The present case study was approved by the FDA under an Investigational Device Exemption (IDE), and Investigational Review Board approval was obtained. The research study followed standard clinical practice guidelines. The subject was a 49-year-old African-American male who reported severe residual limb pain (RLP) secondary to a below-the-knee amputation of his right leg following a motor vehicle accident 33 years prior to enrollment into the study. The subject reported that the RLP remained severe despite a history of using narcotic analgesics, anticonvulsants, non-steroidal anti-inflammatory drugs (NSAIDs), physical therapy, and nerve blocks. The subject perceived pain throughout his residual limb as indicated on the pain diagram () with the most intense pain located just above the level of amputation. The subject reported no phantom limb pain throughout the study with the exception of one diary entry (score of 2 on an 11-point numerical rating scale) on a single day during the baseline period. In addition to the amputation, pain, and related sequelae, the medical history of the subject included sickle cell anemia but did not include diabetes or peripheral vascular disease.
The subject indicated areas of pain (A) and areas of stimulation-evoked paresthesia coverage (B).Arrows indicate level of amputation on the front and back views of the leg, respectively.
The subject enrolled in the study after providing informed consent and meeting all eligibility requirements. Inclusion criteria included a well-healed unilateral lower extremity amputation, daily worst residual limb pain and/or phantom limb pain score ≥ 4 on an 11-point numerical rating scale on the Brief Pain Inventory-Short Form (BPI-SF) Question #3 (BPI3), Beck Depression Inventory (BDI-II) score of ≤ 20, and age ≥ 18 years. Exclusion criteria included the absence of sepsis, infection, diabetes mellitus type I and II, implanted electronic devices, anticoagulation therapy (aside from aspirin therapy), history of valvular heart disease, previous limb injections within the past six months, pregnancy and any previous allergy to skin contact materials and/ or anesthetic agents. The subject had no potential secondary gain issues at the time of enrollment.
After providing informed consent and medical history, the subject was sent home with a diary and asked to record medication usage and worst-pain levels every day for the duration of the 8-week study. Throughout the study, the subject reported taking the following medications daily: one multivitamin (1 time/day), ibuprofen (800mg, 3 times/day), and gabapentin (600 – 800mg, 3 times/day). At the end of the 2-week baseline period, the subject requested that his dose of gabapentin be increased from 600mg to 800mg in response to a recent back injury unrelated to the study. The subject continued to take the 800mg dose of gabapentin for the remaining 6 weeks of the study. The 3-day average of the BPI3 (daily worst pain) scores during baseline was 7.7.
After completing the 2-week baseline period, the subject returned to the clinic for lead placement and electrical stimulation testing. The lead was a fine-wire helical coil wound from a seven-strand, type 316L stainless steel wire with a single anchoring barb and electrode contact. The lead was insulated with perfluoroalkoxy and preloaded in a 20-gauge, insulated hypodermic needle introducer. The subject was placed in a supine position to allow access to the femoral nerve using an anterior approach. The insertion site was cleansed using aseptic technique and local anesthesia was administered. No sedation was used.
Prior to placing the fine-wire lead, a monopolar needle electrode (24-gauge, Jari Electrode Supply, Gilroy, CA) was inserted below the femoral crease and lateral to the femoral artery to within 0.5 – 1 cm of the femoral nerve under ultrasound guidance to deliver test stimulation. Test stimulation (40 μs, 1 mA, 50 Hz) was delivered with a regulated-current stimulator (Maxima II, Empi, Inc., St. Paul, MN) to confirm that the angle of insertion (40° from skin surface) and the length of needle under the skin (3.6 cm) evoked a comfortable paresthesia in the region of pain innervated by the femoral nerve. Once confirmed, the monopolar needle electrode was withdrawn and replaced with the fine-wire lead under ultrasound guidance using the same insertion site and the same approach except that the introducer was only inserted 2 cm under the skin, placing the lead remotely (> 1 cm away) from the nerve.
Correct lead placement was confirmed by evoking a comfortable paresthesia with stimulation (50 μs, 1 mA, 50 Hz) that covered ≥ 75% of the painful area without evoking muscle contractions, qualifying the subject to proceed to the 2-week home trial. The stimulator was replaced with a regulated-voltage stimulator (Rehabilicare NT2000, Empi, Inc., St. Paul, MN) that was approved for the home trial. Stimulation pulse width was set at 30 μs and amplitude was incrementally increased to evoke the maximum comfortable paresthesia coverage (≥ 75%). The lead was deployed by withdrawing the needle introducer while maintaining pressure at the skin surface. The lead was coiled outside the skin to create a strain-relief loop, and the exit site was bandaged with waterproof bandages (Tegaderm by 3M, St. Paul, MN). The subject was instructed regarding the use of the stimulator and care of the bandages before progressing to the first week of the home trial.
The subject returned as planned to the clinic after the first week of the home trial for bandage change, exit site inspection, and an increase in stimulus pulse width from 30 μs to 40 μs. The subject reported improved comfort in response to the change in pulse width, and the subject progressed to the second week of the home trial. The subject returned as planned after the second week of the home trial for lead removal and again for the 1-week and 4-week follow-up visits.
During lead placement and the subsequent 2-week home trial, the subject reported comfortable paresthesia coverage of ≥ 75% of the region of residual limb pan (RLP) (), and no muscle contractions were observed in response to electrical stimulation.
Electrical stimulation of the femoral nerve reduced the RLP by 60% from baseline by the end of the 2-week home trial (). The mean pain interference score for the BPI-SF decreased from 6.3 at baseline to 1.7 (73% improvement) after the first week of stimulation and to 0 (100% improvement) after the second week of stimulation (). The mean Pain Disability Index (PDI) score was 7 at baseline and decreased to 3.8 (45% improvement) after the first week of stimulation and further decreased to 1.8 (74% improvement) after the second week of stimulation (). The sum of scores on the BDI-II was 0 at baseline and at the end of the 2-week stimulation home trial (). Relative to baseline, the subject reported on the Patient Global Impression of Change (PGIC) scale that he felt “Much Improved” after the first week of stimulation and “Very Much Improved” after the second week of stimulation. The lead was removed intact, and no adverse events were reported.
Worst pain in the last 24 hours (BPI3) as reported by the subject in the daily diary.
Table 1 Outcome measures collected during baseline, after the first week of stimulation, after the second week of stimulation, after the first week of follow-up (F/U), and after the fourth week of follow-up. Percent change from baseline is reported in parentheses (more ...)