Effects of sex and lower extremity alignment on orientation of the knee joint line in knee surgery

Background Determination of the proper orientation of the knee articular surface is required both for correction of knee malalignment by osteotomy and for correct component alignment in knee arthroplasty. We sought to determine whether the patients＇ sex and lower extremity alignment （hip-knee-ankle angle） affects proper knee realignment in osteotomy or component alignment in total knee arthroplasty. Methods We examined 199 healthy adult knees with malalignment of 〈5°to determine the mechanical medial distal femoral angle, mechanical medial proximal tibial angle, surgical transepicondylar axis angle, and discrepancies between bone-cut orientations of osteotomy or total knee arthroplasty and the joint line of the distal femoral condyles, posterior femoral condyles and proximal tibial plateaus, using a three-dimensional computed tomography model. Results The mean mechanical medial distal femoral angle and mean mechanical medial proximal tibial angle were （94.4±1.9）° and （87.6±1.8）° respectively for women and （93.8±2.0）° and （87.1±1.4）° respectively for men. The surgical transepicondylar axis angle was （2.9±1.6）° for women and （3.2±1.7）° for men. Independent of sex, the hip-knee-ankle angle was closely related to the mechanical medial distal femoral angle and mechanical medial proximal tibial angle, but not to the surgical transepicondylar axis angle. A slightly more valgus alignment of the knee and a more valgus angulation of the distal femoral joint line were found in women, whereas a more varus angulation of the proximal tibial joint line was found in men. Sex had the greatest effect on knee joint line orientation when the lower extremity was valgus in alignment. Conclusions A more valgus femoral joint line can be expected in women and in persons with valgus lower extremity aliqnment; a more varus tibial joint line can be found in men and in persons with varus lower extremity alignment.