Knee joint 2

Question 1

How should the patient be positioned for a lateral projection of the knee joint?

Answer 1

• The patient lies on the side to be examined, with the knee flexed at 20° to 30°.
• The second limb is brought forward in front of the one being examined and supported on a sandbag.
• A sandbag is placed under the ankle of the affected side to bring the long axis of the tibia parallel to the image receptor.
• Dorsiflexion of the foot helps maintain this position

Question 2

What is the centring point and direction of the central ray for a lateral projection of the knee joint?

Answer 2

• Centring point: 2.5 cm distal to the medial epicondyle.
• Direction of central ray: Angle central ray 5° to 7° cephalad.

Question 3

What are the evaluation criteria for the position in a lateral knee joint image?

Answer 3

• True lateral position of knee without rotation demonstrates posterior borders of the femoral condyles directly superimposed.
• Patella should be seen in profile with femoropatellar joint space open.
• The 5° to 10° cephalad angle of central ray should result in direct superimposition of the distal borders of the condyles.
• Knee joint is in center of collimated field.

Question 3

What anatomy should be demonstrated in a lateral projection of the knee joint?

Answer 3

Distal femur, proximal tibia and fibula, and patella shown in lateral profile. Femoropatellar and knee joints should be open.

Question 4

What are the evaluation criteria for exposure in a lateral knee joint image?

Answer 4

Optimal exposure with no motion visualizes important soft tissue detail, including fat pad region anterior to knee joint and sharp trabecular markings.

Question 5

What are the indications for an antero-posterior weight-bearing knee projection?

Answer 5

Femorotibial joint spaces of the knees demonstrated for possible cartilage degeneration or other knee joint pathologies.

Question 6

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

Answer 6

• Place the patient in the upright position with the back towards a vertical grid device.
• Adjust the patient’s position to centre both knees to the image receptor.
• Place the toes straight ahead, with the feet separated enough for good balance.
• Ask the patient to stand straight with knees fully extended and weight equally distributed on the feet.

Question 6

What equipment is required for an antero-posterior weight-bearing knee projection?

Answer 6

35 x 43 cm image receptor crosswise
Grid

Question 7

What is the centring point and direction of the central ray for an antero-posterior weight-bearing knee projection?

Answer 7

• Centring point: Midpoint between both knee joints at a level 1.3 cm below apex of patellae for average sized patient or 5° to 10° caudad on thin patient.
• Direction of central ray: Horizontal at 90° to image receptor.

Question 8

What anatomy should be demonstrated in an antero-posterior weight-bearing knee projection?

Answer 8

Distal femur, proximal tibia, and fibula and femorotibial joint spaces demonstrated bilaterally.

Question 9

What are the evaluation criteria for the position in an antero-posterior weight-bearing knee projection image?

Answer 9

• No rotation of both knees is evident by symmetric appearance of femoral and tibial condyles.
• Approximately one-half of proximal fibula is superimposed by tibia.
• Collimation field should be centred to knee joint spaces and should include sufficient femur and tibia to determine long axes of these long bones for alignment.

Question 10

What are the evaluation criteria for exposure in an antero-posterior weight-bearing knee projection image?

Answer 10

Optimal exposure should visualize faint outlines of patellae through femora.

Soft tissue should be visible, and trabecular markings of all bones should appear clear and sharp, indicating no motion.

Question 11

What are the clinical indications for an antero-posterior axial projection (Beclere method) of the knee?

Answer 11

Intercondylar fossa, femoral condyles, tibial plateaus, and intercondylar eminence demonstrated to look for evidence of bony or cartilaginous pathology.

Osteochondral defects or narrowing of the joint space.

Question 12

How should the patient be positioned for the antero-posterior axial projection (Beclere method)?

Answer 12

• Place patient in supine position.
• Flex the affected knee enough to place the long axis of the femur at an angle of 60 degrees to the long axis of the tibia.
• Support the affected knee on sandbags.
• Place the IR under the knee and position the IR so that the center point coincides with the central ray.
• Adjust the leg so that the femoral condyles are equidistant from the IR.
• Immobilize the foot with sandbags. Shield gonads.

Question 13

What is the centring point and direction of the central ray for the antero-posterior axial projection (Beclere method)?

Answer 13

Centring point: 1.3 cm distal to apex of patella

Direction of central ray: Perpendicular to long axis of the lower leg (40° to 45° cephalad).

Question 14

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

Answer 14

• Center of four-sided collimation field should be to midknee joint area.
• Intercondylar fossa should appear in profile, open without superimposition by patella.
• Intercondylar eminence and tibial plateau and distal condyles of femur should be clearly visualized.
• No rotation is evidenced by symmetric appearance of distal posterior femoral condyles and superimposition of approximately half of fibular head by tibia.