Subtrochanteric stress fractures in patients on oral bisphosphonate therapy: an emerging problem.

The emergence of a new variant of subtrochanteric stress fractures of the femur, affecting patients on oral bisphosphonate therapy, has only recently been described. This fracture is often preceded by pain and distinctive radiographic changes (lateral cortical thickening), and associated with a characteristic fracture pattern (transverse fracture line and medial cortical spike). A retrospective review (2007-2009) was carried out for patients who were taking oral bisphosphonates and who sustained a subtrochanteric fracture after a low velocity injury. Eleven fractures were found in 10 patients matching the inclusion criteria outlined. All were females, and taking bisphosphonates for a mean of 43 years. Five of the 10 patients mentioned prodromal symptoms, for an average of 9.4 months before the fracture. Although all fractures were deemed low velocity, 5 of 11 were even atraumatic. Two patients had previously sustained contralateral subtrochanteric fractures. Plain radiographs of two patients showed lateral cortical thickening on the contralateral unfractured femur; the bisphosphonate therapy was stopped and close surveillance was started. Patients taking oral bisphosphonates may be at risk of a new variant of stress fracture of the proximal femur. Awareness of the symptoms is the key to ensure that appropriate investigations are undertaken.