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.