Subchondral Bone Plate Classification: A New and More Sensitive Approach for Predicting the Prognosis of Osteonecrosis of the Femoral Head

Background This study explores the impact of subchondral bone plate necrosis on the development of the osteonecrosis of femoral head (ONFH) and its joint collapse. Methods This retrospective study included 76 ONFH patients (89 consecutive hips) with Association for Research on Osseous Circulation stage II who received conservative treatment without surgical intervention. The mean follow-up time was 15.60 +/- 12.29 months. ONFH was divided into 2 types (I and II): Type I with a necrotic lesion involving subchondral bone plate and Type II with a necrotic lesion not involving subchondral bone plate. The radiological evaluations were based on plain x-rays. The data were analyzed using SPSS 26.0 statistical software. Results The collapse rate in Type I ONFH was significantly higher than that in Type II ONFH (P < 0.001). The survival time of hips with Type I ONFH was significantly shorter than those with Type II ONFH and with the endpoint of the femoral head collapse (P < 0.001). The collapse rate of Type I in the new classification (80.95%) was higher compared with that of the China-Japan Friendship Hospital (CJFH) classification (63.64%), and the difference was statistically significant (chi(2) = 1.776, P = 0.024). Conclusion Subchondral bone plate necrosis is an important factor that affects ONFH collapse and prognosis. Current classification using subchondral bone plate necrosis is more sensitive for predicting collapse compared with the CJFH classification. Effective treatments should be taken to prevent collapse if ONFH necrotic lesions involve the subchondral bone plate.