The effects of spinal cord injury and menopause on bone architecture in women
Slade, Jill Michelle
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The primary purpose was to compare the effects of menopause to spinal cord injury on bone architecture, in two at-risk populations for osteoporosis and subsequent fractures. Thus, the effects of estrogen withdrawal on bone architecture were compared to extreme unloading. In addition, these studies were designed to investigate the simultaneous effects of menopause and spinal cord injury on bone architecture. Ambulatory pre- and post-menopausal women were compared to age matched spinal cord injured pre- and post-menopausal women with SCI and a group of younger woman with SCI. The trabeculae of the distal femur and proximal tibia and the mid femoral shaft geometry were studied to determine differences in structural arrangement. Magnetic resonance imaging (MRI), specifically high-resolution MRI, was used to measure apparent trabecular parameters. Standard T1 weighted MR imaging was used to measure marrow, endosteal, and cortical components of the femoral shaft. The main findings were that spinal cord injury had large effects on most measures of bone in the tibia and femur. Women with spinal cord injuries had fewer trabeculae (19-26 % less), less apparent relative trabecular bone volume (22-33% less), and trabeculae were spaced further apart (60% more space). Post-menopausal women with SCI had 34% more trabecular spacing in the tibia compared to 40-yr old pre-menopausal women with SCI, showing an additive effect for SCI and menopause. Measures of bone geometry were also lower for women with spinal cord injury. Although bone size was similar between groups, women with SCI had 38% less cortical volume, 34% greater medullary volume, and had 28-44% thinner cortical wall width. Moderate relationships were detected between relative trabecular bone volume and thigh cross sectional area (r 2 = 0.384-0.424) and a moderate relationship for thigh and cortical volume in ambulatory groups (r 2 = 0.475). This study did not show any differences in structural measures between pre- and post-menopausal, estrogen-free ambulatory women. Despite the major consensus from the literature suggesting that estrogen has significant effects on bone after menopause, particularly trabecular bone, these studies did not show differences in bone structure in 40-50 year old pre-menopausal women compared to 50-63 year old estrogen-free women, approximately 8 years post-menopause.