Coronal alignment behaviour across the knee range of motion is associated with constitutional alignment and soft-tissue balance: The REAL HKA classification.
retrospective_cohort · Level III
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- Record sourced from PubMed, PMID 42360171.
- Also identified by DOI 10.1002/ksa.70506.
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Abstract
To evaluate intraoperative, pre-resection coronal alignment throughout the range of motion (ROM) in knees undergoing robotic-assisted total knee arthroplasty (ra-TKA), and to assess its relationship with the Coronal Plane Alignment of the Knee (CPAK) and the Robotic Evaluation of Articular Laxity (REAL) classifications. Three hundred fifty-two consecutive knees undergoing primary ra-TKA using functional alignment were included in this single-surgeon, platform and implant retrospective cohort study. Intraoperative coronal laxity was assessed before bone resections at 0°, 45° and 90° of flexion, under surgeon-applied manual varus and valgus stress without a tensioning device. Laxity was recorded as the maximum angular deviation from the neutral coronal axis and shown as an excursion bar. At each flexion angle, a coronal phenotype was defined: neutral if the bar crossed the neutral axis, varus if entirely within negative hip-knee-ankle (HKA) values and valgus if entirely within positive. By combining the phenotypes at 0°, 45° and 90°, a composite 'REAL HKA phenotype' was derived. Associations between phenotype stability and the CPAK and REAL classifications were evaluated. Fourteen phenotypes were identified. Overall, 73.6% of knees demonstrated a stable phenotype. Phenotype stability varied significantly across CPAK groups (χ<sup>2 </sup>= 60.12, p < 0.001) and was lowest in valgus knees. Within each alignment group, apex direction influenced phenotype stability; Class IV had lower odds than I (odds ratio [OR] 0.28, 95% confidence interval [CI] 0.11-0.72) and Class V had lower odds than II (OR 0.23, 95% CI 0.09-0.60). REAL flexion grouping was also associated with stability (χ<sup>2</sup> = 9.94, p = 0.007). Multivariable analysis confirmed independent associations of CPAK and REAL flexion grouping with phenotype stability (χ<sup>2 </sup>= 63.26, p < 0.001, Nagelkerke R<sup>2 </sup>= 0.24). Coronal behaviour across the ROM varies in knees undergoing ra-TKA. Both constitutional alignment and soft-tissue balance are associated with dynamic coronal phenotype stability. Level IV, retrospective case series.