Lesion size changes in osteonecrosis of the femoral head: a long-term prospective study using MRI

Osteonecrosis of the femoral head (ONFH) is one of the intractable diseases. It is controversial whether the lesion size assessed by magnetic resonance imaging (MRI) can change over time without any operative treatment. In this study, we used MRI to observe the lesion size changes of ONFH induced by corticosteroid administration in severe acute respiratory syndrome (SARS) patients. The study included 51 SARS patients (84 hips) with early-stage ONFH who did not receive any operative treatment and were diagnosed by MRI. All of the patients underwent MRI follow-ups. Each patient was evaluated on the basis of the lesion volume on MRI at every follow-up for further comparisons. At the first MRI scan, the mean lesion volume was 10.12 +/- 8.05 cm(3) (range: 0.39-41.62 cm(3)). At the mid-term follow-up (2.5 years), the mean lesion volume was 7.82 +/- 7.59 cm(3) (range: 0.11-39.65 cm(3)). At the final follow-up (five years), complete regression of the lesion was observed in six hips, and the mean lesion volume was 5.67 +/- 6.58 cm(3) (range: 0.00-31.47 cm(3)). Overall, the lesion volume was reduced by >15% in 80 hips, and only four hips with relatively larger lesion volumes showed no apparent reductions. The reduction in lesion size of ONFH observed on MRI is a slow, discontinuous and time-dependent process.