Functional alignment restores native kinematics more consistently than mechanical axis alignment in total knee arthroplasty.

Aims: Functional alignment (FA) and adjusted mechanical alignment (aMA) are recognized techniques for performing total knee arthroplasty (TKA). The native femur rolls back further on the lateral tibial plateau than the medial side during flexion, resulting in a medial pivot pattern of movement. We have assessed whether an individualized alignment technique affects the kinematic pattern observed and the clinical outcomes, when compared to a systematic alignment technique in TKA.

Methods: A total of 60 consecutive patients were randomized to a robotically assisted TKA with either FA (n = 29) or aMA (n = 31), using a cruciate-retaining (CR) implant. After definitive implantation of the prostheses, a trial pressure monitor was inserted recording contact points between the femoral component and monitor in the medial and lateral compartments as the knee was taken through a range of motion. The kinematic pattern was observed, contact pressures measured, and patient-reported outcome measures (PROMs) assessed at 12 months.

Results: The FA-TKA group produced a medial pivot in 58.6% of cases (17/29), symmetrical rollback in 37.9% (11/29), and a lateral pivot in 3.4% (1/29). The aMA-TKA group produced a medial pivot in 19.4% of cases (6/31), symmetrical rollback in 45.2% (14/31), and a lateral pivot in 35.5% (11/31) (p < 0.001). No differences in knee balance were recorded between the two alignment groups at any flexion point. Patients with a medial pivot kinematic pattern had superior one-year PROMs in some measures. Patients producing a lateral pivot had lower Kujala scores.

Conclusion: FA CR-TKA generates an intraoperative medial pivot kinematic pattern through soft-tissue balance more often than those that use aMA. Lateral pivot kinematic patterns are more commonly found with aMA. These intraoperative kinematic patterns are related to clinical outcomes, with knees producing a medial pivot performing better than those with lateral pivot.