The Fragile Connection: Understanding Osteoporosis and Spinal Cord Injuries

Authors:
Mona Emadeldin (Clinical Specialist), Helena López (Clinical Manager)

Osteoporosis is a disease that reduces bone mass and increases the risk of fractures, especially in older adults. It affects over 200 million people and places a significant burden on healthcare systems. People with spinal cord injuries face an even higher risk of fractures due to the lack of mechanical load on their bones. However, exercise and the use of robotic exoskeletons can help mitigate bone loss and improve the health of these patients.

For a quick overview of what you’ll find in this article, check out our infographic on osteoporosis and spinal cord injuries at the end of the text.

What is osteoporosis?

Osteoporosis is a condition characterised by a reduction in bone mass, which can lead to fragility fractures. This disease affects over 200 million people worldwide and is a leading cause of fractures, especially in older adults. Its primary consequences include bone fragility and a higher risk of fractures, particularly in the spine, pelvis, and hips, where fractures can significantly impact quality of life and increase mortality rates¹.

These fractures are not only physically debilitating but also associated with increased healthcare costs and a greater burden on healthcare systems globally. For example, hip fractures—one of the most serious outcomes of osteoporosis—can be life-threatening and often result in long-term disability².

Osteoporosis diagnosis

The diagnosis of osteoporosis typically relies on bone mineral density (BMD) testing, which helps identify those at high risk for fractures. As Johnell et al. (2005) found, BMD is a strong predictor of the likelihood of hip and other fractures¹. Early diagnosis and intervention can help reduce the risk of fractures and improve patient outcomes.

Prevention

Preventative measures, including adequate calcium and vitamin D intake, weight-bearing exercise, and medications for those at high risk, are essential in reducing the incidence of osteoporosis-related fractures³.

Osteoporosis and Spinal Cord Injuries

Spinal cord injuries (SCI) immediately result in the disuse of the limbs, leading to a significant reduction in biomechanical stress on the bones. This lack of mechanical loading is a substantial factor in the bone remodelling process, which is primarily regulated by osteocytes. These cells respond to mechanical strain, and in the absence of such stress, the bones start to weaken and lose mass⁴.

Individuals with SCI face a significantly increased risk of fragility fractures, with their fracture rate being twice that of the general population. Moreover, at least 50% of these fractures are associated with clinical complications such as infections, which further contribute to morbidity⁴.

In addition to disuse, SCI causes neurovascular changes in the bones. The reduction in sensory and autonomic nerve fibres below the level of injury disrupts the regulation of bone metabolism, contributing further to bone loss. This reduction in bone mass is most rapid in the acute phase of SCI, but continues at a slower rate in the chronic phases⁴.

The extent of bone loss in individuals with SCI is influenced by several factors, including the level and completeness of the injury. Those with higher spinal cord lesions tend to have lower bone mineral density (BMD) in affected skeletal areas compared to those with lower lesions. However, the severity of bone loss is more dependent on the completeness of the injury than the level of the injury itself⁴. Bone loss also occurs due to vascular dysfunction and mechanical unloading in the paralyzed limbs, which is common in those with a motor-complete SCI⁵.

Given the high risk of fractures in individuals with SCI, measuring areal bone mineral density (aBMD) using dual-energy x-ray absorptiometry (DEXA) is widely recommended. This method has proven effective in assessing fracture risk in both the SCI population and the general population. Individuals with low aBMD have been found to be at increased risk for lower-extremity fractures, particularly in the chronic phase of SCI⁷.

Bone loss after a spinal cord injury occurs in two distinct phases. The first is a rapid phase of bone resorption, which typically plateaus 18 to 24 months after injury. This phase is characterised by a rapid decline in bone mass due to inhibited bone formation and increased bone resorption. After a spinal cord injury (SCI), individuals typically experience a rapid decline in bone mineral density (BMD), particularly in the lower extremities, with an expected 3–4% loss per month during the first year⁸.

Following this acute phase, the chronic phase of bone loss sets in, marked by a slower but continuous loss of bone mass. As a result, approximately 40% of individuals with chronic SCI experience fractures, which is double the fracture risk of those without SCI^5,6.

How do we rebuild strength?

Bone is a dynamic organ that adapts to changes in physical activity and mechanical strain by modulating the rate of new bone formation. In individuals with spinal cord injury (SCI), physical exercise plays a role in mitigating bone loss by promoting bone blood flow and alleviating vascular dysfunction caused by neural denervation⁵. This enhanced blood flow supports bone metabolism and growth, potentially reversing atrophy and bone loss associated with SCI. Research suggests that reintroducing mechanical loading through targeted physical exercise may help restore bone strength. However, the effectiveness of these interventions depends on the intensity, frequency, and duration of mechanical stress applied to the bones, which are key determinants for improving bone health in this population⁵.

Locomotor training using a robotic exoskeleton system has shown promising results in improving body composition and potentially enhancing bone health in SCI patients⁸. Long-term use of these systems may lead to increased bone density, improved bowel function, reduced pain, and a decreased risk of cardiovascular diseases⁹. For optimal results, initiating exoskeleton-assisted walking or standing within the first few weeks after injury is crucial to achieving significant improvements in BMD⁴. Additionally, body composition changes, such as reduced body fat in the lower extremities and increased muscle mass, have been documented following exoskeleton-assisted walking programs⁷.

References:

1. Johnell, O., Kanis, J. A., Oden, A., Johansson, H., De Laet, C., Delmas, P., … & Tenenhouse, A. (2005). Predictive value of BMD for hip and other fractures. Journal of Bone and Mineral Research, 20(7), 1185-1194.
2. Strom, O., Borgstrom, F., Kanis, J. A., Compston, J., Cooper, C., & McCloskey, E. V. (2011). Jonsson B. Osteoporosis: burden, health care provision and opportunities in the EU: a report prepared in collaboration with the International Osteoporosis Foundation (IOF) and the European Federation of Pharmaceutical Industry Associations (EFPIA). Arch Osteoporos, 6, 59-155.
3. Kanis, J. A., Melton, L. J., 3rd, Christiansen, C., Johnston, C. C., & Khaltaev, N. (1994). The diagnosis of osteoporosis. Journal of Bone and Mineral Research, 9(8), 1137-1141. https://doi.org/10.1002/jbmr.5650090802
4. Abdelrahman, S., Ireland, A., Winter, E. M., Purcell, M., & Coupaud, S. (2021). Osteoporosis after spinal cord injury: aetiology, effects and therapeutic approaches. Journal of musculoskeletal & neuronal interactions, 21(1), 26–50.
5. Tan, C. O., Battaglino, R. A., & Morse, L. R. (2013). Spinal Cord Injury and Osteoporosis: Causes, Mechanisms, and Rehabilitation Strategies. International journal of physical medicine & rehabilitation, 1, 127.
6. Shams, R., Drasites, K. P., Zaman, V., Matzelle, D., Shields, D. C., Garner, D. P., … & Banik, N. L. (2021). The pathophysiology of osteoporosis after spinal cord injury. International Journal of Molecular Sciences, 22(6), 3057.
7. Bass, A., Morin, S. N., Guidea, M., Lam, J. T., Karelis, A. D., Aubertin-Leheudre, M., … & Montreal Exoskeleton Walking Program (MEWP) Group. (2024). Potential Effects of an Exoskeleton-Assisted Overground Walking Program for Individuals With Spinal Cord Injury Who Uses a Wheelchair on Imaging and Serum Markers of Bone Strength: Pre-Post Study. JMIR Rehabilitation and Assistive Technologies, 11, e53084.
8. Karelis, A. D., Pinheiro CARVALHO, L., Escalona Castillo, M. J., Gagnon, D. H., & Aubertin-Leheudre, M. (2017). Effect on body composition and bone mineral density of walking with a robotic exoskeleton in adults with chronic spinal cord injury. Journal of Rehabilitation Medicine (Stiftelsen Rehabiliteringsinformation), 49(1).
9. Bryce, T. N., Dijkers, M. P., & Kozlowski, A. J. (2015). Framework for Assessment of the Usability of Lower-Extremity Robotic Exoskeletal Orthoses. American journal of physical medicine & rehabilitation, 94(11), 1000–1014. https://doi.org/10.1097/PHM.0000000000000321