(4.03) A Rare Case of Spontaneous Atypical Tibial and Fibular Fragility Fractures after Bisphosphonate Therapy

Bisphosphonates have been widely used for the treatment of osteoporosis. A rare, but serious complication of long-term treatment is the development of atypical fragility fractures (AFFs), which usually occur in the subtrochanteric and diaphyseal areas of the femur. AFFs elsewhere are extremely rare. We report the case of a patient with osteoporosis who developed AFFs in the tibia and fibula after long-term bisphosphonate therapy. 

Case(s) Description :

An 83-year-old Caucasian female with severe degenerative disc disease and osteoporosis was referred to our endocrinology clinic for evaluation of AFFs of the left tibia and fibula.
She was diagnosed with osteopenia in 2010 (right hip T-score of -1.9) and received raloxifene for 3 years. Due to worsening right hip T-score of -2.3 and elevated hip FRAX score of 4.6% she was then switched to Alendronate 70 mg weekly. Bone density values in the spine were not reliable due to extensive arthritis in the spine. She was treated with Alendronate from 2013-2022 due to persistently low hip T-scores. In 2022, she developed left lower leg pain, erythema and tenderness without any preceding trauma. X-ray of the left lower extremity showed soft tissue swelling, but no bony abnormalities. MRI and bone scan suggested an infectious/inflammatory process within the left distal tibia. She received 6 weeks of antibiotic therapy for suspected osteomyelitis. Due to lack of symptomatic improvement, she was then referred to pain management for suspected diagnosis of complex regional pain syndrome.
A few months later, she developed bowing of the left leg. Repeat x-ray showed complete transverse fractures through the distal left tibia and fibula and evidence of callus formation across the fracture site with increasing sclerosis and mild lateral angulation. She was diagnosed with bisphosphonate induced AFFs of the tibia and the fibula. Alendronate was stopped and she was managed conservatively with dynamic custom ankle foot orthosis. The fractures healed over 6 months. The patient did not want to pursue corrective surgery for bowing in the lower leg. She did not have pain in the hips or the right leg, and imaging at those sites did not reveal any abnormalities suggestive of AFFs.

Discussion :

AFFs of the tibia and fibula are extremely rare complications of bisphosphonate therapy and to date there are only 7 case reports in the literature. This lack of awareness results in delayed diagnosis, as occurred in our patient.
We would like to highlight the importance of having a high index of suspicion for AFFs in patients on long-term bisphosphonate therapy who present with bony pain and tenderness, even if initial imaging studies do not show a clear fracture. The distal tibia and fibula should be considered as potential sites for AFFs. Bisphosphonates should be stopped when suspecting AFFs, as continuation may lead to worsening of the AFF or a new contralateral AFF.