Increasing Prevalence and Risk Factors for Multifocal Osteonecrosis in Patients Who Have Corticosteroid-Associated Osteonecrosis of the Femoral Head: A 15-Year Multicenter Study.

Background: Multifocal osteonecrosis (MFON) is a rare condition affecting multiple bone sites, with limited epidemiological data available. This study investigated the frequency, trends, and risk factors for MFON in patients aged > 15 years who had corticosteroid-associated osteonecrosis of the femoral head (ONFH) using data from a multicenter sentinel monitoring system in Japan.

Methods: Data from 658 patients between 2009 and 2023 were analyzed. The MFON was defined as osteonecrosis involving three or more separate anatomical sites. The frequency and trends of MFON were assessed across three 5-year periods. The risk factors for MFON were analyzed using data from 2014 onward, when smoking history data became available. The group with no necrosis other than that in the femoral head was defined as the non-MFON group, and the demographics and comorbidities were compared between the MFON and non-MFON groups. The risk factors were analyzed using univariate and logistic regression analyses.

Results: The frequency of MFON was 5.3% during the entire period and increased significantly over time (1.6, 7.4, and 8.0%; P < 0.01). The knee joint was the most common site of osteonecrosis, and all patients had knee joint involvement. The MFON group was younger (P < 0.001) and had more women (P < 0.05) than the non-MFON group and had significantly more patients who had systemic lupus erythematosus (SLE) and hematological tumors (both P < 0.01). The independent risk factors for MFON included age < 40 years (P < 0.05), SLE (P < 0.05), and hematological tumors (P < 0.001).

Conclusions: The frequency of MFON in patients who had corticosteroid-associated osteonecrosis of the femoral head was 5.3%. Young patients, those who have SLE, or those who have hematological tumors are at a higher risk of MFON and should be considered for MFON screening.