knee 3 Flashcards
What are the evaluation criteria for exposure in an AP axial projection image for the knee joint?
- Optimal exposure should visualize soft tissue in knee joint space and outline of patella through femur.
- Trabecular markings of femoral condyles and proximal tibia should appear clear and sharp, with no motion.
What are the basic projections for the patella?
- Postero-anterior
- Lateral
- Infero-superior
What is the clinical indication for a postero-anterior projection of the patella?
Evaluation of patella fractures before the knee joint is flexed for other projections.
How should the patient be positioned for a postero-anterior projection of the patella?
- Place patient in prone position on the x-ray couch with legs extended.
- Put a pillow for patient’s head.
- Abduct the unaffected leg and rest in a comfortable position.
- Place anterior aspect of the patella under examination on the image receptor and flex the knee slightly.
- Place support under ankle and lower leg, with smaller support under femur above knee to prevent direct pressure on patella.
- Align and center long axis of leg and knee to midline x-ray couch or image plate.
- The anterior knee should be rotated 5° internally to align the interepicondylar line parallel to the plane of the image receptor (True PA).
- Place anatomical marker, collimate beam and apply radiation protection.
What equipment is required for a postero-anterior projection of the patella?
- 18 x 24 cm image receptor lengthwise, or 24 x 30 cm image receptor if split and a sheet of lead used to cover the unexposed half.
- Foam pad
Lead protective waist apron
What is the centring point and direction of the central ray for a postero-anterior projection of the patella?
Centring point: Midpatella area found in the midpopliteal crease.
Direction of central ray: Vertical at 90° to image receptor.
What are the evaluation criteria for the postero-anterior projection image of the knee?
Knee joint and patella are shown, with optimal recorded detail of patella.
What equipment is required for a lateral projection of the patella?
- 18 x 24 cm image receptor lengthwise, or 24 x 30 cm image receptor if split and a sheet of lead used to cover the unexposed half.
- Large foam pad.
- Lead protective waist apron.
How should the patient be positioned for a lateral projection of the patella?
- Place patient in lateral recumbent position with the affected side down.
- Provide a pillow for patient’s head.
*Provide support for knee of opposite limb placed behind affected knee. - Adjust rotation of body and leg until knee is in true lateral position (femoral epicondyles directly superimposed and plane of patella perpendicular to plane of image receptor).
- Flex knee only 5° or 10° (additional flexion may separate fracture fragments if present).
- Align and center long axis of patella to central ray and to centerline of table or image receptor.
- Place anatomical marker, collimate beam and apply radiation protection.
What is the centring point and direction of the central ray for a lateral projection of the patella?
Centring point: Mid-femoropatellar joint.
Direction of central ray: Vertical at 90° to image receptor.
What anatomy should be demonstrated in a lateral projection of the patella?
- Profile images of patella,
- femoropatellar joint
- femorotibial joint.
What are the evaluation criteria for the position in a lateral patella projection image?
- True lateral: Anterior and posterior borders of medial and lateral femoral condyles should be directly superimposed, and femoropatellar joint space should appear open.
- Centering and angulation are correct if patella is in center of the IR and collimated field with joint spaces open.
What equipment is required for an infero-superior projection of the knee?
18 x 24 cm image receptor lengthwise.
Large foam pad.
Sandbag.
Lead protective waist apron.
How should the patient be positioned for an infero-superior projection of the knee?
- Lie the patient prone on the x-ray couch.
- Rest the unaffected leg in a comfortable position with a sandbag or pad under the ankle.
- Flex the knee of the affected leg at 90° with the foot extended.
- Immobilize the leg by supporting it in flexion with the bandage looped around the ankle and held by patient.
- Place anatomical marker, collimate beam and apply radiation protection.
What is the centring point and direction of the central ray for an infero-superior projection of the knee?
Centring point: Behind the apex of the patella.
Direction of central ray: Central ray angled 15° to 20° cephalad.
