The prevalence and natural history of early osteonecrosis (ON) of the femoral head.

We performed limited MRI exams of the hips of renal transplant patients to determine the prevalence of osteonecrosis (ON) and the natural history of early lesions. Of 132 subjects, ten patients and 15 hips were considered positive for ON (prevalence = 7.6%, bilaterality = 50%). Eleven of the MRI-positive hips were Ficat Stage 0 (asymptomatic, pre-radiographic) and were followed with serial radiographs and MRI exams. With an average follow-up of 22 months, only one of these early lesions progressed beyond Ficat 0. The other ten hips neither developed progressive MRI changes nor progressed to radiographic stages. Although our follow-up of 22 months is short, the results suggest that early ON may have a benign course in many cases. This supports the recent work of Kopecky et al., who found that many early lesions in renal transplant patients seemingly stabilize or disappear. While the prevalence was lower than in some previous reports, a significant number of patients did demonstrate previously unsuspected disease. Given the recent reports of poor results and high complication rates using "prophylactic" surgery such as core decompression for early ON, we recommend further study into the natural history of these lesions to assess the need for such procedures. In addition, we describe the use of a simple, quick and cost-effective method to screen high risk patients for early ON.