Femoral rotation influences dynamic alignment of the lower extremity in total knee arthroplasty.

Abstract

Besides the long-leg standing X-ray film focusing on static standing mechanical alignment of the lower extremity, dynamic alignment from full extension to 90° flexion after total knee arthroplasty (TKA) is rarely mentioned. Computer-assisted surgical technology enables surgeons to measure and assess knee behaviour during surgery. This study was designed to analyse the influences of femoral rotation on dynamic alignment of the lower extremity in TKA. Seventy-six consecutive patients with end-stage knee osteoarthritis were enrolled. External rotation osteotomy of the distal femur during TKA was completed according to the pre-operative external rotation angle (ERA), intra-operative transepicondylar axis (TEA) and anteroposterior (AP) line. Passive dynamic alignment of the lower extremity during knee flexion was recorded. The variation trend of hip-knee-ankle (HKA) alignment and the influences of femoral external rotation osteotomy were analysed. Postoperative deviation of HKA alignment from 0° to 90° flexion was associated with the rotational alignment of the femoral component (r = -0.769, p < 0.001). Variation trend of HKA alignment during knee flexion tended to be varus, valgus and neutral according to the selected angle of external rotation osteotomy of the distal femur. External rotation osteotomy of the distal femur played a crucial role in determining dynamic HKA alignment in TKA.