Early intervention is a critical consideration in efforts to preserve the musculoskeletal system after spinal cord injury

Richard Shields, Ph.D., University of Iowa professor in the Graduate Program in Physical Therapy and Rehabilitation Science, can foresee a time when it might be possible to cure spinal cord injury (SCI). However, if SCI patients injured today are to benefit from a future cure, Shield's work may hold a vital key.

Shields and colleagues have found that early intervention and long-term treatment with electrical stimulation, which causes muscle contraction and exerts mechanical loading on the targeted bone, can significantly reduce the loss of bone mineral density (BMD) in SCI patients.

Virtually every SCI patient develops severe osteoporosis and muscle atrophy after injury. The bone thinning, which occurs very rapidly -- an average loss of 30 percent in BMD in just three years -- makes the paralyzed limbs particularly vulnerable to fracture.

"The question is will an 18 year old injured today be a good candidate for that cure or repair if their bone is so brittle that it can't bear weight or their muscles are virtually useless?" Shields asks.

In addition, secondary complications, including multiple fractures leading to amputation, and kidney problems caused by excess calcium leached from the bones into the blood, can seriously impair the health of SCI patients. Thus, maintaining the integrity of bone has important implications for improving health of SCI patients.

"The long-range issues relate to helping people injured now remain good candidates for a future cure. The short-term effects are improving the patient's health quality and preventing secondary complications," Shields said.

Muscle contraction exerts forces greater than body weight to bones and is the best way to apply therapeutic stresses to keep the skeletal system (bone) healthy. This simple biomechanical principle comes into play whenever exercise is used to strengthen bones and muscles.

The UI team used a computer-controlled device to deliver defined, measurable doses of load (about 1.5 times body weight) to the tibia (lower leg bone) in one leg of each participant. The electrical stimulation protocol followed normal exercise principles, training the targeted muscle and bone 20 to 30 minutes each day, five days a week.

By the end of the three-year studies, BMD for the stimulated limbs was, on average, 32 percent greater than the untrained limbs. In addition, the cross-sectional area of trained muscles averaged 30 percent larger than untrained muscles, and trained muscles could generate about 50 percent more force than untrained muscles. The studies appear in the January 11 issue of the Journal of Neurophysiology and the March 1 issue of Spine.

Because the training device recorded the amount of electrical stimulation delivered to the muscle and only recorded data when it was in contact with the patient's skin, the researchers were able to accurately quantify how much stimulation patients' muscles and bones received. Patients initiated the stimulation by attaching electrodes to their skin and pushing a button to start the program. No study participant was below 70 percent compliance with this training protocol and average compliance was 80 percent.

"That would translate to someone going to the gym four days a week rather than five," Shields said. "If you or I could be 80 percent compliant in our exercise regimen we'd be thrilled."

Several aspects of the UI work examining the effect of loading on preserving the integrity of the musculoskeletal system are unique. These studies were the first to intervene with mechanical loading very early after SCI - all participants started the protocol within six months of the injury. Also, the studies were long-term, with patients receiving the stimulation for three years, which covers the period of most rapid BMD loss in SCI patients. Finally, the experiment was very focused, with only one muscle and bone examined and only in one leg of each participant, thus the effects could be clearly observed.

The results showed that this quite straightforward intervention was sufficient to produce significant results. Shields noted that it should be feasible and easy to translate this finding directly into useful treatments.

"This research emphasizes that early intervention is a critical consideration in efforts to preserve the musculoskeletal system after SCI and that future studies must address efficient methods to deliver these therapeutic stresses to the entire lower extremity," Shields said.

The results may also be useful for astronauts who experience bone loss and muscle wasting similar to SCI patients due to long periods spent in low gravity.