Effects of stimulating hip and trunk muscles on seated stability, posture, and reach after spinal cord injury

Objective: To determine the stimulated strength of the paralyzed gluteal and paraspinal muscles and their effects on the seated function of individuals with paralysis.

Design: Case series with subjects acting as their own concurrent controls.

Setting: Hospital-based clinical biomechanics laboratory.

Participants: Users (N=8) of implanted neuroprostheses for lower extremity function with low-cervical or thoracic level injuries.

Interventions: Dynamometry and digital motion capture both with and without stimulation to the hip and trunk muscles.

Main outcome measures: Isometric trunk extension moment at 0°, 15°, and 30° of flexion; seated stability in terms of simulated isokinetic rowing; pelvic tilt, shoulder height, loaded and unloaded bimanual reaching to different heights, and subjective ratings of difficulty during unsupported sitting.

Results: Stimulation produced significant increases in mean trunk extension moment (9.2±9.5Nm, P<.001) and rowing force (27.4±23.1N, P<.012) over baseline volitional values. Similarly, stimulation induced positive changes in average pelvic tilt (16.7±15.7°) and shoulder height (2.2±2.5cm) during quiet sitting and bimanual reaching, and increased mean reach distance (5.5±6.6cm) over all subjects, target heights, and loading conditions. Subjects consistently rated tasks with stimulation easier than voluntary effort alone.

Conclusions: In spite of considerable intersubject variability, stabilizing the paralyzed trunk with electrical stimulation can positively impact seated posture, extend forward reach, and allow exertion of larger forces on objects in the environment.