Scoring System for Identifying Impending Complete Fractures in Incomplete Atypical Femoral Fractures

Context: Although impending incomplete atypical femoral fractures (AFFs) require prophylactic fixation, there is still a lack of study on predicting complete fracture among the incomplete AFFs. Objective: Our purposes are to develop a scoring system to predict progression into complete fracture and to evaluate its reliability and validity. Design, Setting, and Patients: We reviewed 46 incomplete AFFs in 44 patients who did not undergo prophylactic fixation. A weighted scoring system, including four identified risk factors (the site, severity of pain, status of the contralateral femur, and the extent of radiolucent line), was developed. We evaluated its interobserver reliability by using intraclass correlation coefficiency (ICC) and its accuracy using receiver operator characteristic (ROC) curve. The validity of the scoring system was tested in a different cohort. Intervention: Observational study. Main Outcome Measure: Progression to complete fracture within 6 months. Results: Among 46 incomplete fractures, 13 developed a complete fracture within 6 months. The probability of complete fracture increased abruptly when the score was 8 points or more. The proposed scoring system showed an almost perfect reliability (ICC, 0.997; 95% confidence interval, 0.995 to 0.998) and higher accuracy than any single risk factor in ROC curve. In the different series, the positive predictive value was 100% and the sensitivity was 75%, when cutoff value was 8 points. Conclusion: The progression to complete fracture could be predicted by using our scoring system. Incomplete AFF with scores <8 points can be treated conservatively, whereas lesions with scores ≥8 require prophylactic fixation.