Knee joint

Question 1

What are the clinical indications for an x-ray of the knee joint?

Answer 1

Fractures,
lesions,
bony changes related to degenerative joint disease involving the distal femur, proximal tibia and fibula, patella, and knee joint.

Question 2

What equipment is required for an antero-posterior projection of the knee?

Answer 2

24 x 30 cm image receptor lengthwise
Sheet of lead rubber
Sandbag
Gonad shield

Question 3

What are the basic projections for the knee joint?

Answer 3

Antero-posterior projection
Lateral projection

Question 4

What factors should be considered when deciding to use a grid for knee radiographs?

Answer 4

• The size of the patient’s knee
• The preference of the radiographer and physician

Question 5

How should the patient be positioned for an antero-posterior projection of the knee?

Answer 5

• Place patient in supine position with no rotation of pelvis.
• Provide pillow for patient’s head.
  Leg should be fully extended.
• Centre leg and knee to central ray and to midline of table or image receptor.

Question 6

How should the leg be positioned for a true AP knee projection?

Answer 6

Rotate leg internally 3° to 5° (or until interepicondylar line is parallel to the plane of the image receptor).

Question 6

What is the centring point for an antero-posterior projection of the knee?

Answer 6

1.3 cm below the apex of the patella

Question 7

What anatomy should be demonstrated in an AP projection of the knee joint?

Answer 7

Distal femur and proximal tibia and fibula, with the femorotibial joint space open and the articular facets of the tibia seen on end with minimal surface area visualized.

Question 7

How should the central ray be directed for different body types in an AP knee projection?

Answer 7

• <19 cm (thin thighs and buttocks): 3° to 5° caudad
• 19 to 24 cm (average thighs and buttocks): 0° angle
• 24 cm (thick thighs and buttocks): 3° to 5° cephalad

Question 8

What are the evaluation criteria for the position in an AP knee joint image?

Answer 8

• No rotation evidenced by symmetric appearance of femoral and tibial condyles and the joint space.
• The approximate medial half of the fibular head should be superimposed by the tibia.
• The intercondylar eminence is seen in the center of the intercondylar fossa.
• Center of collimation field should be to the midknee joint space.

Question 9

What are the evaluation criteria for exposure in an AP knee joint image?

Answer 9

• Optimal exposure visualizes the outline of the patella through the distal femur.
• The fibular head and neck do not appear overexposed.
• No motion should occur; trabecular markings of all bones should be visible and appear sharp.