Bone Abstracts

Background: Treatment of osteoporosis with long-term bisphosphonates is associated with increased risk of atypical fractures; commonly in the subtrochanteric region and the diaphysis of the femur. We present a patient who developed a spontaneous patellar insufficiency fracture while on long-term alendronate which, to our knowledge, has not been reported previously.

Methods: A 63-year-old female with difficult to treat psoriatic oligoarthritis was taking prednisolone for 13 years. Current dose was 10mg daily. She took weekly alendronic acid 70mg for a total of 9 years for steroid-induced osteoporosis (two years, followed by a four year drug pause, then a further seven years). She experienced anterior right knee pain and giving way for six months. An MRI showed an undisplaced fracture line in the upper pole of the patellar without bone marrow oedema. Alendronic acid was stopped. Three weeks later, she developed sudden onset right knee pain after sitting. An X-ray showed a complete patellar fracture, for which she had surgical repair. Femur X-rays were subsequently done which showed bilateral femoral cortical thickening. She was referred urgently to orthopaedics and commenced romosozumab. A SPECT CT showed uptake in both femurs consistent with impending atypical femoral fractures. She then had a fall from standing and sustained an open right midshaft femoral fracture that was managed with an intermedullary nail. On MRI imaging several months later, cortical oedema of the unoperated left femur had improved.

Results: DXA two years prior showed lumbar spine T-score -0.6 and Z-score 0.8, and femoral neck T-score -1.6 and Z-score 0.3. Five months following romosozumab, lumbar spine T-score was -0.4 and Z-score 1.1. Femoral neck scores were stable. Bone biochemistry including vitamin D were normal. Genetic testing for monogenic causes of fractures (R154 panel for hypophosphataemia or rickets) was negative. She had serum monoclonal lambda free light chains and was diagnosed with smouldering myeloma. The case was discussed at a regional specialist bone meeting where it was confirmed that the fractures were not related to myelomatous lytic bone lesions.

Conclusion: This case is the first to describe an atypical insufficiency fracture of the patella associated with long-term bisphosphonate use.