Postoperative CPAK phenotype and switching patterns are not associated with mid-term clinical outcomes or...

To determine whether postoperative coronal plane alignment of the knee (CPAK) phenotype influences mid-term clinical and sport-related outcomes after high tibial osteotomy (HTO) for medial compartment osteoarthritis and varus alignment. Secondary objectives were to analyse CPAK phenotype switching patterns and to evaluate joint line convergence angle (JLCA) behaviour following correction.

Patients undergoing high tibial osteotomy were retrospectively reviewed at a minimum follow-up of 2 years. Postoperative CPAK phenotype was defined based on mechanical axis alignment and joint-line orientation, and phenotype switching was assessed by comparing pre- and postoperative classifications. Clinical outcomes were evaluated using the WOMAC score, Tegner activity scale, and modified Weiss score. JLCA behaviour was analysed in relation to postoperative alignment, CPAK phenotype, and phenotype switching.

At a mean follow-up of 7.5 years, no significant differences in WOMAC, Tegner, or modified Weiss scores were observed across the most frequent postoperative CPAK phenotypes or between knees achieving neutral versus valgus alignment. CPAK phenotype switching occurred in more than 90% of cases and was not associated with differences in clinical or sport-related outcomes. JLCA demonstrated heterogeneous postoperative behaviour; ΔJLCA showed a weak association with ΔMPTA (R² = 0.052, p = 0.006) and no meaningful relationship with postoperative HKA, final MPTA, or postoperative CPAK phenotype.

Postoperative CPAK phenotype and phenotype switching were not significantly associated with mid-term clinical or sport-related outcomes after high tibial osteotomy. Clinical improvement was primarily associated with correction out of pathological varus, whereas coronal phenotype configuration and JLCA behaviour showed limited association with patient-reported outcomes.

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