Reliability of the CPAK classification assessed on long-leg X-rays in patients undergoing total knee arthroplasty

Article Article scientifique Article Reliability of the CPAK classification assessed on long-leg X-rays in patients undergoing total knee arthroplasty eng 2026-04-02 2026-12 author Gasparutto Xavier 0000-0001-8617-6522 Kinesiology Laboratory, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. xavier.gasparutto@hug.ch.,Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland. xavier.gasparutto@hug.ch.,Centre of Research On Skeletal Muscle and Movement, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. xavier.gasparutto@hug.ch. 891356 author Chantre Daniel Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland. 823884 author Bonnefoy Alice Kinesiology Laboratory, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland.,Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland.,Centre of Research On Skeletal Muscle and Movement, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. 762239 Département de chirurgie (CHIRU) author Bouché Pierre-Alban Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland. author Hannouche Didier 0000-0003-2060-2394 Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland.,Centre of Research On Skeletal Muscle and Movement, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. 842478 Département de chirurgie (CHIRU) author Armand Stéphane 0000-0001-9144-4982 Kinesiology Laboratory, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland.,Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland.,Centre of Research On Skeletal Muscle and Movement, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. 636265 Département de chirurgie (CHIRU) author Miozzari Hermès Howard 0000-0002-6783-2296 Division of Orthopedic Surgery and Musculoskeletal Trauma Care, Geneva University Hospitals, 1205, Geneva, Switzerland.,Centre of Research On Skeletal Muscle and Movement, Geneva University Hospitals and University of Geneva, 1205, Geneva, Switzerland. 105055 Département de chirurgie (CHIRU) 24 10.1186/s42836-026-00381-y 41928311 2524-7948 PMC13045113 Background: Patient-specific knee alignment is regarded as a major target for improving total knee arthroplasty (TKA) outcomes. The Coronal Plane Alignment of the Knee (CPAK) classification has been proposed to capture the native patient-specific knee alignment, according to the Joint Line Obliquity (JLO) and arithmetic Hip Knee Ankle angle (aHKA), themselves based on the Lateral Distal Femoral Angle (LDFA) and Medial Proximal Tibial Angle (MPTA). This study aims to evaluate intra-operator, inter-operator, and test-retest reliability of the CPAK classification and associated angles in both knees with osteoarthritis (KOA) and TKA. Methods: From our local arthroplasty registry, patients who sequentially underwent TKA on both knees within 18 months, with long-leg X-rays before and after each surgery between 2018 and 2023, were retrospectively selected. The contralateral knees before the 1st and 2nd TKA were used as test-retest for KOA and TKA knee, respectively. Four operators with increasing experience performed two measures of MPTA and LDFA for each image. The intra-operator, inter-operator, and test-retest reliability were assessed with Intraclass Correlation Coefficient (ICC(3,1)), Smallest Detectable Change (SDC), and Cohen's Kappa. Results: The study included 34 patients. Angles showed good to excellent ICC apart from JLO in the KOA condition (moderate). Measures of LDFA on KOA and all TKA angles presented good to excellent SDC (< 3°), including test-retest conditions. MPTA, JLO, and aHKA on KOA showed moderate SDC (< 4.2°). CPAK classification was moderate to substantial for KOA (Kappa of 0.5 to 0.64) and substantial to almost perfect for TKA (Kappa of 0.69 to 0.81). Reliability increased with experience. Conclusions: For experienced operators, CPAK classification and associated angles demonstrated levels of inter-rater reliability acceptable for clinical use in knees with TKA but at the limit of acceptability for knees with severe OA. In severe OA, one should interpret CPAK types cautiously, and angles may be preferable. MPTA in the knees with OA appeared as the main factor undermining reliability. Clarification on this angle may be needed to improve reliability, especially when using philosophies aiming at restoring the native alignment. Finally, test-retest reliability levels suggested that these measures are appropriate for longitudinal assessment. Alignment Arthroplasty CPAK Knee Phenotype Replacement Dewey 617 57 Département de chirurgie 222 false 955 Mécanismes physiopathologiques de l'arthrose 960 900 Laboratoire de cinésiologie 943 https://doi.org/10.26037/yareta:zd6lopqfincqbborhfh2jhb2mu Arthroplasty 8 1 7c77bbbe-176e-43aa-84b1-a67f10d6395a Article (Published version) Public Article_scientifique_from_crossref.pdf 2764534 application/pdf CC BY-4.0 d46ccdcb583ae24bec945cd12be18f679231dbed9b2cc997d906bace2538ecf4 openAccess Faculté de médecine / Section de médecine clinique / Département de chirurgie

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Reliability of the CPAK classification assessed on long-leg X-rays in patients undergoing total knee arthroplasty	Arthroplasty			2026	9	9

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