A correlative study of the geometry and anatomy of the distal femur.

Sixteen knees were examined roentgenographically in the lateral plane. Ten knees were examined from autopsy subjects. The distal articular femur may be represented by three circular surfaces: (1) the floor of the patellar groove (articulating with the patella from 10 degrees to 100 degrees), (2) the posterior femoral condyles (articulating with the tibia from 10 degrees to 150 degrees), and (3) the distal condyles (articulating with the tibia from 0 degrees to 10 degrees). The radii of these surfaces, their angular arcs, and the distances between their centers varied with the size of the femur but fell within a narrow range. The radii of the patellar groove and the posterior femoral condyles averaged 24 mm and 21 mm, and the average angle subtended by these arcs was 90 degrees and 140 degrees, respectively. The average distance between the centers of these two circles was 20 mm. The femoral attachment of the synovial and patellar retinacular reflections was found in the area of the center of the patellar groove circle. The femoral attachments of the medial collateral and posterior cruciate ligaments and of the lateral collateral and anterior cruciate ligaments were found to be in the area of the center of the circle of the medial and lateral posterior femoral condylar circles, respectively.