We present a case of a 61-year-old female with history of long-term (>5 years) bisphosphonate therapy for osteoporosis initially diagnosed by screening dual-energy X-ray absorptiometry (DXA). Her only risk factor for low bone mass was that she was postmenopausal. After 4 years of treatment with bisphosphonates, the patient presented to primary care with left hip pain. Diagnostic hip radiographs were interpreted as normal, and she continued to take bisphosphonates. Two months later, she experienced a complete transverse subtrochanteric left femur fracture after minimal trauma. The patient underwent open reduction and internal fixation. Review of the patient's postoperative films revealed lateral subtrochanteric cortical beaking at the fracture site (Fig. 1D). Although this type of “atypical” fracture has been described in patients without prior use of bisphosphonates, these findings appear to occur at higher frequencies in patients undergoing chronic treatment with these medications.1–3 In addition, the right femur (Fig. 2) also showed cortical beaking with a horizontal linear lucency in an identical location, suggesting an impending fracture. Longitudinal review of both the diagnostic radiographs as well as DXA images shows a stepwise development of these subtrochanteric abnormalities in both hips. The referring clinician thought the left femur fracture was a result of low bone mass rather than prolonged use of bisphosphonates and initially continued the treatment of the medication.
Much controversy still exists over bisphosphonate-associated fractures, including the causative pathophysiology and clinical diagnosis. A current hypothesis regarding the pathophysiology of bisphosphonate-associated fracture is that the medication inhibits bone turnover and repair of microscopic trauma. A cycle of defective repair and continual microtrauma compounded over time gradually weakens the bone and creates an architectural conduit for transverse or “atypical” fracture.4 Standard practice is not to use DXA as a diagnostic “image.” We present this case to show that a common location and classic appearance of subtrochanteric bisphosphonate-associated fractures may be clearly visualized on absorptiometry images long before fracture. This observation is important because the majority of patients taking bisphosphonate therapy also receive regular DXA scans where the early detection of these abnormalities could potentially lead to timely changes in treatment.
In summary, with the anticipation of further study on this phenomenon and in the absence of accepted imaging guidelines for patients on chronic bisphosphonate treatment, it is advisable for the clinician to be aware of the described imaging abnormalities. Because of the chronicity of standard bone-density monitoring for these patients throughout their treatment regimen, DXA may find an important role for early detection of cortical abnormalities. It is not yet known if the DXA is sufficient for this task, but it would be advisable for the clinician to be aware of the described imaging findings.
All the authors state that they have no conflicts of interest.
This case report is not the result of internal or external funding.
Authors' roles: Report design: MA, MR, LG; study conduct: MA, MR; data collection: MA, MR; data analysis: MA, MR; data interpretation: MA, MR, LG; drafting manuscript: MA, MR; revising manuscript content: MA, MR, LG; approving final version of manuscript: MA, MR, LG. MA takes responsibility for the integrity of the content of the manuscript.