Introduction: Whether or not to surgically treat osteonecrosis of femoral head (ONFH) when patients are asymptomatic is controversial. The goal of this study was to determine: 1) if spontaneous resolution of ONFH does occur, 2) how long does it take for resolution to occur, and 3) if there are predictors of spontaneous resolution.

Materials and Methods: For this prospective study, patients with asymptomatic ONFH were identified from two National Institute of Health funded, Institutional Review Board approved screening studies. A prospective screening study for ONFH after organ transplantation was begun in 1997 by performing routine MRI examinations after transplantation. In a second prospective study on surgical treatment for symptomatic ONFH, the contralateral hip was screened for asymptomatic disease. A cohort of patients having hips with asymptomatic ONFH was then analyzed.

Results: As of December 2000, 13 asymptomatic hips in 10 patients were identified from the prospective screening study after organ transplantation and 17 hips in 17 patients were identified from the contralateral hip screening study. There were 3 hips with ARCO stage I disease showing evidence of spontaneous resolution. The modified index of necrotic extent measured 11.10, 12.72, and 20.83, with the estimated femoral head involvement being 15–30% in 2 of the hips and less than 15% in the third. Resolution on MRI was complete in 2 of the 3 hips, and nearly complete in the third.

Discussion: Spontaneous resolution of ONFH does occur. Factors associated with resolution are early, asymptomatic disease (ARCO stage I), small lesion size (modified index of necrotic extent < 25), and the absence of symptomatic disease in the contralateral hip. Initial signs of resolution may take up to one year to occur. For patients fitting these criteria, we recommend withholding surgery and monitoring hips with serial MRI observation to monitor the course of their disease.