Reversing Bone Loss in Spinal Cord Injury

Early and severe bone loss is a serious problem in persons with spinal cord injury (SCI). Loss of bone calcium can occur in any of the bones below the level of injury.

Fracture incidence is reported to be as high as 4.6% per year in persons with chronic SCI, with a prevalence of 15% to 34% and rising. More than 90% of fractures in persons with chronic SCI are in the lower limb, largely in the distal femur and proximal tibia. These are usually low-velocity fractures, with falls from a wheelchair as the most common cause.

Hormonal deficiency, nutritional changes, alterations in circulation, and loss of autonomic nervous system influences all seem to contribute to bone loss associated with SCI, but loss of mechanical strain appears to be the single most important factor.

Determining how to slow or reverse bone loss in patients with SCI is an important area of study. The simple act of falling out of a wheelchair can cause painful fractures that can lead to many problems, all creating secondary disability. Problems include:

• Pressure ulcers
• Deep vein thrombosis
• Neuropathic pain
• Autonomic dysreflexia

As neuroscientists get closer to understanding how to restore motor function in patients with SCI, identifying effective methods to strengthen weight-bearing bones so patients can stand again will be an important development.

Numerous published studies have examined whether active or passive verticalization in SCI patients affects bone demineralization. To date, studies using techniques like passive standing or standing on a vibrating surface have failed to establish that any of these therapies used alone significantly slows or reverses SCI-induced osteoporosis.

Approaching this problem from a new angle, a team of Mayo Clinic researchers plans to study whether repeated exposure to vertical oscillation, rather than just a vibrating surface, will help restore bone mass.

Previous studies have shown heavy loading is not necessary to produce results. Mayo researchers are looking for a very specific pattern of motion that is osteogenic, something that mimics the rapid on–rapid off motion that occurs when a person walks.

The Mayo project uses a standing frame that supports patients (those with no voluntary motor control in the legs and trunk) and positions their feet on a unique foot plate that oscillates vertically.

Patient standing on oscillating foot plate

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The team will enroll 20 patients in a pilot study and follow them for 6 months. Half the study subjects will use the standing frame and vertical oscillator for 20 minutes daily, 5 times a week. The other half will continue their usual activity and serve as a comparison group.

All study subjects will undergo bone densitometry testing of the distal tibia after 6 months and again at 12 months to allow researchers to measure both the response to the treatment and what happens to subjects' bone density after treatment stops.

Mayo researchers are hopeful that this study will yield results that can benefit care of patients with SCI and also help shed light on how to slow or reverse bone loss in people with mobility impairment due to other disabilities.