Cam Impingement of the Posterior Femoral Condyle in Medial Meniscal Tears

POA on sitting XP. Sitting XP was taken as follows: Each patient maintained a sitting-square position on the radiography table with the weight of his or her buttocks on the heels. An X-ray film cassette was placed vertically between the thighs. X-rays were emitted horizontally from the lateral to the medial side of the knee so that the direction of the X-rays and the axis of the femoral shaft created an angle of about 97° posteriorly. The angle formed by the maximum gradient tangent of the medial femoral condyle (L1) and the maximum gradient tangent of the medial tibial plateau (L2) was assumed to be the POA (θ). When the angle opened posteriorly to the knee joint, it was considered positive; when it opened anteriorly, it was considered negative.

Sagittal MRI was performed at full flexion of the knee joint (sitting MRI). The knee joint to be examined was fully flexed and the patient sat square on the heel while the other knee joint was extended with a cushion placed under the buttock. The patient's back was reclined on a backrest so that he or she could be slid into the gantry.

Sagittal MRI scans showing PMTFI of knee joint: posterior segment on extension (left), posterior segment on full flexion (middle), and middle segment on full flexion (right). (A) In a knee joint without PMTFI, there is no deformation of the middle or posterior segment of the medial meniscus on full flexion. (B) In some cases of PMTFI, only the posterior segment of the medial meniscus is deformed on full flexion. (C) In some cases of PMTFI, the middle and posterior segments are deformed and dislocated anteriorly on full flexion. The lines show the maximum gradient tangent of bone contour of the medial femoral and tibial condyles. The angle formed by the 2 tangents is usually larger than the POA, which is measured on lateral X-ray films of the knee joint at full flexion (Fig 1).

Surgical technique. (A) MRI scan showing determination of the range of bone resection performed so that the posterior segment was not compressed by the most proximal part of the medial femoral condyle. The shape of the posterior segment of the intact medial meniscus was copied from the sagittal MRI scan of the contralateral extended knee joint. The line on the medial femoral condyle shows the expected maximum gradient tangent of bone contour of the medial femoral condyle after bone decompression. (B) Posterior capsule incised at proximal end of joint cartilage (arrow). (C) Approach to redundant bone tissue (black area), which is excised with a bur. (D) Reattachment of capsule to original position by absorbable sutures.