[Music] rights um i was giving you a tutorial the other day about the movement muscles around here muscles of the hand and stuff and i thought of the thumb and i've had another student recently who's actually injured one of the muscles that moves the thumb and i i think i've done a video about the muscles of the thenar eminence here and i've done a video about muscles of the forearm i don't know if i've ever pulled it all together because the thumb's quite special so we are going to look at the muscles of the thumb so what we need to do is we need to look very briefly at the bones that are involved the muscles attach to because those are the things that the muscles are going to move and we will talk about the movements of the thumb because the movements of the thumb are crucial to naming the muscles identifying the muscles understanding what the muscles do and also understanding thumb function and uh then we'll throw in a a sprinkle of innovation so you can better understand the the functional deficits the things that don't work when a nerve has been injured all right because there's muscles in different places that are innovated by different nerves that's the plan [Music] okay then right my other models are right hands so we should stick to the right hand um the thumb is a little bit so the fingers right things have got three phalanges the thumb has only got two so it's got two phalanges each one is a phalanx and then this bone here is a metacarpal bone these are the metacarpal bones of the fingers so when i if i if i talk about the movement of the metacarpophalangeal joint i'm talking about this joint here in terms of the carpal bones the bones of the wrist at the base of the thumb is the trapezium and then between the trapezium and this bone here this is the scaphoid bone uh most students know about the scaphoid bone because it's the most commonly fractured bone in the wrist so trapezium and scaphoid and then next to trapezium we have trapezoid trapezoid next to it and then the big bone in the center of the carpal bones in this row is capitate like a big head right i always think of like an easter island head the decapitate bone and this is lunate we're not going to talk about all of them but those bones there are bones that the muscles of the thumb are going to attach to now if we talk about intrinsic and extrinsic muscles of the thumb intrinsic means that they are within the hand they're in here so intrinsic muscles of the thumb are here this is the thenar eminence and there's another muscle there the extrinsic muscles of the of the hand and the thumb are in the forearm this gives us more room to make a bigger muscle that can exert more force more power more strength through a tendon so that gives us much greater strength in our grip than if we would just use these little tiddy muscles in here so the little diddy muscles in their hand then are really important in fine movement and dexterity and if we're talking about the thumb this is what the thumb is about largely the thumb is absolutely crucial in almost every grip that we do um so the most the muscles we're going to talk about are really important to normal thumb function and you won't notice a you know how important normal thumb function is until you lose a part of it um so the other bones that are important then are they on the thumb side we have the radius this is where the radial pulse would be found here right so we've got the the radius and the ulna so those are the bones that we're talking about next movements the movements of the thumb the names of the movements are difficult i get i get surgeons coming up to me and asking me so we not hand surgeons hand surgeons know this really really well i mean surgeons from other part of the body who you think would have a really good knowledge of anatomy ask me about the movements of the thumb okay so the fingers right the fingers are the easy bit this is flexion of the fingers and this is extension of the fingers flexion extension so what we're doing there is we're flexing the metacarpophalangeal joint and we're flexing the interphalangeal joints and extending and then the fingers we can abduct and we can adduct that's where you start from then you remember that the thumb is on a plane at 90 degrees to the fingers it's out here right so the thumb is on a plane at 90 degrees to the fingers so that means that if the thumb moves that way that is flexion of the thumb and again we're flexing the metacarpal phalangeal joint and this interphalangeal joint here so that's flexion flexion of the fingers flexion of the thumb right so if that's flexion then that means that the opposite the the opposite movement on the same plane that is extension got it so that is extension of the thumb flexion extension okay so we're still on that plane at 90 degrees to the fingers so if that's extension and flexion if we move the thumb this was a little difficult to demonstrate in 2d but if we move the thumb that away that is abduction so what i've done there is is that that's abduction if you do this yourself now to prove that you've abducted the thumb this web this web of skin here this web space that that becomes full that that appears right that is abduction of the thumb so if you if you extend the thumb that's not that's not fully stretched out there right if you fully stretch out that web space of skin that's abduction of the thumb and now we've abducted the thumb we can adduct the thumb abduction adduction abduction adduction okay you can see why you can see why it's difficult now the the names of the muscles are named for the movements that they cause which is why these movements and understanding these movements is the first step in this and is important for example when we abduct the thumb this web space that appears here the muscle in there is called adductor police the adductor of the thumb so that muscle is now long if we make that muscle shorter it adducts the thumb and we'll see more examples of that as we go um now the thumb is also special in that it can oppose the other fingers so this movement of the thumb and the little finger is opposition and then the reverse movement is reposition reposition reposition so opposition and reposition opposition reposition and what's happening here is we've got flexion going on and we also have a little bit of rotation of that metacarp see how the see how the palm of the hand is cupping you can do this yourself you know flexion versus all right and now uh for bonus points which probably doesn't have much to do with what we're talking about today but there is another movement if you put your hand like flat on a surface then you lift the thumb away from the surface see what i'm doing there that is called retropulsion that's kind of high level stuff that's not that's not so useful today but if you hear of retropulsion you wonder what it meant that's it there can you see how that that's not that's not extension because that would be extension it's not flexion it's not abduction it's not adduction it's that funky movement there it's lifting it off the flat surface that's retropulsion and we can see lots of tendons popping up on the back there so the movements are clueing us into what muscles are doing the movements right how makes your hand hurt that uh muscles okay so i think i think we should look at the the thenar eminence first so if you look at your hand at the base of your hand base of your thumb rather there's a nice rounded muscular mass that moves it gets thicker gets more you know gets tougher as you move your thumb around so the muscles in there are moving the thumb right hand right hand so this is what we're looking at here right hmm okay so here's there are actually a lot of little muscles here um and i can there's a couple of layers of muscle there i can take a muscle off right so what we've got here so there are four intrinsic muscles that move the thumb in hand and four extrinsic muscles that move the thumb that are in the forearm so this muscle here is running from here to here so it's out there so if that muscle contracts what movement do you think that's going to cause it's gonna cause that movement isn't it right so that movement there is abduction of the thumb and um i happen to know that of the muscles that abduct the thumb there is a long version and a short version and i also happen to know that the name for the thumb is the pollex so anything policies or police depending upon how you want to pronounce your seas refers to the thumb so this muscle here that is abducting the thumb is abductor policis brevis because there's a long one further away now the second muscle here so these are two separate little muscles this muscle here so it's it's in here if this muscle contracts how do you think it's going to move the thumb it's going to shorten on this side so it's going to pull the thumb that away and that is flexion of the thumb and again i happen to know that there is a short version and a long version of muscles that cause flexion of the thumb so this muscle is called flexor pollicis brevis the short flexor of the thumb all right now if we take these muscles off and we look at this muscle here which is deep to that then if you can see but these fibers kind of wrapping around that away this deeper muscle is going is the one that's also going to help rotate the thumb so this is opponent's policies there isn't a short one and a long one there's just one opponent's police so it just gets called opponents polices and that is going to help with opposition by rotating spinning these bones around here now these muscles are coming from the flexor retinaculum here which is which is the connective tissue tying down the tendons that are running to the fingers and that sort of thing and also from the trapezium and the scaphoid bones that are down here so they're starting from there and then they're running up to the base of the proximal phalanx or in the cane in the case of opponents pelysis they're running around the metacarpal bone here these muscles in the thenar eminence at the base of the thumb are innervated by the median nerve so long-term damage to the median nerve will cause wasting of this muscle belly group here and will of course affect movements of the thumb okay median nerve these guys there's another muscle here right let me put this muscle back on again so that's our thenar eminence those three muscles that we've just talked about and this was the muscle that i mentioned earlier see this here this is that when you abduct your thumb this full web space appears here and there's a muscle in there that's the muscle and this is adductor polycis or a dr polycus whatever you like but this is the only muscle that's going to adduct the thumb bring it back from an abducted position so there's no long and short just adductor policies and this is like all of these muscles of the hand around here it is innervated by the ulnar nerve so that's different right so you can test on the nerve function by you know testing the strength of that action so look these bones here are metacarpals metacarpal one two and three and adductor polycis is it's actually got two heads it's got an oblique head and a transverse head meaning it's got a couple of parts but it comes from metacarpals two and three and runs to the medial side of the base of the proximal phalanx of the thumb which makes complete sense because it's pulling here and it pulls the thumb back to there so you abduct the thumb at doctor pelysis and that that is the four intrinsic muscles of the hand okay that was probably the easy bit because now we need to look at the extrinsic muscles of the thumb down here let's do the easy one first so this is the anterior compartment of the forearm this is a flexor compartment that is the muscles are flexing the fingers and also the thumb as it would turn out so we've got one extrinsic muscle of the thumb here now so i've taken off the layers of muscles that are going to move the wrist and move the fingers although we can see here this muscle here is flexor digitorum profundus this is going to move the fingers you can see the tendons there but you see here all right see where we are so this is there's the radial pulse there this lovely big muscle here which is attached to the radius it's attached to the interosseous membrane there's like a membrane between the bones there right this is gonna send a tendon up through here to oh that's it there this is a big strong muscle yeah i'm a big fan of this muscle because i'm a rock climber this is when it pulls on the thumb it's also going to flex the thumb this is flexor pollicis longus this is the long muscle there's the short muscle there let's see how the tendons running around here how it's going to have the same sort of effect as that of flexopolysis brevis the reason i like this one climbing is most the time climbing you're doing this right you're crimping on things but then you get a pinch and you can yeah you can pinch something when you're pinching something you can now recruit flexor polycis longus nice big muscle you haven't been using it all your other muscles have been getting pretty tired this muscle feels like it feels fresh and you feel like you've got a good hold for a minute until then that muscle gets tired as well as well but you move on right so flexor pollicis longus this is in the anterior compartment of the forearm the muscles here are mostly innervated by the median nerve so flexopolysis longus is also innervated by the median nerve just like the muscles of the thenar eminence good now you know the back of your hand like the back of your hand right so look at the back of your hand you can see see some of those tendons already but now when you move the thumb around you can see these tendons here are moving around right so these tendons are pulling on the thumb and causing these movements we need to go back to our our rule of remembering the movement of the thumb so that we can then work out the name of the muscle i really struggle to remember the names of these tendons um there is i mean there's so this is the anatomical snuff box here it's an anatomical landmark because in there is the scaphoid bone so if somebody fractures the scaphoid bone and if you go poking in there and it hurts they probably practice the scaphoid bone but this is the anatomical snuff box formed by the borders of these tendons oh i think i've probably done a video on that as well so i have talked about these before okay the trick is uh there is one tendon here and there are two tendons here now look at the movements so i said that that is extension of the thumb right so flexion extension now when i extend the thumb both of those tendons are sticking up proud which means they're being they're being pulled on there are two extensor pollicis muscles here one of them is short and one of them is long this tendon here doesn't have far to go so this is the tendon of extensor pollicis brevis this muscle this tendon here is going to run around here has much more room to move to so it's a bigger muscle a longer muscle so this is the tendon of extensor pollicis longus yeah makes sense right so look when you extend the thumb both of those tendons appear but if that's extension of the thumb right extension of the thumb extension of the thumb um that is abduction of the thumb isn't it so when i when i abduct the thumb let me see how those tendons are moving only this tendon there's a there is another tendon here so neither of those two extensor tendons are pulling to cause abduction of the thumb but there is and i can feel it there is a tendon under tension here so this will be abductor policis and we saw an abductor policies brevis muscle in here so this tendon is going to be abductor polycis longus that's the method and when students challenge me i will struggle to remember all of that and have to go and look at an illustration in a textbook but that's all right so extension of the thumb those two tendons abduction of the thumb only this tendon is now active let's have a look on the model wow so these are the extensor muscles and tendons of the fingers and the wrist can't take those off but look as we spin around whoa so we can see these tendons here running from the thumb to these two muscles here look that's yeah so we've got these two tendons here i said we have two tens on on this side and a single tendon on this side that's our anatomical snuff box so then this tendon here is extending the thumb and it's running around here so now it's see the tendon runs down here but it's deep to these muscles so we can't see it but that muscle is coming from the bones down here and that is extensor polycis longus that's the long one because there's more room for it and look can you see how this tendon is attached here and its origin is actually it's going all the way over here it's going um so it's attached to the posterior parts of the the ulna bone and that interosseous membrane that runs between the two bones extensor pulleysis longus so then this tendon here when i extend my thumb we can see both of those tendons so that's that tendon there is this tendon here and again look its insertion is into the base of the proximal phalanx of the thumb this is the extensor pullisys brevis it's already looking like a smaller muscle it's got less room to move into and that's going to be attached to the radius bone which is on this side and that interosseous membrane as well probably but look you can see these two muscles are quite close together right this muscle here this is running from both the ulna and the radius posterior on the posterior surfaces back here and the interosseous membrane and this muscle is sending a tendon now where does the tendon go oh it only goes that far so this is the base of the metacarpal bone of the thumb so that tendon is actually only going that far which is what explains some of the change of shapes that we see here so down here we've actually got the two tendons and remember so that's extension that's abduction so that tendon is abducting the thumb so that is uh this tendon and muscle here are abductor pollicis longus one two three four those are the four extrinsic muscles of the thumb now these muscles are in the posterior compartment of the forearm the nerve of the posterior compartment of the forearm is the radius nerve so these muscles are innervated by the radius nerve all right what do you think the thumb is called the pollux the muscles that move the thumb are called something pullisus the movements of the thumb give names to the muscles that move the thumb there are four muscles intrinsic to the hand three of them are in the thenar eminence and are innovated by the median nerve one of them is innervated by the ulnar nerve like the other muscles of the hand and we have four extrinsic more powerful muscles of the thumb one of which is in the anterior compartment of the forearm and is innervated by the median nerve three of which are in the posterior compartment of the forearm and are innervated by the radial nerve yes there's a lot going on there but the thumb is pretty important to us humans right it's a you know it's pretty important so those muscles are also important which means that damage to a nerve can lead to loss of function of the thumb but which function with that knowledge you can work it out oh the thumb haha okay that'll do see you next week [Music] [Applause] [Music]