Impact of Axial Component Alignment in Total Knee Arthroplasty on Lower Limb Rotational Alignment: An In Vitro Study

Correct rotational implant alignment is associated with increased postoperative function and implant survival in total knee arthroplasty (TKA). Due to conformity between tibial and femoral implants, particularly in full extension, we assumed a mutual interference of femoral and tibial component rotations. We, therefore, hypothesized that different rotational alignments of the tibial or femoral components change the rotational postures between the tibia and femur after TKA. In 10 healthy knees of whole body cadavers, TKA was performed. Both femoral and tibial components were implanted in different internal (6 degrees) and external (3 and 6 degrees) rotational alignments. Consequential osseous rotational changes between the tibia and the femur were measured in full extension using a commercial computer navigation device. External rotation of the femoral component resulted in significant external rotation of the tibia, while external rotation of the tibial component caused a significant internal rotation of the tibia. The opposite applied to femoral and tibial component internal rotations. Therefore, largest changes of the osseous tibiofemoral rotational postures were found by the combination of 6 degrees femoral component internal and 6 degrees tibial component external rotations (mean 11.2 degrees, standard deviation 5.0, p < 0.001), as both cause tibial internal rotation. In conclusion, the present results suggest that axial component alignment significantly affects lower limb rotational alignment. However, its clinical impact on forefoot progression, Q-angle, the patella, collateral, and cruciate ligaments, and surrounding soft tissues has to be clarified in further clinical and biomechanical studies.