Endocrine Abstracts

Objective(s): Atypical femoral fractures (AFFs) are an important complication of treatment with anti-resorptive treatment, which remains the cornerstone of osteoporosis treatment. Recognition of this rare clinical entity is exceedingly important, as ongoing treatment with anti-resorptives is contraindicated. The American Bone and Mineral Research (ASBMR) have devised diagnostic criteria which are qualitative and subjective. Recent attempts have been made to create more quantitative and objective guidance for clinicians, but diagnosis remains challenging. This study aimed to assess the global performance, sensitivity and specificity, and interobserver agreement/variability of both the ASBMR and the recently devised Sydney AFF Score (SAS) criteria (a score of ≥2, 1 point for each of the following: lateral cortical width (LCW) >5 mm, femoral neck width (LCW) <37 mm, age <80).

Design: Retrospective observational study involving inpatients at two teaching hospitals in Queensland, Australia. Adult patients aged 18 years or older presenting with low-energy mechanism, subtrochanteric fractures between January 2012 and February 2022.

Primary outcomes measure(s): Sensitivity, specificity and performance of each of the ASBMR and SAS criteria. Patients were divided into two groups for comparison: AFFs and ‘typical’ femoral fractures (TFFs). Measurement of interobserver variability/agreement using ASBMR criteria and the SAS using Kappa Fleiss statistic (FK). Accuracy of radiological reports by retrospective review

Results: A total of 869 femoral shaft fractures were screened. 46 AFFs were identified following expert panel review by 2/3 majority. A comparator group of 40 were selected from the remaining 149 TFFs. The sensitivity and specificity of the ASBMR criteria were: predominantly transverse orientation (TO) (91.4% [range 85.42 – 95.24%], 89.1% [81-94.6%]), minimal comminution (MC) (99.2% [range 97.7-100%], 63.9% [51.4-72.9%]) and periostial reaction (PR) (89.4% [84.1 – 97.6%], 96.4% [91.8% - 100%]). The Sydney AFF Score had comparable performance in this cohort compared to the index and validation cohorts (AUC 0.73). The ASBMR criteria showed good interobserver agreement (FK TO 0.72, MC 0.64, PR 0.76, P=<0.001). The agreement with the anthropometric indices using the SAS were (FK LCW 0.25, FNW 0.66, P=0.002, <0.001) Of the AFFs, just 13.2% of radiology reports referenced atypical or drug-related fracture.

Conclusion: Qualitative criteria outperform the most accurate quantitative indices. Incorporating fracture angle into the the SAS may yield superior diagnostic value and remove. This study demonstrates that AFFs are under-recognised by reporting radiologists.