A mechanism for carpal tunnel syndrome

(Last Updated On: April 1, 2016)

From an upcoming, much longer, post detailing my visit to Stanford University’s Clinical Anatomy Lab, where I worked with cadavers:

One area a cadaver made things easier was understanding the carpal tunnel. From the top there is a bunch of stuff covering it.

Once you get down to it though, it’s really a simple tunnel formed by the bones.

We can get a little fancier by looking at things through a cross section:

Adding other structures:

We talked a bit about carpal tunnel surgery. If you don’t know, it’s pretty simple. The idea behind it is the transverse carpal ligament becomes thickened; putting pressure on the median nerve, so it’s cut to relieve this pressure:

I started thinking what would cause this pressure on the nerve. Why would the ligament become thickened? Is that always the case, that it’s always the ligament? I don’t know much about carpal tunnel syndrome; it’s not something I see in my clients, so I looked around a bit. Pretty much all I found was “It’s likely congenital,” “May be associated with previous trauma,” “Nobody really knows why it happens.”

A couple places reference “women get it more than men and this is likely because their tunnel is smaller.” These places also reference carpal tunnel syndrome is only in adults; never children. Don’t children have the smallest tunnels of all? These explanations didn’t sit well with me.

I went cruising through the second edition of Movement System Impairment Syndromes, which deals with the hand, thinking there has to be some possible movement issue(s) with carpal tunnel too. I found something that made a lot of sense.

“CTS may be aggravated during gripping or prehension when using the finger flexors with the wrist flexed because this movement pattern results in anterior movement of the flexor tendons.”

Let’s go back to our drawing to put this in easier to understand terms.

This explanation is saying when you bend your wrist and grab something at the same time, the flexor tendons move forward, possibly putting pressure on the median nerve.

You can easily see this connection with your own hand. Bend your wrist, flex your fingers, and watch how the tendons in front of your wrist bulge out:

Different angle:

Now notice the difference if the wrist is stationary and only the fingers flex:

The tendons don’t glide forward.

This seems to coincide with a much greater amount of people who grab a lot, such as assembly workers, getting carpal tunnel issues compared to desk workers. Think grabbing a box: Wrist and fingers both flex.

If you’re someone with carpal tunnel symptoms, who grabs a lot, you may very well need to change how you’re grabbing things i.e. keep your wrist straighter. This meshes with how many people seem to get relief from a wrist splint -it keeps the wrist straight, preventing anterior glide of the tendons.

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