Knee Femur Projections

These flashcards cover important vocabulary and key terms from the lecture on knee imaging projections.

AP Knee: Part Positioning

Patient in supine position with the leg fully extended. Ensure the femoral epicondyles are parallel to the IR to prevent rotation, and the entire pelvis is stable without rotation. Center the knee to the midline of the image receptor.

AP Knee: CR Angulation

CR is directed perpendicular to the IR, centered to a point approximately 1/2 inch inferior to the apex of the patella. Angulation may vary based on patient body habitus (e.g., 3-5 degrees caudad for asthenic, 0 for sthenic, 3-5 degrees cephalad for hypersthenic) to open the femorotibial joint space.

AP Knee: Structures Shown

Visualizes the distal femur, proximal tibia, and proximal fibula. The femorotibial joint space, patella (superimposed over the distal femur), and intercondylar fossa are demonstrated.

AP Knee: Evaluation Criteria

The femorotibial joint space should appear open and clear. The femoral epicondyles should be symmetrical, indicating no rotation. The patella should be centered within the intercondylar fossa. Clear bony trabecular detail and proper marker placement are essential.

AP Weight-Bearing Knee: Part Positioning

Patient stands upright with full and even weight distribution on both feet. Knees are fully extended during exposure. Ensure the femoral epicondyles are parallel to the IR and the pelvis remains non-rotated, especially for bilateral views.

AP Weight-Bearing Knee: CR Angulation

CR is typically directed perpendicular to the IR, centered to the mid-patella. Angulation (e.g., 5-10 degrees caudad or cephalad) may be used to effectively open the femorotibial joint space under stress, based on clinical need and knee anatomy.

AP Weight-Bearing Knee: Structures Shown

Demonstrates the distal femur, proximal tibia, and proximal fibula under physiological weight-bearing stress. Crucial for assessing true joint space narrowing in the femorotibial articulation.

AP Weight-Bearing Knee: Evaluation Criteria

Images should include bilateral lower limbs (if applicable) with evidence of even weight distribution. The femorotibial joint spaces should appear as they truly are under weight, allowing assessment of narrowing. Minimal rotation is critical, indicated by symmetrical femoral epicondyles/tibial plateaus. Clear bony trabecular detail should be visible.

Lateral Mediolateral Knee: Part Positioning

Patient is in a lateral recumbent position (lying on the affected or unaffected side). The affected knee is flexed 20-30 degrees. Ensure the medial and lateral femoral epicondyles are accurately superimposed, positioning the patella perpendicular to the IR.

Lateral Mediolateral Knee: CR Angulation

CR is typically angled 5-7 degrees cephalad to prevent superimposition of the medial femoral condyle and to better open the joint space. The CR is directed to a point 1 inch distal to the medial femoral epicondyle or roughly to the patellofemoral joint space.

Lateral Mediolateral Knee: Structures Shown

Provides a true lateral profile of the patella, an open patellofemoral joint space, and superimposed femoral condyles. Also demonstrates the proximal tibia and fibula, and can show signs of joint effusion, such as in the suprapatellar bursa.

Lateral Mediolateral Knee: Evaluation Criteria

Key criteria include clearly superimposed femoral condyles (indicating no rotation), an open patellofemoral joint space, and a distinct lateral profile of the patella. The proximal tibiofibular joint should be slightly separated or minimally overlapped. Clear bony trabecular detail is required.

AP Oblique Knee Medial Rotation: Part Positioning

Patient is in a supine position with the knee fully extended. The entire leg is internally (medially) rotated by 30-45 degrees.

AP Oblique Knee Medial Rotation: CR Angulation

CR is directed perpendicular to the IR, centered to a point approximately 1/2 inch below the apex of the patella.

AP Oblique Knee Medial Rotation: Structures Shown

This projection optimally demonstrates the lateral femoral condyle, lateral tibial plateau, the fully open proximal tibiofibular joint, and the lateral femorotibial joint space, along with the fibular head and neck.

AP Oblique Knee Medial Rotation: Evaluation Criteria

The proximal tibiofibular joint must be clearly open. The lateral femorotibial joint space should be visibly open. The lateral femoral condyle and tibial plateau should be well demonstrated with clear bony trabecular detail.

AP Oblique Knee Lateral Rotation: Part Positioning

Patient is in a supine position with the knee fully extended. The entire leg is externally (laterally) rotated by 30-45 degrees.

AP Oblique Knee Lateral Rotation: CR Angulation

CR is directed perpendicular to the IR, centered to a point approximately 1/2 inch below the apex of the patella.

AP Oblique Knee Lateral Rotation: Structures Shown

This projection best visualizes the medial femoral condyle, medial tibial plateau, and the medial femorotibial joint space. The patella is also demonstrated, often less superimposed than in a true AP view.

AP Oblique Knee Lateral Rotation: Evaluation Criteria

The medial femorotibial joint space should appear open. The medial femoral condyle and tibial plateau must be clearly demonstrated. Clear bony trabecular detail should be visible.

PA Axial (Camp-Coventry Method for Intercondylar Fossa): Part Positioning

Patient is in a prone position. The knee is flexed 40-50 degrees. A bolster or specialized device is used to maintain this flexion, ensuring the long axis of the femur and tibia form the required angle.

PA Axial (Camp-Coventry Method for Intercondylar Fossa): CR Angulation

CR is angled 40-50 degrees caudad, precisely matching the degree of knee flexion. The CR is directed to the popliteal crease, centered to the intercondylar fossa.

PA Axial (Camp-Coventry Method for Intercondylar Fossa): Structures Shown

The intercondylar fossa is clearly demonstrated in an open profile. The posterior (posteroinferior) surfaces of the femoral condyles, tibial spines, and a portion of the tibial plateau are also visualized.

PA Axial (Camp-Coventry Method for Intercondylar Fossa): Evaluation Criteria

An open intercondylar fossa is the primary evaluation criterion. Absence of rotation is indicated by symmetrical margins of the fossa. Clear visualization of the femoral condyles and tibial spines, along with bony trabecular detail, confirms image quality.

Tangential Patella (Settegast Method): Part Positioning

Patient lies prone with the affected knee greatly flexed, to a minimum of 90 degrees, with the foot positioned near the thigh (often stabilized with a compression band or held by the patient).

Tangential Patella (Settegast Method): CR Angulation

CR is angled 15-20 degrees cephalad relative to the lower leg (the angle may vary between 90-110 degrees depending on the degree of knee flexion). The CR is directed to the patellofemoral joint space.

Tangential Patella (Settegast Method): Structures Shown

This method projects the patella in profile, demonstrating an open patellofemoral joint space and the trochlear groove of the distal femur. It is excellent for assessing patellar fractures or chondromalacia.

Tangential Patella (Settegast Method): Evaluation Criteria

An open patellofemoral joint space and the patella visualized free of superimposition are essential. Symmetrical appearance of the patellar facets indicates no tilt or rotation. Clear bony trabecular detail of the patella and trochlea should be present.

Tangential Patella (Merchant Method - Bilateral): Part Positioning

Patient is in a supine position with both knees flexed 30-45 degrees over the end of the imaging table or a specialized Merchant apparatus used to support the femurs and position the lower legs.

Tangential Patella (Merchant Method - Bilateral): CR Angulation

CR is angled 30 degrees caudad. The CR is centered between both patellae, specifically to the midpoint of the bilateral patellofemoral joint spaces.

Tangential Patella (Merchant Method - Bilateral): Structures Shown

This projection provides bilateral visualization of the patellofemoral joint spaces, allowing for comparative assessment. It demonstrates the patellar outlines and their relative position to the femoral trochlea, useful for evaluating patellar tracking and alignment issues.

Tangential Patella (Merchant Method - Bilateral): Evaluation Criteria

Bilateral patellofemoral joint spaces should be clearly demonstrated, open, and symmetrical. Both patellae should appear in profile without significant superimposition or tilt. Clear bony trabecular detail confirms image quality.