The difference in trochlear orientation between the natural knee and current prosthetic knee designs; towards a truly physiological prosthetic groove orientation.

The patella groove of total knee replacements has evolved from a groove with a neutral orientation to a groove with a lateral (also referred to as valgus) orientation. In this study the authors questioned whether femoral components with a lateral groove orientation more closely approximate the configuration in the natural knee. The groove orientations of an implanted CKS femoral component, available in different sizes and with different groove orientations, were determined and compared with formerly published measurements of the natural trochlear orientation. It was found that the prosthetic groove orientations differed considerably from human anatomy, up to a maximum deviation of 6.4 degrees. The orientations of the prosthetic grooves were all equal within the area of the natural trochlea. The area of the natural trochlea guides the patella between about 30 degrees and 120 degrees of knee flexion. The orientations of the prosthetic grooves were different in the area of the supracondylar pouch/proximal anterior flange. This area guides the patella between about 0 degrees and 30 degrees of knee flexion. As this study showed a considerable deviation between natural and prosthetic groove orientation, an optimal prosthetic groove orientation, matching the average orientation in the natural knee, was mathematically determined.