Injecting into the Carpal Tunnel

In Medical Concepts by Brent Thoma5 Comments

It’s been awesome working in the ED with the benefit of the knowledge gained on off-service rotations in specialties like Plastic and Orthopedic Surgery. Great learning experiences on these rotations have led to a run of success with injections into all sorts of places and have given me a desire to inject into… well… most things that there is evidence for treating with needles. Recently I’ve treated a carpal tunnel syndrome (median nerve steroid/lidocaine injectin), frozen shoulders (steroid/lidocaine), Colle’s fractures (lidocaine/bupivicaine hematoma block) and traumatized hands (lidocaine/bupivicaine median and ulnar nerve blocks) with the little pointy things. Of course, all patients were followed-up (or seen with) the appropriate specialty service.

I have found that some of my EM Attendings are more comfortable than others with my needle fascination. In general, there is a fair amount of of comfort with the hematoma block and shoulder injection, less familiarity (but still acceptance) with the median and ulnar nerve blocks, and no EM experience with injecting into the Carpal Tunnel. Most of my experience with the latter procedures came under the watchful eye of a surgeon during my Plastics rotation. I find the blocks and carpel tunnel injections intensely satisfying – which leads me to the topic of the day:

Carpal Tunnel Syndrome: to inject or not to inject?

I posed this question on twitter (thanks for the responses Minh, ElishaT, Alex and TheSGEM!) and got the same response as I did in my department. The summary: No one does this, you Weirdo. If you want to provide conservative treatment, hook them up with a splint and send them to Plastics.

Fair enough. However, after examining the literature I’m unsure why there’s such a hate-on for the injection. The procedure itself is similar to one clearly within our scope (median nerve block), there’s evidence that it works (see below), and it can effectively treat many patients while they wait to see Plastic Surgery. In fact, this is likely the treatment they’ll get on their first visit with the surgeon anyways. Certainly, its not a super urgent problem, but the same could be said for many of the other conditions that we treat. Why not get them started on their treatment and give them some relief before the potentially long wait to see the surgeon??

Do Carpal Tunnel injections really work?

A Cochrane review was done to answer this (and related questions) in 2008. It found evidence that steroid injections were effective relative to placebo for up to one month. Unfortunately, this limited conclusion was reached because there were only two trials included in the analysis that examined this particular question and neither maintained control groups longer than 1 month.

The first RCT from Dammers et al in 1999 posed the following PICO question: In a Population of patients with carpel tunnel symptoms for >3 months is the Intervention of injecting 40mg of methylprednisolone (Depo-Medrol) proximal to the carpal tunnel more effective than the Control treatment of placebo at improving the Outcome of no or minor symptoms that require no further intervention (the “responders”) at 1, 3, 6, 9 and 12 months. Criticisms of this study include its largely female (84%) population and lack of clarity on the population’s carpal tunnel severity. There were no complications.

While the population was small (30 control, 30 intervention), the treatment was effective with 50% of patients in their treatment group still responsive at 12 months versus 7% in the placebo group (NNT = 2.3). However, at one month 23/30 (77%) intervention vs 6/30 (20%) control patients responded (NNT = 1.75). Nonresponders were moved to open treatment (injection or surgery as indicated) at each follow-up appointment. The Cochrane review concluded that this prevented comparison beyond 1 month, but I’m not sure why we can’t continue to draw conclusions from the data of the patients that continued to respond. As nonresponders could not become responders again in the subsequent data, it seems to me that the proportion of responders/non-responders in each group would still be accurate in follow-up (EBM people – thoughts on this? Leave a comment please).

A related but more complicated RCT by Armstrong et al from 2004 included 81 patients and compared 6mg of Betamethasone versus placebo but was more difficult to interpret because it allowed for up to q2month injections and only provided data for responders/non-responders at 2 weeks post-injection. It found a NNT 2.8 for patients being “highly” or “somewhat” satisfied with their outcome at 2 weeks when nonresponders were offered surgery (intervention group) or steroid injection (treatment group).

A larger, 52 week trial to answer this question has been proposed.

So does it work? The data available (limited as it is) suggests that it does work in a significant proportion of patients for at least a limited period of time.

How would do you do a Carpal Tunnel injection?

The procedure is similar to a median nerve block and could be done using ultrasound guidance. It can be done with an injection both at the wrist and more proximally with equal efficacy. I will not try to reinvent the wheel:

-eMedicine has a good overview here.
This is a decent youtube video discussing two blind injection techniques.
-The Ultrasound Podcast has a great video uploaded to GMEP on identifying the median nerve. Injecting near it after you find it shouldn’t be much of a problem.

Multiple steroids are mentioned in the literature. The ones used in the two studies discussed above were 40mg/1mL Methylprednisolone (Dammers) and 8mg/1mL Betamethasone (Armstrong). 10mg (1mL of 1%) of Lidocaine can also be added to help confirm the correct location of the injection.

Just like with a median nerve block, you want to avoid damaging the nerve by injecting directly into it. Some of the techniques described above help you to avoid that, but you should still advise the patient to let you know if they have any shooting pain/numbness during the injection.


Based on the tepid response that I received to the idea of doing these injections in the ED and acknowledging that I have no business being innovative at this point in my baby career, this review will likely be my only experimentation with these injections out of the sight of a plastic surgeon. If someone smarter, more experienced and better respected ever comes along and decides to advocate for doing this, I’ll be happy to follow their coat-tail. Until then, I’ll keep leave the steroids in the pharmacy and wouldn’t advise anyone else to start injecting into the (Carpal) Tunnel.

Despite its potential, with that conclusion this is a “negative” (ie – I’m not recommending that we do this) review. I imagine its readership will be as low as a negative study’s? Guess I’ll find out! If you’ve stuck with me this long, I hope you enjoyed the diversion.

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Thanks for reading!

Brent Thoma @boringem

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Dr. Brent Thoma is a medical educator, blogging geek, and trauma/emergency physician who works at the University of Saskatchewan College of Medicine. He founded BoringEM and is the CEO of CanadiEM.