KSSTA - 2026-06-26 - Journal Article
Coronal alignment behaviour across the knee range of motion is associated with constitutional alignment and soft-tissue balance: The REAL HKA classification.
Mylonakis N, Kenanidis E, Maslaris A, Sculco PK, Tsiridis E
Topics
Key Takeaway
In 352 knees undergoing robotic-assisted TKA with functional alignment, 73.6% demonstrated a stable coronal phenotype across ROM, with valgus knees (CPAK groups) showing the lowest stability and apex direction independently reducing odds of stability by 72-77% (OR 0.23-0.28).
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Summary
This study evaluated intraoperative pre-resection coronal alignment behavior across 0°, 45°, and 90° of flexion in 352 consecutive ra-TKA knees using manual stress testing to derive a composite REAL HKA phenotype. Fourteen distinct coronal phenotypes were identified; 73.6% of knees had a stable phenotype, with stability significantly associated with CPAK classification (χ²=60.12, p<0.001) and REAL flexion grouping (χ²=9.94, p=0.007). Multivariable analysis confirmed both constitutional alignment and soft-tissue balance as independent predictors of dynamic coronal phenotype stability (Nagelkerke R²=0.24).
Key Limitation
Single-surgeon, single-center design with manual laxity assessment limits generalizability and reproducibility of the REAL HKA phenotype classification across different surgeons and robotic platforms.
Original Abstract
PURPOSE
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.
METHODS
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.
RESULTS
Fourteen phenotypes were identified. Overall, 73.6% of knees demonstrated a stable phenotype. Phenotype stability varied significantly across CPAK groups (χ 2 = 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 2 = 9.94, p = 0.007). Multivariable analysis confirmed independent associations of CPAK and REAL flexion grouping with phenotype stability (χ 2 = 63.26, p < 0.001, Nagelkerke R 2 = 0.24).
CONCLUSIONS
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 OF EVIDENCE
Level IV, retrospective case series.