Bone mineral and geometric changes through the femur with immobilization due to spinal cord injury

This cross-sectional study describes bone mineral and geometric properties of the midshaft and distal femur in a control population and examines effec ts of immobilization due to spinal cord injury (SCI) at these skeletal, sit es. The subject populations were comprised of 118 ambulatory adults (59 men and 59 women) and 246 individuals with SCI (239 men and 7 women); 30 of th ese were considered to have acute injury (SCI duration <1 year). Bone miner al density (BMD) was assessed at the femoral neck, and midshaft and distal femur by dual energy absorptiometry. Geometric properties, specifically cor tical area, polar moment of inertia, and polar section modulus, were estima ted at the midshaft from cortical dimensions obtained by concurrent radiogr aphy. Reduction in BMD was noted in all femoral regions (27%, 25%, and 43% for femoral neck, midshaft, and distal femur, respectively) compared with c ontrols. In contrast, although endosteal diameter was enlarged, geometric p roperties were not significantly reduced in the midshaft attributable to th e age-related increase in periosteal diameter. These results suggest that s imultaneous assessment of bone mineral and geometric properties may improve clinically relevant evaluation of skeletal status.