Femoral component rotation in mobile-bearing total knee arthroplasty.

The surgical technique utilized for the LCS mobile-bearing since 1977 has been a tibial cut first method which requires determination of femoral rotation with tension spacing. We evaluated 38 randomly selected mobile-bearing TKA in which this technique was utilized. All cases had satisfactory clinical results. Spiral computed tomography scans measured the posterior condylar angle which is the angle of the femoral component posterior condyles in relation to the surgical transepicondylar axis. The mean femoral component alignment was 0.3 degrees of internal rotation to the transepicondylar axis (S.D.=2.2 degrees ; range=6 degrees internal to 4 degrees external). Four cases (10%) were outside of 3 degrees from the TEA. Lateral patellar tilt and subluxation was identified in one female who had a femoral component position of 5 degrees internal rotation. In 90% of cases, the posterior condylar angle was within 3 degrees of the surgical transepicondylar axis which is regarded as the functional ideal for conventional methods.