Natural History and Conservative Treatment of Osteonecrosis (ON) of the Femoral Head

Until now the natural history of nontraumatic osteonecrosis of the femoral head (ON) has been poorly understood. The spontaneous course of ON with radiographic changes (even asymptomatic) is regarded as poor with progression in 50–80% of the cases within two years. In contrast, stabilisation or disappearance of the lesions on MRI can occur in early ON with normal radiographs (stage 1), leading to the definition of a purely “magnetic ON”. Furthermore MRI allows us to study the volume of the necrotic area, which seems to be the most important prognostic factor in early ON. If this volume is less than 20% of the femoral head, the percentage of spontaneous progression is very low. The natural history of ON, especially in the early onset of the disease, has be redefined by MR imaging studies.

Conservative treatment in ON is generally regarded as not very successful. Discontinuing weightbearing has shown to be ineffective in numerous studies. Pulsed electromagnetic fields have given promising results in some studies, but the value of this approach is still controversial. Vasoactive drugs have been shown to reduce pain significantly in ON and there might be a possible role for treating early cases. Some other ON disease modifying drugs may be helpful in carefully selected patients in the future. Nevertheless so far no conservative or surgical therapeutic method has been shown to heal the necrotic lesion. Therefore prevention is the only way which may prevent collapse in patients with a high ON risk, other than treatable aetiological factors.