Hindlimb Immobilization in a Wheelchair Alters Functional Recovery Following Contusive Spinal Cord Injury in the Adult Rat

Background. Locomotor training of rats with thoracic contusion spinal cord injuries can induce task-specific changes in stepping but rarely results in improved overground locomotion, possibly due to a ceiling effect. Thus, the authors hypothesize that incompletely injured rats maximally retrain themselves while moving about in their cages over the first few weeks postinjury. Objective. To test the hypothesis using hindlimb immobilization after mild thoracic contusion spinal cord injury in adult female rats. A passive stretch protocol was included as an independent treatment. Methods. Wheelchairs were used to hold the hindlimbs stationary in an extended position leaving the forelimbs free. The wheelchairs were used for 15 to 18 hours per day, 5 days per week for 8 weeks, beginning at 4 days postinjury. A 20-minute passive hindlimb stretch therapy was applied to half of the animals. Results. Hindlimb locomotor function of the wheelchair group was not different from controls at 1 week postinjury but declined significantly over the next 4 weeks. Passive stretch had no influence on wheelchair animals but limited functional recovery of normally housed animals, preventing them from regaining forelimb-hindlimb coordination. Following 8 weeks of wheelchair immobilization and stretch therapy, only the wheelchair group displayed an improvement in function when returned to normal housing but retained significant deficits in stepping and coordination out to 16 weeks. Conclusion. Hindlimb immobilization and passive stretch may hinder or conceal the normal course of functional recovery of spinal cord injured rats. These observations have implications for the management of acute clinical spinal cord injuries.