Musculoskeletal changes in women with spinal cord injury: a twin study

Bone mineral density (BMD), bone geometry, and muscle cross-sectional area (CSA) were investigated in two sets of monozygotic female twins, where one of each pair had sustained a spinal cord injury (SCI). Twin pair 1 (TP1) and twin pair 2 (TP2) were 32 and 47 yr old and were 7 and greater than 20 yr postinjury, respectively. BMD was measured using dual-energy X-ray absorptiometry. Computed tomography was used to measure volumetric BMD, bone geometry, and muscle CSA of the thigh and calf. For the SCI twin of TP1, BMDs of hip, distal femur, proximal tibia, and spine were 59.5, 46.6, 53.1, and 93.3%, respectively, of values of the noninjured twin. For TP2, corresponding values in the SCI twin were 36.2, 35.9, 39.2, and 62.2%, respectively, of the non-SCI twin. Average muscle CSAs of the SCI twins were 31.2+/-2.3% and 31.0+/-6.1% of the values for their non-SCI twin, indicating that muscle CSAs were reduced by 70%. Among the SCI twins, volumetric BMDs were 83.4+/-2.4% and 87.0+/-3.45% of the non-SCI twins' values. Moments of inertia in the SCI twins ranged from 62.4 to 97.9% of the non-SCI twins' values at mid-femur and calf. This study reveals that in addition to the declines in muscle CSA and BMD, important changes in bone geometry occur in women after SCI.