So now let’s turn to the carpal tunnel. Very
similar to the arrangement we had on the dorsum
of the hand, at the wrist joint where we had
the extensor tendons passing between the extensor
retinaculum and the carpal bones. But this
time, we’re looking at the flexor retinaculum.
And deep to the flexor retinaculum are a series
of tendons from those long extrinsic muscles
in the forearm, that are passing through this
carpal tunnel towards the hand. And we can
see this here. We can see the flexor retinaculum
in this section, and we can see we’ve got
the tendons here surrounded by a flexor sheath.
And we can just talk through these tendons.
So the long tendons of extrinsic muscles enter
the hand through the carpal tunnel. This carpal
tunnel is formed by the flexor retinaculum,
and the concave palmar aspect of the carpal
bones. So the way the carpal bones are arranged
is that along their palmar surface, they are
actually concave. And then with the flexor
retinaculum passing over, they then create
this tunnel, includes the flexor tendons
of flexor digitorum profundus, flexor digitorum
superficialis, and flexor pollicis longus.
So the tendons of these forearm muscles, these
extrinsic muscles pass through the carpal
tunnel. And we can see this here. In this
diagram with the carpal tunnel opened up,
we can see the tendons of flexor digitorum
profundus here, and these are passing
towards the palm.
If we look here, we can see the cut tendons
of flexor digitorum superficialis and this
also would have entered through the carpal
tunnel. We can see that here. We have the
most superficial tendons of flexor digitorum
superficialis. And then deeper between those
tendons and the row of carpal bones here,
we can see flexor digitorum profundus.
We can also see flexor carpi radialis tendon
here, and we can see flexor pollicis longus
tendon here. So we can see these tendons passing
through the carpal tunnel. We can also see
that we have the median nerve. We can see the
median nerve is deep to the flexor retinaculum.
So if you were to have swelling within the sheaths,
overuse of the tendons perhaps, irritation
of the tendons could lead to inflammation
and swelling, and that could push the tendon
against the tight flexor retinaculum, and
you could develop carpal tunnel syndrome.
We also have passing superficial to the flexor
retinaculum. We have the ulnar artery
and nerve. And this is within a region known as
the ulnar canal. So also running towards the
hand, we know passing towards the hand has
to be the ulnar nerve because it supplies
those hypothenar muscles. But importantly,
the ulnar artery and its accompanying nerve
do not pass into the hand via the carpal tunnel.
We can see here that they lie above the carpal
tunnel, superficial to the flexor retinaculum.
So these do not in fact run within the carpal