The cartilaginous and osseous geometry of the femoral trochlear groove.

Photography was used to study the geometry of the cartilaginous and osseous contours of the distal femur and the orientation of the trochlear groove in 9 fresh-frozen and 24 embalmed knees. The sulcus angle (146.1 degrees +/-5.5 degrees ) decreased from 0 degrees to 50 degrees of femoral flexion then increased afterwards. The maximum slope of the lateral femoral condyle (20.2 degrees +/-5.2 degrees ) also decreased with flexion. Both the sulcus angle ( p=0.0007) and maximum slope ( p=0.0001) were larger at 0 degrees than they were for 60 degrees cartilaginous surfaces. The lateral femoral condylar height decreased, whilst the medial femoral condylar height increased as the flexion increased. The femoral groove was midway between the two femoral epicondyles (49.5+/-3.9%), but deviated laterally as the flexion angle increased. The groove axis deviated distally and laterally from the femoral anatomical axis for both cartilaginous and bony surfaces, and the angle between the groove and anatomical axes was similar for both cartilaginous (19.1 degrees ) and osseous (16.8 degrees ) surfaces. Articular cartilage is not well represented on radiography yet it had a significant effect on the distal femoral geometry, and should be taken into account when evaluating the patellofemoral joint.