FP7.4 Beyond Alpha Angle: A Composite Classification of CAM Morphology Using Height, Width, and Length With High Interobserver Reliability

Abstract

Abstract ICLB07 - The Digital Surgeon: Practical Tools and Navigation Basics for Your Everyday Practice, Session Room 12 (BMCC Level 3), October 8, 2026, 14:00 - 16:00 Background Traditional assessment of cam morphology relies primarily on alpha angle, which incompletely characterizes the three-dimensional deformity. A simple and reproducible classification incorporating lesion prominence, circumferential extent, and distal extension may better define cam morphology and guide surgical osteoplasty. Purpose To develop and validate a simplified composite cam classification (Type 1–3) based on height, width, and length, and to evaluate its association with demographic and morphologic variables, including head-neck offset (HNO), head-neck offset ratio (HNOR), and sex. Methods A retrospective review was performed of 100 consecutive hip arthroscopies with standardized Dunn radiographs and preoperative 3D CT hip mapping. Two independent orthopedic surgeons assessed each hip. Cam morphology was scored using: (1) height based on alpha angle (45–59°, 60–74°, ≥75°), (2) width based on number of involved clock-face sectors, and (3) length based on distal extension along the femoral neck. Composite scores (3–9) were categorized into Type 1 (3–4), Type 2 (5–7), and Type 3 (8–9). Demographic variables, femoral version, HNO, and HNOR were recorded. Interobserver agreement was assessed using Cohen’s kappa and intraclass correlation coefficients. Results Cam distribution was Type 1 in 43–45%, Type 2 in 43–45%, and Type 3 in 12% of hips. Lesions were predominantly anterolateral (62–66%). Type 3 morphology was strongly associated with male sex (approximately 90%), while Type 1 lesions were more common in females. A stepwise decrease in head-neck offset was observed with increasing cam severity: mean HNO was approximately 8.3–8.5 mm in Type 1, 6.4–6.7 mm in Type 2, and 4.9–5.1 mm in Type 3, with corresponding reductions in HNOR. Males demonstrated lower HNO and HNOR compared to females. Interobserver agreement was high for cam type (84%, kappa 0.73; weighted kappa 0.83) and excellent for lesion location (96%, kappa 0.87). Measurement reliability was good to excellent, including alpha angle (ICC 0.81) and width (ICC 0.95). CAM severity demonstrated strong associations with head-neck offset and sex, but not with femoral version, suggesting that CAM morphology represents a localized structural phenotype independent of global femoral torsion. Conclusion A simplified composite CAM classification incorporating height, width, and length demonstrates high interobserver reliability and identifies meaningful morphologic patterns. Our findings support a spectrum-based model of CAM morphology, in which subtle, Type 1, lesions demonstrate measurable structural abnormalities despite lower alpha angles. Increasing cam severity is associated with progressive loss of head-neck offset and distinct sex-based differences. To our knowledge, few clinically applicable classification systems have integrated these dimensions into a single, reproducible framework. This system may improve identification of subtle cam morphology and better guide complete osteoplasty to reduce residual impingement.