Atypical femoral fractures (AFF) are stress fractures occurring at the lateral cortex of the subtrochanteric region (1). AFFs are associated with anti-resorptive use; the risk increases with increasing duration of exposure (2). The optimal management of patients with osteoporosis in the context of AFFs is challenging.
An 82 year old Caucasian woman with osteoporosis was treated with 7 years of oral bisphosphonates when she presented with bilateral thigh pain aggravated by mobilisation. Imaging revealed bilateral incomplete stress fractures in the lateral cortex of each femoral shaft (Fig. 1a).
Bisphosphonate (BP) therapy was discontinued and the patient agreed to a trial of teriparatide for 18 months. At the completion of this treatment she reported a reduction in thigh pain. Serial imaging showed healing of the stress fractures (Fig. 1b).
As this patient had osteoporosis and microstructural deterioration, assessed using high-resolution computed tomography, to preserve any benefits derived from teriparatide and to prevent structural decay, denosumab was commenced 12 months after cessation of teriparatide. Six months later, the patient reported increasing bilateral thigh pain. Repeat imaging confirmed the presence of recurrent bilateral mid shaft stress fractures (Fig 1c). The patient had prophylactic bilateral internal fixation.
This case illustrates the challenge in treating patients with osteoporosis and severe structural decay who suffer atypical femoral fractures associated with BP therapy. If left untreated after stopping BP, remodelling will increase, leading to continued structural decay. If anti-resorptive treatment is recommenced, remodelling is likely to be suppressed, and this may result in altered material composition predisposing to recurrent AFFs. Novel approaches such as sclerostin antibodies, which stimulate bone formation and reduce remodelling, combined or sequential use of denosumab or odanacatib plus PTH, or use of SERMs like raloxifene, which improve bone toughness – may play a role in the management of osteoporosis and AFF.