FP17.7 Increased Distal Femoral Epiphyseal Cupping is Associated with Cam Deformity: Insights on Cam Etiology

Abstract ICL17 - The Full Picture: Shaping the Future of Global Hip Preservation, Ground Floor Session Room (BMCC Level 0), October 9, 2026, 14:00 - 16:00 Introduction Increased cupping of the proximal femoral epiphysis around the metaphysis is associated with cam morphology and has been proposed to be a physeal adaptation to resist shear stress. Distal femoral cupping has been described as an adaptive response to physeal shear stress in apes that ambulate in a flexed-knee gait. Given that athletes load their proximal and distal femoral physes in a flexed-knee position during sports, we hypothesize that increased distal femoral cupping may be seen in those with cam morphology. The purpose of this study was to evaluate the relationship between distal and proximal femoral epiphyseal cupping in adolescent patients undergoing hip preservation surgery for femoroacetabular impingement (FAI) or developmental dysplasia of the hip (DDH). Methods We retrospectively reviewed patients previously enrolled in a large multi-center prospective database. Patients aged 14 to 19 undergoing surgery for FAI or DDH were included. Preoperative CT scans were evaluated for femoral/acetabular version, alpha angle, proximal femoral epiphyseal cupping, and coronal/sagittal medial and lateral distal femoral epiphyseal cupping. Data also included age, sex, surgery performed, UCLA Activity Score. Cohorts were subdivided into two groups, cam (alpha ≥60°) and no cam (alpha <60°). Results We analyzed 102 patients (55.9% female) with mean age of 16.8±1.5 years, evenly distributed into the cam (49%, 50/102) and no cam 51% (52/102) cohorts. The cam cohort demonstrated increased cupping in the proximal femur (31.6±6.0% vs 22.2±5.7%, p<0.001) and the distal femur in the coronal and sagittal planes (all p<0.001), with largest difference in the sagittal medial distal femur (23.1±4.6% vs 19.0±2.5%, p<0.001). There were also moderate, positive linear correlations between sagittal medial and lateral distal femoral cupping and both proximal femoral cupping and alpha angle (correlations range from 0.40 to 0.54, all p<0.001), but no association with UCLA Activity score (all p>0.05). Conclusion In this retrospective cohort of patients undergoing hip preservation surgery, distal femoral epiphyseal cupping was found to be increased in patients with cam morphology. There are also moderate positive linear correlations between distal femoral cupping and alpha angle/proximal femoral cupping. The positive correlations found between these markers may illustrate a shared developmental response in both the proximal and distal femur. Significance/Take Home Message This study illustrates a possible association between cam morphology of the hip and distal femoral morphology, and thereby provides further unique evidence that formation of cam morphology may be secondary to adaptive changes to the proximal femoral physis to resist physeal shear stress. Level of Evidence III