An Atraumatic Femoral Fracture in a Patient with Rheumatoid Arthritis and Osteoporosis Treated with Denosumab

Osteoporosis is responsible for a significant burden both individually and socially, but is readily treated with antiresorptive agents and mineral supplementation. However, long-term usage of these agents, notably bisphosphonates, is rarely associated with atypical fractures. Denosumab is a monoclonal antibody that reduces osteoclast activity and thus increases bone mineral density. In this case report, we present a 78-year-old woman with a background of rheumatoid arthritis and osteoporosis who presented with an atypical diaphyseal femoral fracture. 1. Introduction Osteoporosis is a significant cause of morbidity and mortality. Following a neck of femur fracture, there is up to 50% loss of independence [1] and 20% mortality in the first 12 months [2]. Pharmacological therapy has been shown to significantly reduce fracture risk and therefore the subsequent morbidity and mortality [3]. Denosumab is a fully humanized monoclonal immunoglobulin that binds the receptor activator of nuclear factor-κB ligand (RANK-L), a member of the tumour necrosis factor cytokine family, essential for the formation, function, and survival of osteoclasts [4]. Denosumab is thought to sequester RANK-L, preventing it from activating NF-κB and subsequently reducing the resorption of bone. In the United Kingdom, Denosumab is recommended by the National Institute for Health and Care Excellence (NICE) for the treatment of postmenopausal women with osteoporosis who are unable to tolerate or comply with the administration of oral bisphosphonates, which remains the first line treatment option. However, since the introduction of antiresorptive therapy in the management of osteoporosis, concern has arisen that these medicines are associated with atypical fractures with long-term use [5]. The extension of the phase 3 FREEDOM trial, which had shown the benefits of Denosumab in the treatment of osteoporosis [6], has suggested that atypical femoral fractures do rarely occur after prolonged exposure. In this case report we present a 78-year-old female with a history of rheumatoid arthritis and osteoporosis who presented with an atraumatic diaphysial fracture of her right femur. 2. Case Report A 78-year-old female had been followed up in our Rheumatology outpatient clinic since being diagnosed with rheumatoid arthritis in 1987. Treatment has included occasional intraarticular and intramuscular corticosteroid injections, but never long-term oral corticosteroids. Current immunosuppressive therapy consists of methotrexate and hydroxychloroquine. She also has a background history of an idiopathic