The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty.

This study evaluated a technique using the anteroposterior axis of the distal femur, rather than the transepicondylar or posterior femoral condylar axis, to establish rotational alignment of the femoral component in valgus knees. The anteroposterior axis of the distal femur was defined by a line through the deepest part of the patellar groove anteriorly and the center of the intercondylar notch posteriorly. Total knee arthroplasty was done in 46 valgus knees between 1980 and 1986 using the posterior femoral condyles as landmarks for rotational alignment. From January 1986 through January 1992 total knee arthroplasty was done in 107 valgus knees using the anteroposterior axis for rotational alignment of the femoral component. In the group of knees using the posterior condylar axis, medial tibial tubercle transfer was needed intra-operatively in 8 knees to prevent lateral dislocation of the patella. In the first 2 postoperative years, 4 knees had recurrent patellar dislocation or subluxation that required surgical correction. In the group of knees using the anteroposterior axis, patellar tracking problems that required realignment were significantly reduced. One knee required medial tibial tubercle transfer to correct a Q angle > 20 degrees. In the remaining knees, the Q angle was < 10 degrees, and patellar tracking was acceptable. Two years after surgery, no knees had patellar instability.