Wheelchair Neuroprosthesis for Improving Dynamic Trunk Stability.

Trunk instability is a major problem for individuals with thoracic and cervical spinal cord injury. Functional electrical stimulation (FES) neuroprosthesis, a technology that uses small electrical currents to artificially contract muscles, has previously been utilized to improve trunk stability during quasi-static and dynamic sitting. The aim of this paper was to develop the first powered wheelchair-based neuroprosthesis and to test its feasibility for improving trunk stability. Eleven male, able-bodied individuals participated in the feasibility study. While participants were seated, the wheelchair was moved in the forward or backward directions with slow and fast accelerations. Two different FES protocols were tested: 1) co-contraction and 2) directionally-dependent contraction of trunk extensors and flexors. Sham stimulations with intensities below the motor threshold were applied as the control conditions. Inertial motion sensors were used to quantify the maximum angular displacement and velocity of the trunk. Results showed that both directional contractions and co-contraction reduced trunk displacement and velocity, compared with the control conditions. However, directionally-dependent muscle contractions were more effective in improving trunk stability, compared with co-contractions. Overall, feasibility of the wheelchair-based neuroprosthesis was demonstrated. Future research will incorporate feedback from wheelchair movements and test the neuroprosthesis with individuals who sustained spinal cord injury.