Intraoperative Coronal Alignment Safe Zones Influence Patient Outcomes Following Total Knee Arthroplasty: A Systematic Review and Network Meta-Analysis

Background: Despite surgically successful total knee arthroplasties, up to 20% of patients are dissatisfied postoperatively. A factor thought to influence dissatisfaction is the alignment strategy utilized. Inconsistencies in safe zone definitions between neutral and kinematic alignment strategies have limited previous systematic reviews. The systematic review aimed to identify whether different intraoperative coronal alignment safe zones influence patient-reported and functional outcomes. Methods: A literature search in Medline, Scopus, PubMed, Web of Science, CINAHL, and Cochrane databases was conducted in November 2024. Articles reporting patient outcomes at a minimum 12-month postoperatively, and coronal alignment safe zones were included. The Methodological Index for Non-Randomized Studies was used to conduct a quality assessment for each article. The Forgotten Joint Score pain measures, the Oxford Knee Score, and knee flexion were compared between safe zones. Random-effects network meta-analyses were conducted with treatment rankings, and a back-calculation method determined consistency between direct and indirect measures. A publication bias analysis was conducted for each outcome measure. Of the 26 studies eligible, 13 (knees n = 1,653, approximately 57% women) were included in the network meta-analysis. Results: There were four coronal safe zones identified: 0° (neutral), ± 3°, 6° varus to 3° valgus (6VR-3VL), and unrestricted. The 6VR-3VL was superior for the Forgotten Joint Score (standardized mean difference [SMD] = 1.59, 95% confidence interval [95% CI] = 0.25 to 2.92), pain measures (SMD = −0.85, 95% CI = −1.64 to −0.05), and knee flexion (SMD = −1.04, 95% CI = 0.08 to 1.99). There was significant publication bias in studies reporting pain. Unrestricted alignment was associated with greater knee flexion (SMD = 0.28, 95% CI = 0.02 to 0.53). Conclusions: The outcomes suggest 6VR-3VL had consistently better patient outcomes, and unrestricted alignment had better functional outcomes, than neutral alignment. This was potentially due to better restoration of the patient's prearthritic alignment.