O3230: Comparison of Distal Femoral Epiphyseal Cupping in SCFE Patients and Athletic Controls: Implications for Cam Etiology

Background: Cupping of the proximal femoral epiphysis around the metaphysis is directly associated with the development of cam in athletes. It is also decreased in patients with slipped capital femoral epiphysis (SCFE). It can be hypothesized that epiphyseal cupping is an adaptive response to physeal shear stress that stabilizes the physis at the long-term cost of cam development. These shear stresses would be expected to create a similar response in the distal femur. The purpose of this study was to compare distal femoral epiphyseal cupping in SCFE patients to healthy athletic controls and evaluate the relationship of distal and proximal epiphyseal cupping.

Methods: We retrospectively reviewed all patients diagnosed with SCFE at a single institution to identify those patients who had concurrent knee x-rays obtained during their diagnostic workup. Patients with an AP knee x-ray obtained within 2 months of diagnosis of SCFE were included. Age-and sex-matched athletic controls were obtained from a database of patients at our institution who underwent anterior cruciate ligament reconstruction with an AP knee x-ray. Distal femoral epiphyseal extension and cupping was measured on the medial and lateral condyles on AP knee XR in both cohorts (Figure). Pre-operative AP pelvic radiographs were used to measure AP epiphyseal extension ratio (EER) and epiphyseal cupping of the proximal femur in the SCFE group. Distal femoral epiphyseal extension and cupping were compared between cohorts. Association analysis was performed to understand the relationship of proximal and distal cupping and their individual relationship with age.

Results: 94 SCFE patients with an available preoperative knee XR were evaluated and age- and sex-matched against 94 athletic controls. There was no difference in age between the SCFE and control group (12.64yrs ±1.34 vs 12.80yrs ±1.24, respectively, p=0.39) or sex distribution (34% Female, p>0.99). The SCFE cohort had significantly decreased distal femoral epiphyseal extension compared to controls both medially (0.12±0.02 vs 0.13±0.02, respectively, p=0.01) and laterally (0.10±0.02 vs 0.13±0.02, respectively, p< 0.0001). The SCFE cohort also had significantly decreased epiphyseal cupping medially (0.06±0.02 vs 0.07±0.02, respectively, p=0.02) and laterally (0.05±0.02 vs 0.07±0.02, respectively, p< 0.0001). Medial distal femoral cupping and extension had a positive linear association with proximal femoral epiphyseal extension and cupping (see Table).

Conclusion: The conserved phenomenon of decreased epiphyseal cupping in the distal femur in SCFE patients compared to athletic controls provides further evidence that epiphyseal cupping may be related to physeal stability and may be a physiologic response to increased physeal shear stress. This also suggests that proximal femoral epiphyseal extension and cam development is not related to impingement itself given that mirrored epiphyseal changes occur in the proximal and distal femur.