Implantable Stimulator Shows Promise for Chronic Knee Pain

Implantable Stimulator Shows Promise for Chronic Knee Pain

Stimulation of the infrapatellar branch of the saphenous nerve with an implantable electrical device is, potentially, an effective treatment for chronic and intractable knee pain.

In a series of small cases consisting of five patients with chronic knee pain, pain intensity scores on the analog visual scale (VAS) decreased from an average of 8 of 10 before implantation to 1.4 of 10 when they were measured 6 months later.

Pain relief was also long lasting, with an average score at 2 years still significantly reduced from the start, to 3 out of 10 in the VAS. "We have many patients with chronic knee pain and, unfortunately, our hands are tied in terms of what we can do for them," lead author Dr. Kwo Wei David Ho, MD, PhD, Stanford University, California told Medscape Medical News.

Dr. Ho further stated, "They can use NSAIDs, physiotherapy, some receive steroid injections or blockages of the genic nerves, but they don't work as well. Some undergo knee replacement surgery and may still have persistent knee pain after the operation, as well. That here we are using an alternative therapy called peripheral nerve stimulation of the saphenous nerve. This provides a way to relieve pain without nerve destruction or motor dysfunction."

The findings were presented at the 2020 Annual Meeting of the American Academy of Pain Medicine (AAPM). For the study, the researchers surgically implanted five patients with StimRouter from  Bioness Inc. The device takes between 15 and 30 minutes to implant, just like a pacemaker, and reduces pain by mild electrical stimulation directly to an objective peripheral nerve, in this case the saphenous nerve, to interrupt the pain signal.

"A thin or filiform cable, or noodles, is implanted under the skin, next to the target peripheral nerve responsible for the pain signal under ultrasound guidance, and then an external pulse transmitter (EPT) patch is used on the part upper skin. sends electrical stimulation through the skin to the lead, "explained Dr. Ho. The patient can control the EFA and adjust the stimulation with a handheld wireless programmer.

"Some patients turn it on at night for a couple of hours and then turn it off, some leave it on all night or all day if they prefer. What we have noticed in our series is that after a while, patients use less and less and the pain improves and improves, and eventually they stop using it completely because the pain is completely resolved, "said Dr. Ho. Good candidates for this treatment are knee replacement patients with residual pain, he added. Of the five patients in the case series, four had prior knee arthroplasty.

To determine the possibilities of a good response to the implant, the study participants underwent a diagnostic blockade of the saphenous nerve, with the justification that if the blockade successfully reduced knee pain by 50% or more in the short term, patients would probably respond well to the implant. "This study provides preliminary evidence that saphenous nerve stimulation may be effective for selected patients with chronic knee pain," said Dr Ho. 

Commenting on the findings, Dr. Patrick Tighe, MD, MS, University of Florida, Gainesville, said chronic knee pain continues to present "numerous diagnostic and therapeutic challenges for many patients. It may be surprising, but there is still so much we don't know about the innervation of the knee, and we are still learning about different ways to alter the behavior of those nerves. This work points to some exciting opportunities to help patients suffering from chronic knee pain. We certainly need more research in this area to discover the optimal approach to apply these findings more widely," he said.

The future for alternative knee pain therapies certainly looks brighter with innovative technologies such as StimRouter on the horizon.

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