifacts on the image. Rolling up the pant leg can also obscure the diagnosis of a joint effusion. So have the patient slip the leg out of clothing when the material is questionable for artifact.

Radiograph #93

image093 Consider these two radiographs of the patellofemoral joint taken on the same individual. Give the name of this projection and discuss in your critique the reason for the two projections.

Critique of Radiograph #93

image093

These radiographic projections are commonly called the Hughston views. Orthopedic surgeons prior to total knee prosthetic replacement surgery often request them. What is of interest is the relationship of the patella and patellar surface of the femur during flexion of the knee joint. The top radiograph is at 60 degrees flexion and the lower radiograph is taken at 20 degrees knee flexion. Sometimes the 20-degree view may not present an opened joint space due to the patient’s condition. In this case the joint space is opened on both views. The exposure technique is adequate for bone and soft tissue detail. Again, clothing artifacts are seen on both view and may simulate degenerative changes. So always remove the clothing when taking this projection.

Radiograph #94

image094 This patient fell on an unknown object, now presents with “a feeling that there is something like glass under the skin. Clinical examination indicated a small puncture just below the patella. The technologist marked this area with a pointer that is seen in the radiograph. Does this radiograph meet the diagnostic criteria for the lateral patella view?

Critique of Radiograph #94

image094a

This image was intentionally collimated to the area of interest. A pen was used to mark the location of the puncture wound. Keep in mind that the patient did report a traumatic event in which a foreign body is felt below the skin. Therefore, the entire knee must be demonstrated; this radiograph does not meet the diagnostic criteria for the lateral view. Another reason this radiograph should be repeated is because the exposure technique displays high contrast. As a result, the bony architecture of the knee cannot be evaluated. Choosing an exposure that demonstrates bone and soft tissue is preferred over one that demonstrates just soft tissue. A subtle fracture must be ruled out since the clinical history revealed trauma. Repeating this radiograph to include the entire knee using a low contrast exposure technique is required. Good contrast between bone and soft tissue can be achieved by increasing the kVp to penetrate the bone. Increasing the kVp will also add more densities to the radiograph, which favors soft tissue detail.

Radiograph #95

image095 Consider this radiograph of the patella taken as part of a three view knee series. The patient fell injuring the anterior portion of the knee. Chief complaint, “pain X 2 days and difficulty flexing the knee.“ Does this radiograph meet the diagnostic criteria, state why or why not?

Critique of Radiograph #95

image095

There is good positioning of the part for this projection; however, significant motion artifact is present. The patellofemoral joint space is open and the patella is properly profiled above the intercondylar sulcus. The anterior femoral condyle is symmetrically aligned. The lateral femoral condyle is demonstrated slightly higher than the medial condyle, which indicates the knee is not rotated. The main reason this radiograph should be repeated is that motion artifact has obliterated the bone trabecular pattern. This could cause a subtle fracture to be missed. Never accept a radiograph of this poor quality as some technologists may be fooled into believing the amount of motion artifact is acceptable. To reduce motion you can use the 50/15 rule to decrease the mAs and increase the kVp. Then, adjust the exposure technique by increasing the mA so that the exposure time is further reduced. This will eliminate motion that is seen here without changing the overall radiographic contrast.

Radiograph #96

image096 This radiograph was taken to evaluate the patellofemoral joint space. Does this radiograph meet the diagnostic criteria, why or why not? If you say it does not, then tell what should be done to correct the errors seen on the radiograph.

Critique of Radiograph #96

image096

The knee is properly bent evidenced by the tibia seen through the femur not obscuring the joint space. The reason this radiograph should be repeated is that the patellofemoral joint is projected closed. An alternative point of view is that the patella is dislocated superiorly causing the joint space to appear closed. In this case the joint space is not properly opened due to improper tube angle. The degree of tube angle is dependent on the amount of flexion at the knee joint. To project the patellofemoral joint open the CR must enter the knee tangential to the joint. Clearly the inferior and superior margins of the tibial condyles are not superimposed. The radiographic exposure technique is adequate for this view. The femur, tibia and patella are well penetrated. The reason this radiograph should be repeated is to demonstrate an open patellofemoral joint space. Adjustment of the tube angle is required if the position of the knee is unchanged.

Radiograph #97

image097 This radiograph was rejected by the radiologist. Give reason(s) why this radiograph should have been repeated.

Critique of Radiograph #97

image097

Unfortunately this radiograph reached the radiologist for evaluation. There is nothing about this radiograph that is diagnostic. The exposure displays poor penetration of the femoral condyles and patella. No information can be gleaned from it because bone detail is lacking. It is not even possible to comment on positioning because the image quality is so poor. It is worth mentioning that the technologist thought there was enough information about the patella to rule out a fracture and therefore passed this radiograph. The diagnostic criteria clearly states that the following structures must be seen: the patellofemoral joint, the anterior femoral condyles and intercondylar sulci superiorly, and the lateral and medial femoral condyles. This radiograph should be repeated using higher kVp to penetrate the part and demonstration of the required anatomy for the sunrise view.

Radiograph #98

image098 This patient presented to a local emergency room with a chief complaint of knee trauma and pain. The emergency room physician requested an AP, lateral, and sunrise views of the knee. Does this radiograph meet the diagnostic criteria for the sunrise view?

Critique of Radiograph #98

image098

This is a well positioned radiograph that correctly demonstrates the patellofemoral joint opened and the intercondylar sulcus and patella relationship. The anterior femoral condyles are properly aligned and the tibia well below the intercondylar sulcus. The radiographic exposure shows slight underpenetration of the part. There is also a slight bit of motion artifact present. The motion artifact appears to be caused by the patient holding the cassette. This commonly occurs with the sunrise projection because there is a gap between the part and the cassette. It is recommended that a high mA and short exposure time be used when performing the sunrise view. Also a radiolucent sponge can be used to support the cassette. Because subject detail is not degraded we can apply the principle of ALARA by not repeating this radiograph. Overall, this is an acceptable radiograph that meets the diagnostic criteria.

Radiograph #99

image099 This patient’s chief complaint was knee pain over the patella. The clinical history included fixation of a distal femoral fracture some six months earlier. The orthopedist requested a sunrise view along with the AP and lateral projections. Does this radiograph meet the diagnostic criteria for the sunrise view?

Critique of Radiograph #99

image099

Because the patellofemoral joint space is not open this radiograph does not meet the diagnostic criteria for the sunrise view. The knee is properly flexed and aligned with the cassette. It appears that the tube angle is not angled properly. When properly aligned, the CR should enter the knee just below the patella parallel to the patellofemoral joint. Another option is to decrease the amount of flexion of the knee so that the combined angle of the tube and knee is about 105 degrees. This too will open the patellofemoral joint space without projecting the tibia onto the femur. The radiograph shows good penetration of the femur and patella. The trabecular pattern of the distal femur is well demonstrated as well as clear cortical bone margins. This radiograph should be repeated to open the patellofemoral joint.

Radiograph #100

image100

This radiograph is included to show the relationship of the popliteal artery to the knee. Dislocation of the knee and or crush fractures cause popliteal artery injury in approximately 40% of these patients. Usually the pulse below the site is weak, but may return to full strength following reduction. The purpose of this radiograph is to remind you that proper handling of knee fractures is a must. While the popliteal artery is demonstrated on this angiogram radiograph, it should be noted that the femoral nerve runs closely parallel with the artery and is at risk from injury.

Summary of Critiques: Obliques, Holmbald, and Merchant Views of the Knee

  • For the medial or lateral oblique projections of the knee the condyles of the femur are rotated internally or externally 45 degrees. When rotated too much the condyles will show slight superimposition. An over rotated lateral projection will show superimposition of the femoral condyles and the fibular head slightly free or along the posterior edge of the tibia.
  • Most anatomical relationships seen on the AP projection apply to the obliques. For example, when properly positioned the oblique demonstrates the femorotibial joint opened, the anterior and posterior margins of the tibial condyles superimposed, and the fibular head slightly below the level of the tibial plateau.
  • The medial oblique should demonstrate the fibular head without superimposition on the tibia. The lateral condyle is seen in profile with the portion of the joint space distal to it opened.
  • The lateral oblique should demonstrate the fibula and tibia superimposed, the medial condyle profiled, and the joint space distal to it opened.
  • The Holmbald projection should demonstrate the relationship of the femoral and tibial condyles, the eipcondyles of the femur are profiled, and the intercondylar eminences within an opened femorotibial joint displayed. The patella should not be seen obscuring any portion of the femorotibial joint space. Optimum exposure should visualize soft tissues surrounding the knee joint and within the knee joint. The patella is visualized through a well-penetrated distal femur, and trabecular markings of the femoral condyles and proximal tibia clearly demonstrated.
  • The Merchant or sunrise projection is made to accurately demonstrate the relationship of the patella and patellar surface of the femur. This view allows for accurate diagnosis of a patella dislocation, or a vertical fracture of the patella. It is mandatory that an open femoropatellar joint space be demonstrated. Often poor positioning can make this view ambiguous. A properly positioned Merchant projection will demonstrated the anterior femoral condyles and intercondylar sulci, an opened patellofemoral joint space, and the lateral femoral condyle is often projected slightly higher than the medial condyle.
Always ask, "Did I meet the diagnostic criteria for this view?"

Diagnostic Criteria for Imaging the Tibia/Fibula-AP and Lateral Views




Diagnostic Criteria for Imaging the AP Projection of the Leg
  • A request for the leg is made the entire tibia/fibula including both the knee and ankle joints should be made. If it cannot be included as a single film then two films with overlapping parts should be made.
  • A properly positioned AP view will demonstrate proximal tibia with slight superimposition of the fibular head. The midshaft of the tibia and fibula are seen without superimposition and the distal tibia and talus are partially superimposed on the fibula. The entire tibia, fibula, ankle joint, knee joint, and surrounding soft tissues must be demonstrated. The leg should not be requested if the ankle is the structure in question. This is because the AP leg will demonstrate the femorotibial and tibiotalar joint spaces closed. This is due to the divergent x-ray beam as the area of coverage is great and the central ray does not pass through either joint. For the AP tibia/fibula radiograph neither the knee joint nor the ankle joint are parallel with the cassette or perpendicular to the x-ray beam.
  • The leg is positioned so that the anode-heel-effect maximizes use of the concentrated part of the divergent beam over the proximal tibia. To take advantage of the heel effect the cathode is positioned over the knee and the anode over the ankle.
  • Radiographic exposure technique should demonstrate good bone penetration at the ankle and knee joints without “burn out” of the fibular shaft. The surround soft tissues should be demonstrated in a way that will reveal any soft tissue injury such as a laceration of foreign object.



image266
These three images demonstrate the anatomy that should be demonstrated on the AP leg view. The image on the left is a surface rendered 3-D CT image. The middle and right radiographs demonstrate what should be demonstrated on the AP view. All three pictures demonstrate the entire tibia/fibula and the knee and ankle joints. The importance of demonstrating both joint is seen on the middle radiograph where the proximal fibula is fractured, and the distal tibia is fractured. Likewise, it is required that the entire tibia is demonstrated when internal fixation for fracture of the leg has been performed (right radiograph). Notice that the joint spaces at the extremities are not opened because of the divergence of the x-ray beam.



Diagnostic Criteria for Imaging the Lateral Projection of the Leg
  • A properly positioned lateral leg radiograph will demonstrate the entire tibia/fibula, knee and ankle joints, and surrounding soft tissues.
  • The tibia will partially superimpose the fibular head with their midshaft portions free of superimposition, and the fibula superimposed by the distal half of the posterior portion of the tibia. The femoral condyles will be superimposed when the knee is flexed 45 degrees.
  • The anode-heel-effect is used to gain maximal exposure over the proximal leg and reduce exposure over the ankle. The purpose for using the heel effect is to get uniform density at both ends of the leg. The desired exposure will show good density without motion, and sharp trabecular marking and sharp edges of the tibia and fibula. Soft tissues should not be “burned out” and good bone penetration showing bone detail is required.



image267
These three images demonstrate the anatomy that should be demonstrated on the lateral projection of the leg. The CT 3-D volume rendered image on the left shows the bony skeleton perspective of the tibia and fibula. The x-ray in the middle shows what should be included on the lateral projected radiograph. Notice that both joints are included and the midshaft of the tibia and fibula is not superimposed. The leg is requested when the ankle or knee joints are not the major concern for injury, but are included on the radiograph for general evaluation. The radiograph on the right shows the inclusion of the entire internal fixation of the tibia and both the knee and ankle joints. This is required when this scenario presents and the leg is requested.


Radiograph #101

image101 This patient presented to a local emergency room with an injury to the proximal leg with a deep laceration. Does this radiograph meet the diagnostic criteria for the AP projection of the leg?

Critique of Radiograph #101

image101a

This is a good radiograph of the leg that meets the diagnostic criteria. The positioning of the part is accurate for diagnosis with the required anatomy included. The distal fibula is partially clipped; however, the view does not need repeating because the site of injury is proximal and lateral. What would have helped in the interpretation of this radiograph is for the technologist to indicate where the soft tissue injury occurred like the arrow on the radiograph above. The radiographic exposure technique shows good bone detail and great soft tissue detail. Notice the sharp distinction between muscle and fat along the soft tissue edge.

Radiograph #102

image102 This lateral view of the leg was taken on the same patient presented in radiograph #101 above. Does this radiograph meet the diagnostic criteria for the lateral projection of the leg given a history of laceration to proximal leg?

Critique of Radiograph #102

image102a

Noted again is that the entire tibia/fibula, the knee joint, the ankle joint, and all surrounding soft tissue is demonstrated. The positioning is good as the condyles of the femur are nearly superimposed and the ankle joint is seen in the lateral position. Soft tissue detail is also very good. The laceration of the proximal leg is easily seen and can be evaluated for glass, metal, or other foreign body. Always mark the site of a laceration injury or suspected foreign body like in the radiograph above. As for the exposure technique, a slight increase in kVp would demonstrate better bone penetration. It is important to see the track of soft tissue injury and determine if it reaches the bone. An injury of this type is called an open injury because it can seed bacteria to the bone and cause bone infection if not properly diagnosed and treated.

Radiograph #103

image103 This radiograph clearly does not meet the diagnostic criteria for the lateral view of the leg. What can be done to improve the quality of the radiograph when imaging through a newly placed plaster splint?

Critique of Radiograph #103

image103

Although the required anatomy is presented on this radiograph we cannot see it because the part is underpenetrated. Too improve image quality begin by putting the ankle under the cathode. Routinely, the cathode is aligned with the proximal leg; however, with a plaster splint on the ankle the ankle is denser. Making this adjustment will place the most concentrated portion of the x-ray beam over the ankle where it is needed. Also, the kVp should be increased at least 15%, which is equivalent to doubling radiographic density. So using the anode-heel-effect and increasing the kVp will result in a more penetrated image that will meet the diagnostic criteria.

Radiograph #104

image104 Now we are looking at a repeated image of radiograph #103. The technologist increased the kVp from 70 to 80 and used the anode-heel-effect. Did these changes result in the radiograph meeting the diagnostic criteria?

Critique of Radiograph #104

image104

The goal of imaging when a cast has been placed is to include the require anatomy in its correct radiographic anatomical presentation, and provide uniform density over the part. Correcting the exposure technique and using the heel effect did greatly improve this radiograph. The distal leg is better penetrated and we see more uniform density on the radiograph. While the ankle is not optimally demonstrated, this radiograph shows alignment of the bones of the leg meeting the diagnostic criteria for this view.

Radiograph #105

image105 This patient presented to a local emergency room with a clinical exam suspicious for fracture of the distal tibia and fibula. The orthopedic surgeon placed a temporary splint on the lower leg to support it. Does this radiograph meet the diagnostic criteria for the AP leg projection?

Critique of Radiograph #105

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When the leg is requested for evaluation, both the knee and ankle joints must be included. Because neither the knee nor the ankle is entirely demonstrated, this radiograph must be repeated. Did you notice the fracture at the fibular neck although the proximal leg is clipped? Omission of the required anatomy is not acceptable. With careful positioning almost any average length leg can be fitted on a 14 X 17 cassette positioned diagonally. The radiographic exposure appears to be good for bone detail. The fracture of the distal leg and proximal fibula is well visualized. So this radiograph should be repeated to include both extremities of the leg. Two separate images may be taken with the proximal and distal joints so long as the two images overlap.

Radiograph #106

image106 This is a radiograph of a patient with healing fractures of the distal tibia and fibula. The patient complains of distal leg pain when walking. Does this radiograph meet the diagnostic criteria for the AP leg projection?

Critique of Radiograph #106

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Whenever the leg is requested and either extremity is omitted (in this case the distal tibia is clipped) the diagnostic criterion is not satisfied. In follow up to this is the question “should this radiograph be repeated?” The clinical history suggests that this is a follow up study to check bone healing and the patient presents with distal extremity leg pain. Therefore, the ankle should be included since the leg pain could originate from the ankle. The reason the entire leg was not included is that the midsagittal plane was not aligned with the diagonal axis of the cassette. It is better to clip the knee in this scenario than to omit part of the ankle. Notice the deformity in the tibia and fibula from a healing fracture. Bone remodeling is incomplete, although there is a significant amount of bony callus and lamellar bone formation. The exposure technique adequately demonstrates bone and soft tissue detail in the visualized area.

Radiograph #107

image107 Here is a situation in which the patient would not fit on a standard 14 X17 cassette turned diagonally. The technologist split the cassette to put the upper and lower leg on one film. Does this imaging method meet the diagnostic criteria for the AP view of the leg?

Critique of Radiograph #107

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This is an “old school” style of radiography of the tibia/fibula when the leg is too long. I remember making a radiograph like this on a 19y/o patient who was 6’11” and still growing. Certainly this is an acceptable way to image the long bones of the leg in this scenario. When imaging an extremely long leg it is acceptable to split the AP or lateral view into two images. It is important that when two images are placed on the same film that: 1) the demonstrated anatomy overlaps, 2) that scatter does not fog adjacent images, and 3) that no parts of the images are superimposed. Using a lead blocker to cover each side is recommended. Using a lead blocker to cover each side is recommended. Now for the critique of this radiograph, the required anatomy is presented in correct anatomical position. Good bone and soft tissue detail is demonstrated. The ankle is slightly underpenetrated. You should include a coned down AP view of the ankle that is well penetrated through the talus.

Radiograph #108

image108 This lateral view of the leg was taken on the same patient as in radiograph #107. Does this radiograph meet the diagnostic criteria for the lateral projection of the tibia/fibula?

Critique of Radiograph #108

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In this example we see that the technologist was able to get the entire leg with overlap of the midshaft using two exposures. This is an acceptable way to image when the length of the leg will not include both joints on a single projection. What is important here is that when positioning this way that the knee is put in a true lateral with the condyles superimposed. Likewise, the ankle should be positioned in a true lateral for the distal leg view. Doing so will give the maximum diagnostic value to the joints at the extremities of the leg. In this example, the knee is not properly positioned with the femorotibial joint and the femoropatellar joint spaces open. This radiograph does not need to be repeated; however, greater diagnostic value would have been presented had the knee and distal leg been better positioned. The radiographic exposure technique shows good bone density and detail as well as good soft tissue detail. Overall, this is an acceptable radiograph.

Radiograph #109

image109 This radiograph was taken on a patient following internal fixations of the tibia and fibula. This is a post surgical film taken was to demonstrate the fracture reduction and alignment of the internal fixation. Does this radiograph meet the diagnostic criteria for the lateral leg projection?

Critique of Radiograph #109

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The knee is positioned in a true lateral without rotation. The proper anatomical relationship should show the tibia partially superimposing the fibular head; no superimposition in the mid-shaft, and the posterior distal tibia superimposes the distal fibula. Another good point about this radiograph is that sharp contrast between bone and metal is seen. The screws and plates are well defined so that any loosening of them can be detected. The entire tibia and fibula is demonstrated, but the talus bone of the foot is not entirely seen which makes it appear to not be inclusive of all the anatomy of the leg. However, all of the anatomy is demonstrated and this is a great radiograph. The ankle should be requested if the relationship of the leg and the foot are in question. The radiographic technique is good, demonstrating metal, bone, and soft tissue detail.

Radiograph #110

image110 This radiograph was taken on a patient following internal fixations of the tibia and fibula. This is a post surgical film was to specifically demonstrate the internal fixation and reduction of the tibia and fibula. Does this radiograph meet the diagnostic criteria for the lateral view and for the requested evaluation?

Critique of Radiograph #110

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Positioning is excellent; the knee is not rotated and the patellofemoral joint space is demonstrated. Distally, the ankle joint is not fully appreciated on the film. This is not a post surgical film because there is no air in the soft tissues commonly seen immediately following surgery. More likely this radiograph was taken a few weeks post surgical fixation. The healing fracture of the distal fibula is not fully appreciated on this film because of poor subject detail. There are epiphyseal and metaphyseal lines seen in the distal tibia and distal fibula. Subject detail is very much needed on this follow up radiograph because the “tightness” of the screws cannot be fully evaluated unless there is sharp contrast between bone and metal. At the same time the exposure should not obliterate the sharp edge detail between soft tissue and bone. Compare the exposure technique on this radiograph with radiograph #109 above. Notice this radiograph shows low contrast that favors soft tissue detail. We cannot say this is a bad technique because we do not know the exam history. I would assume the image was taken because of pain and they wanted to rule out bone infection. In such case we would be looking for gas produced by bacteria in the soft tissues. It certainly is not a good exposure technique for bone detail. Be careful when making this type of radiograph that your technique reflects the history for diagnosis. This radiograph should be repeated using an exposure technique closer to that seen in radiograph #109. Use the 50/15 rule to increase subject contrast and detail is recommended.

Radiograph #111

image111 Following surgery involving open reduction internal fixation (ORIF) of the tibia this radiograph was requested. Clinical history for the exam stated, “To evaluate surgical fixation of the proximal tibia and shaft.” Does this radiograph meet the diagnostic criteria for the AP view of the leg?

Critique of Radiograph #111

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This radiograph raises a very important point about post surgical imaging. The clinical history for the requested exam “is to evaluate surgical fixation.” Subject detail is lacking in the image. The fixation screws appear smooth and we cannot see their spiral design detail. Sharp contrast between bone and metal should be displayed. When you have clear borders of the tibia and fibula displaying differences between cortical and spongy bone then you have a good post surgical exposure technique. The second point is that when imaging a prosthetic implant the entire fixation must be demonstrated on a single view. Failure to demonstrate bone proximal and distal to the fixation hardware is reason to repeat a radiograph. To complete the diagnostic criteria you may only need to add a collimated AP knee projection; however, some orthopedic surgeons require that the entire fixation be seen on a single view.

Radiograph #112

image112 This patient presented to a local emergency room with a chief complaint of knee and leg pain, an inability to bear weight. The clinical history revealed trauma due to a fall down approximately 10-12 steps just an hour prior to presentation at the ER. Does this radiograph meet the diagnostic criteria for the AP projection of the leg?

Critique of Radiograph #112

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Just using the diagnostic criteria for the AP view of the tibia/fibula we can see that this radiograph does not meet the diagnostic criteria and should be repeated. Including the entire tibia and fibula is required. Just because a fracture is demonstrated in the proximal tibia and fibula does not mean this is a diagnostic radiograph. Notice that the patella seen in the midline of the distal femur is not well penetrated indicating the exposure technique is inadequate. A small portion of the talus is seen; notice it displays high contrast (very bright relative density). Increase the kVp 15 percent to penetrate the leg and include both extremities on the radiograph. This should give sharp bone margins and penetrate the tibia to reveal any occult fractures not seen. Also use the anode-heel-effect to place the concentrated portion of the x-ray beam over the knee. Also increase the target-to-image distance to reduce magnification of the part.

Summary: Critique of Tibia/Fibula AP and Lateral Radiographic Views

  • For the AP and lateral views of the leg the entire tibia/fibula including both the knee and ankle joints must be included on the radiograph. If both joints cannot be included as a single film then two films with overlapping parts of the midshaft should be made.
  • A properly positioned AP view will demonstrate proximal tibia with slight superimposition of the fibular head. The midshaft of the tibia and fibula are seen without superimposition and the distal tibia and talus are partially superimposed on the fibula. All soft tissue surrounding the entire tibia, fibula, ankle joint, and visualized knee joint must be demonstrated.
  • For the AP and lateral projection the leg is positioned so that the anode-heel-effect maximizes use of the concentrated part of the divergent beam over the proximal tibia. To take advantage of the heel effect the cathode is positioned over the knee and the anode over the ankle. This may be reversed when a plaster cast immobilizes the ankle, but not the proximal leg.
  • Radiographic exposure technique should demonstrate good bone penetration at the ankle and knee joints without “burn out” of the fibular shaft. The surround soft tissues should be demonstrated in a way that will reveal any soft tissue injury such as a laceration of foreign object. The radiograph should be free of motion artifact, and sharp trabecular marking and sharp edges of the tibia and fibula seen. Soft tissues should show contrast between muscle, bone, and fat.
  • When properly positioned, the tibia will partially superimpose the fibular head proximally, their midshaft portions free of superimposition, and the fibula superimposed distally by the posterior portion of the tibia. The femoral condyles will be superimposed when the knee is flexed 45 degrees.



Summary Points

  • Annually more than 352,000 hip fractures occur in the United States. Women over the age of 50 years are 2 to 3 times more likely to suffer hip fractures than men.
  • The hip joint is a diarthroses, or synovial joint. It is normally capable of flexion, extension, abduction, adduction, circumduction, and internal and external rotation.
  • The knee is composed of four bones, the femur, tibia, fibula, and patella. The knee joint is a hinge-type joint, which is capable of flexion and extension motions. Flexion and extension are not the only motions of the knee, in the last 50 years it has been discovered that the knee performs slight rotational movement.
  • The patella is a sesamoid bone developed within the tendon of the quadriceps femoris tendon. The two primary functions of the patella are to strengthen the tendon of the quadriceps femoris muscle, and to protect the knee joint.
  • The proximal tibia has two concave surfaces, the medial and lateral condyles, which articulate with the femoral condyles. Between the condyles is an upward projection called the intercondylar eminence.
  • The stabilizing ligaments of the knee include the medial collateral ligament (MCL) and lateral collateral ligament (LCL), and are located outside the knee joint proper; the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are stabilizer ligaments located within the knee joint. The patellar ligament is located outside the knee joint; it also provides support for the knee by shielding it, and strengthening the actions of the quadriceps femoris muscle.
  • The knee contains two semi-lunar C-shaped menisci composed of fibrocartilage. The two menisci lie on the tibial plateaus along the lateral peripheries of the joint. The function of the meniscus is to provide shock absorption to the knee during the stress of weight bearing and movement.
  • The functions of the anterior cruciate ligament are to resist rotational motion of the knee and prevent the femur from translating backwards on the tibia. In other words, it limits hyperextension of the knee joint. The most common mechanism of ACL injury is internal rotation of the femur when the knee is in full extension.
  • The PCL functions to reduce internal rotational movements of the knee, and to prevent the tibia from sliding backwards on the femur. In other words, the PCL prevents hyperflexion of the knee joint.
  • The CR should enter the part parallel with the tibial plateau. A well positioned AP view of the knee will demonstrate the femorotibial joint space open, the anterior and posterior margins of the tibial condyles superimposed, the proximal tibia slightly superimposes the proximal fibula, and the patella is seen above the patellar fossa and slightly lateral to midline.
  • The knee lateral view should include the distal one-fourth of the femur and proximal one-forth of the tibia/fibula. All surrounding soft tissue must be entirely demonstrated. Keep in mind that joint effusion is best diagnosed when the knee is flexed no more than 20 degrees. This is because flexing the knee more than 20-degrees causes tightening of the muscles/tendons across the knee joint and patella resulting in the patella to obscure the fat pads. The anterior and posterior suprapatellar fat pads must be visualized to evaluate joint effusion.
  • The tunnel (Holmbald) view should demonstrate the femoral and tibial condyles, the eipcondyles of the femur in profiled, and the intercondylar eminences within an opened femorotibial joint. The patella should not be projected inferiorly so that it obstructs the femorotibial joint space.
  • The Merchant view is used to accurately demonstrate the relationship of the patella to the patellar surface of the femur. This is a preferred projection to demonstrate dislocation of the patella and an open femoropatellar joint space.
  • When imaging the entire leg making use of the anode-heel-effect places the concentrated part of the divergent beam over the proximal tibia. This will provide uniform density over the thick and thin parts of the leg. To take advantage of the heel effect the cathode is positioned over the knee and the anode over the ankle.
  • A request for the leg is made the entire tibia/fibula including both the knee and ankle joints should be made. If it cannot be included as a single film then two films with overlapping parts should be made.
  • When imaging an extremely long bone it is acceptable to split the view into two images placed on a single radiograph. When doing so be sure that 1) the required anatomy shows overlap on the projection, 2) that scatter does not fog adjacent images, and 3) that no part of the images are superimposed. Using a lead blocker to cover each side of the cassette is recommended.
  • When imaging a prosthetic implant the entire fixation must be demonstrated on a single view. Failure to demonstrate bone proximal and distal to the fixation hardware is reason to repeat a radiograph.
  • A properly positioned lateral leg radiograph will demonstrate the entire tibia and fibula, knee and ankle joints, and surrounding soft tissues. The tibia will partially superimpose the fibular head with their midshaft portions free of superimposition, and the distal fibula superimposed by the distal half of the posterior portion of the tibia. The femoral condyles will be superimposed when the knee is flexed 45 degrees.
  • Always mark the site of a penetrating injury such as a laceration or foreign body entry. Often a fracture that presents with a track leading from the skin to the fracture (called an open fracture) requires surgical intervention to render the site aseptic.
  • The leg should not be requested if the ankle is the structure in question. This is because the AP leg will demonstrate the femorotibial and tibiotalar joint spaces closed. This is due to the divergent x-ray beam as the area of coverage is great and the central ray does not pass through either joint. For the AP tibia/fibula radiograph neither the knee joint nor the ankle joint are parallel with the cassette or perpendicular to the x-ray beam.






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Copyright image Copyright 2006 Nicholas Joseph Jr.




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