Bone Abstracts

Background: Bisphosphonates are increasingly used to treat disorders of low bone mineral density (BMD) in children and adolescents. Long-term bisphosphonate use in adults has been associated with and increased risk of atypical subtrochanteric and diaphyseal femoral fractures (AFFs). To date, bisphosphonate-related AFFs have not been reported in children or adolescents.

Presenting problem: A 16-year-old girl presented with a 3-week history of left thigh pain. Her past medical history was significant for idiopathic juvenile osteoporosis diagnosed at age 11 years after presenting with a 1-year history of back pain and thoracic compression fractures. A DXA scan at that time showed decreased BMD with a lumbar spine z-score −3.9 and total body less head z-score −2.0. An extensive workup including a vertebral biopsy and testing for COL1A1/1A2 mutations did not reveal an etiology for her low BMD. She was treated with intravenous pamidronate over a 2-year period, receiving a cumulative dose of 12 mg/kg. During the treatment period she had partial reconstitution of her vertebral bodies and no additional fractures. At pamidronate discontinuation (age 14 years), her lumbar spine z-score had improved to −1.6 and total body less head to −0.6. Just prior to the onset of thigh pain at age 16, she had joined a cross-country team after several years of inactivity, and was running 3–4 miles 7 days per week. Plain films showed diffuse cortical thickening of the bilateral femoral diaphyses, and a localized periosteal reaction at the medial cortex of the proximal left femur. A technetium-99 bone scan showed focal tracer uptake in the medial aspect of the proximal left femur, consistent with a stress fracture.

Clinical management: The patient was treated with restricted weight-bearing and relative rest. She received physical therapy and was placed on a program of muscle strengthening and generalized conditioning. After a protracted 16-week course her pain improved and she was able to resume regular activities. Plain films obtained 8-months after her initial presentation with thigh pain showed resolution of the periosteal reaction.

Discussion: This adolescent’s presentation with a femoral stress fracture following high-dose pamidronate treatment shares several features in common with AFFs, including subtrochanteric location, localized periosteal reaction, and generalized cortical thickening of the femoral diaphysis. However unlike bisphosphonate-associated AFFs in adults, which typically develop on the lateral tensile cortical surface, this patient’s stress fracture occurred at the medial cortex. Thus, while suggestive, the contribution of bisphosphonate treatment to the development of this patient’s stress fracture is not known. Nevertheless, practitioners should evaluate thigh pain in children and adolescents with a history of bisphosphonate treatment, and should include AFFs and other femoral stress fractures in the differential.

Disclosure: The authors declared no competing interests.