Implanted electrical stimulation of the trunk for seated postural stability and function after cervical spinal cord injury: a single case study

Abstract

Objectives: To explore and quantify the physical and functional effects of stabilizing the torso with electrical stimulation of the paralyzed hip and trunk musculature after motor complete tetraplegia.

Design: Single-subject case study with repeated measures and concurrent controls.

Setting: Academic outpatient rehabilitation center.

Participants: Forty-four-year-old man with C4 American Spinal Injury Association grade A tetraplegia 20 years postspinal cord injury.

Intervention: A surgically implanted multichannel pulse generator and intramuscular stimulating electrodes to activate lumbar erector spinae, quadratus lumborum, and gluteus maximus muscles bilaterally.

Main outcome measures: Outcomes assessed with and without stimulation included (1) spinal alignment and pelvic orientation, (2) pulmonary function and ventilatory volumes, (3) forward bimanual reaching distance, (4) seated stability and resistance to externally applied disturbances, (5) maximal force and speed of rowing-like movements, and the ability to (6) independently return to an erect seated position from full forward or lateral flexion and (7) roll in bed without assistance.

Results: Stimulation improved spinal convexity and kyphosis by 26 degrees and 21 degrees , reduced posterior pelvic tilt by 11 degrees , increased forced expiratory volume and vital capacity by 10% and 22%, and improved forward reach by more than 7cm. Average resistance to sagittal disturbances increased by more than 40% (P<.002), and mean force exerted during underhanded pulling more than doubled (P=.014) with stimulation. Restoration of upright sitting in both sagittal and coronal planes and bed turning was made possible through appropriately timed activation of the hip and trunk muscles.

Conclusions: A neuroprosthesis for controlling the paralyzed torso can positively impact spinal alignment, seated posture, pulmonary function, trunk stability, and reach. Stimulation of hip and trunk muscles can improve performance of activities of daily living as well as enable independent wheelchair and bed mobility.

Figure 1

Experimental set-up to assess the effects of hip and trunk stimulation on seated stability. Resistance to externally applied forces (a), and ability to actively pull against resistance during simulated rowing motions (b) were determined under isokinetic conditions with a robotic dynamometer with and without FES. Direction of dynamometer rotation and linear translation of attachment indicated by arrows.

Figure 2

Effects of hip and trunk stimulation on seated posture. Without stimulation a right lateral curve, scapular asymmetry (a) and significant posterior pelvic tilt (b) are evident during unsupported sitting. Stimulation restored a more nominal lumbar curve, reduced posterior pelvic tilt and improved shoulder position which allowed the subject to increase the relative angle between his head and torso and elevate his gaze (c).

Figure 3

Effects of FES on coronal vertebral alignment. Anterior-posterior radiographs show typical spinal convexity without stimulation (a), and during application of FES (b). Stimulation provided a more erect vertebral alignment and reduced both coronal spinal convexity and sagittal spinal kyphosis (not pictured).

Figure 4

Effects of FES on seated stability and active pulling. Both mean and peak resistance to anteriorly directed forces applied isokinetically at 10°/sec (a) increased with FES and allowed larger moments to be resisted prior to loss of balance and forward hip and trunk flexion. Stiffening the hip and trunk with stimulation allowed significantly larger maximal moments to be generated voluntarily by the subject during underhanded pulling motions at all speeds tested (b)

Figure 5

Mobility functions enabled by FES. Ability to return to an upright and erect sitting posture from full forward flexion (a) was restored by activating the trunk and hip extensor muscles, and independent bed turning (b) was made possible by adding a flexion withdraw reflex to stimulation to stiffen the trunk.