Lateral classification system predicts the collapse of JIC type C1 nontraumatic osteonecrosis of the femoral head: a retrospective study

PURPOSES: The aim of this study was to construct a lateral classification system for nontraumatic osteonecrosis of femoral head (NONFH) through three-dimensional reconstruction of the necrotic area to assist in evaluating the prognosis of patients with JIC type C1. METHODS: Retrospective analysis of patients with JIC type C1 NONFH from January 2018 to December 2020. All patients were followed up for more than 3.5 years. The patients were divided into collapse group and non-collapse group according to whether the femoral head collapsed during the follow-up.Lateral classification system for femoral head necrosis is constructed through three-dimensional reconstruction of the necrotic area.Comparison of lateral classification system,midsagittal necrosis angle(MNA)and general data between the two groups.Furthermore, ROC curve analysis and survival analysis were performed. RESULTS: 318 patients were included in this study.There was a significant difference between the two groups in the lateral classification system (P < 0.05). In addition, the MNA in the collapsed group was significantly greater than that in the non-collapse group(P < 0.05). As revealed by the results of ROC analysis, the cutoff point of MNA was 104.5° (P < 0.05).According to the survivorship analysis, the mean survival time of the hips of patients with MNA less than 104.5°was greater than that of patients with MNA over 104.5° (P < 0.05). The survival rates of 3.5 years femoral head were 45.8%, 33.7%, 14.8%, 93.0%, and 100% for lateral classification system 1, 2, 3, 4, and 5, respectively. CONCLUSION: Necrosis involving the anterior aspect of the femoral head is an important risk factor for collapse. The Lateral classification system can effectively predict the femoral head collapse in JIC C1 type NONFH patients, supplementing the deficiency of JIC classification in evaluating the front of the femoral head.