Exploring changes in bone mass in individuals with a chronic spinal cord injury.

Abstract

People experience rapid bone loss shortly after a spinal cord injury (SCI), but the long-term bone changes are yet to be confirmed. This study showed that trabecular bone may have reached a steady state, whereas cortical bone continued to decline in people with a chronic SCI (mean time post injury: 15.5 +/- 10 years). INTRODUCTION: (1) To explore changes in bone [primary measure: trabecular volumetric bone mineral density (vBMD); secondary measures: cortical vBMD, cortical thickness, cortical cross-sectional area (CSA), and polar moment of inertia] over 2 years in individuals with a chronic spinal cord injury (SCI). (2) To explore whether muscle density changes were potential correlates of the observed bone changes. METHODS: This study is a secondary data analysis of a prospective, observational study involving 70 people with a chronic SCI (>/= 2 years post injury). The study included 4 strata of participants with diverse impairments: (1) Paraplegia (T1-T12) motor complete American Spinal Injury Association Impairment Scale (AIS) A/B (n = 23), (2) Paraplegia motor incomplete AIS C/D (n = 11), (3) Tetraplegia (C2-C8) AIS A/B (n = 22), and (4) Tetraplegia AIS C/D (n = 14). Peripheral quantitative computed tomography scans were taken at the 4% (distal tibia), 38% (diaphyseal tibia), and 66% (muscle cross-sectional area) tibia sites by measuring from the distal to proximal tibia starting at the inferior border of the medial malleolus. The tibia sites were assessed annually over a span of 2 years. Comparisons were made using a paired-samples t test and simple linear regression was used to adjust for sex, time post injury, and bisphosphonate use. RESULTS: We observed no changes in trabecular vBMD at the 4% tibia site, but there was a statistically significant decline in cortical vBMD, cortical thickness, and CSA at the 38% tibia site. Changes in muscle density were not associated with the decreases observed in cortical bone. CONCLUSION: Our findings suggest that individuals with chronic SCI (mean duration of injury: 15.5 +/- 10 years) may have reached a plateau in bone loss with respect to trabecular bone, but cortical bone loss can continue well into the chronic stages.