Atypical femoral fractures bilaterally in a patient receiving denosumab

Abstract

We present a case of bilateral low-energy femoral shaft fractures over a 1-year period in a woman after discontinuation of long-term alendronate therapy and initiation of treatment with denosumab. A 73-year-old woman with diabetes mellitus and an 8-year history of post-menopausal osteoporosis presented to the emergency department in June 2011 with a spontaneous left femur fracture. It was 3 weeks after the discontinuation of an 8-year therapy with vitamin D supplement and 70 mg alendronate weekly, and 1 week after the first subcutaneous injection of denosumab. Radiographs revealed a transverse femoral shaft fracture with lateral cortical hypertrophy and medial spiking (Figure 1). Figure 1. The patient’s left femur at the time of the first fracture. A transverse femoral shaft fracture with lateral cortical hypertrophy and medial spiking. The fracture was stabilized with a cephalomedullary nail. Routine blood investigations were within normal range and myeloma was excluded. Bone densitometry revealed an increase in bone density relative to baseline values before the initiation of alendronate therapy, but the T-score of at least 1 site was still in the osteoporotic range (femoral neck T-score: –2.95). 5 months postoperatively, the fracture had healed with callus formation. 1 year after the first fracture, the patient sustained a similar atypical fracture of the right femoral shaft (Figure 2) and she described mild, diffuse pain in the thigh during the previous 6–7 months. She was still on treatment with denosumab 12 months after the first injection (she had received 3 injections of denosumab at 6-month intervals). This fracture was also stabilized with a cephalomedullary nail and a pathological fracture was excluded. Figure 2. Both femurs at the time of the right femoral shaft fracture. This fracture also healed in 5 months with callus formation (Figure 3). In view of reports linking this pattern of femoral shaft fractures to long-term alendronate therapy (Neviaser et al. 2008) and considering the anti-resorptive mechanism of action of the denosumab, treatment with teriparatide (20 µg subcutaneously once a day) and vitamin D was commenced and denosumab was stopped. Figure 3. Anteroposterior radiograph of both femurs 5 months after the second operation, showing healing of the fracture with callus formation.