JAAOS - 2026-08-17 - Journal Article
Comparison of Patellofemoral and Motion Outcomes Between Unrestricted Kinematic and Mechanical Alignment in Primary Total Knee Arthroplasty: A Systematic Review and Meta-Analysis.
Siddiqi A, Yousuf KM, Boyle K, Chen AF, Jacob PB
Topics
Key Takeaway
Unrestricted kinematic alignment TKA yields 4.58° greater postoperative flexion and 66% fewer intraoperative soft-tissue releases (RR 0.34) versus mechanical alignment, with no significant difference in patellofemoral complications or revision rate.
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Summary
This PRISMA-compliant systematic review and meta-analysis compared unrestricted kinematic alignment (KA) versus mechanical alignment (MA) in primary TKA across 7 studies using random-effects models and GRADE certainty grading. KA produced significantly greater flexion (MD 4.58°, 95% CI 1.83–7.32°) and marginally better terminal extension (MD -0.99°, 95% CI -1.86 to -0.12°), both with moderate certainty. Patellofemoral complications (RR 1.90), MUA (RR 0.47), and all-cause revision (RR 1.96) showed no statistically significant differences, though all carried low certainty due to wide confidence intervals.
Key Limitation
Patellofemoral complication and revision outcomes carry low GRADE certainty with wide confidence intervals, leaving the question of long-term PF safety statistically unresolved despite the pooled null result.
Original Abstract
BACKGROUND
Unrestricted kinematic alignment (KA) in total knee arthroplasty (TKA) seeks to restore patient-specific limb geometry and ligamentous balance, yet uncertainty persists regarding patellofemoral (PF) complications and postoperative interventions. Comparative evidence centered on objective mechanical outcomes remains limited, and prior meta-analyses have included heterogeneous alignment strategies or mixed implant constructs. The purpose of this study was to compare unrestricted KA with mechanical alignment (MA) in primary TKA with respect to PF safety, postoperative motion, and intraoperative soft-tissue release requirements.
METHODS
A systematic review and meta-analysis was conducted in accordance with PRISMA guidelines. Randomized and comparative observational studies directly comparing unrestricted KA with MA in primary TKA were eligible without language or date restrictions. Studies were required to report at least 1 predefined objective outcome: postoperative flexion, terminal extension, manipulation under anesthesia (MUA), PF complications, intraoperative soft-tissue releases, or all-cause revision surgery. Data were extracted in duplicate, and random-effects models were used for pooled analyses. Risk of bias was assessed using ROB2 for randomized trials and ROBINS-I for observational studies, and certainty of evidence was graded using GRADE methodology.
RESULTS
Seven studies (five randomized trials and two comparative cohorts) comprising 1,068 primary TKAs met inclusion criteria. Compared with MA, KA resulted in greater postoperative flexion (mean difference [MD], 4.58°; 95% confidence intervals (CI), 1.83° to 7.32°; moderate certainty) and slightly improved terminal extension (MD, -0.99°; 95% CI, -1.86° to -0.12°; moderate certainty). KA required substantially fewer intraoperative soft-tissue releases (risk ratio [RR], 0.34; 95% CI, 0.24 to 0.49; moderate certainty). No significant differences were observed for PF complications (RR, 1.90; 95% CI, 0.63 to 5.74; low certainty), MUA (RR, 0.47; 95% CI, 0.09 to 2.44; low certainty), or all-cause revision surgery (RR, 1.96; 95% CI, 0.75 to 5.14; low certainty). Sensitivity analyses demonstrated stable effect direction across fixed-effects and random-effects models.
DISCUSSION
Unrestricted KA TKA improves postoperative flexion, slightly enhances extension, and markedly reduces soft-tissue releases without increasing early PF complications, MUA, or revision surgery compared with MA TKA. Longer term randomized studies are needed to refine PF-specific risk estimates and assess survivorship.
LEVEL OF EVIDENCE
II.