Age-related bone loss in mouse lumbar vertebrae is affected by region, sex, and level: Implications for spinal loading and analysis methods.

Abstract

Human bone quality varies with age and spinal level, with upper lumbar vertebrae more prone to fracture. Mouse studies of bone health often focus on a single lumbar vertebral level and limited regional analysis with no comprehensive study evaluating how sex, lumbar level, vertebral region, and reconstruction method contribute to patterns of age-related vertebral bone loss in mice. This micro-computed tomography (μCT) study measured lumbar spinal level- and vertebral region of interest (ROI)-specific patterns of bone quantity, structure, and density in relation to age and sex in mice. Lumbar vertebrae (L1-L6; <i>n</i> = 4/sex/age) from young adult (4-month), middle-aged (12-month), and old (24-month) mice were analyzed for trabecular bone volume fraction (BV/TV), volumetric bone mineral density (vBMD), cortical thickness (Ct.Th), and tissue mineral density (TMD). Parameters were measured for full vertebrae, cranial, middle, and caudal vertebral regions, comparing both 1/3-vertebral and standardized 30-slice reconstruction approaches. Age was associated with a reduction in vBMD and BV/TV in both sexes, with bone volume, structure, and density most significantly reduced at L1 and cranial vertebral regions. Females exhibited greater declines than males, particularly in BV/TV and vBMD. Ct.Th was the greatest mid-spine but declined with age at L1 and L5. Regional differences were observed for both cortical parameters. Trabecular bone is affected by age, sex, lumbar level, and vertebral region in mice. The greatest sensitivity to age-related bone loss was detected in the L1 lumbar level and cranial vertebral regions in female mice. These findings highlight the need for region- and method- specific analysis in bone research and exhibit age-related changes in vertebrate by level and region that exhibit similarities to humans.