Radiographic lateral hip joint view can predict contralateral asymptomatic osteonecrosis of the femoral head

Background: Even in cases of bilateral osteonecrosis of the femoral head (ONFH), only one side often collapses and the contralateral side is often asymptomatic at the time of initial diagnosis. This study aimed to evaluate the presence of asymptomatic ONFH based on the radiographic necrotic area on the symptomatic side. Methods: The study included 89 hips of patients with ONFH who were divided into two groups: unilateral ONFH and bilateral ONFH groups, with a minimum follow-up of 3 years. The extent of the necrotic area in the anteroposterior (ANA) and lateral (LNA) radiographic hip joint views on the symptomatic side in the groups was assessed using plain radiography. The most effective cut-off value was extracted from the receiver operating characteristic (ROC) curve of the radiographic necrosis area of symptomatic ONFH in the absence of contralateral ONFH. Results: The unilateral ONFH and bilateral ONFH groups included 36 and 53 patients, respectively. There was a significant difference in ANA and LNA between the unilateral ONFH and bilateral ONFH groups (ANA: 66.5 ± 16.3% vs. 77.2 ± 16.4%, p < 0.01; LNA: 62.2 ± 17.7% vs. 72.9 ± 17.6%, p <0.01). Multivariate analysis revealed that only LNA of the symptomatic side was a predictor of contralateral ONFH (odds ratio 1.052, 95% confidence interval 1.01-1.12, p = 0.028). A cut-off value of 67% of the LNA was extracted from the ROC curve analysis. The 4-year survival rates with the collapse progression as the endpoint were 30.6% in LNA ⩾67% and 80.0% in LNA <67% (p <0.01 and p <0.01, respectively). Conclusions: The LNA of ONFH on the symptomatic side is a useful indicator of the presence and prognosis of contralateral ONFH. The findings of this study provide useful information for planning treatment strategies and predicting the prognosis of patients with ONFH.