Jenny L.F. Andrus, MD
As a practicing Interventional Pain Management physician, I can tell you that patients are very different in how they approach the treatment of pain. Some want to immediately tackle the pain in the most direct way possible, and if that means surgery, well so be it. Some take the “wait and try everything else before surgery” approach. Other patients adamantly refuse surgery as a treatment, no matter what. A Genicular Nerve Block (GNB) is a diagnostic procedure that can serve all these patient groups who have knee pain. In this article, I will discuss the GNB, why it is used and how it helps both patients and physicians determine next steps in treatment for knee pain.
There are a small percentage of those who have had knee replacement surgery which failed to provide pain relief, even though the surgery was performed successfully. Some patients have terrible knee arthritis but aren’t healthy enough to withstand knee replacement surgery. Others simply choose not to have the knee replacement surgery and desire other non-surgical treatment for their chronic knee pain.
The knee joint is supplied with sensation by articular branches of many nerves, including the peroneal, tibial, femoral, obturator, common peroneal and saphenous. Don’t worry, there won’t be a quiz! The important thing to remember is that all these branches combined are called the genicular nerves. We can treat a few of the genicular nerves to effect pain relief for the whole knee. I perform diagnostic genicular nerve blocks to determine if indeed these nerves are sending pain signals to the brain. If the nerve blocks prove effective at reducing pain by at least 50%, we can then decide if we should move forward with radio frequency ablation of the genicular nerves for longer-term pain relief.
By the time patients are sent to me for a consultation, they have been to see their PCP and an Orthopaedic physician multiple times for their knee pain. They may or may not have had surgery, with or without knee replacement. These patients have tried pretty much every home treatment, physical therapy, steroid injections, visco-supplementation injections, prescription anti-inflammatory medications, etc. I typically will do a chart review of their medical history before they arrive in my office, so I am aware of what treatments have been tried.
Performing a GNB is an outpatient procedure done in the office here at OSC. It is performed under fluoroscopy, which is live x-ray, which helps me precisely pinpoint where the numbing medication is placed near the nerves. It is a sterile procedure that takes about 5-10 minutes to perform. I inject the anesthetic into two nerve locations inside the knee and one outside the knee, with two of those being above the knee joint and one being below. A band aid will be placed on the injection sites and the patient will be released to go home. If the knee injected is their right (driving) leg, we will ask that they have a driver accompany them to their appointment, for safety’s sake.
What I am going to ask the patient to discern carefully is the percentage of pain reduction that they perceive within the next 24 hours after the injections. If the pain is reduced by at least half (50%), then I consider this a positive response to the diagnostic test. If their pain is not reduced by at least half, then the test result would be negative.
A positive test result would then clear the way for a radiofrequency ablation of the genicular nerves (RFAGN), which is an outpatient procedure done in our office used to provide longer term pain relief. I will discuss the RFAGN in my next article.