Effect of Spinal Cord Stimulation on Gait and Balance in Chronic Low Back Pain Patients

Spinal Cord Stimulation (SCS) uses electrical signals to disrupt noxious signals arising from painful areas, thereby reducing pain perception. Successful SCS implants lead to a broad range of positive outcomes: 1) long-term pain can be expected to be reduced by at least by 50%; 2) quality of life as assessed by subjective measurements improves substantially; 3) patients can significantly reduce opioid medication intake.1 However, the impacts of SCS intervention on neuromuscular and biomechanical outcomes including gait and balance have not been fully explored. Fifty subjects with symptomatic leg pain and/or low back pain (LBP) who are deemed appropriate SCS candidates and are scheduled for surgery will undergo gait and balance analyses preoperatively as well as 6 weeks and 3 months post operatively. In addition, 50 control subjects having no pain will undergo 1 session of gait and balance assessment. Objective spine and lower extremity motion and neuromuscular control will be evaluated using dynamic surface EMG and a video motion capture system during functional evaluation. Also, explored will be the relationship of changes in gait and balance to psychosocial factors that have previously been shown to be correlated with SCS outcomes.

Low back pain is reported in 75-80% of the population and can significantly influence patients' quality of life. Fortunately, 80-90% of individuals recover from their back pain, whether they receive treatment or not. However, the small percentage of people who do not recover quickly present a costly problem to society and a great challenge to health care providers. Low back pain is the second leading cause for missed days at work, potentially having disability and major socioeconomic consequences. Chronic LBP can also limit flexibility and/or range of motion, which may contribute to an overall decrease in functional capacity, and may ultimately heighten the risk for additional lower extremity injury. Many chronic LBP patients have conditions not amenable to spine surgery, or they have failed to achieve successful outcome with previous spine surgery. For these patients, SCS can be an effective alternative. For example, in a recent demonstration, randomized 100 failed back surgery syndrome (FBSS) patients to either SCS or conventional medical management. At 6 months post-implant, 64% of patients had achieved the 50% reduction in leg pain criterion (vs. 18% of conventional medical management patients). Similarly, North et al. found 52% of patients had achieved at least the 50% reduction in pain when they investigated 171 patients treated with SCS.

SCS uses electrical signals to decrease nociception of impulses arising from painful areas in the spine and or leg. In order to accomplish this goal, SCS involves implantation of a small electrical pulse generator, along with thin leads strategically placed into the epidural space. Stimulation provided by the generator to electrodes on the leads inhibits ascending pain signals, thereby decreasing pain perception. Occasionally, some patients feel a mild paresthesia as a result of the stimulation.

While the effectiveness of SCS on reduction of subjective pain complaints is now well-established, such improvement may not translate into improved functional ability. Previous research found that, for FBSS patients treated with SCS, patients' scores on Oswestry Disability index did not correlate significantly with improvements in function as measured by an accelerometer contained within the stimulator device. Very few studies have examined the effect of SCS on objectively-measured functional abilities, including gait and balance. Those studies suffer from a small sample size and lack of electromyography (EMG) and full body kinematics analyses. Despite that, those studies did find improvement in the spatiotemporal variables (i.e. gait speed, step length and width) while other variables (ground reaction force and trunk motion) were not significantly different using the SCS.

Therefore, the purpose of this study is to evaluate the effect of SCS, on the biomechanics of the lower extremities and spine, using dynamic EMG, video motion capture, and force plate analysis, during gait and static balance testing, in patients with chronic low back and/or leg pain, before and after intervention. In addition this study will compare these same biomechanical parameters found in the chronic low back pain and /or leg pain patients to an asymptomatic control group.

Eligibility Criteria:
Inclusion Criteria:

1. Age 18 years and older
2. Considered to be a candidate for SCS

   1. Leg pain and/or LBP lasting than 6 months.
   2. Therapy consists of a short trial with a percutaneous implantation of neurostimulator electrode(s) in the epidural space for assessing a candidate's suitability for ongoing treatment with a permanent surgically implanted SCS. Performance and documentation of an effective trial is required for consideration of permanent SCS.
   3. The implantation of the stimulator is used only as a late or last resort for patients with chronic intractable pain.
   4. Other treatment modalities (pharmacologic, surgical, physical/and psychological therapies) have been tried and did not prove satisfactory; were judged unsuitable, or were contraindicated for the patient.
   5. Patient has undergone appropriate psychological screening, including psychometric testing using the Minnesota Multiphasic Personality Inventory-2 Restructured Form (MMPI-2-RF), and diagnosis by a multidisciplinary team before implantation; to include patient education, discussion and disclosure including an extensive discussion of the risk and benefits of therapy.
   6. All the facilities, equipment, and professional support personnel required for the proper diagnosis, treatment, training, and follow-up of the patient are available.
   7. All trials which proceed to permanent implantation should demonstrate adequate documentation to support the decision. A successful trial should be associated with at least 50% reduction of target pain, a reduction of analgesic medications and show some element of functional improvement (i.e. sitting, standing and walking tolerances).
3. Able to ambulate without assistance and stand without assistance with eyes open for a minimum of 10 seconds
4. Able and willing to attend and perform the activities described in the informed consent within the boundaries of the timelines set forth for pre-, and post-operative follow-up

Exclusion Criteria:

1. Major lower extremity surgery or previous injury that may affect gait (a successful total joint replacement is not an exclusion)
2. BMI higher than 35
3. Neurological disorder, diabetic neuropathy or other disease that impairs the patient's ability to ambulate or stand without assistance
4. Major trauma to the pelvis
5. Pregnant or wishing to become pregnant during the study
6. Previous spinal surgery that would preclude the safe percutaneous or permanent implantation of the SCS leads
7. Previous history of spinal infection either iatrogenic or denovo
8. Previous SCS attempts either successful or not