Material and Method: The authors retrospectively reviewed plain radiographs of 856 patients who were diagnosed with subtrochanteric or femoral shaft fractures between 2002 and 2013. Only those who had major radiographic features of AFF according to the 2010 ASBMR criteria were included. Next, the prevalence of atypical fracture was recalculated based on the revised 2013 ASBMR criteria. Furthermore, the specificity and sensitivity of each radiological finding to detect bisphosphonate treatment were calculated.

Results: The prevalence of atypical femoral fracture based on 2010 ASBMR criteria at this institution was 5.7%. Two patients had all radiographic features of AFF but sustained a high-energy trauma and could be diagnosed with AFF based on the 2013 ASBMR criteria. Among all of the radiographic features to define AFF, a localized periosteal thickening of the lateral femoral cortex was the most specific sign to detect bisphosphonate treatment (0.98; 95% CI 0.96-0.99).

Conclusion: The prevalence of AFF in Thai patients at a single institution was approximately 6%. Although the prevalence of AFF did not dramatically change after applying the 2013 revised ASBMR criteria, this reflected some gap in the diagnosis criteria, which should require further refinement. The authors suggested that the ASBMR criteria should be used only with those having acute fractures.

Keywords: Atypical femoral fracture (AFF), Subtrochanteric fracture, Femoral shaft fracture, Bisphosphonate, American Society of Bone and Mineral Research, ASBMR