Two-year functional outcomes of kinematic versus mechanical alignment in primary total knee arthroplasty: a single-surgeon propensity-matched study in an Asian population

Background Optimal coronal alignment in total knee arthroplasty (TKA) remains controversial, with kinematic alignment (KA) emerging as a patient-specific alternative to conventional mechanical alignment (MA). This study compared 2-year functional outcomes, patient-reported outcome measures (PROMs) and complication rates between KA-TKA and MA-TKA in a propensity score–matched cohort. Methods This retrospective single-surgeon study included 1978 consecutive primary TKAs (KA: n = 921, 2018–2023; MA: n = 1057, 2010–2014). After excluding 76 revision TKAs, 1902 primary TKAs were eligible. A further 441 patients with incomplete follow-up were excluded (KA: n = 293, 33.1%; MA: n = 148, 14.6%), leaving 1461 patients who underwent propensity score matching. Following 1:1 nearest-neighbour propensity score matching for age, sex, body mass index (BMI) and baseline PROMs, 536 matched pairs ( n = 1,072) were analysed. Outcomes included range of motion, Knee Society Knee and Function Scores (KSKS, KSFS), Oxford Knee Score (OKS), SF-36, MCID attainment, satisfaction, complications and revision rates at 6 months and 2 years. Results Both groups showed substantial postoperative improvement across all outcomes. At 6 months, KA achieved higher postoperative KSKS (86.7 versus 85.3, p < 0.001), greater flexion (113.1° versus 110.9°, p = 0.010), greater arc of motion (109.8° versus 107.5°, p = 0.032) and greater physical functioning, while MA showed greater improvement and higher MCID attainment in SF-36 role physical and bodily pain. Satisfaction at 6 months was higher with KA (95.6% versus 90.8%, p = 0.003). At 2 years, KA demonstrated statistically higher KSKS (89.2 versus 86.3, p < 0.001), higher KSFS (77.6 versus 75.6, p = 0.022), improved range of motion and better physical functioning. Satisfaction remained high and comparable (95.3% versus 95.7%, p = 0.838). Complication and revision rates were comparable, with no significant difference in 2-year revision-free survival (99.8% versus 100%, p = 0.317). Conclusions KA-TKA was associated with statistically higher scores in selected functional domains and comparable MCID attainment, patient satisfaction and revision-free survival at 2 years. These findings suggest KA is a feasible alignment strategy for primary TKA in the short term, although longer-term prospective data are required to confirm these associations.