膝関節の冠状面アライメント分類の変化は、制限運動学的アライメント全人工膝関節置換術後の転帰に有意な影響を与えない

The coronal plane alignment of the knee (CPAK) classification helps understand knee alignment variability, guiding personalised total knee arthroplasty (TKA) strategies. However, evidence regarding the impact of postoperative CPAK classification changes on patient-reported functional outcomes after restricted kinematic alignment (rKA) TKA remains limited. This study aimed to investigate whether CPAK classification changes after TKA with rKA influence functional outcomes, measured by the International Knee Society score (IKS).

A retrospective cohort study included 464 patients who underwent primary TKA with a posterior stabilised implant (KNEO^®) between January 2020 and May 2024. The inclusion criteria were primary or secondary osteoarthritis with complete radiographic and clinical follow-up at 2 years; patients with incomplete data or intraoperative complications requiring implant change were excluded. Pre- and postoperative CPAK classifications were compared, and functional outcomes were assessed using IKS knee and function scores at 2 years of follow-up. Radiographic assessment was performed on standing long-leg radiographs by a single experienced observer.

A significant redistribution of CPAK classifications was observed postoperatively (p < 0.001), with 22.2% of CPAK I changing to CPAK II and 19.1% changing to CPAK V. In total, 33.3% of all knees retained their initial CPAK classification. No significant differences were observed in the postoperative IKS Knee (85.2 ± 12.3 vs. 83.9 ± 11.8; p = 0.62) or IKS Function scores (78.5 ± 13.1 vs. 76.9 ± 12.7; p = 0.54). Given the small sample sizes within certain CPAK subtype transitions, subgroup analyses were not feasible.

Changes in CPAK classification following rKA-TKA were common but did not significantly influence functional outcomes at 2 years. These findings suggest that CPAK phenotype transition alone may not be a reliable predictor of clinical success, although larger studies are needed to explore subtype-specific effects.

Level IV.