Closed reduction of slipped capital femoral epiphysis: high-risk factor for avascular necrosis.

How should we treat acute/unstable slipped capital femoral epiphysis (SCFE) without the development of avascular necrosis (AVN)? To answer this question, we investigated the risk factors of AVN development after SCFE. Seventy-six hips of 64 patients were classified using two kinds of classification systems, Loder's classification based on instability and the conventional classification based on the duration of symptom, because both classifications are related to AVN development. Of 21 unstable SCFEs, seven hips developed AVN. Of 35 hips defined as acute or acute on chronic, nine hips developed AVN. Two stable SCFEs of Loder's classification developed AVN, one was acute and the other was acute on chronic. No hips of chronic SCFE developed AVN. The factor that had influenced AVN development was only closed reduction, whether purposefully or inadvertently, in an acute or unstable SCFE. On the basis of the findings of this study, one should not embark on any modality of closed reduction for an unstable or acute form of SCFE, as there is a high risk for occurrence of AVN. For the same reason, a traction table should not be used for SCFE fixation, so as to avoid an inadvertent reduction or force that can lead to AVN.