Effect of Epidural Stimulation on Muscle Activation and Sensory Perception

Summary

Each year, an estimated 34,000 individuals undergo epidural spinal cord stimulation (SCS) surgery to address debilitating chronic low back and leg pain (CLBLP). Although the commercial application of SCS to treat CLBLP was approved by the FDA in 1989, only in the past decade have significant advancements in stimulator technology been introduced. For instance, traditional SCS devices achieved reduction in pain using a type of stimulation known as low-frequency tonic stimulation (LFTS, below 100 Hz), which was dependent on induction of paresthesias (i.e., a tingling sensation) over the areas of pain perception. However, investigators now know that LFTS compromises sensory information flowing back to the spinal cord, which can be important in other spinal cord functions such as proprioception and movement. On the other hand, recent innovations in stimulator technology now provide the capability to apply stimulation frequencies up to 10,000 Hz along with complex waveform patterns - known as high frequency burst stimulation or HFBS - that can mitigate pain perception without the induction of paresthesias and the negative consequences on proprioception and movement. We propose to study the effects of these recently introduced features in SCS technology on motor and sensory spinal thresholds, proprioception and movement in subjects with CLBLP.

The spinal cord relies on input from the motor cortex and surrounding extremities to initiate specific muscle recruitment, and recent evidence suggests that preservation of temporally specific proprioceptive information via dorsal column primary afferent fibers is critical for natural motor behaviors such as ambulation. Since the spinal cord is exposed during the placement of the SCS device, information about a subject's motor and sensory spinal pathways can be easily obtained during the regular course of the procedure and compared to proprioceptive and motor responses once the subject is awake and moving with the device turned on. Our lab specializes in electrophysiological recordings in subjects undergoing spinal cord stimulator (SCS) implantation for CLBLP, while MUSC's Locomotion Laboratory specializes in quantifying proprioception and movement in human subjects. In this proposal, investigators will apply these techniques to subjects with CLBLP to determine effects of spinal neuromodulation on motor and sensory thresholds, proprioception, and kinematics.

Conditions

• Chronic Pain

Interventions

DEVICE

Intraoperative Parameter Testing

Step 1: Recording and stimulation of spinal potentials during insertion of epidural spinal stimulator paddle Once the epidural paddle is placed, study procedures will begin by connecting the terminals of the paddle to an electrophysiological recording device for signal amplification and filtering. Using this recording setup, motor evoked potential (MEP) and somatosensory evoked potential (SSEP) protocols will be performed to determine motor and sensory thresholds, respectively. Next, the surgical procedure will resume and after the implantable pulse generator (IPG) has been placed, study procedures will begin again and include activation of both low-frequency tonic stimulation (LFTS) and high-frequency burst stimulation (HFBS) patterns from the inserted paddle while recording EMG signals.

DEVICE

Proprioception Testing During Stimulation

Step 3: Proprioception testing The research team will investigate the perceived change in knee joint angle and direction of movement reported by the subject in a Threshold to Detect Passive Movement (TTDPM). The TTDPM protocol will begin with the subject sitting in the Biodex testing seat, with the non-tested leg hanging freely and the tested leg strapped to the rotating arm of the dynamometer at the lower shank. The subject will be blinded as to the mode and intensity of stimulation: HFBS, LFTS, or no stim. The TTDPM will consist of at least 10 trials for each stimulation condition chosen based on SCM outcomes. The subject has control of a kill-switch that immediately halts movement of the rotating arm, which is to be activated once the subject perceives movement OR if the subject begins to feel any pain or discomfort throughout the task.

DEVICE

Gait Analysis During Stimulation

Step 4: Body weight support and treadmill (BWST) testing Similar to step 2, LFTS and HFBS patterns will be compared by systematically testing each individual contact on the paddle while investigating for changes in stepping speed, pattern and EMG moduling complexity. Regarding EMG module analysis, muscle activity will be recorded bilaterally via surface EMG from lower extremity musculature. Furthermore, subjects will also have active LED markers placed over their clothes in order to track whole body kinematics throughout this portion of the study. To optimize capture of steady state data on the treadmill, each subject will walk for approximately 10 sec prior to the 30 sec of data collection (40 sec per trial). This will allow capture of at least 10 consecutive steady state gait cycles (depending on cadence) per each amplitude selection for each stimulation delivery technique, which will be defined by parameters found during walking SCM.

Sponsors & Collaborators

• Medical University of South Carolina

  lead OTHER

Principal Investigators

• Nathan Rowland, MD · Medical University of South Carolina

Study Design

Allocation

NA

Purpose

BASIC_SCIENCE

Masking

NONE

Model

SINGLE_GROUP

Eligibility

Min Age

18 Years

Max Age

80 Years

Sex

ALL

Healthy Volunteers

No

Timeline & Regulatory

Start

2019-11-26

Primary Completion

2021-11-01

Completion

2021-11-01

FDA Device

Yes

Countries

• United States

Study Locations