To explore the condition of "survival with collapse" of femoral head necrosis (ONFH) and evaluate its reliability in diagnosing the outcome of patients with International Association Research Circulation Osseous (ARCO) stage ⅢA by using the integrity rate of femoral head weight-bearing area.

Patients with non-traumatic femoral head necrosis in the First Affiliated Hospital of Guangzhou University of Traditional Chinese Medicine from 2010 to 2017 who belonged to ARCO stage ⅢA "with collapse" were selected. The enrolled patients had normal communication skills, complete imaging data of clinical visits, informed consent and were regular followed up. The elderly patients with other severe chronic diseases, the patients with incomplete imaging data, inappropriate medication and history of total hip arthroplasty or hip-preserving surgery were excluded. The patients were categorised by the Japan  Investigation Committee (JIC) type, and divided into the collapse progression group and the survival with collapse group according to the outcome. Anteroposterior-view intact ratio (APIR) and frog-leg view intact ratio(FLIR) were measured by standard anteroposterior view(AP) and frog-leg view (FL) of radiograph, the relationship between this index and the outcome was clarified. Univariate and multivariate logistic regression analyses were then performed to identify risk factors for progression of collapse. The reliability of weight-bearing zone integrity on the diagnosis of collapse progression and survival with collapse was analyzed using the receiver operating characteristic (ROC) curve.

A total of 72 patients (90 hips) with ONFH of ARCO stage ⅢA were enrolled. Among them, 37 hips survived with collapse were followed up for 85(72, 166)months , and 53 hips with collapse progression were followed up for 24 (6, 78) months. JIC type was the key influent factor of the survival with collapse (χ²=21.312, P<0.001). ROC curve analysis showed that the critical value of APIR was 16.6%［area under curve(AUC)=91.0%, Youden index=0.78, P<0.0001］. APIR≥16.6% was significantly related to survival with collapse. The critical value of FLIR was 16.1% (AUC=89. 7% , Youden exponent = 0.82, P<0.001), which suggested that FLIR≥ 16.1% was significantly related to survival with collapse. APIR and FLIR were significantly correlated with the outcome.

The anterolateral femoral head weight-bearing area integrity rate is closely related to "survival with collapse", which suggests that patients with ONFH of ARCO stage ⅢA can be judged whether they are eligible for "survival with collapse" according to the APIR and FLIR, so as to rationally choose the treatment.