Category: Calcium/Bone Disorders
Antiresorptive agents like Bisphosphonates and RANK ligand inhibitor Denosumab reduce bone loss and have been shown to decrease fracture risk at various sites. Long-term use of antiresorptive therapy is associated with an increased risk of Atypical femoral fractures(AFF). Osteoclasts reabsorb microscopic cracks formed by microtrauma by target remodeling. This process is inhibited by antiresorptive therapy which leads to AFF. We report a case of AFF which was detected as bone marrow edema on MRI and treated conservatively.
81 y/o female with the history of osteoporosis presented to the clinic with right thigh pain. Patient has a long-standing history of Osteoporosis and has been on various osteoporosis treatments including Reclast, Fosamax, Denosumab, Forteo, Hormone replacement therapy in the past 20 years. She was on Denosumab for 5 years prior to her presentation and was switched to Fosamax 6 month prior. The patient reported a gradual onset of right thigh pain without any other trauma, the pain being more noticeable on weight bearing.
Because of ongoing pain and long duration of antiresorptive therapy use, there was a concern for AFF. Fosamax was stopped, and plain films of the right hip and femur were obtained and were normal. MRI of the femur was subsequently done which showed a subtle bone marrow edema pattern at the proximal, mid femur, but no distinct fracture line was seen. These findings were not characteristic of AFF. She was then referred to an Orthopedic surgeon; an ultrasound was done which showed stress fracture in the right femur. Imaging of the contralateral femur was normal. She was managed conservatively with rest and non-weight bearing for two months with the resolution of pain. The patient used Forteo in the past and hence we could not use it for treatment of her AFF.
AFFs are a rare complication of chronic antiresorptive therapy and evolve over time; patients typically have prodromal symptoms including dull or aching pain in the groin or thigh. Bisphosphonates have been shown to increase microdamage accumulation and alter bone mineralization and collagen formation which can contribute to AFFs. Plain X-ray can be normal early in the presentation. Characteristic MRI findings include localized periosteal and endosteal thickening of the lateral cortex with breaking and flaring. There are very few case reports of early detection of AFF which can be seen as bone marrow edema radiologically. Early fractures can be managed conservatively before considering surgical intervention.
Early impending atypical fractures can be seen as bone marrow edema on imaging. Early detection and management can prevent progression to complete AFF.
Clinical instructor, Division of Diabetes Endocrine and Metabolism, University of Nebraska Medical Center