Feasibility of functional electrical stimulation for control of seated posture after spinal cord injury: A simulation study

We performed this study to determine the feasibility of controlling and stabilizing seated posture with functional electrical stimulation (FES) after paralysis from spinal cord injury (SCI) using computer simulations and a 3-dimensional model of the hip and trunk. We used the model to approximate the range of postures in the sagittal and transverse planes attainable by a seated subject and to estimate the maximum restorative moment that could be produced in a neutral posture in response to a disturbance. The simulations predicted that approximately 28 degrees of forward flexion in the sagittal plane (combined hip and trunk) and 9 degrees of lateral bending in the transverse plane should be possible with FES and that a maximum disturbance rejection moment of approximately 45 newton meters could be expected with the chosen muscle set. We tested a subject with a motor complete thoracic SCI and implanted electrodes in a subset of the selected muscles to compare the moments the subject required to maintain various hip and trunk positions with those predicted by the model. Although a significant range of seated postures was possible with FES, the data demonstrated that more complete activation of the paralyzed muscles would be needed for the subject to fully achieve the theoretical range of motion. With further refinements, we could apply these techniques to the design of control systems for regulation of seated posture and dynamic motion of the torso.