Increased Bone Fracture After SCI: Can Exercise Reduce Risk?
Bone density decreases rapidly in spinal cord injured (SCI) individuals to approximately 60 % of normal bone mass within the first 3 years after injury. The loss of bone mass, called disuse osteoporosis, results in low energy fractures, which are prevalent and extremely debilitating in this population. Bones are sensitive to their mechanical environment, promoting formation under high loads and resorption under low loads. In the SCI population, bone becomes osteoporotic solely due to the lack of mechanical stimulus. The bone loss after injury is site specific, occurring particularly at sites rich in trabecular bone, such as proximal tibia and distal femur. Harnessing the mechanosensitivity of human bone has been the central idea of therapeutic interventions to maintain bone mass and ensure bone strength in the SCI population. Numerous studies have investigated activities based training exercises such as passive weight bearing, gait training, isometric functional electrical stimulation (FES), cycling loading, FES-cycling, and FES-rowing. Only a few of these interventions have been effective in maintaining bone health and none of them have led to promoting bone formation. The most promising results in mechanical loading therapies for maintaining bone health are in acute patients. Mechanical interventions in the early stages post-injury might take advantage of the bone’s ability in young, acute SCI individuals to adapt to mechanical load.
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