EP3.9 A Novel Classification of Cam Morphology in Femoroacetabular Impingement

Abstract

Abstract Background Cam morphology is prevalent in many athletes, and is a risk factor for hip pain and osteoarthritis. However, a standardized classification system for the various types of bony morphology has yet to be established. A robust classification system should reproducibly group similar morphologies to guide treatment strategies. We developed a novel classification system incorporating alpha angle and head-neck offset ratio (HNOR) to better stratify can morphology and inform surgical planning. Purpose To evaluate the intra- and inter-rater reliability of a novel cam morphology classification system. Methods An a priori sample size calculation determined that a minimum of 72 patients was required, assuming a kappa of 0.7 and a precision of 0.2. A retrospective review was conducted of 115 patients with cam morphology who underwent surgery by a single surgeon between 2021-2024. One case was excluded due to inadequate imaging, leaving 114 patients for analysis (67 female and 47 male). Standardized Modified Dunn View radiographs were independently reviewed by three blinded reviewers (two fellowship-trained orthopaedic surgeons and one orthopaedic surgery resident). Each reviewer completed two assessments separated by at least two weeks. Inter-rater reliability was assessed using Fleiss’ kappa, and intra-rater reliability was assessed using Cohen’s kappa. Subgroup analysis compared the distribution of each cam type by gender. Statistical significance was set at p < 0.05. Results Inter-rater reliability demonstrated substantial agreement across both review sessions (κ = 0.678 and 0.726), with an overall κ of 0.702. Intra-rater reliability was near-perfect overall (κ = 0.824), ranging from substantial to near-perfect across reviewers (κ = 0.740–0.872). No significant differences in intra-rater agreement were observed between orthopaedic surgeons and the orthopaedic surgery resident. Type 1 morphology was significantly more common in females, whereas Types 2 and 3 were significantly more common in males. Conclusion This novel cam morphology classification system demonstrates substantial inter-rater and near-perfect intra-rater reliability, supporting its reproducibility and clinical utility. The consistency of agreement across reviewers with varying levels of experience highlights its generalizability. By integrating alpha angle and HNOR, this system provides an objective framework that may enhance surgical planning, facilitate communication, and improve standardization in hip preservation.