Osteoporosis Risk in People with Spinal Cord Injury

Physical mobility and weight bearing limitations for some people with disabilities make them more likely to experience osteoporosis than the general population. Osteoporosis is a major complication in people with spinal cord injury (SCI; Biering-Sorensen et al., 1998), and this population experiences lower limb bone loss and increased fracture susceptibility (Bauman et al., 2006; Biering-Sorensen, Bohr, & Schaadt, 1998; Garland et al., 1992). Factors influencing bone mass for people with SCI include: severity of injury, muscle spasticity, age, gender, and duration after injury (Jiang, Dai, & Jiang, 2006). An identical twin study comparing bone mineral density for one twin with SCI and the other without SCI found that over time there was an increasing loss of bone mineral content and density in the lower limbs and pelvis of the twin with SCI (Bauman et al., 1999). There is also evidence that women with spinal cord injuries have rapid bone loss of 25-50% in the lower extremities within the first few years following their injury.

Within the first months post-injury, weight-bearing bone structures including the distal femur and proximal tibia are primarily affected by demineralization (Nance et al., 1999). The imbalance between bone formation and bone resorption, beginning immediately after injury and peaking within 3-5 months post-injury, is responsible for bone loss for people with SCI. It is thought that approximately 2 years post-injury, a new steady state level of bone resorption and formation is established which alters bone structure and microstructure. This restructuring is believed to contribute to fracture risk (Jiang et al., 2006).

Although mobility limitations and disuse affecting mechanical force applied to bone (Zerwekh et al., 1998) are thought to be primary contributors to osteoporosis for people with SCI, some researchers postulate that neural factors may impair calcium and phosphate metabolism (Jiang et al., 2006). Associated hormonal deficiences (Bauman et al., 1994) and bone circulation problems linked to the injury may also be contributors to increased osteoporosis risk for this population (Chantraine et al., 1979). Little is known about the exact cause of osteoporosis in this population, and future research and treatments will need to focus on this issue.