BACKGROUND: Kinematically aligned (KA) and mechanically aligned (MA) total knee arthroplasty (TKA) have been widely compared; however, the relative impact of alignment strategy versus other factors on clinical outcomes remains unclear. This study aimed to investigate the independent influence of alignment strategy, soft-tissue balance, and muscle strength on subjective outcomes.
METHODS: A prospective randomized controlled trial was conducted in patients undergoing TKA with a medial pivot design. Patients were randomized to receive either KA-TKA (n = 25) or MA-TKA (n = 25) and followed for two years. Soft-tissue balance was assessed intraoperatively. Outcomes including the Knee Society Score (KSS) 2011, quadriceps muscle strength, functional scores, and radiographic coronal plane alignment of the knee (CPAK) were evaluated pre- and postoperatively. Multiple regression analyses identified independent predictors of subjective outcomes.
RESULTS: There were no significant differences between groups in demographics, preoperative parameters, or intraoperative soft-tissue balance. Postoperatively, CPAK phenotype distributions differed between two groups (P < 0.01). However, alignment strategy (KA versus MA) was not identified as a significant independent predictor of subjective outcomes. Soft-tissue balance in extension (coronal gap angle) was independently associated with KSS 2011 satisfaction (partial regression coefficient: 2.85, 95% confidence interval (CI): 0.69 to 5.02, P < 0.01). By contrast, older age (partial regression coefficient: -1.90, 95% CI: -2.85 to -0.96, P < 0.01) and greater quadriceps muscle strength loss (partial regression coefficient: 0.56, 95% CI: 0.03 to 1.09, P = 0.03) were identified as independent negative predictors of KSS 2011 functional activity.
CONCLUSION: Postoperative subjective outcomes following TKA are influenced more by soft-tissue balance and muscle strength than by the alignment strategy per se.
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