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The use of facet joint injections is widely misunderstood. They’re often portrayed as a treatment for back pain. Instead, they’re a diagnostic tool used to determine whether the facet joint is the primary cause of someone’s back or neck pain.
When we zoom out to the 30,000 foot view, the primary issue with back pain is that the spine is such a complex structure. It’s difficult to know which element is causing pain. For a long time, the medical world believed MRI, CT and other scans would be able to do this.
However, large studies have shown that using only a scan as a diagnostic tool for back pain is extremely inaccurate.
Back to facet joints and back pain…
When people are in their 20s and 30 facet joint problems are the primary cause of around 20% of back pain. As you get older and the facet joints become more worn, they become more common as a cause of back pain.
However, just because a facet joint shows up as the most worn on an MRI scan, doesn’t necessarily mean it’s the one causing pain.
Because of this, one of the ways to discern whether a facet joint is the cause of pain is to block the nerve messages coming from the joint. You can do this in one of two ways.
The first way is to put local anesthetic and cortisone into the joint under imaging. This is a facet joint injection. If the primary cause of your back pain is that facet joint, the pain should go away for the period of time that the local anesthetic is working.
The second way is to block messages from a facet joint using a medial branch block, which sedates the tiny little nerves that supply the joint.
The first issue with facet joint injections is that as you get older your facet joint becomes more worn. This makes the injection more technically difficult because the joint is already very small, and it becomes narrower.
You also get small bony growths called osteophytes which you often can’t see on an x-ray. When this happens, it looks like the joint is nice and big but when you put your needle down you find you can’t actually get into the joint. Often the practitioner fails to get the needle into the joint. This is the first technical difficulty.
The only way to know if you’ve put your needle into the facet joint is to inject a small amount of dye. If you only use imaging to do the procedure, you could see in the picture that your needle looks like it’s directly over the joint. But it could be sitting on an osteophyte outside, not in the joint.
However, there’s also a problem to putting dye into the joint. The joint space so is small it will only take about a milliliter of fluid. When you put dye into the joint, you may in fact put half a mil of dye, which means that you’ve only got now half a milliliter left for local anesthetic, which is the diagnostic test.
If you’ve also mixed in cortisone, the results of pain relief from facet joint injections may not be that good. So unless you’re technically proficient, it’s easy to get a false negative from this test ie. you think the facet joint isn’t the problem when in reality you haven’t managed to get enough local anaesthetic accurately into the joint.
This questions comes back to misunderstanding the purpose of the injection. If the facet joint is the cause of your back pain, and if you accurately inject into the joint, you will still only get short term pain relief from the local anesthetic.
It is very rare to get long-term pain relief just from the injection. The cortisone usually lasts for two to three months, but it’s unusual to get anything like two to three months of decent pain relief.
The last problem with facet joint injections is that there’s quite a large placebo effect. If you have back pain and somebody sticks a needle in and they’re using a big image intensifier or a CT scan so you can see what they’re doing, and you believe that this treatment will help you, this is a very strong placebo.
This placebo effect is a problem because it produces a false positive. It makes it look like you’ve found the facet joint responsible for someone’s pain, when in fact their pain relief was due to the placebo effect of having injections.
The other way to isolate and test for facet joint pain is by doing medial branch blocks. These are a very useful test because it’s easier to get to the nerve than the facet joint.
Like a facet joint inejction, if medial branch block is positive, it can lead on to doing a radiofrequency neurotomy of the small nerves that supply the facet joint, effectively switching off the pain.
The main issue with medial branch blocks is they aren’t always done to a high standard. In certain parts of the world, people just do one medial branch block to test whether they’ve found the facet joint causing pain. However, many people will get pain relief due to a placebo effect, meaning the test gets a false positive. .
This false positive can be very high. It’s often in excess of 30 to 40%. Therefore, using just one medial branch block as a diagnostic test is only a little better than chance.
When this test is properly done, you do two medial branch blocks, one of them with short-acting local, one with long-acting local. The person you’re doing the blocks on doesn’t know which is long-acting, and which is short-acting.
If the test is positive, it should take away 90-100% of your pain, otherwise, you don’t go on and do a radiofrequency neurotomy. Also, the pain relief should last shorter with the shorter-acting anesthetic and longer with a longer-acting one.
Doing the test in this way, you have an 80 to 90% chance of pain relief if you test positive and go on to have a radiofrequency neurotomy.
This is the definitive treatment for facet joint pain. After you’ve properly tested whether the facet joint is causing pain (using facet joint injections or medial branch blocks,) you can then zap the nerves supplying the facet joint. This switches off all messages coming from the joint, effectively stopping the pain.
When you’ve done the tests correctly, this is a great procedure because the diagnostic tests are very low-risk, and the procedure itself is minimally invasive.
You’re using strict criteria with short and long-acting anesthetic, and you should be getting 90% or more pain relief with the block. That’s when you know you’re going to get a great outcome from the radiofrequency neurotomy.
The one issue with this treatment is that the nerves supplying the facet joint (which you’ve zapped) will grow back. It usually takes about 12 to 18 months. As they’re growing back you get about a year of pain relief.
In that year, one of three things will happen. The first is that people will say: “I can feel the pain, but it’s not as bad as it was.” That’s the most common result.
The second is the pain stays away completely which is not so common – maybe 10-15% of people experience this.
The third result is people find the pain has come back just as bad. If that’s the case, you just repeat the procedure because you’ve proven that that joint is, in fact, the cause of the pain.
In summary, facet joint injections are not primarily a treatment for back or neck pain. They’re a diagnostic test to determine whether the facet joint is the primary cause of a person’s pain.
If the test is positive (and the injection has been technically correct) you can then go on and get a radiofrequency neurotomy, which will zap the nerves supplying that particular facet joint.
It’s a minimally invasive procedure, and if applied to the right people (who test positive) it can be highly effective for long term pain relief.