Kinematic and Restricted Kinematic Alignment Versus Mechanical Alignment in Total Knee Arthroplasty: A Systematic Review of Randomized Trials

Abstract

Background: Mechanical alignment has traditionally been used in total knee arthroplasty to restore a neutral mechanical axis. However, residual dissatisfaction after technically successful surgery has encouraged increasing interest in individualised alignment strategies, including kinematic and restricted kinematic alignment. Methodology: This systematic review synthesised randomised evidence comparing kinematic or restricted kinematic alignment with mechanical alignment in primary total knee arthroplasty with at least two years of follow-up. The review considered patient-reported outcomes, pain, range of motion, joint awareness, satisfaction, gait-related outcomes, implant fixation, tibial component migration, radiographic alignment, complications and reoperations. Owing to heterogeneity in alignment protocols, surgical techniques, implant designs and outcome reporting, the evidence was summarised narratively rather than pooled quantitatively. Results: Six randomised controlled trials met the eligibility criteria. Overall, kinematic and restricted kinematic alignment showed clinical outcomes that were generally comparable with mechanical alignment. Some studies reported advantages in pain relief, satisfaction, joint awareness and selected functional scores, particularly in specific patient phenotypes or with medial pivot implant designs. Range of motion, gait outcomes, complications and reoperations were generally similar between strategies. Available radiostereometric evidence did not show increased early tibial component migration or compromised fixation. Conclusion: Kinematic and restricted kinematic alignment appear to provide short- to mid-term outcomes comparable with mechanical alignment in selected patients undergoing primary total knee arthroplasty, although longer follow-up and standardised protocols remain necessary.