Femoral matched tibia component rotation has little effect on the tibial torsion after total knee arthroplasty

Purpose Tibiofemoral synchronization technique matches the rotational alignment of the tibial component to the femoral component during the total knee arthroplasty (TKA). The rotational axis of the proximal tibia can be changed by this technique, which affects tibial torsion postoperatively. The purpose of this study was to investigate whether the tibiofemoral synchronization technique affect the tibial torsion, and the lower limb rotation after primary TKA. It was hypothesised that the tibial torsion would change after primary TKA. Methods Ninety-three posterior stabilised TKAs from 89 patients were included from January 2017 to December 2018. Mechanical hip-knee-ankle axis (mHKA), in plain radiographs, femoral anteversion, tibial torsion, femoral neck-malleolar angle (FNMA), and rotational alignment of the femoral and the tibial components in pre- and postoperative CT scans were measured by two blinded observers. The primary outcome was a postoperative change in femoral anteversion, tibial torsion and FNMA. Clinical outcomes were evaluated using the American Knee Society Knee Score (AKSKS)/Function Score (AKSFS), and Oxford Knee Score (OKS) preoperatively and at 1 year after TKA. Patients' perception of changes in the foot progression angle after TKA was investigated. Statistical significance was set at p < 0.05. Results The mean rotational mismatch between the femoral and the tibial component was 0.6 +/- 3.2 degrees. There was a significant decrease in femoral anteversion (9.5 +/- 6.7 degrees vs. 5.2 +/- 6.6 degrees, p < 0.001), and a significant increase in the FNMA (17.6 +/- 9.7 degrees vs. 21.8 +/- 10.5 degrees, p = 0.005) after TKA, while no significant change in tibia torsion was observed (25.4 +/- 8.8 degrees vs. 24.9 +/- 9.3 degrees, p = 0.739). AKSS (37.8 +/- 15.1 vs. 92.8 +/- 8.8, p < 0.001), AKSFS (53.9 +/- 18.1 vs. 89.9 +/- 5.3, p < 0.001), and OKS (18.0 +/- 7.3 vs. 39.9 +/- 4.8, p < 0.001) were significantly improved at 1 year after TKA. Ten knees (11%) had changes in tibial torsion greater than +/- 10 degrees postoperatively. Four of five patients who had changes in FNMA greater than 15 degrees perceived the external rotation of the foot progression angle after TKA. All four patients had an increase in tibial torsion larger than 10 degrees. Conclusion Our study shows that the tibiofemoral synchronization technique less likely affects the tibial torsion after primary TKA.