Using ultrasound to enhance recovery of function after peripheral nerve injury

Regeneration of peripheral nerve after a proximal injury can take up to two years in humans and recovery is often incomplete. It would be desirable to develop treatments to accelerate and improve the recovery process. A single published study suggested that application of ultrasound to a partially injured peripheral nerve could promote recovery as assessed electrophysiologically. We elected to confirm whether focused ultrasound could enhance behavioral recovery as well as axonal regeneration. If successful, our aim was then to determine the optimal ultrasound parameters. Rat sciatic nerve was crushed mid-thigh for three 10 second intervals using fine forceps, which resulted in a complete paralysis of the injured leg postoperatively. Ultrasound was then applied to the injured nerve for one minute, three times per week for four weeks in four groups of animals undergoing different ultrasound parameters, plus a control group (n=3 per group). Recovery of gait function was assessed by quantifying toe spread once or twice per week. After 28 days, the animals were sacrificed and counts of regenerating axons were made approximately 8mm distal to the crush site. Our results showed a statistically significant improvement in gait using two ultrasound protocols at 15 and 22 days after crush injury. All animals regained normal gait function by 28 days. Axon counts at 28 days showed no statistically significant difference between groups. These preliminary results are encouraging but warrant further research to provide confirmation as well as an understanding of the underlying mechanisms.