Coronal Plane Alignment of the Knee Classification and Its Correlation with Post-operative Functional Outcomes in...

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.

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.

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).

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.