Background: The reported prevalence of osteonecrosis of the femoral head in patients who have undergone a solid organ transplant has ranged from 3% to 41%. The wide variation is due to the retrospective nature of most studies and the inability to capture data on asymptomatic patients. The primary goals of this study were to determine the true prevalence of osteonecrosis of the femoral head following solid organ transplantation, the time to the development of the osteonecrosis, and whether findings on magnetic resonance imaging precede the onset of symptoms.

Methods: Beginning in 1997, patients who had undergone a solid organ transplant were asked to participate in a prospective study in which they would be screened for osteonecrosis of the femoral head. Inclusion criteria included an age of greater than fourteen years, a first-time transplant, and magnetic resonance imaging performed within six months after the transplant. Exclusion criteria were pre-existing osteonecrosis of the femoral head in the hip included in the study, a history of inflammatory arthritis, previous hip surgery, any contraindication to magnetic resonance imaging, a prior organ transplant, prior systemic corticosteroid treatment, and mental health issues preventing adequate follow-up. Screening magnetic resonance imaging was performed every four months. Survivorship analysis was used to determine the prevalence of osteonecrosis of the femoral head.

Results: Fifty-two patients (103 hips) were enrolled in the study. Their ages ranged from twenty-four to sixty-five years (mean, forty-three years). Sixteen patients were dropped from the study, but the data collected on them before they were dropped were included in the analysis. Osteonecrosis of the femoral head was diagnosed in eight of the 103 hips. Survivorship analysis revealed that, at one year after the transplant, 89% ± 7% of the hips and 80% ± 13% of the patients were free of osteonecrosis of the femoral head; thus the prevalence of osteonecrosis one year after transplantation was 11% or 20%, respectively. The mean duration of follow-up of the remaining hips was 2.3 years. In two hips the osteonecrosis of the femoral head was seen on the initial screening magnetic resonance imaging, and in the other six it developed after the initial magnetic resonance imaging revealed negative findings. All cases of osteonecrosis of the femoral head developed within ten months after the transplant. Seven of the eight hips were asymptomatic at the time of diagnosis. There was a significant difference in the one-year osteonecrosis-free survival rate between the patients who were less than forty years old (78%) and those who were at least forty years old (97%) (p = 0.011). Diabetes, smoking, and rejection episodes were not risk factors for osteonecrosis of the femoral head.

Conclusions: Our study of patients who had had a solid organ transplant revealed that the true prevalence of osteonecrosis of the femoral head in such patients is lower than that reported in most previous studies, osteonecrosis of the femoral head develops prior to the onset of symptoms, an age of less than forty years is a risk factor for osteonecrosis of the femoral head, and osteonecrosis of the femoral head develops within one year after transplantation. We recommend that magnetic resonance imaging be used to screen for osteonecrosis of the femoral head within one year after transplantation. The utility of additional magnetic resonance imaging after one year has not been established.