Dorsum – Anatomy of the Hand

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.