00:01
In this lecture, we’re going to look at
the hand. So first of all, we’re going to
look at the dorsal aspect of the hand, and
we’ll look at some of the extrinsic extensor
tendons that originate from muscles in the
forearm and pass on to the dorsal surface
of the hand. We’ll then look at the anatomical
snuff box which we mentioned in the previous
lecture, and we’ll also look at the tendinous
sheath. We’ll then move on to the palmar
aspect and look at the carpal tunnel where
some important flexor tendons from extrinsic
muscles pass through. We’ll look at numerous
compartments within the palmar aspect of
the hand. We’ll look at the muscles and then
the extrinsic flexor tendons.
00:46
So here, we can see the dorsal aspect of the
hand. It’s the posterior surface.
00:52
We’ve got the thumb over on this side. So this
is the lateral aspect. And here we have with
the fifth digit, we have the medial aspect.
We can see we have the extensor retinaculum
here, and we can see the tendons from the
extensor muscles in the forearm are passing
deep to this structure as they pass into the
dorsum of the hand. And this extensor retinaculum
is an important thickening of the antebrachial
or the forearm deep fascia. It prevents them
from bowstringing. It prevents those extrinsic
tendons from bowstringing.
01:29
We can see that we have the tendons of extensor
digitorum and extensor digiti minimi and extensor
indicis, all passing through this tunnel which
is created dorsally to the wrist, so between
the carpal bones of the wrist and the extensor
retinaculum. We can see the extensor digitorum
tendons here. We can see extensor digiti minimi
here. And we can see extensor indicis passing
all the way to the index finger. Each extensor
expansion covers the dorsal aspects of the
metacarpals and phalanges. And these extensor
expansions are triangular-shaped aponeurotic
hoods that lie over the dorsal and sides of
the metacarpals and phalanges. And it is this
that the tendons of extensor digitorum,
extensor digiti minimi and extensor indicis
pass to. We can see if we look at the
tendinous sheath
that they actually divide into two tracts
and they pass to both the middle phalanx and
the distal phalanx. So we can see here we have
the medial tracts that are passing towards
the middle phalanx of each digit. And then
we have the lateral tracts which are passing
towards the distal phalanx. And these are
specialized tracts of the extensor expansions
that pass over the dorsum of the digits. This
means that you don’t have as much control
over the extension of the digits and it tends
to act as one. You have less ability to extend
the individual interphalangeal and metacarpophalangeal
joints as you do with flexion,
and they seem to act as one smooth movement.
We can see that adjacent tendons from extensor
digitorum are joined by some obliquely running
interconnections. We have three of them running
between the long tendons that are passing
towards these extensor expansions. And like
I say, this helps to limit the independent
extension of the fingers. So it’s very difficult
just to extend one finger. You either extend
them all or you don’t. Because you have
extensor indicis, this does offer this specific
finger a certain amount of independent control.
04:09
So I mentioned the anatomical snuff box when
we spoke about the forearm in the previous
lecture. And I just want to talk about it
a little bit more here. It’s formed by those
outcropping deep muscles that come from the
extensor compartment of the forearm, and they
create the tendons of these muscles, create
a shallow depression on the lateral aspect
of the hand. So here, we can see the thumb, and
here, we can see we have the anatomical snuff
box. We can see its borders. So medially,
we have a border here, and this
border is formed by EPL, extensor pollicis
longus. So that forms this medial border.
04:56
And laterally, it’s formed by two tendons,
the tendons extensor pollicis brevis which
we can see here, extensor pollicis brevis,
and also the tendon abductor pollicis longus
which is a little bit harder to see in this
diagram but would be running alongside extensor
pollicis brevis here as it passes towards
the thumb.
05:19
So laterally, we have two tendons, extensor pollicis
brevis and abductor pollicis longus. And medially,
we have one tendon, extensor pollicis longus.
This space in between these tendons is known
as the anatomical snuff box. The floor of
the snuff box is formed by two carpal bones
and these can be palpated, the scaphoid and
the trapezium. These two carpal bones can
be palpated, and it contains the radial artery.
So when we look at the blood supply to the
hand, you’ll see that the radial artery
runs over this anatomical snuff box.
06:00
You can also palpate the styloid process from
the radius quite proximally within the space
and the base of the first metacarpal distally
within the space. So it’s important
you recognize the features in the anatomical
snuff box. And as the scaphoid bone is prone
to fracture, palpation here and eliciting
pain could indicate a fracture to this carpal
bone, so the anatomical snuff box. Let’s
look at the tendinous sheaths that
I mentioned as the extensor tendons pass through
the extensor tunnel really running between
the carpal bones and the extensor retinaculum.
Again on this slide, on this picture of the
hand, we can again see the extensor retinaculum
here, we can see the medial aspect down here,
we can see the lateral aspect down here
with the thumb. Now, we can actually clearly
see the two tendons that make up the lateral
border of the anatomical snuff box, both extensor
pollicis brevis here and abductor pollicis
longus. So now we can see those two tendons.
07:12
And what you can recognize is that as these
tendons pass deep to the extensor retinaculum,
they have within them, they’re surrounded
by a tendinous sheath. And we can see that
here if we look at a section through the wrist.
This is going to be the dorsal aspect, and
this is going to be the palmar aspect. So
we are not really worried about this side for
the moment. But we can see we have the skin here,
we have the extensor retinaculum running
between the skin and these tendons. And these
tendons are tightly held against the
carpal bones. So, we have these tendinous
sheaths so that
the friction within these osseous tunnels
is reduced. They reduce the friction within
the osseous tunnels. Here, with some added
detail, you can see the plane of the section
through the wrist. Here, we’ve got the extensor
retinaculum again, and you can see that these
tendons are surrounded by an individual tendinous
sheath. So as the tendons cross the dorsum
of the wrist and they enter the hand, they
are covered by these synovial tendon sheaths.
08:24
This reduces the friction within the osseous
tunnel created by the extensor retinaculum
spanning the radius and the ulna. So the friction,
as the muscles are contracting and the tendons
run alongside the carpals is reduced by
the presence of this tendinous sheath.
08:42
So these are very important.