Positioning - Knee/ Patella

Where does the CR enter for the AP and AP oblique projections of the knee?

½ inch distal to the apex of the patella

Describe the CR angle for the AP projection of the knee based on the size of the patient’s thigh

Thin: 5 degrees caudal

Average: no angle

Thick: 5 degrees cephalic

How are the epicondyles in respect to the IR for an AP projection of the knee?

Parallel

What are 2 ways you can identify the AP projection of the knee when looking at a radiograph?

1. Patella is centered to femur

2. Medial half of fibular head superimposed by tibia

What is the degree of oblique for a medial or lateral oblique of the knee?

45 degrees

What is best demonstrated on an AP oblique with medial rotation of the knee?

Open proximal tib/fib joint + lateral condyles of femur

What is best demonstrated on an AP oblique with lateral rotation of the knee?

Medial condyles of femur and tibia

What are 2 ways you can identify the medial oblique of the knee when looking at a radiograph?

1. Open proximal tib/fib joint

2. ½ of patella without superimposition of femur

What are 2 ways you can identify the lateral oblique of the knee on a radiograph?

1. Proximal fibula superimposed by the tibia

2. ½ of patella free of superimposition of femur

Is there an angle on the tube for a medial or lateral oblique of the knee?

No

Where does the CR enter for the lateral position of the knee?

1 inch distal to medial epicondyle

What is the CR angle range for the lateral projection of the knee? What does it superimpose?

5-7 degrees cephalic, it superimposes the femoral condyles

How are the epicondyles in respect to the IR when positioning for a lateral knee?

Perpendicular

What is the degree (range) of flexion of the knee when positioning for the lateral knee? Why is more than 30 degrees not good?

Flex 20-30 degrees, more than 30 will close the patellofemoral joint

If the distal condyles are not superimposed on the lateral knee, what needs to be done to correct it?

More cephalic angle on the tube

If the posterior condyles are not superimposed on the lateral knee, what do you look at?

The fibular head, and tibia

Where is the fibular head if the patient is over-rotated for a lateral knee?

Fibular head is not superimposed on the tibia/ barely

Where is the fibular head if the patient is underrotated for a lateral knee?

Fibular head will be completely superimposed