Spontaneous resolution of osteonecrosis of the femoral head

Background: The decision to proceed with surgical treatment of asymptomatic osteonecrosis of the femoral head is controversial. The purpose of the present study was to determine (1) if spontaneous resolution of osteonecrosis of the femoral head occurs, (2) how long it takes for resolution to occur, and (3) if there are predictors of spontaneous resolution. Methods: Patients with asymptomatic osteonecrosis of the femoral head were identified from two National Institutes of Health-funded screening studies: a prospective screening study for osteonecrosis of the femoral head after organ transplantation and a study in which patients who had had surgical treatment of symptomatic osteonecrosis of the femoral head were screened for osteonecrosis of the contralateral, asymptomatic hip. The cohort of patients with asymptomatic osteonecrosis of the femoral head was then analyzed. Results: Thirteen asymptomatic hips in ten patients were identified in the prospective screening study for osteonecrosis after organ transplantation, and seventeen hips in seventeen patients were identified in the contralateral hipscreening study. Three hips, all from the group of patients who had had organ transplantation, had Association Research Circulation Osseous staged disease with spontaneous resolution occurring later as evidenced by serial magnetic resonance imaging scans. In these three hips, the modified index of necrotic extent measured 11.10, 12.72, and 20.83, with the estimated percentage of femoral head involvement being 15% to 30% in two of the hips and <15% in the third. Resolution on magnetic resonance imaging was complete in two of the three hips and was nearly complete in the third. Resolution was not observed when the contralateral hip had symptomatic disease. Conclusions: Spontaneous resolution of osteonecrosis of the femoral head can occur. The factors that appear to be related to resolution are early, asymptomatic disease (Association Research Circulation Osseous stage 1) and small lesion size (a modified index of necrotic extent of <25). A larger series is necessary before these factors can be verified as being independent predictors of resolution. Initial signs of resolution may take as long as one year to occur. Level of Evidence: Prognostic study, Level I-1 (prospective study). See Instructions to Authors for a complete description of levels of evidence.