Radiographic Progression in the Pre-Radiographic Stage of Osteonecrosis of the Femoral Head

Early and accurate diagnosis of osteonecrosis of the femoral head (ONFH) is crucial for the success of joint-preserving treatments. Although multimodal diagnostic criteria, including radiographs, enhance diagnostic accuracy, they are limited in detecting preradiographic stages. Magnetic resonance imaging (MRI) is widely utilized; however, it is associated with the risk of overdiagnosis. This study aimed to characterize the preradiographic stage of ONFH diagnosed solely by MRI and to elucidate its progression and factors influencing it.

This retrospective study included 538 newly diagnosed stage 1 (pre-radiographic) ONFH cases with consecutive radiographic follow-ups from the registry of a nationwide hospital-based sentinel monitoring system established by the Japanese Investigation Committee between 2010 and 2018. Demographic and clinical characteristics were analyzed, and factors influencing radiographic progression were identified.

Among the stage 1 ONFH, 90.1% of cases were diagnosed solely by MRI, with 79% potentially attributed to systemic corticosteroid administration. Of the 485 patients who have ONFH diagnosed solely by MRI, 156 hips (32.2%), 56 hips (11.5%), eight hips (1.6%), and one hip (0.2%) progressed to stage 2, stage 3A, stage 3B, and stage 4, respectively, over an average duration of 22.7 months. The remaining 264 hips (54.4%) showed no progression after a mean follow-up duration of 49.6 months. Sex, bilaterality, and type classification were significantly associated with the progression of ONFH, which was diagnosed solely by MRI.

Although MRI is essential for detecting pre-radiographic stage ONFH, less than half of preradiographic ONFH cases progress to stage 2 or higher. These findings highlight the potential for overtreatment if management decisions rely solely on MRI findings.