Is There a Gold Standard for TKA Tibial Component Rotational Alignment?

Joint function and durability after TKA depends on many factors, but component alignment is particularly important. Although the transepicondylar axis is regarded as the gold standard for rotationally aligning the femoral component, various techniques exist for tibial component rotational alignment. The impact of this variability on joint kinematics and stability is unknown. We determined how rotationally aligning the tibial component to four different axes changes knee stability and passive tibiofemoral kinematics in a knee after TKA. Using a custom surgical navigation system and stability device to measure stability and passive tibiofemoral motion, we tested 10 cadaveric knees from five hemicorpses before TKA and then with the tibial component aligned to four axes using a modified tibial tray. No changes in knee stability or passive kinematics occurred as a result of the four techniques of tibial rotational alignment. TKA produces a 'looser' knee over the native condition by increasing mean laxity by 5.2A degrees, decreasing mean maximum stiffness by 4.5 N center dot m/A degrees, increasing mean anterior femoral translation during passive flexion by 5.4 mm, and increasing mean internal-external tibial rotation during passive flexion by 4.8A degrees. However, no statistically or clinically important differences occurred between the four TKA conditions. For all tibial rotations, TKA increased laxity, decreased stiffness, and increased tibiofemoral motion during passive flexion but showed little change based on the tibial alignment. Our observations suggest surgeons who align the tibial component to any of the axes we examined are expected to have results consistent with those who may use a different axis.