Prognostic analysis of different morphology of the necrotic-viable interface in osteonecrosis of the femoral head

Purpose The purpose of this study was to investigate the collapse progression in different morphologies of the necrotic-viable interface in osteonecrosis of the femoral head (ONFH). Methods A total of 168 patients (202 hips) with Association Research Circulation Osseous (ARCO) stage II ONFH were included. Ending with the collapse of the femoral head, all patients received conservative treatment but without surgical intervention and were followed for three to 91 months. Bilateral hip-joint radiographs and magnetic resonance imaging (MRI) were examined, and the largest layer of necrosis within the coronal section of MRI images was selected together with its anteroposterior radiograph to observe the morphology of the necrotic-viable interface. The morphology was divided into four types: I, type transverse; II, type "V"; III, type zigzag; IV, type closed. The collapse rate and the time to collapse in different morphologies were assessed. Results A total of 120 hips collapsed in two years or less, 61 were type-I, 51 were type-II, and 8 were type-III. Non-collapse occurred in all 17 hips with type-IV ONFH during long-term follow-up. In 202 hips with ARCO stage-II ONFH, the collapse rate in type-I ONFH was significantly higher than that of type-II and type-III ONFH (P < 0.01 for both). The time to collapse was markedly shortened. Conclusions The risk of ONFH-induced collapse is influenced by the morphology of the necrotic-viable interface. Effective mechanical support for preventing the collapse of the femoral head is necessary when the morphology of the necrotic-viable interface is type transverse.