Effects of Trunk Stimulation on Seated Wheelchair Function after SCI

Effects of Trunk Stimulation on Seated Wheelchair Function after SCI

Principal Investigator: Alicia Koontz PhD and Ronald Triolo, PhD

Co-Investigator(s): Michael L. Boninger, MD; Yusheng Yang, MA, OT

2002–2004

Trunk instability after SCI leads to a seated posture with a flexed trunk, which may be one of the primary contributing factors to upper extremity injury and painful chronic health problems due to long term use of manual wheelchairs. It has also been shown that individuals with higher level SCI, who have decreased trunk control, have a greater propensity to develop rotator cuff disorders. Furthermore, lack of trunk control compromises the ability to manipulate objects in the environment by forcing individuals with SCI to rely exclusively on unimanual reach, since one hand is always required for maintaining balance and stability in the wheelchair. For these individuals, stabilizing the trunk may provide a posture that better supports the shoulder during activities of daily living, wheelchair propulsion and bimanual reaching.

Stabilizing the pelvis and trunk with electrical stimulation has great potential to improve the function of wheelchair users with SCI. This remains to be explored and optimized. The purpose of this collaborative project between the VA Rehabilitation Research and Development Centers in Cleveland (The Cleveland FES Center) and Pittsburgh (Wheelchairs and Related Technologies) was to determine the effects of electrical stimulation of the hip and trunk muscles on seated function in the wheelchair. In particular, it focused on the effects of functional electrical stimulation (FES) on wheelchair function in terms of both propulsion and bimanual reach.

This collaborative project was comprised of two studies: 1) investigation of trunk muscle activity of unimpaired individuals during wheelchair propulsion, and 2) examination of the effect of the implanted/surface FES system in individuals with SCI. This project is complete. Sixteen unimpaired subjects (13 male and 3 female) participated in the first study. The activity of their trunk muscles was measured using surface EMG (Noraxon Inc., Scottsdale, AZ) during wheelchair propulsion. OPTOTRAK motion analysis system (Northern Digital Inc., Ontario, Canada) and SMART^Wheels (Three Rivers Holdings, LLC., Mesa, AZ) were synchronized with the EMG system to record kinematics of the upper limbs, and propulsion forces. The preliminary results showed that back and abdominal muscles produced high activity levels during the pre-push and early push phase. This synchronized activation may provide trunk stability during the push phase. Researchers may use this profile of trunk muscle activation from the first study to develop a muscle stimulation pattern that will increase trunk stability and improve propulsion efficiency of manual wheelchair users with spinal cord injury. The results of this first study have been presented and a manuscript presenting the study findings is in review.

Three implanted FES subjects and eleven surface FES subjects participated in the second study to examine the effect of FES during wheelchair propulsion. The kinetic variables, such as propulsion forces, and kinematic data of upper limbs movement were recorded synchronously by SMART^Wheels (Three Rivers Holdings, LLC., Mesa, AZ) and OPTOTRAK motion analysis system (Northern Digital Inc., Ontario, Canada) during wheelchair propulsion at various speed conditions with/without stimulation given. Subjects also negotiated several obstacles activities, such as propelling through various surfaces, curbs and ramps, with the electrical stimulation turned on and without stimulation. A self-reported questionnaire was given to reflect the subject’s perception of using FES system during negotiating the obstacles. The preliminary results of the implanted FES subjects indicate that stabilizing the trunk by continuous stimulation of the lumbar erector spinae appears to improve manual wheelchair propulsion. With activation of back muscles, implanted FES users were able to lean forward and thereby increase mechanical effective forces. The results of this second study have been presented and published in two conference proceedings.

In addition to the kinetic and kinematic measures we recorded upper extremity muscle activity (sEMG) from the surface FES subjects during propulsion to examine the effect of stimulation on shoulder muscle activation. The results of this study showed that using the highest level of stimulation produced higher propulsion power output and gross mechanical efficiency (GME) during propulsion in comparison to low levels of stimulation or no stimulation. No differences were found in shoulder sEMG activity, energy expenditure, and trunk motion between stimulation levels. FES applied to the trunk musculature has potential advantages in helping manual wheelchair users with SCI improve propulsion efficiency without placing additional demands on the shoulder musculature. The increased trunk stability provided by FES may alter the biomechanics of wheelchair propulsion enough to reduce the possibility of future upper extremity injury. As well, it may allow individuals with SCI enough stability to reach and hold objects with both hands while seated in their wheelchairs.