Epidural Stimulation of the Lumbosacral Spinal Cord Improves Trunk Lean Distances in Individuals with Cervical Spinal Cord Injury

<b>Background/Objectives</b>: Preliminary observations support the view that spinal cord epidural stimulation (scES) combined with trunk-specific training can improve trunk stability during functional activities in individuals with thoracic spinal cord injury (SCI). We studied the acute effects of trunk-specific stimulation on sitting postural control. <b>Methods</b>: Twenty-three individuals with severe cervical SCI were implanted with an epidural stimulator. Postural control was assessed before any activity-based training, without and with trunk-specific scES. In particular, participants performed sitting with upright posture, forward/back lean, and lateral lean activities while sitting on a standard therapy mat. Full-body kinematics and trunk electromyography (EMG) were acquired. Anterior-posterior and lateral trunk displacement along with trunk velocity in all four directions were obtained and used to classify postural control responses. <b>Results</b>: Compared to no stimulation, application of trunk-specific scES led to trunk anterior-posterior displacement increases during forward/back lean (2.79 ± 0.97 cm; <i>p</i>-value = 0.01), and trunk lateral displacement increases during lateral lean (2.19 ± 0.79 cm; <i>p</i>-value = 0.01). After digital filtering of stimulation artifacts, EMG root mean square amplitudes for bilateral external oblique, rectus abdominus, and erector spinae muscles were higher with stimulation for all activities (all <i>p</i>-values < 0.03). <b>Conclusions</b>: The results indicate improvements in trunk lean distances and muscle activation when leaning activities are performed with trunk-specific epidural stimulation.