Kinematic Alignment Versus Mechanical Alignment in Total Knee Arthroplasty: A Systematic Review of Mid-term Functional Outcomes.

Abstract

Total knee arthroplasty (TKA) is frequently performed for advanced knee osteoarthritis. Mechanical alignment (MA) targets restoration of a neutral limb axis, whereas kinematic alignment (KA) aims to reproduce an individual's native pre-arthritic knee alignment. This systematic review evaluates comparative mid-term outcomes (≥2 years) following KA and MA in primary TKA. Electronic searches of MEDLINE (PubMed), Embase, and Cochrane CENTRAL were undertaken, with additional screening of Google Scholar. Following duplicate removal and eligibility assessment, 16 primary comparative studies were included. Evaluated outcomes comprised patient-reported outcome measures (PROMs), range of motion (ROM), radiographic alignment, gait parameters, postoperative complications, and implant survivorship. At the mid-term follow-up, ROM was comparable between KA and MA (mean difference = +2.8 degrees, 95% confidence interval (CI) = -1.5 to 6.9, p = 0.21). PROMs showed statistically significant improvements with KA, including Oxford Knee Score (mean difference = +6.2, 95% CI = 1.9 to 10.4, p = 0.005) and Western Ontario and McMaster Universities Osteoarthritis Index (mean difference = -9.8, 95% CI = -16.2 to -3.5, p = 0.004), though these differences may not consistently exceed minimal clinically important differences. However, multiple high-quality randomized trials reported no clinically meaningful differences between the techniques. Radiographic analyses demonstrated alignment patterns consistent with the KA philosophy without evidence of adverse clinical impact at the mid-term follow-up. Gait studies did not show reproducible differences between techniques. Revision rates were low in both groups (0-2%), though statistical power for survivorship comparison was limited. KA achieves mid-term clinical outcomes that are generally comparable to MA in primary TKA, with some studies reporting statistically significant PROM improvements that may not consistently represent clinically meaningful benefits. Evidence regarding long-term durability remains limited, and concerns regarding aseptic loosening with certain alignment variations require further investigation.