SLIPPED CAPITAL FEMORAL EPIPHYSIS ACETABULAR ORIENTATION AND SHAPE: A THREE-DIMENSIONAL CT STUDY

BACKGROUND: Previous studies have analyzed the acetabulum in patients affected by slipped capital femoral epiphysis (SCFE), however controversy remains over how the acetabular shape may be altered in hips experiencing SCFE. In particular, changes in acetabular over-coverage and acetabular version are thought to contribute to SCFE. HYPOTHESIS/PURPOSE: The purpose of this study was to determine the acetabular morphology in hips with SCFE and compare them to normally developing children. METHODS: Images from patients with the diagnosis of SCFE who had a computed tomography (CT) exam of their pelvis were compared to images from an age- and sex-matched cohort of patients with CT exams of the pelvis/abdomen for a non-orthopedic related evaluation (controls). Three dimensional (3D) reconstructions were created from each CT exam (MIMICs software). Custom MATLAB software was used to uniformly align and calculate acetabular parameters from the 3D reconstructions. The acetabular parameters calculated were articular surface area, acetabular tilt, acetabular version, and acetabular coverage angles measured in a radial fashion in 5 out of 8 octants. RESULTS: Two-hundred-ninety-eight hips were evaluated, including 67 hips with SCFE, 39 unaffected contralateral hips in patients with SCFE, and 192 normal controls. The SCFE group consisted of 33 males and 34 females. Acetabular version was similar amongst all SCFE affected hips, unaffected contralateral hips, and normal controls (p=0.575). Control hips had higher acetabular tilt than SCFE affected hips (p=0.001) and unaffected contralateral hips (p=0.012). Acetabular surface area was higher in SCFE affected hips compared to controls (p=0.003)(Table 1). SCFE affected hips had significantly increased acetabular coverage compared to controls in the superior, superior-anterior, and anterior octants (p<0.01). The unaffected contralateral sides had significantly increased acetabular coverage compared to controls in all five regions (p<0.02)(Table 2). CONCLUSIONS: Contrary to some previous studies, we did not find the acetabulum to be retroverted in hips with SCFE compared to normal hips. Both the affected and unaffected hips of SCFE patients have decreased acetabular tilt. Acetabular surface area is high in both the affected and unaffected sides in SCFE, suggesting it may be involved in the pathogenesis of the condition. There is increased acetabular coverage in the superior regions of SCFE hips. The shared morphological characteristics of both affected and unaffected sides in SCFE patients suggest that their hip anatomy may predispose them to slips.