Bilateral Femoral Neck Insufficiency Fractures after Use of a Long-term Anti-resorptive Drug Therapy for Osteoporosis: A Case Report

Abstract

A 78-year-old woman developed an insufficiency fracture on her right femoral neck without trauma after four years of treatment with a bisphosphonate. Her fracture was fixed by two screws and her anti-osteoporotic drug was changed from an anti-resorptive to an anabolic agent. Seven months later, however, she sustained similar insufficiency fracture on the left femoral neck and was treated with the same method. She developed right inguinal pain again approximately eight months after her right side operation. The results of imaging tests revealed that her insufficiency fracture was converted to complete fracture, and that the fracture gap had widened as well. Her right hip was revised with hemiarthroplasty. A histological exam of the fracture site revealed evidence of decreased bone healing. Long-term administration of anti-resorptive drug prevents bone healing and remodeling and can result in atypical fractures of the femoral neck. Osteosynthesis was difficult to accomplish despite the application of proactive fixation. Therefore, more rigid fixation and careful postoperative treatment should be considered.

Keywords: Anti-resorptive drug; Bilateral; Femoral neck; Insufficiency fracture.

Fig. 1. (A) A plain radiograph shows no specific finding. (B) A magnetic resonance imaging T2 weighted image shows high signal bend (arrow) above the right femur neck. (C) A postoperative radiograph shows two well fixed cannulated hip screws.

Fig. 2. (A) A plain radiograph shows sclerotic thickening (arrow) in the upper cortex of the left femoral neck. (B) A magnetic resonance imaging shows high signal lesion (arrow) above the left femur neck. (C) A postoperative radiograph shows two well-fixed cannulated screws.

Fig. 3. A computed tomography scan shows a sclerotic fracture gap without union at the fatigue fracture site of the right femur neck. The two screws seem to be relatively well fixed.

Fig. 4. (A) Histological findings of the fracture site (hematoxylin and eosin [H&E] stain, ×40). Multilayer thickened trabeculars of cancellous bone under the cortical bone can be seen, as well as cartilarge and fibrotic tissue in the portion of the fracture gap on the left (arrow). (B) The magnified (white square in A) histological findings (H&E stain, ×100) show some osteoclasts (arrows), chondrocytes, and a few osteoblasts on the fracture lesion. New bone formation can be seen, but at relatively low levels.