Fracture threshold in the femur and tibia of people with spinal cord injury as determined by peripheral quantitative computed tomography

Objective: To determine bone traits of the femur and tibia with peripheral quantitative computed tomography (pQCT) that best distinguish between spinal cord injury (SCI) subjects with and without fractures. Design: Cross-sectional study. Setting: In- and outpatient paraplegic center in Switzerland. Participants: Ninety-nine motor complete SCI subjects (duration of paralysis, 2mo-49y), 21 of whom had sustained fractures of the femur or tibia. Interventions: Not applicable. Main Outcome Measures: Subjects with SCI were questioned about the occurrence, location, and approximate date of fractures to their lower extremities. Trabecular and cortical bone mineral density (BMD), as well as bone geometric properties of distal epiphyses and midshafts of the femur and tibia, were measured by pQCT. Results: Trabecular BMD of the femur and tibia distal epiphyses was found to distinguish best subjects with fractures from those without. Fractures occurred in subjects with trabecular BMD of less than 114mg/cm(3) and less than 72mg/cm(3) for the femoral and tibial distal epiphysis, respectively (corresponding to 46% and 29% of mean values of an able-bodied reference group). Approximately 50% of the subjects with chronic SCI (defined as time postinjury >5y for femur data and >7y for tibia data) had trabecular BMD values above the fracture threshold in the femur and about one third above the fracture threshold in the tibia. Conclusions: By using pQCT, it may be possible to identify subjects with SCI who are at risk of sustaining fractures of the femur and tibia through minor trauma.