Atypical femur fractures (AFFs) are rare adverse events linked to chronic bisphosphonate therapy for osteoporosis (median treatment seven years)(1). AFFs have also been reported in patients on denosumab, a monoclonal antibody that reduces osteoclastic activity. Patients typically present with prodromal symptoms of thigh or groin pain and diagnosis is made on plain x-ray, bone scan, CT or MRI. Immediate management of AFFs includes cessation of antiresorptive therapy, calcium and vitamin D supplementation, modified physical activity, analgesia and surgical intervention as required. Ongoing management of bone health post AFF is challenging, particularly in patients treated with denosumab where discontinuation results in acute bone loss (2). Options for further osteoporosis therapy include raloxifene and calcitriol, both have been shown to improve bone mineral density (BMD) and not associated with AFF. Parathyroid hormone has been used to advance healing (3) and drug holiday may be appropriate. Regardless, the benefit of antiresorptive therapy for prevention of osteoporotic fractures outweighs the risk of AFFs (4). We present a case of a 59 year old menopausal woman of Sri Lankan heritage with an atypical left subtrochanteric fracture in the context of a single zoledronic acid infusion followed by 36 months of denosumab therapy for osteoporosis. A cortical lesion in the right medial femur was found incidentally albeit an unusual location for an AFF. Acutely she was managed with prophylactic left intramedullary nailing. A therapeutic dilemma ensued from the cessation of denosumab for her AFF and risk of contralateral femoral fracture, and mitigating the risk of rebound bone loss and osteoporotic fracture. She was commenced on raloxifene, calcitriol and calcium supplementation. Interval dual-energy x-ray absorptiometry (DEXA) at 12 months showed stable BMD. Regular follow up on metabolic bone biochemistry and BMD along with close monitoring of at risk changes on the contralateral side are crucial.
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