Internal rotation of femoral component in total knee replacement: Is it safe?

Abstract

Introduction: The target for femoral component rotation in total knee arthroplasty has often been parallel to transepicondylar axis (TEA), yet outliers can still occur. The objective of this study was to investigate the mid-term results of patients with internally rotated femoral components. Materials and Methods: In total, 79 TKAs performed between September 2016- March 2017 were prospectively followed up. Femoral component rotation determination was randomised to either measured resection (MR) or gap balancing GB) technique. CT scans performed showed internal rotation of the femoral component was more common using either method. The effect of internal rotation of femoral components on clinical outcomes was analysed. Results: In total, 79 patients completed the study with mean follow-up of 43 months. Of them, 61 knees (77%) had internally rotated femoral components with 17 (21.5%) exceeding 3°. The mean rotation of the MR and GB groups were 1.51° (SD 1.72) and 1.47° (SD 2.21), respectively and not significantly different. All implants survived without patella dislocation. Using >3° internal rotation from TEA as cut-off for acceptable internal rotation, Knee Society functional assessment at 3 months was marginally inferior in the internally rotated group (KSFA 3 months: 52 vs 58, p=0.06) but the effect washed out beyond 6 months. No differences were observed in Knee Society knee score. Discussion and Conclusion: Mild internal rotation of femoral components did not jeopardise clinical or functional outcomes. Femoral component rotation can be safely adjusted to achieve soft tissue balancing such as in the setting of robotic TKA.