Variable Axial Rotation is Needed to Achieve a Balanced Flexion Gap in Total Knee Arthroplasty

The purpose of this study was to quantify femoral rotation in the axial plane for posterior-stabilized total knee replacements performed with a modified gap-balancing technique. In total, 2442 knees were selected from a computer-assisted orthopaedic surgery navigation system database. The knees were stratified into three groups based on preoperative coronal plane alignment. The computer navigation recorded distal femoral and tibial resection angles, and the rotational position of the femoral component. Means were calculated for each of the three groups. There was substantial variation of femoral axial rotation in all three groups. In aggregate, the mean rotational position for all knees was 2.4º external (-10.2º – 20.9º). The mean rotation for the varus group was 2.5º (-9.8º – 15.7º), 2.5º (-9.8º – 20.9º) for the neutral group, and 1.1º (-10.2º – 9.9º) for the valgus group (p < 0.0001). The data indicates that choosing a predetermined rotational position for the femoral component may lead to flexion gap asymmetry more frequently than by adjusting the rotational position intraoperatively to achieve a rectangular flexion space. This is the first study to quantify differences between varus and valgus knees related to flexion gap stability. Correlation of these findings to clinical outcomes is needed. There is no single rotational position for the femoral component that will produce a balanced flexion gap for every knee. There is a statistically significant difference between mean rotational position for femoral components for varus and valgus knees. (Journal of Surgical Orthopaedic Advances 34(4):193–195, 2025)

Key words: gap balancing, femoral componet rotation, flexion gap, knee instability