Acute pain relief after orthopedic surgery was markedly enhanced by an interactive, noninvasive, electrical nerve stimulation device in two studies conducted in Russia. However, the most exciting application for this type of neurostimulation will be in chronic pain, predicted James N. Dillard, MD, who presented data (abstract PF360) at the 2008 World Congress on Pain of the International Association for the Study of Pain in Glasgow, Scotland.

“Noninvasive interactive neurostimulation [NIN] is an emerging technology that offers some real promise in chronic pain,” said Dr. Dillard, a private-practice pain specialist and attending physician at Stamford Hospital in Stamford, N.Y. The unique feature of NIN is that the device measures tissue adaptation to electrical stimulation—changes in impedance—and rotates the amplitude and frequency of the waveform to compensate (Figure).

Fifteen studies are under way or have been completed—seven of which are in patients with chronic pain—according to Neuro Resource Group, the device manufacturer. Dr. Dillard, an unpaid adviser to the company, has provided input on study design.

The NIN device appears to be “very effective for the treatment of pain and swelling in an acute postoperative condition,” said Philip J. Siddall, MB, PhD, a pain specialist at the University of Sydney and Royal North Shore Hospital in St. Leonards, Australia. The cost of the NIN device and electrodes is about $5,000.

According to Dr. Siddall, the potential is good for providing at least short-term relief of chronic pain with the NIN device. However, sustained relief is a more difficult therapeutic goal. Dr. Siddall said he looks forward to results from similar randomized controlled trials in chronic pain populations with longer follow-ups.

Dr. Siddall noted that evidence is limited that classic transcutaneous electrical nerve stimulators, as well as technologically modified ones, provide significant long-term relief of chronic pain. If these impressive results in treating acute pain can be approached in chronic pain, “it would be great,” he said.

Each of the two randomized controlled trials involved 60 patients. The first enrolled patients who had undergone hip fracture stabilization (J Bone Joint Surg Br 2007;89:1488-1494) and the second enrolled patients who had undergone open reduction and internal fixation of unstable, bimalleolar ankle fractures. In these studies the device was tested in the setting of postoperative pain, which Dr. Dillard described as “very clean, representing an episode of care.”

In both studies, pain was relieved after the first active treatment with NIN, compared with the sham treatment. Lower pain scores in the NIN groups were sustained throughout the 10-day study periods. At the same time, functional outcomes were improved and the requirement for nonsteroidal anti-inflammatory medication was decreased.

In the ankle study, active NIN or sham treatments were administered twice daily for 20 to 30 minutes for 10 consecutive days after surgery. Mean pain scores (visual analog scale [VAS]) decreased from 8 to 6 after the first active treatment, compared with no change in the sham treatment group. By day 5, patients undergoing active treatment had minimal pain (mean VAS <1) compared with moderate pain (mean VAS >5) in the control group. All differences were statistically significant (P<0.001).

Also in the active treatment group, edema decreased and ketorolac consumption was halved (both, P<0.001). Range of motion was greater in the active treatment compared with the sham group (P<0.001). Dr. Dillard said the reductions in pain and inflammation are clinically significant and would certainly have an effect on patient comfort.

In the hip study, patients received NIN therapy once a day. Pain scores were reduced after the first active treatment (mean VAS decreased from 9 to 4) compared with sham treatment (9 to 7.3); the difference was sustained during the 10-day study period (P<0.001). Parallel results were found for range of motion, ketorolac consumption, patient-reported functional capacity (especially walking) and the surgeon’s assessment of recovery (all, P<0.001).

NIN is another tool among many for pain specialists, said Dr. Dillard. “I have found it to be helpful in my practice.” He called for larger, robust studies on NIN technology, including in patients with chronic pain.