Comparison of Transcutaneous and Epidural Spinal Stimulation for Improving Function

Inclusion Criteria: 1. have a spinal cord injury at least one-year duration; 2. are between 21 and 70 years of age; 3. have difficulty with leg functions and mobility in activities of daily living (e.g. walking, transferring surface to surface, standing); 4. are candidates for an implanted stimulator; 5. are willing and able to have surgical implantation of the epidural stimulator for the treatment of pain according to the study timeline; 6. experience chronic pain; 7. are in stable medical condition without cardiopulmonary disease or frequent autonomic dysreflexia that would contraindicate participation in lower extremity rehabilitation or testing activities; 8. are capable of performing simple cued motor tasks; 9. have the ability to attend 3-5 sessions per week physical therapy sessions and testing activities over three months; 10. have adequate social support to be able to participate in assessment sessions occurring between once per week to once per month for up to 9 months; 11. are volunteering to be involved in this study; 12. are cleared for gait training by primary physician of the subject; 13. and have ability to read and speak English Exclusion Criteria: 1. have autoimmune etiology of spinal cord dysfunction/injury; 2. have a history of additional neurologic disease, such as stroke, MS, traumatic brain injury, etc.; 3. have peripheral neuropathy (diabetic polyneuropathy, entrapment neuropathy, etc.); 4. have rheumatic diseases (rheumatoid arthritis, systemic lupus erythematosus, etc.); 5. have significant medical disease; including uncontrolled systemic hypertension with values above 170/100 mmHg; cardiac or pulmonary disease; uncorrected coagulation abnormalities or need for therapeutic anticoagulation; 6. have active cancer; 7. have cardiovascular or musculoskeletal disease or injury that would prevent full participation in physical therapy intervention; 8. have unhealed fracture, contracture, pressure sore, or urinary tract infection or other illnesses that might interfere with lower extremity rehabilitation or testing activities; 9. have any condition that would render the patient unable to safely cooperate with the study tests as judged by the screening physician; 10. are pregnant; 11. are dependent on ventilation support; 12. have implanted stimulator (e.g. epidural stimulator, vagus nerve stimulator, pacemaker, cochlear implant, etc.); 13. have depression or anxiety based on the Center for Epidemiologic Studies Depression Scale (CESD) (score \>16/60) and General Anxiety Disorder-7 item Questionnaire (score \>9/21), respectively. 14. have alcohol and/or drug abuse; 15. have cognitive impairment based on Short Portable Mental Status Questionnaire (SPMSQ) (score \>2/10); 16. are unable to read and/or comprehend the consent form; 17. are unable to understand the instructions given as part of the study; 18. have established osteoporosis and are taking medication for osteoporosis treatment; 19. have bone mineral density T scores ≤ -2.0 in anteroposterior lumbar spine and/or proximal femur measured by DEXA (if participants are clear for other criteria and have not been examined by DEXA at the screening, we will ask participants to undergo DEXA to reveal any risk of weight bearing activity); 20. have a low-energy fracture history before or after spinal cord injury; 21. have a history of orthopedic surgery in lower extremities that may be a confounding factor for interpretation of the results (such as tendon transfer, tendon or muscle lengthening for spasticity management, etc.); 22. have fixed lower extremity joint contractures; 23. are taller than 80 inches and/or weighs more than 350 pounds (due to the limitation of the experimental equipment such as the body weight support system); 24. lack the ability to fully comprehend and/or perform study procedures in the investigator's opinion/judgement