Osteoporosis in spinal cord injury: using an index of mobility and its relationship to bone density

This study was undertaken to improve quantification of the extent of osteoporosis that accompanies spinal cord injuries (SCI) of various types, using single photon densitometry. In this study, we evaluated subjects with complete and incomplete SCI to determine whether there is a correlation between mobility and bone density. We created an index to rank the various levels of mobility among SCI subjects. Mobility index parameters ranged from 1, for complete immobility, to 9, for the full mobility of the uninjured control population. Incomplete SCI subjects (motor and/or sensory) ranked from 2 to 8 on the mobility scale. We also attempted to define clearly the mechanism of osteoporosis in those with predominantly unilateral SCI (Brown-Sequard syndrome). Using single photon absorptiometry (SPA), we found a strong correlation between our mobility index and observed bone density. These observations clearly show that osteoporosis is affected by the subject's level of physical activity. These observations also support the hypothesis that SCI individuals benefit from efforts to maintain a standing posture with some regularity. This effort to improve bone density slows the development of osteoporosis, a process that results in physical impairments in the SCI population.