Efficacy of functional alignment in total knee arthroplasty in restoring in vivo cruciate ligament forces and knee kinematics compared with mechanical alignment.

Abstract

The impact of coronal alignment on cruciate ligament forces in bicruciate-retaining total knee arthroplasty (TKA) remains unclear. We aimed to clarify in vivo cruciate ligament forces and knee kinematics among mechanically aligned (MA) and functionally aligned (FA) TKAs and normal knees. Normal, MA TKA and FA TKA knees were assessed during squatting using fluoroscopy. Tibiofemoral kinematics was measured using a two-dimensional/three-dimensional registration technique, including axial rotation, varus-valgus angle, and anteroposterior translation (APT) of the surgical epicondylar axis (SEA) and low contact points (LCPs). Ligament tensions during knee flexion were analysed in the anteromedial anterior cruciate ligament (aACL) and posterolateral anterior cruciate ligament (pACL) and anterolateral posterior cruciate ligament (aPCL) and posteromedial posterior cruciate ligament (pPCL). Both MA and FA TKA knees exhibited greater external femoral rotation and less varus alignment. Medially, MA TKA knees were positioned more anteriorly at 0° flexion. Laterally, both TKA knees were positioned more posteriorly up to 10° flexion. Medially, MA TKA knees were positioned more anteriorly at 0° flexion. Laterally, both TKA knees were positioned more posteriorly up to 10° flexion. In lateral LCPs, both TKA knees were more anteriorly positioned. aACL and pACL tensions decreased with flexion, with no significant differences between TKA and normal knees, whereas aPCL and pPCL tensions increased with flexion. Beyond 80° flexion, MA TKA knees exhibited greater aPCL tension. Beyond 90° flexion, pPCL tension was higher in MA TKA knees. PCL tension was notably higher in MA TKA knees. However, FA TKA and MA TKA demonstrated comparable kinematics and changes in ACL force. Although FA TKA more closely restored the physiological balance of the cruciate ligaments, the overall effect appeared to be limited. Level II.