A novel stage and classification system of ONFH based on the radiologic-histopathological correlation

Abstract Background: To explore the influence of the new staging and classification system based on the correlation between MRI and pathological features on the collapse, symptoms and function of femoral head necrosis. Methods: This retrospective study included 100 patients (200 hips) who were diagnosed with bilateral ONFH. According to the degree of fibrosis in the necrotic area in a mid-coronal section on hip MRI, the MRI stage of ONFH can be divided into three types. Based on the level of inflammatory response, the MRI classification of ONFH can be divided into two types (S1 and S2), and S2 can be divided into three subtypes (S2a, S2b, S2c). The radiological evaluations were based on plain X-rays and MRI. The data were analysed using SPSS 26.0 statistical software. Results: There was a significant difference in the collapse rate between Type Ⅰ (7.1% ),Type Ⅱ (66.3% ) and Type Ⅲ (92.1%) (P＜0.001). The collapse rate in S1 (11.1%), S2a (66.7%), S2b (85.3%), S2c (77.8%) was significantly different (P＜0.001). There was also a significant difference in pain level and hip function between MRI staging and classification (P＜0.001). The later the stage, the higher the pain level, and similar results in hip functions. With the aggravation of bone marrow edema, the patient’s pain level increases and hip function decreases. Conclusion: Pathological fibrosis and inflammatory response are important factors that influence ONFH collapse and prognosis. The new MRI stage and classification based on pathology is a supplement to the existing stage and classification.