Coronal Plane Alignment of the Knee Classification and Its Correlation with Post-operative Functional Outcomes in Total Knee Arthroplasty: A Prospective Cohort Study.

Introduction: Total knee arthroplasty (TKA) is widely performed for end-stage osteoarthritis; however, 15-20% of patients continue to experience dissatisfaction despite successful surgery. Traditional mechanical alignment (MA) aims for a neutral limb axis, but this approach may not restore the individual's constitutional coronal alignment, potentially affecting functional recovery. The coronal plane alignment of the knee (CPAK) classification offers a phenotype-based system to characterize native knee alignment and joint line obliquity (JLO). This multicentric prospective randomized study aimed to evaluate whether CPAK-guided alignment leads to superior early post-operative functional outcomes compared with conventional MA in TKA. Materials and Methods: This multicentric, prospective, randomized cohort study was conducted over 18 months across three tertiary orthopedic centers. Fifty patients undergoing unilateral primary TKA were enrolled and randomized into two groups: CPAK-guided alignment (n = 25) and MA (n = 25). Inclusion criteria were patients aged 45-80 years with primary osteoarthritis and available long-leg radiographs for CPAK classification. Exclusion criteria included post-traumatic arthritis, inflammatory arthropathy, neuromuscular disorders, and prior major knee surgery. Standardized surgical protocols and post-operative rehabilitation pathways were followed across all centers. Functional outcomes were assessed using knee society score (KSS), oxford knee score (OKS), and Visual Analog Scale (VAS) for pain at baseline, 3 months, and 6 months. Radiographic parameters included hip-knee-ankle (HKA) angle deviation and JLO. Statistical analysis included independent t-tests and correlation analysis. Results: Both groups demonstrated significant post-operative improvement; however, the CPAK-guided group achieved superior functional outcomes. At 6 months, mean KSS was significantly higher in the CPAK group (89.4 ± 7.2) compared with the mechanical group (82.1 ± 9.0; P = 0.004). OKS also favored the CPAK group (41.6 ± 4.1 vs. 37.9 ± 5.0; P = 0.01). VAS pain scores were significantly lower in the CPAK group at both follow-up intervals (1.4 ± 0.8 vs. 2.4 ± 1.0; P = 0.002). The need for medial soft-tissue release was markedly lower in the CPAK group (12% vs. 40%; P = 0.02). Radiographically, the CPAK-guided group showed significantly closer restoration of constitutional alignment and reduced joint line deviation. Correlation analysis demonstrated that greater deviation from native alignment was associated with poorer functional outcomes (r = -0.48, P = 0.004). Conclusion: CPAK-guided alignment resulted in better early functional outcomes, reduced pain, and fewer soft-tissue releases compared with traditional MA in TKA. Personalized coronal alignment based on CPAK phenotype appears to enhance post-operative recovery and may offer a more physiological approach to knee arthroplasty.