Spinal Cord Stimulation for Restoration of Function in Lower-Limb Amputees, 90-Day

The goals of this study are to provide sensory information to amputees and reduce phantom limb pain via electrical stimulation of the lumbar spinal cord and spinal nerves. The spinal nerves convey sensory information from peripheral nerves to higher order centers in the brain. These structures still remain intact after amputation and electrical stimulation of the dorsal spinal nerves in individuals with intact limbs and amputees has been demonstrated to generate paresthetic sensory percepts referred to portions of the distal limb. Further, there is recent evidence that careful modulation of stimulation parameters can convert paresthetic sensations to more naturalistic ones when stimulating peripheral nerves in amputees. However, it is currently unclear whether it is possible to achieve this same conversion when stimulating the spinal nerves, and if those naturalistic sensations can have positive effects on phantom limb pain. As a first step towards those goals, in this study, the investigators will quantify the sensations generated by electrical stimulation of the spinal nerves, study the relationship between stimulation parameters and the quality of those sensations, measure changes in control of a prosthesis with sensory stimulation, and quantify the effects of that stimulation on the perception of the phantom limb and any associated pain.

During the study, FDA-cleared spinal cord stimulator leads will be placed in the lumbar epidural space of lower limb amputees and steered laterally towards the dorsal spinal roots under fluoroscopic guidance. This approach is essentially identical to the FDA-cleared procedure in which these devices are placed in the lumbar epidural space for treatment of intractable low back and leg pain. In that procedure, it is common clinical practice to place 2-3 leads temporarily in the epidural space through a percutaneous approach and perform a multiday trial to determine if the patient experiences any pain reduction from spinal cord stimulation. Following the trial, the percutaneous leads are surgically removed, and the patient is referred to a neurosurgeon for permanent surgical implantation.

Similarly, in this study, the device will be tunneled percutaneously through the skin and anchored in place. Using the stylet included with the spinal cord stimulator leads, the devices will be steered laterally under fluoroscopic guidance to target the dorsal spinal nerves. During lab experiments, the leads will be connected to an external stimulator. In this study, the devices will remain in the epidural space for up to 90 days and will be surgically removed. Throughout the study, the investigators will perform a series of psychophysical evaluations to characterize the sensory percepts evoked by epidural stimulation, along with functional evaluations of the effects of stimulation on the ability to control a prosthetic limb. In addition, the investigators will perform surveys to characterize changes in phantom limb sensation and pain that occur during stimulation.

Eligibility Criteria:
Inclusion Criteria:

1. Subjects must have an amputation of one lower limb, at a level between the ankle and knee joints. Minor amputation of the contralateral limb (i.e. toes or partial foot) is not exclusionary.
2. Subjects must be over 6 months post-amputation at the time of lead placement.
3. Subjects must be between the ages of 22 and 70 years old. Participants outside this age range may be at an increased medical risk and have an increased risk of fatigue during testing.
4. Subjects must have used their current prosthesis for at least 6 months and achieved at least K-1 ambulator status at the time of lead placement, as determined by the Amputee Mobility Predictor.

Exclusion Criteria:

1. Subjects must not have any serious disease or disorder that could affect their ability to participate in this study.
2. Female subjects of childbearing age must not be pregnant or breast-feeding.
3. Subjects must not be receiving medications that affect blood coagulation.
4. Subjects must not have an allergy to contrast medium or renal failure that could be exacerbated by the contrast agent used in MRIs. For this study, renal insufficiency will be determined through blood work and defined as BUN of 30 or less and Creatinine of 1.5 or less.
5. Subjects may not have a hemoglobin A1c level above 8.0 mg/dl at time of implant.
6. Subjects may not have any implanted medical devices that are not cleared for MRI.
7. Subjects with a T-Score higher than 63 on the 18-question Brief Symptoms Inventory (BSI-18) who have undergone discussions with and been deemed unsuitable by the Principal Investigator, a study physician, and a psychologist
8. Subjects may not have a cardiac pacemaker.
9. Subjects may not have a cardioverter defibrillator.
10. Subjects may not be currently receiving diathermy therapy.
11. Subjects may not have an implanted infusion pump.
12. Subjects may not be immunosuppressed or currently receiving immunosuppressive medications.
13. Subjects may not have a profession (e.g. radiology technologist) or medical condition (e.g. remissory cancer involved regular follow-up x-rays) that would increase radiation exposure in the 12 months prior to starting or after ending participation in the study.