A Study on the Evaluation of a Risk Score of Osteonecrosis of the Femoral Head Based on Survival Analysis.

BACKGROUND

This study aimed at developing a risk score predicting the probability of developing an osteonecrosis of the femoral head (ONFH) in patients with femoral neck fracture within 3 years after closed reduction internal fixation and evaluating its performance, clinical utility, and internal validity.

METHODS

A retrospective follow-up study of 378 newly injured femoral neck fracture patients treated with 3 partially threaded parallel cannulated screws in 3 hospitals in Shanghai from March 2013 to January 2017 was performed. The patients were divided into development (n = 284) and validation (n = 94) cohorts. The risk score was constructed by Cox regression analysis in a form of nomogram. The performance and clinical utility were illustrated by box plots, calibration plots, and decision curve analysis.

RESULTS

Eighty-three of 378 patients had developed ONFH within 3 years. Garden alignment index, time to surgery, preoperative displace, impaction, and postoperative malposition were used as predictors to construct the risk score in a form of nomogram. In the development and validation cohort, the concordance index was 0.96 and 0.94, respectively; the discrimination slope was 0.51 and 0.47, respectively. In both cohorts, the calibration slopes and intercepts were 1 and 0, respectively. The risk score was clinically useful between the risk threshold of 0% and 88%. The performance and utility in the validation data illustrated good repeatability.

CONCLUSION

The risk score had satisfactory discrimination and calibration performance and demonstrated clinical utility with good internal validity. It managed to distinguish high-risk groups for post-traumatic ONFH.