Introduction: Functional restoration of limb movement remains the ultimate goal in treatment of traumatic spinal cord injury. Previously we demonstrated functional limb movement in rats using a wirelessly controllable Mayo Investigational Neuromodulation Control System (MINCS). Here, we present limb movement in a large animal model controlled by epidural and intraspinal microstimulation (ISMS) using MINCS.
Methods: An 8-contact epidural electrode (St. Jude Medical, St. Paul, MN) was placed via left L6 hemilaminotomy in an anesthetized pig. Stimulation was performed at each contact from 100-1000 uA, at 50 Hz, pulse-width 200 us, in 1s intervals. Hindlimb movement was analyzed using motion analysis and EMG. Stimulation repeated at threshold, midpoint, and saturation amplitudes for 3s intervals assessed muscle fatigue. Bilateral L4-L6 laminectomy with durotomy was performed. A stainless steel, polyimide coated 300 um wire was inserted into the left ventral horn at levels corresponding to epidural electrodes. ISMS was performed using MINCS at 90-230 uA. Other parameters mirrored the epidural stimulation protocol.
Results: Hindlimb movement was observed during epidural stimulation at spinal levels L5-L6 (contacts 3,4,5,6, Figure 1), and during ISMS at L5. During epidural stimulation, threshold response was observed at 500 uA and saturation response at 1000 uA at low L5 (Table 1), with a 27 degree joint angle change (Figures 2A, 3). During ISMS, threshold response was observed at 110 uA and saturation response at 230 uA at low L5, with a 38.5 degree joint angle change (Figures 2B, 4). EMG responses were observed in hindlimb muscles to epidural and intraspinal stimulation. 9T MRI of the resected spinal cord confirmed ISMS electrode placement in the ventral horn.
Conclusions: Epidural and MINCS controlled ISMS of the lumbar region produce congruous hindlimb movement in the porcine model. These findings show promise for spinal stimulation for restoration of limb function after paralysis in humans.
Patient Care: This report demonstrates that limb movement can be produced through both epidural and intraspinal microstimulation techniques. Such technology, applied to humans with spinal cord injury, may restore limb function, permitting greater independence for these patients.
Learning Objectives: By the conclusion of this session, participants should be able to:
1 Discuss advantages and disadvantages of various spinal stimulation techniques
2 Describe the concept of central pattern generators in ambulation
3 Identify roadblocks to developing protocols for testing spinal stimulation in humans with spinal cord injury