Osteonecrosis of the femoral head associated with slipped capital femoral epiphysis

We performed a retrospective analysis of 212 patients (299 hips) with slipp ed capital femoral epiphysis (SCFE) over a 9-year period to assess the inci dence of osteonecrosis of the femoral head. Risk factors fur the occurrence of osteonecrosis and the influence of treatment on the development of oste onecrosis were determined. Osteonecrosis occurred in 4 hips with unstable S CFE (4/27) and did not occur in hips with stable SCFE (0/272). The proporti on of hips in which osteonecrosis developed was significantly higher among the unstable hips (4/27 vs. 0/272, p < 0.0001). Among those with an un stab le hip, younger age at presentation was a predictor of a poorer outcome. Ma gnitude of the slip, magnitude of reduction, and chronicity of the slip wer e not predictive of a poorer outcome in the unstable group. Tn situ fixatio n of the minimally or moderately displaced "unstable" SCFE demonstrated a f avorable outcome. We have identified the hip at risk as an unstable SCFE, T he classification of hips as unstable if the epiphysis is displaced from th e metaphysis or if the patient is unable to walk is most useful in predicti ng a hip at risk for osteonecrosis.