AP Axial Intercondylar Fossa Beclere is a radiography positioning projection of the Lower Extremity. Supine, knee flexed 40-45 degrees (Bontrager) or femur 60 degrees to tibia (Merrill's), CR perpendicular to lower leg. SID 40". The centering point is located 1/2 inch distal to the patellar apex, with patient supine and knee flexed 40-45 degrees. The central ray is about 40 to 45 degrees cephalad, perpendicular to the long axis of the lower leg, matching the knee flexion. Image-quality criteria include intercondylar eminence and notch clearly visualized, intercondylar fossa in profile and open, not superimposed by the patella. A sample technique is 70 kVp with DR 2.5 or CR 5 mAs, at an SID of 40 inches (102 cm).
Anatomy demonstrated
- Intercondylar eminence in axial plane.
- Intercondylar fossa and notch.
- Femoral condyles in axial relationship.
- Tibial plateau with intercondylar topography.
Patient preparation
- WARNING: with possible spinal injury or severe trauma, do not attempt to move the patient; do not rotate a severely injured part or remove splints (Bontrager). Merrill's: do not attempt true AP or lateral positioning of a severely injured limb; take two projections 90 degrees apart, moving it as little as possible, and move the IR and tube if the patient cannot reach the position.
- Verify patient identity using two identifiers.
- Remove shoes and any radiopaque items from the leg.
- Position patient supine on table with knee extended initially.
- Flex the affected knee 40 to 45 degrees over a support.
- Support the IR so it rests firmly against the back of the thigh and lower leg.
- Keep the whole leg in anatomic position with no rotation.
Position & centering point
1/2 inch distal to the patellar apex, with patient supine and knee flexed 40-45 degrees.
Central ray
About 40 to 45 degrees cephalad, perpendicular to the long axis of the lower leg, matching the knee flexion.
Exposure / technique
- kVp
- 70
- mAs
- DR 2.5 / CR 5
- SID
- 40" (102 cm)
- Notes
- For patients who cannot lie prone. Bontrager calls it not preferred: CR-angle distortion, more part-IR distance, more gonadal exposure. Bontrager prints a grid and digital 75 +/- 5 kV; the sample is Merrill's nongrid tabletop row. Sample technique: DR 2.5 / CR 5 mAs at 70 kVp, 40 in SID, for a 14 cm part. Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Intercondylar eminence and notch clearly visualized.
- Intercondylar fossa in profile and open, not superimposed by the patella.
- No rotation: posterior femoral condyles symmetric, about half the fibular head behind the tibia.
- Tibial plateau visible in axial plane.
- Collimation: four sides to the knee joint area (Bontrager); 1 inch beyond the sides (Merrill's).
Common errors
- 1 Patella superimposed on the fossa, which should appear open in profile.
- 2 CR not perpendicular to the lower leg.
- 3 Rotation: posterior femoral condyles not symmetric.
Clinical indications
- Intercondylar eminence fracture evaluation.
- Osteochondral defects or joint space narrowing in patients who cannot lie prone.