The metaphyseal fossa surrounding the epiphyseal tubercle is larger in hips with moderate and severe slipped capital femoral epiphysis than normal hips

PURPOSE: To compare the 3D morphology of the metaphyseal fossa among mild, moderate and severe stable slipped capital femoral epiphysis (SCFE) and normal hips. METHODS: We identified pelvic CT of 51 patients (55% male; mean 12.7 years (sd 1.9; 8-15)) with stable SCFE. In all, 16 of 51 hips (31%) had mild, 14 (27%) moderate and 21 (41%) severe SCFE. A total of 80 patients (50% male; mean age 11.5 years (sd 2.3; 8 to 15)) with normal hips who underwent pelvic CT due to abdominal pain made up the control cohort. CT scans were segmented, and the femur was reformatted using 3D software. We measured the metaphyseal fossa depth, width, length and surface area after the epiphysis was subtracted from the metaphysis in the 3D model. RESULTS: The metaphyseal fossa width was significantly larger in severe (adjusted difference: 6.9%; 95% confidence interval (CI) 2.1 to 11.8; p = 0.001), moderate (6.5%; 95% CI 0.8 to 12.2; p = 0.02) and mild SCFE (6.2%; 95% CI 0.8 to 11.6; p = 0.01), in comparison with normal hips. Severe SCFE showed larger fossa length compared with mild SCFE (6.8%; 95% CI 0.6 to 13.0; p = 0.02) and normal hips (6.0%; 95% CI 1.4 to 10.6; p = 0.004). The fossa surface area was larger in severe (3.5%; 95% CI 1.3 to 5.7; p < 0.001) and moderate SCFE (2.7%; 95% CI 0.1 to 5.2; p = 0.03) when compared with normal hips. There were no differences in fossa depth between SCFE and normal hips. CONCLUSION: The metaphyseal fossa is wider and more extensive but not deeper in hips with moderate and severe SCFE in comparison with normal hips. Although hips with severe SCFE had larger length and surface area than mild SCFE hips, further research is needed to clarify whether enlargement of the metaphyseal fossa is a consequence of slip progression. LEVEL OF EVIDENCE: III