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.