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Short Muscles and Extrinsic Tendons – Anatomy of the Hand

by James Pickering, PhD
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    00:01 tunnel. So now let’s move on to the short muscles and how they’re arranged alongside the extrinsic tendons. So here we can see some deep dissections of the hand. We can see that we’ve cut away some of the tendons and we’ve opened up the carpal tunnel. And here, we have removed some of those tendons as well to look deep and see some dorsal and palmar interossei muscles. So if we have a look, we can see the all eight tendons, see them here, flexor digitorum profundus. And we can see the cut tendons here, flexor digitorum superficialis, enters to the central compartment of the hand by passing through the carpal tunnel. And if we remember, FDS, flexor digitorum superficialis, pass to the middle phalanx of digits 2 to 5, whereas, FDP, flexor digitorum profundus, pass to the distal phalanx of digits 2 to 5. So there’s an important arrangement here that we need to observe. As the tendons of flexor digitorum superficialis pass to the middle phalanx, the tendons actually split, and we can see that here. Here, we can see the tendon of FDS passing towards the middle phalanx and its tendons splitting.

    01:24 You see it here. We can also see it happening here. See the tendons splitting into two as they go and attach to the middle phalanx. We can see it again here once these tendons are actually being reflected somewhat. See the tendon of flexor digitorum superficialis here. And we can see it actually splits, one going down onto this lateral side and one just going down this medial side. It’s a little bit covered by this, the tendon of flexor digitorum profundus. The tendon of flexor digitorum profundus, as we can see, passes deep through this split. So as the tendon of flexor digitorum superficialis split, so the deeper tendon of flexor digitorum profundus passed through this split as it passed the distal phalanx. And this is a really important arrangement. We can see it again here. Flexor digitorum profundus is passing deep to flexor digitorum superficialis.

    02:26 And then as it splits, the tendon here is splitting, FDP passes deep to it. And this enables the tendon of FDP to pass to the distal phalanx. We also have some vincula tendinum. We have two of these, and these are very small little slips of tissue. And they actually attach the tendons of FDP and FDS to each other and also to the phalanx. We can see these small little tendinous slips. We can see them passing down here. And here, we have a longum and a brevia. We have a long one and we have a short one. And these are important in connecting those two tendons to the tendinous sheaths, and also in permitting some microcirculation.

    03:17 So these carry some micro blood vessels to the tendons for their blood supply.

    03:24 So they’re really important in connecting the tendons to each other and also to the phalanges and also permitting some micro circulation so the tendons can receive their oxygen and nutrients.

    03:39 So if we now move on to the short muscles of the hand, we can see that we have a whole series of what’s known as lumbricals. We have lumbricals going from fingers 2 and 3.

    03:53 These are known as lumbricals 1 and 2. And lumbricals going from fingers 4 and 5, and these are known as 3 and 4. So we can see these lumbricals here. We’ve got a lumbrical here, we’ve got a lumbrical here, we’ve got a lumbrical here, and we have a lumbrical here. And these lumbricals are coming from the lateral two tendons of flexor digitorum brevis. And they’re coming from the medial two tendons of flexor digitorum profundus.

    04:24 So now let’s turn to a series of short muscles known as your lumbricals. And we can see the lumbricals here. We have four of them. And the lumbricals are either unipennate or bipennate in arrangement.

    04:39 They either have one kind of head or they have two heads originating from different places. And we can see we have a unipennate lumbrical here. And this lumbrical is important.

    04:51 It’s coming from the tendon of flexor digitorum profundus. So, all of the lumbricals come from the tendons of flexor digitorum profundus. And as they run over towards the extensor expansion, they are running over the metacarpal phalangeal joints and then over the interphalangeal joints. So these muscles are capable of working across two different joints. We have a lumbrical here. We have another lumbrical here, our two lateral unipennate lumbricals. And then we have two bipennate lumbricals. We can see we have one here and we have one here. So we have four lumbricals together. Notice how they all originate from the tendon of flexor digitorum profundus, and they don’t work on the thumb. They don’t work on the first digits. They’re only associated with digits 2, 3, 4, and 5. So if we have a look, we can see lumbricals 1 and 2. These are originating from the lateral two tendons of FDP, and these are our unipennate one as I indicated. And then we have lumbricals 3 and 4 and they’re originating from the medial two tendons of FDP, and these are bipennate. They insert onto the lateral surface of the extensor expansions as I mentioned of the digits 2 and 5. So they don’t work on the thumb, just digits 2 to 5. The lumbricals 1 and 2, the lateral two lumbricals are innervated via the median nerve, whereas the lumbricals 3 and 4 associated with the medial tendons of FDP are innervated via the ulnar nerve. So we can see the lumbricals have a different innervation, a different nerve supply. The function of these lumbricals is important because they can both flex and extend different joints, so they can flex the metacarpophalangeal joint, the joint between the phalanges and the metacarpals. So they can flex that joint, the phalanges here and the metacarpals. They can flex that joint. And they’re also capable of extending the interphalangeal joints. So they’re capable of flexing that joint but also extending the interphalangeal joint. And that is because of their position. They run anterior to the metacarpophalangeal joint so they can flex it.

    07:24 And by passing to the extensor expansion, they’re running posterior to the interphalangeal joint. So a contraction of these muscles allows flexion of that joint, the metacarpophalangeal, and extension of the interphalangeal joint. This position here is important if you’re holding a pencil if you’re about to write. So these muscles are important for the digits to assume complex positions. Now let’s carry on looking at a series of short muscles, and these are known as your interossei muscles. We have two different types of interossei muscles. We have dorsal interossei positioned on the dorsal aspect of the hand. And we have palmar interossei muscles positioned on the palmar surface.

    08:11 Here, we can see the dorsal interosseous muscles. We have four of them. We can see one, two, three, four. And we can see these have two heads. They’re running from the adjacent surfaces of all of the metacarpals. So we can see the dorsal interosseous here is running from the medial surface of the first metacarpal and the lateral surface of the metacarpal here of the second metacarpal. And we have similar arrangements. And these are passing towards the extensor expansion, those extensor hoods over the digits.

    08:49 And then we have the palmar interossei. These are just running from one of the metacarpal surfaces, and we can see they’re coming from digits 2. They’re coming from digit 4, and coming from digit 5. Digit 3 does not have an attachment of these interossei muscles.

    09:11 The interossei muscles do not attach. So we can see that these muscles are going to be associated with abducting and adducting the fingers. We can see the dorsal interossei are coming from the dorsal sides of all the metacarpals, these are bipennate muscles.

    09:30 And the palmar interossei, as I said, comes from the palmar sides of metacarpals 2, 4, and 5.

    09:36 They insert onto the base of the proximal phalanges and also the extensor expansions.

    09:44 The nerve supply for these interossei is via the ulnar nerve, the deep branch. And the dorsal interossei are associated with abducting digits 2 to 4, abducting digits 2 to 4. Palmar interossei are associated with adducting digits 2, 4, and 5, this time towards the axial line.

    10:07 I’ve put that here; towards the axial line and away from the axial line. What does that mean? Well, if you imagine the axial line is running down in line with the middle finger, so an axial line is running down here. This is the line at which these fingers are going to be abducted or adducted. And we can see that with contraction of these muscles, we can put the muscles in cartoon form here. With this axial line, we can see that the dorsal interossei are going to pull the fingers away from this axial line.

    10:44 So this dorsal interossei can pull that away. This dorsal interossei can pull this middle finger away. It can also, because we have the dorsal interossei on the other side, abduct it the other way. For the fingers, we don’t talk about abduction and adduction as moving them towards the midline of the body. We talk about moving away from this axial line.

    11:08 Therefore, the middle finger can both abduct this way, and it can abduct that way, whereas the other fingers will all abduct away from this axial line like that. The middle finger can abduct away either sides. If we look at the palmar interossei, then we look at adducting. So palmar interossei are adducting and they’re going to draw the fingers towards the middle finger, towards the axial line. So we can see that this interossei will move it across. This interossei will move it across. This interossei will also move it across. So we’ve got our middle finger. We can adduct here, we can adduct here, we can adduct here. So, all the fingers are together. Don’t forget we have adductor pollicis so we can move the thumb across. It doesn’t need an interosseous muscle. So here, we can see the origins and insertions of these muscles. The easy way to remember the function is for the dorsal interossei to use the D from dorsal and the AB, so you can DAB, dorsal interossei abduct. And you can have PAD, using the P from palmar interossei. PAD as the palmar interosseis adduct.

    12:18 So in this lecture, we’ve looked at the dorsal aspects of the hand. We’ve looked at the extrinsic extensor tendons and tendinous sheath. We’ve looked at extensor expansions and the anatomical snuff box, its boundaries and contents. We then looked at the palmar aspects. We looked at the carpal tunnel and the ulnar canal, the boundaries and contents.

    12:41 We then looked at compartments, central hypothenar, thenar, adductor, and interosseous, and we looked at the muscles within each of the compartments. And then we looked at the extrinsic flexor tendons.


    About the Lecture

    The lecture Short Muscles and Extrinsic Tendons – Anatomy of the Hand by James Pickering, PhD is from the course Upper Limb Anatomy.


    Included Quiz Questions

    1. Abductor digiti minimi
    2. Abuctor pollicis brevis
    3. Flexor digiti minimi
    4. Flexor pollicis brevis
    5. Opponens digiti minimi
    1. They flex the metacarpophalangeal and extend the interphalangeal joints
    2. They extend both the metacarpophalangeal and interphalangeal joints
    3. They flex both the metacarpophalangeal and interphalangeal joints
    4. They extend the metacarpophalangeal and flex the interphalangeal joints
    5. The only flex the metacarpophalangeal joints
    1. Opponens pollicis
    2. Abductor digiti minimi
    3. Flexor digiti minimi
    4. 3rd and 4th Lumbricals
    5. Opponens digiti minimi
    1. Adductor pollicis brevis
    2. Flexor pollicis brevis
    3. Abductor pollicis brevis
    4. Opponens pollicis
    1. Flexor digitorum profundus
    2. Flexor digitorum superficialis
    3. Palmaris longus
    4. Flexor digitorum indicis
    5. Flexor pollicis longus
    1. Lumbricals 1 and 2 are bipennate
    2. Lumbricals 1 and 2 originate from the lateral two tendons of flexor digitorum profundus
    3. Lumbricals 3 and 4 originate from the medial two tendons of flexor digitorum profundus
    4. Lumbricals 3 and 4 are bipennate
    5. Lumbricals 1 and 2 are unipennate
    1. Deep branch of ulnar nerve
    2. Palmar cutaneous ranch of the ulnar verve
    3. Recurrent branch of median nerve
    4. Superficial branch of ulnar nerve
    5. Median nerve
    1. 3
    2. 5
    3. 2
    4. 4

    Author of lecture Short Muscles and Extrinsic Tendons – Anatomy of the Hand

     James Pickering, PhD

    James Pickering, PhD


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