Atypical subtrochanteric fractures, bisphosphonates, blinded radiological review

Recent reports have suggested that a certain type of subtrochanteric and diaphyseal femoral fractures maybe associated with bisphosphonate (BP) therapy. We assessed the association between BP use in atypical and typical femoral fractures in a retrospective study and also looked at the rate of coding errors.

All cases between July 2003 and June 2008 with International Classification of Disease, 10th revision discharge codes for femoral fractures (S72.2 subtrochanteric and S72.3 fracture of shaft of femur) were reviewed. Cases were excluded if there was significant trauma, underlying bone disease or coding error. The remaining cases' films were assessed by an independent, blinded, single radiologist to assess for atypical features (thickened cortices, transverse fractures, medial cortical spike) with additional exclusion criteria of periprosthetic fractures and bone pathology. Odds ratios were calculated comparing BP use in atypical and typical fractures.

Six atypical fractures were found in the study period. Compared with the 65 typical fractures, there was an association between BP use and atypical fractures (odds ratio 5.5) but it did not reach statistical significance (0.97-31). Atypical femoral fractures accounted for <0.1% of total fracture admissions during this period. There was a 20% rate of miscoding.

This study shows a nonsignificant trend towards alendronate/BP use and atypical femoral fractures compared with typical femoral fractures. These fractures were rare <0.1% and the benefit and treatment of osteoporosis with BPs currently seems likely to outweigh the perceived risks. Individual case and radiology review is important as coding errors were frequent.