DIP Episode 148 - The Why’s of Anatomy For The USMLE Step 1 (Upper Limbs 2, Brachial Plexus)

Okay, welcome. My name is Divine. I am a resident. This is episode 148 of the Divine Intervention Podcast. And in this podcast, I'll be covering again, I'll be continuing my series that I entitled the Wies of Anatomy. Okay, for the USM in step one. This is going to talk about the upper limbs as well. This will be the second part of the upper limbs talk. And again, I'll be focusing on the brickelplexes because really, so we're perfectly honest. The only thing they essentially test on the USM in use with regards to the upper extremities and like muscles and innervation and all that crap is all from a brickelplex perspective. And again, if you're a person in a med school anatomy course, I really do think that these two parts, like these Wies of Anatomy podcasts will help you tremendously, tremendously because the thing is I explain anatomy, but I also kind of try to explain the mechanisms of anatomy. So you're not just again memorizing a ton of stuff. You're actually like, you know, actually like learning information pretty well. And the thing is again, like everything in med school, if you focus on understanding, the memorization is super easy. Like if for example, like I hopefully pounded into your heads from the first Wies of Anatomy podcast, if you if you really, really, really, really get the material from the first podcast into your head, then this podcast is going to be a joke. Essentially, it's going to be pretty easy.

Yes, there's going to be a lot more detail in this podcast, but that lot more detail is it like I promise you, like it's not that hard to remember if you understand what I talked about in in a podcast one. So let's jump right into it. So the first thing I will have to say is I'll have to, you know, make my apologies. Last time I kept saying Lombra calls to do five Lombra calls to do five Lombra calls to do five. The thing is most resources seem to refer to the Lombra calls to do five insiders Lombra calls one to four. So purposes of exams, I think I will encourage you to go with Lombra calls one two three and four as being representative of digits two three four and five. Okay, I'll say it again. Lombra calls one two three and four as being representative of digits two three four and five. Okay. And I guess let me also maybe go ahead and talk about the Lombra calls right now. Just go ahead talk about the Lombra calls. Give them out of the way so that we don't have to worry about them anymore. Because I have some heavy stuff. I need to get off my chest today. So basically, right, the Lombra calls essentially what they do is that they flex the MC Ps right so like your metacopal, phallanjo joints, but they extend your IP joints, they extend your interphallanjo joints. It's almost like making your hand into an in what facing are. I mean like if you look at any wrap video, rappers tend to use the Lombra calls a ton. And the thing is the Lombra calls for digits two and three.

Those actually in a video by the median nerve, but the Lombra calls for digits four and five actually in a video by the owner nerve. And again, it should make sense right. If you're looking at a person's hand, the median nerve runs in the lateral side. I guess you can see the radial side. If you're standing in the anatomic position, the owner of runs runs on the medial side. Okay. So just something to sort of you know keep at the back of your mind for example. So the thing is if you injured the Lombra calls right, your fingers would essentially be held in the reverse function of what the Lombra calls do. Right. So your fingers would kind of like be extended at the MC Ps or the metacapal phallanjo joints. And they'll be extended. I mean yeah, they'll be extended at the MC Ps and they'll be flexed at the IP joints. Remember your IP joints include your PI Ps and the I Ps. Okay. That's essentially what's known as a claw hand. Right. So if you notice that digits two and three are clawed, then that's a median claw. Right. Because again, that's on the radial side of the hand. If you notice that digits four and five are clawed, then that's an owner claw. Right. Again, it's pretty simple. And these are things you have really observed at rest. You don't need to tell the parents do anything to observe these are movements. They have things that you literally observe at observe at rest. But actually think about it. What if you lose all your Lombra calls like you're like a total claw. Right.

Obviously there's a terrible terrible situation for the patient. What kind of injury can do something like this? I mean, if you think about it, right, you have to be some kind of lower trunk injury, right? Well, to be some kind of a lower trunk injury like C8 T1. Because if you think about it, actually all the intrinsic muscles of the hand, of which the Lombra calls actually one of them, they actually are rated by C8 T1. So essentially the lower trunk of the brachial plexus. So if you want to kind of stretch this because again, remember last time I said that C8 T1 is owner nerve, but C5 to T1 is median nerve. Okay. So again, you can see why that overlap exists where oh, Lombra calls one and two, I killed off if you have a C8 T1 injury and Lombra calls three and four, I also killed off if you have a C8 T1 injury. Right. And I mean, if you want to stretch this a little further, right, if you again, injure C8 T1, you will again, nuke all intrinsic muscles of the hand, right? So like your Lombra calls, your thinner muscles, so think about your thumb, your hypothenom muscles, think about your pinky, and also your interosseous muscles, you will nuke all those muscles if you have a C8 T1 injury. Since, I mean, if you think about it, right, C8 T1 injury kills off all of the owner nerve. You will also lose like sensation on the dorsal and parmer surfaces of your medial one and a half digits of the hand, right? Remember we talked about that last time. And you may say, okay, divine.

What can, what can, you know, what can screw up my, my, what can screw up the lower trunk of the brichial plexus? What can screw up the lower trunk of the brichial plexus? If you really think about it, you can actually screw it up if you, you know, have like, let's say like the classic video tested on exempts is, you'll talk about a person that is trying to grab a tree trunk in the process of like breaking a fall or sometimes, although this is more like something you'll learn in like a pulmonary block in medical school, where a person will have, you know, like, like something called like thoracic outlet syndrome or like a cervical rib. These are essentially like things that can happen and sort of compress the lower trunk of the brichial plexus when the lower trunk is exiting the neck, okay? Now, we've talked about lower trunk injury, right? Sometimes you may want to see like a kind of a lower trunk injury called I mean, another common like lower trunk injury, like clunky spalsy, like clunky spuralysis, so KLU MPKE, right? So clunky spuralysis, so I guess that's something you can keep at the back of your mind. But again, let's talk about the upper trunk, right? So upper trunk injury, that's like C5 C6, it's called a herbs, so ERB, like herbs palsy, some people call it herbs, do shame palsy, it's one of the same thing. If you kind of remember the gradient I talked about from last time, right?

Because again, remember I told you that the brichial plexus is C5 to T1 and I told you that C5 C6, you know, does essentially everything at the shoulder, but C8 T1 does essentially everything in the hand. You can see why, if a person has like clunky spuralysis and all that, they have like mostly hand problems, but if a person has like herb to shame palsy, they'll have mostly like shoulder problems. Again, that gradient I mentioned and I talked about it in the first podcast, so encouraging go back and listen to that. So all the proximal muscles are your shoulder, okay? They will essentially die if you have an upper trunk, I mean not die, but they'll be paralyzed, I mean if you have like upper trunk injury, right? From like a dinner vision, right? So what are the big ones there? Kind of like your deltoids, your titer cough, your teris major, right? And the thing is there are multiple functions that are held by these muscles, but to be perfectly honest with you, the big ones you're probably need to remember for essentially every exam you take, remember this a numonic called a saber, so like S-A-B-E-R, the saber numonic, what do I mean by the saber numonic, right? So your shoulder muscles, that's the S, participate in abduction, A Bduction, so that's the AB in saber, and then they also help with external rotation of the shoulder, right? So that's the E-R, so remember saber. So basically if you scrub C5, C6, you'll effectively lose abduction, right?

Your deltoids are knocked out, you lose external rotation, right? And also maybe to I guess maybe maybe a little more complicate here, you also lose sensation on the lateral arm and on the lateral forearm, right? Remember lateral arm sensation is controlled by the axillary nerve, lateral forearm sensation is controlled by the muscular cutaneous nerve, right? And again, this should be hopefully a easy to remember based on what I discussed last time, right? And essentially if you take this cluster of findings where you've lost abduction, so A Bduction, and you've lost external rotation, then that means that your arm will be abducted, so it will be AD ducted, like Anthony Davis, AD ducted, you can probably tell at this point of the leaker's fan, so your arm will be AD ducted and you'll be internally rotated, right? That's something actually called the witters tip sign, right? Classically the things that cause this on exams will be things like birth trauma, right? So like for example, like it's an infant of a diabetic mom and the baby is like huge, like a 10 pound, 11 pound baby, getting that baby out, you have to do some of these weird maneuvers that is done in your learn on an OB-GYN rotation. Those maneuvers tend to separate the head from the shoulder, so that forceful separation of the head from the shoulder and the process of birth trauma can cause an upper trunk injury. And for the most part it results, I mean they will do like some stretch and exercise, but it gets better.

I mean if you have to choose between the baby dying and you know the baby having a witters tip deformity that will result within a few weeks, two months, I think most mothers tend to make the other choice. Okay, so kind of like going to a last time, right? So last time I said that in this podcast we will do something where it's almost like organic synthesis, where we then instead of looking at all from the concept of the nerve, we'll start saying, okay, what is the injury and mechanism of injury to a nerve, like how will it present clinically? Because ultimately that's what matters for for example. The good thing is again, these are fairly easy to remember. If you again, I'm telling you, I promise you if you listen to this podcast, listen to podcast one, it's worth it. It's a 30-35 minute podcast, but it will make all the difference for you. I promise you, I promise you. And really if you know what I talk about today, what I talked about in podcast one, you'll be like a brickel plexus and I guess opera extremity, muscle and innervation like master. Like if you're learning really well from these two podcasts, like all these things will just be like cemented in your brain. So again, listen to podcasts, when you'll meet this podcast, the joke, it'll make you super easy. But before I jump further into this podcast, I want to go ahead and talk about three rules.

There are three rules that I want to introduce here that can make your life profoundly easy with the opera extremities, especially with hand muscles. So, rule number one is that for every muscle that has brevis in the knee, there is also a muscle that has longest in the knee. You'll see why this is important as we proceed further. For every muscle that's called a brevis, there is also a muscle called a longest. And as a rough approximation, most of those brevis muscles start in the hand, remember like brevis like brief, something as brief, it means it's short versus the longest, right? So the longest muscles, they tend to, you know, start in the in the forearm, right? So they're long, that's why they are called longest muscles. Believe it or not, this rule also works for the lower extremities, more lower extremities. That's a different podcast. Hopefully I'll meet those podcasts sometime this week, time permitting. So, if you remember this rule, it'll make your life super easy with a hand muscles. And then rule number two, right, is that for every digit of your, like every, like digit you have, like your fingers, essentially, there are two flexors for every digit, okay? And really, if you think about it, I sort of divided the digits of the hand into three groups. There's your thumb, right? There's digits two and three, right? Which are, yeah, there's digits two and three.

So like your index finger, your middle finger, you know, the finger used to do signs that are not like socially appropriate. And then there is your ring finger, so like digits four, and your pinky digit five. So three groups of fingers in the hand, in the hand, there's your thumb, right? There's digits two and three, and then there's digits four and five. Now, the thing is, again, for each of those groups, you have two flexors, okay? You have two flexors. For the thumb, the flexors have like brevis and longest in the names. I'll talk about those later. You can probably already predict what those names should be. Policus, whenever you say the word policus, it means thumb. So you can already imagine that, oh, it will be flexor, policus, brevis and flexor, policus, longest. But again, I'll talk about that later. So for your thumb, the two groups of flexors, we have the brevis flexor, we have the longest flexor. For digits two and three, we have the superficialis and the profondis, okay? I'll say that again. For digits two and three, we have the superficialis and the profondis. For digit four and five, it's also the same deal. We have the superficialis and the profondis. So some of you may say, oh, the one, come on, now why are you repeating yourself twice? I promise, I don't like repeating myself for the fun of it. I like to receive my words. But the thing is, flexor digital and profondis has for digit two and three actually gets integrated by the median nerve.

But flexor digital profondis for digits four and five is actually integrated by the owner nerve, okay? So that's something that's actually very high yield to know for exams. So the thing is, for the flexor, so with that said, for the flexor of a particular digit to die, you need to knock out both flexors. If you knock out only one, the other one will take take up the rates, okay? And you'll start controlling those movements. That's something that's extremely important to know, okay? To have total paralysis of flexion of a digit, you need to get rid of both flexors, okay? So you can already see why sometimes in a median nerve injury, a person may not necessarily lose flexion of a digit. Maybe the flexor, maybe in a little week, but you will not have paralysis of a flexion. Again, this is a critical route to understand. And then the final route, which is, which actually kind of makes a lot of sense, is that whenever you have more proximal defects in a nerve, you will tend to have more issues. But if you have more distal injury, like if you injure a nerve like, let's say in the forearm or whatever, you obviously have a lot less in the way of, like a clinical presentation, and if you injure that nerve like in the arm, okay? Because if you injure the arm, you've given off less nerves, so you get more deficits. But if you're lesioning the elbow, for example, you'll, you'll, you'll get fewer deficits, right? Because again, more nerves have been given off already.

So hopefully, you understand these rooms. Again, if you, I promise you, like they're very, very, very, really, do I promise people things. Actually, I take that back. I do promise people a lot because I work with a ton of people. But if you really pay attention, you understand this podcast and podcast one again, Brickial Plexus, Junk, okay? Hopefully, that's like literally my goal in making these podcasts. And not just for like a med school course, but unfortunately, this stuff is tested on step one, is tested on the surgery shelf exam, is tested on the medicine shelf exam, is tested on step two, CK, is tested on step three. So just one of these things you want to learn well, if you're just want to for the rest of your test taking career in medicine. And I guess kind of also depending on the field, you're going to. So for example, right? So let's begin to get after these nerve, right? So let's, as you know, you get a question about a person that cannot ab docked, the arm at the shorter joint, right? Or you can see on the exam, they can call it the Glenoghimo or the person like Luzzi sensation on the lateral arm, right? What's the nerve that's gone? I hope you're saying Accelerator. Right? So how can you injure the Accelerator? You can injure the Accelerator. Remember, Accelerator those are your deltoids and your Terry Salminer. Remember the security company, Ed, that we talked about last time. So how can you injure the Accelerator?

Well, you can injure the Accelerator if you have like dislocation of the shoulder. And you want to be careful, you anterior dislocation of the shoulder is what can injure the Accelerator. You see that is match Accelerator and Terrier shoulder dislocation. Posture shoulder dislocation does not do squat to your Accelerator. Usually on exams, on NVME exams posture shoulder dislocations tend to be caused by electric problems. What are mean by electric problems? Like literally getting electrocuted or if you have like a seizure, that's kind of like an electrical problem in the brain or if a person gets struck by lightning, that we're almost always caused posture shoulder dislocations on NVME exams. So an anterior shoulder dislocation, screws of the Accelerator. If you also have a fracture of a part of the humor is called the surgical neck, a surgical neck fracture of the humor that's kind of like the upper shaft area of the humor. So that will also cause Accelerator injury. The next nerve I will jump to is the Mosulocutinius nerve. So Mosulocutinius nerve, the classic video tests on exam as they can say, oh, a person has problems flexing the elbow, right? And then they'll tell you that, oh, this person has lost sensation on the lateral forearm or this person has like issues with a supination. If you see that, I really want you to think about a Mosulocutinius nerve injury.

The thing is, Mosulocutinius nerve injury is very, very tested on exams because it's super hard for this to be injured or clinically, right? So it really doesn't pop up a ton of exams. Now, the next big nerve I will go to is the radion nerve. Right? The radion nerve is a very, very, very high old nerve to nerve. Right? And the thing is the radion nerve, you know, it's a little more complicated than axillary or, or, um, moxulocutinius, right? The thing is the radion nerve itself, I'll encourage you and you'll see what I mean by this. I will encourage you if you're trying to learn the radion nerve, just sort of draw a flow chart. Because the thing is the radion nerve is in, like, presents, like, in a fairly different means if you enjoy that certain parts along the upper extremity. Right? So there are like classic things that you can get if you enjoy the radion nerve at the shoulder, at the wrist, at the elbow, bloody, bloody, black. Right? And I'll talk about all those different stations, right? So I'll encourage you to learn, to sort of build a flow chart. So you may see, oh, divine flow chart. That sounds like a ton to memorize. I promise you it's not that much and I'll give you a trick for remembering most of these things. So again, the radion nerve, it's a complicated nerve, has a very long course, right? So there's kind of like more risk, there are like more spot-rate can be injured in the upper extremities.

So again, you want to, again, know how proximity levels of, of injury, right? And to be honest with you, the one thing I would say that would really help you on tests is that kind of like a good starting point to tell you that, okay, radion nerve is all screwed up is if a person has risked drop, okay? If a person has risked drop, if you see a risked drop in any exam question, you know that the person has radion nerve injury because the thing is a risked drop is the most distal, pure, modal, radion nerve function, okay? So once you see a risked drop, you know that, okay, it's a radion nerve and then after that you just have to essentially work your way upwards, right? So again, once you see risked drop, right? Because remember, your radion nerve deals with extension and again, that should make perfect sense because I talked about the radion nerve doing like posterior compartment stuff and I talked about the mechanism behind why the radion nerve does the posterior compartment stuff in the first podcast. So again, once you see like risked drop because you've lost the risk extension, think about radion nerve injury. That's like your radion nerve injury alert. And then the extra deficits that they describe in the question stem will tell you exactly where, okay? Obviously, the more proximal the defect, right? So like an earlier part of the upper extremity, the larger the number of issues and vice and vice versa. So what if we injured the radion nerve at the axilla, right?

So radion nerve at the axilla, right? So like again, five dollar word for armpit, you lose a ton of stuff, right? This is obviously the bad, bad, bad radion nerve injury. You lose a ton of stuff, right? So you lose your elbow extension, wrist extension, digit extension, all those things will be gone, okay? And again, extensor, posterior compartment, radion nerve. I've talked about all these mechanisms in podcast one. And you also have problems, excuse me, you also have problems with like supination, right? And you also lose like sensation on your posterior forearm and hand, okay? And really the mechanisms, right? So what can cause this kind of injury? If remember, the radion nerve actually kind of runs through the floor of the axilla, right? So if for example, a person has, I don't know, let's say a person has like a crutch injury, so crutch, right? I don't mean like, you know, crutch, like crutch and average remedies. Let's say a person has like, you know, they have some kind of injury and they need like crutches for a while. That crutch, if they put it like right under the axilla, right? They continuously compress the radion nerve that can cause a lot of problems, right? That's why I want to use your crutches properly so you don't get into trouble. Okay. On the other hand, right? There is this thing called a Saturday night policy, right? Saturday night policy. Basically, that just happens where, you know, you drink, you know, too much booze, right?

So you fall asleep at the bar, you sort of put your axilla over like the hard part of like a chair, that again will compress the axilla, the radion nerve right in the floor of the axilla and that can cause injury. Okay. So again, you lose again, extension of everything in your prick extremities, elbows, wrists, digits, the all gone. So penition is gone, sensation on your posterior forearm and hand will be gone. But what if you injured the rion nerve at the arm? So notice, the first one was the axilla, that's the arm. At the arm, right? You should expect to see fewer findings, right? You should expect to see fewer findings because this is a more distal kind of injury. And remember, I said that for the radion nerve try to make a flow chart. The thing I tell people is, especially people that I tell people, learn all the radion nerve deficits at the axilla since that's the most proximal you have the most deficits. And then just learn the deficits that drop off along the way as you go more distal in the upper extremities. It just makes your life so much easier. Again, we want to rule, there's this podcast I made I think like a couple months ago, if you look back on the website, you'll find it. I talk about like how to study like the central dogma, I think I call the podcast like the central dogma of learning. One of the principles I talk about in that podcast is you want to learn the least amount of information to control the most amount of knowledge.

Because and this is that principle is especially useful when you have like you know like a course that you're teaching or you're in a body like a field that demands no inner crap ton of stuff like Met School for example, and the way you can learn the least amount of information to control the most amount of knowledge is to try to be as conceptual as possible and what you're trying to learn. So distal injuries cause fewer deficits right so proximal injuries cause the most deficits. So learn all the deficits you get with injury to the radio nerve at the axilla and then just remember the things that drop off with more distal injuries. Again, really cost down on your memorization. So basically if you injure the radio nerve at the arm, you lose all the deficits I've talked about for the axilla, but your elbow extension will be intact. Your elbow extension will be intact because actually most of the functions of the triceps is actually given off in the axilla. And really how can you injure the radio nerve in the arm? You can do this if you like fracture the mid shaft of the humors. The thing is there's a part of the mid shaft of the humors called the spiral groove. The spiral groove of the radio nerve actually runs runs within it. So again, that's a high u thing to know for for exams. And then if you injure the radio nerve at the elbow again, the deficits will be everything I've talked about like for the axilla, but your elbow and wrist extension will be intact.

Your elbow and your wrist extension will be intact. And again, how can you injure the radio nerve at the elbow? This can happen if you you know fracture the radio head. So like a fracture of the radio head or if you dislocates the radio head, that can also again impinge on the radio nerve and then you get into trouble. And then if you're looking at like radio nerve injury of the wrist, really this one is super easy to remember. Essentially what happens is the only deficit you have is you lose sensation on the posterior hand. If you lose sensation on the posterior hand, okay, like the lateral like remember from last from the first podcast I talked about this middle of the fourth digiadena big big big time advisor. If you're trying to learn sensory novice of the sensory novice of the hand, right? So if you lose sensation on the posterior hand, right, like the lateral or you can see the radio thread and half parts of thread and half digits, right? That's that's a that's a re-earner of injury of the wrist. Everything else re-earner of wise is fine. And really the big mechanism here is if you have like a laceration on the dorsum of the hand, right? So you can see the one who will last read the dorsum of the hands. Classicly on MBMI exams these are people by polar disorder, right? So if you see a bipolar disorder question and the person lacerates the dorsum of the hands. So dorsum is like the side of your hand that is not the Palmer surface, okay?

That's that's a that's a re-earner of injury. As you'll see later if you'll last read the the ventrum of your hands, you actually so like your Palmer surface that's a different kind of injury. But again, it's something that can also happen in people with bipolar disorder. Now the thing is for the median nerve, the big thing I think I'll talk about is just because this is essentially how they always test median nerve. Median nerve, you want to learn it from like two spots, right? Like injury of the wrist, injury of the elbow, okay? Injure of the wrist, injury of the elbow. And the thing is before I leave the re-earner of I guess let me give you a numonic that may help. And there's this numonic that I learned to like, I don't know, like this was this was a long time ago like 2014. Just kind of dropped in my mind. I know I've created somewhere. I'm trying to remember where. When I learned that the re-earner is the best nerve, right? The re-earner is the best nerve. And best, right? Just tells you that you know, like you extensors, that's the E, your supination, and your triceps, right? Those are controlled by your re-earner. So that's I guess re-earner best nerve that may also help you there. So again, re-earner best nerve. I don't know if I'm forgetting what the B stands for. Come on, divine think. Oh, the B is actually the brachioridialis, yep. Brachioridialis has radialis in the name brachioridialis, right?

So like re-earner best nerve, B brachioridialis, E extensors, S supination, T triceps, right? Again, not that heart, not that heart, not that heart. Okay, so let's talk about what happens if you injure the median nerve at the wrist, right? Remember last time I said that if you injure the median nerve at the wrist, right, you have a lot of like hand problems, right? Although remember I said that the primary innervator of the hand is the owner nerve, right? But again, there are some exceptions that going to median nerve at territory, right? So people that have median nerve injury at the wrist, they obviously have like flattening of the thinner eminence, right? So they have like thinner flattening and they'll have paralysis of all their thinner muscles, right? So what can cause this kind of problem? You'll be an issue like like covered tonic syndrome, right? So if you have like chronic median nerve injury, right? You have like flattening of the thinner eminence, you have paralysis. The reason you have the flattening right is because your thinner muscles have essentially atrophied. I'll talk about those thinner muscles in a second. But if for example you just notice that you know, presence thinner muscles, you know, they're just paralyzed, they're not necessarily flat. And that means enough time has not expired for those things to flatten, right? And if they've not flattened, then that tells you that, okay, this is likely not chronic injury.

So that, so this flattening, you know, like like what in the world are you talking about with regards to like flattening of the thinner eminence? Well, here's what I mean. What I mean is that your three thinner muscles, the other things that make up that bulge, right? That's right beneath your thumb, okay? So they have three big large muscles, right? And those muscles, the way I remember them is I remember them as an opponent first aid. First aid is this book as a med student that you know, you have to commit to memory at some point. It's like an 800 page, a big month that you have to memorize at some point. But as you go through your first two years, you should be learning all the different parts now. We help you remember all that, all that stuff, right? So opponent first aid. So the opponent stands for opponent's polycus, okay? And then the first aid, the F.A stands for like flexor polycus brevis. And then the A stands for AB doctor, abductor, polycus brevis, okay? So again, if you have the chronic denervation of those muscles, you have flattening because those muscles actually feel, okay? So some may say, oh, so divine. Are you seeing that if you injure the median nerve at the wrist, flexion and thumb abduction will be gone? No, unfortunately, okay? So here's why, here's why. So that's why I went over all those rows in the beginning. Remember I said that for every longest, there's a brevis, right? For every longest, there's a brevis.

And if you notice, I just said that the thinner muscles, we have opponent's polycus, we have flexor polycus brevis. And we have flexor, I mean, we have abductor polycus brevis, right? So the thing is, if there's a flexor polycus brevis, well, guess what? He tells you that they should be such a thin as flexor polycus longus, okay? And they should also be such a thin as abductor polycus longus, okay? So flexor polycus brevis, abductor polycus brevis means they should also be a flexor polycus longus and then abductor polycus longus, right? So the thing is, if you injure the median nerve, flexor polycus longus and abductor polycus longus will take over it, okay? If you injure the median nerve at the wrist. So the only thumb function that will be leftist opposition, I mean, if you can notice, right? Opponence polycus, there is no term like, oh, opponents polycus, there is no such thing as up opponents polycus brevis, or opponents polycus longus, there is only one opponent's polycus, okay? So these things don't have like, opponents polycus doesn't have brevis in the name, right? So you will actually lose thumb opposition, you actually lose thumb opposition when you have a median nerve injury at the wrist. So your thumb will essentially be on a post and that's something called a pen. The thing is, if you look at apes, if you look at them at rest, they have like a certain configuration of their fingers of their thumb, especially that's why the phenomenon is called a pen.

Since this is a podcast, I'll encourage you to kind of look at pictures of this online and again, your median nerve does the number goes one and two, right? So you have like a median clock, I already talked about that earlier. And again, you lose sensation on the Palmer surfaces of the first, you know, the first three and a half digits, right? So your thumb, your index finger, your middle finger, okay? I remember again that middle of the fourth finger device, or I talked about from the first podcast. Remember though, again, very important thing to mention, I mentioned it at the end of the first podcast. Remember, those people will not have a loss of sensation like over like the actual palms. It's their fingers that will lose sensation, not the palm. So remember, the palm of cutaneous branch of the median nerve is given off before the median nerve traverses the the coupled tunnel. And you may say, okay, divine. How can I injure the median nerve at the rest? Well, coupled tunnel syndrome already talked about that. But if you, you know, last rate the the the rest on the Palmer surface, right? The ventral surface that will cause those kinds of problems as well. Okay, remember, if you if you last rate the risk at the dose of surface on the dorsum, that'll be radion nerve injury. If you last rate the risk at the ventrum, that'll be that'll be median nerve injury. So now, what if we injure the median nerve at the elbow, right? At the elbow, right?

So obviously, this is a more proximal problem, right? So you would have a ton of a ton of things, right? So and for this part, I will say a lot of stuff, but the a lot of stuff I'm saying is just explaining mechanisms, not necessarily adding like an extra ton of knowledge to you, right? So the thing is, how do I put this? Come on, divine think. Okay, let me present it this way, right? So again, try to memorization, right? Essentially, if you have like median nerve injury at the elbow, you lose everything that I talked about with median nerve injury at the wrist. So just learn the stuff that's added on, right? Because again, at the elbow, that's more proximal injury. So you should have more deficits. So one thing you'll classically observe when people injure the median nerve at the elbow is when those people try to flex the wrists and behave on our deviation. This actually happens, right? Because flexocopular idealis has been eliminated, right? So flexocopy on our wrist is working on our post. So some of you may see divine. Come on. You're saying that flexocopular idealis is killed when you have median nerve injury at the elbow. Here's the thing. Before you go off on me, just think about this for a second. Go back to podcast one I said. Remember, look at the name flexocopy radialis. It's a flexor. Well, guess what? All flexors in the upper extremities are anterior compartment muscles, right?

So the radion nerve cannot touch any of this because the radion nerve does stuff only in the posterior compartment. I really hope you see why those principles I talked about in the first podcast are like very critical. They're very, very critical. You know, I really encourage you to listen to a podcast one. The reason it's called flexocopy radialis is because the muscle just runs on the radial side or you can see the lateral side of the forearm, okay? So that's why it's called flexocopy radialis. But again, because it's a flexor, it's an anterior compartment muscle on the lateral side of the upper extremity. So it has to be done but innovated by the median nerve. Again, I really encourage you to go back listen to podcasts when you make your life profoundly easier. Really, this podcast is a joke if you know podcasts one really well. Again, anatomy is not, don't get me wrong, anatomy is hard, right? But anatomy is not as hard as people make it out to be. People think it is, right? So I guess let's keep going. Let me get off my soapbox and let's keep going. So you have like again, like I said, you have owner deviation of the rest because flexocopy radialis is out of commission. Flexocopy on iris is working on a post. You will also lose a flexion of the digits. And again, remember for your digits, remember I broke them up into three groups. I talked about this earlier but I'm going to read it again. Repetition always helps. The thing is for your digits, right?

Again, there are three groups and again, remember if we're looking at the digits 2 to 5, right? So flexor, digital, superficial, right? Does flexion of digits 2 through 5 flexor, digital and profoundness does, like I guess like you can see like the radio or the lateral half, right? Of those, like those four digits other than your thumb, right? So essentially like digits 2 and 3, right? And again, please don't forget, remember I've kind of hushed this so many times already. Flexor, digital and profoundness, right? For digits 4 and 5 is in the territory of the owner nerve. So let me back up. Let me repeat this again. Flexor, digital and superficialis, right? Does digits 2, 3, 4 and 5? All of flexor, digital and superficialis gets innervation from the median nerve. But flexor, digital and profoundness is different. Flexor, digital term profoundness for digits 2 and 3, right? So like your index finger and your middle finger is innervited by the median nerve, right? And that should make sense because the median nerve is the radio, the lateral side of your hand. But flexor, digital term profoundness for digits 4 and 5 is owner nerve because again, the owner nerve runs on the owner surface of your upper extremity. So you should essentially be able to add on the knowledge that if a person injures the median nerve at the elbow, some flexion will be lost because flexor polycos bravis, right?

Remember, I told you that if you injure the median nerve at the wrist, flexor polycos bravis will be gone. But the thing is flexor polycos longus is also innervated by the median nerve, right? But again, it's long, so it's giving up in the forearm, right? Again, remember that rule? I talked about earlier. That's why those rows are so important, okay? Flexor polycos longus is given off in the forearm. So by, and remember, I said that for every digit of your hand, you have two flexors. So by killing the median nerve in the, in the elbow, you've killed flexor polycos longus, that's the long one, and flexor polycos bravis, that's the brief one, right? So you've knocked off both flexors of the thumb, okay? So you have a more proximal, from this more proximal injury, you've lost, you lose thumb flexion in addition to losing thumb opposition, okay? Very, very important to understand. So again, let me summarize all these things. Well, I guess, yeah, let me, let me summarize all these things because the thing is exam riders, right? They like to see if you can differentiate between median nerve injury at the wrist versus the elbow by knowing if thumb flexion is lost, okay? By knowing if thumb flexion is lost. If you lose thumb flexion, that tells you that the median nerve has been injured at the elbow. If you don't lose, so if you lose thumb flexion and opposition, median nerve has been lesion at the elbow. If you lose only thumb opposition, median nerve has been lesion at the wrist.

Again, this is floridly high you to know for for exams. And again, I've repeated this, diagnosing repeated this multiple times again. Flexor due to term perfundus, it does digits two and three, and also does digits four and five, FDP for digits two and three is median nerve, FDP for digits four and five is oner nerve, right? So if you injure the median nerve at the elbow, you lose flexion of digits two and three, right? Because again, both flexors will be gone, right? Like flexor due to term perfundus for the median nerve is gone, right? But flexor due to term superficial is will also be gone. Because remember the flexor due to term superficial is for all four digits besides your thumb is all median nerve, okay? But you will not have any issues with digits four and five because yes, flexor due to term superficial is will be gone. But flexor due to term perfundus for the oner nerve is alive and well, okay? So again, this is super, super high you again, I'm going to repeat it again because this is stuff is just way, way, way, way too high yield to know for exams, right? So let's summarize the flexors. If you injure the median nerve distally at the wrist, you will not cause any flexion issues, right? But if you injure the median nerve more proximally at the elbow, you will cause trouble with the thumb, right? Because flexor polytas longis and flexor polytas bravis will both be gone.

But you also have flexion problems with digits two and three because flexor digit terms superficial is and the median contribution to the flexor digit term perfundus right which does digits two and through will also be gone, okay? So if you tell these patients to make a fist, they will only be able to flex digits four and five. So you have something called the hand of benediction, okay? It's not something you will observe at the wrist, it'll be something you observe where you tell the patient to do something active like make a fist, okay? And you may say, okay, divine, how can I injure the median nerve at the elbow? Really the way you can injure the median nerve at the elbow is if you like fracture like the superconduille humerus, the superconduille humerus is like the most one of the more distal parts of the hemerus. So if you have like a superconduille fracture of the humerus, that will kill the median nerve at the elbow. Again, these are all high-eal things to know for exams. Okay, now let's jump to the on and earth and then we're done, right? We're done. So your on and earth really on and earth injury at the wrist, really the kind of the ways you'll this will present, right? Like the person will have like problems like AB ducting and AD ducting the digits, right? Because the interosseous muscles will be gone. Remember I talked about that last time, your hypothyneur muscles will also be gone, right? So hypothyneur, right? Hypothyneur, you're pinkies, right?

And you'll also like loose sensation on like the dorsum and the parma surfaces of your pinky and the middle and also like the you know like the mom medial side of digit four. You can remember from podcasts one that divisor, digit four. Remember I kind of talked about that and you also lose like lumbarcos 3 and 4. So you'll get an owner claw. Again, I've talked about all this, I talked about this early in the podcast. So you may say, oh, define how can I injure the owner of the wrist? That's actually kind of easy. You can have like trauma to the wrist. So like because actually actually like you know like blunt loss trauma to the wrist can actually scrub the owner nerve because the owner is actually superficial to the capital tunnel. Okay. And another high old one and I'll talk about these bones in another podcast because I feel like this podcast is kind of going along on and try to hopefully keep things below like 50 minutes. But if you fracture the hook of the hammock, now also destroy your owner nerve. Okay. A fracture of the hook of the hammock will also destroy the owner nerve. Now, owner of injury at the upper again, this shouldn't be that hard. Okay. Essentially everything from owner of the wrist plus some other stuff. Right. The thing is people that injure the owner of the elbow, right. If they try to flex their wrists, their forearms will deviate radially. Right. Again, this is just a corollary from when I talked about the median nerve.

The reasons that the reason that their forearms will deviate radially is because flexo-capillonaris will be gone, is taken out of commission. Well, flexo-capillonaris is intact. Remember flexo-capillonaris is interviewed by the median nerve. Okay. So please don't mix this up. If you flex the wrist and you have radio forearm deviation, that's owner nerve injury at the elbow. If you flex the wrist and you have like medial, I guess you can say like owner deviation of the forearm that occurs from median nerve injury at the elbow. Okay. And remember that if a person has like owner nerve injury at the flexo-capillonaris, flexo-capillonaris is a little bit more than normal. Flexo-capillonaris is a maybe a little bit but it will not be gone because remember flexo-capillonaris is working just fine. Right. Even if like the owner contributions to like flexo-capillonaris, so basically like for the use forearm five is all screwed up. Flexo-capillonaris is working just fine, right. So that's that shouldn't be a problem. Again, remember all flexo-capillonaris is interviewed by the median nerve. So how can you enjoy the median nerve at the elbow? Really for the most part, this kind of sunrise. You know, if you have like injury to like your funny bone, there's sometimes people call it like that. There's this thing called cubital tonal syndrome. That's owner nerve injury at the elbow. If you have like issues that like injury to like the medial, it be condyl of the hemorrhus.

Those things all cause those things will all cause an owner nerve injury at the elbow. So I'm going to go ahead and stop here. As I do at the end of every podcast, I do offer one on one tutoring for all the USMLE exams, right. So step one, step two C case, step two C S step three. I also offer tutoring for the pre-clinical med school exams, the 30-year flagship or shelf exams. And then I also do this then I call like longitudinal tutor, right. Where I I tutor, let's say like you're newly minted like first or second year med student, I tutor you for all your class exams, but at the same time, I also infuse step one knowledge. And it's actually like tutor for your class exams and step one on a longitudinal basis as you're going through all those things. And then when you did a kid appear comes like tutor you as well then everyone I've done this with they have been like wildly successful on the USMLE exams with this. Same thing for 30 years, right. Like a newly minted 30 year, I tutor you for your shelf exams and then I tutor you for during your dedicated period. But the thing is as I'm tutoring for your shelf exams, I'm also tutoring you for step two C case at the same time, right. So again, when you get to your dedicated period, most of these people that I've done this with, they tend to have very short and brief brevis if you may dedicated periods because again they are like super well prepared from the get go.

So if that's something you're interested in, feel free to reach out to me. And then if you're an internal medicine resident, I do offer tutoring for the internal medicine, training exam, the internal medicine board exams. And then if you're I don't know if you have a buddy that's a college student and needs to learn in general chemistry or getting chemistry, physics, biochemistry, histology, physiology, all those things. And then if you're a med student applying to residency, where it's like an ERAS application or a college student applying to med school so an AMCA application, I do offer like one-on-one like advice and a consultant, I guess consulting for that. I have tutor, I have worked with tons of people and most of the people I've worked with have all matched at their at their first choice. I mean yes, some people second maybe third choice but most people like maybe like 90% of people have worked with them all matched at their first choice. So like personal statement writing, letters of recommendation, mock interviews, editing and going through your applications, those are all things I offer. So if any of those things feel free to reach out, I really do hope you've gotten something from this podcast. Have a wonderful rest of your day. God bless you. I'll see you in the next podcast. Thank you.

Thumb; Digits 2 and 3 (index/middle); Digits 4 and 5 (ring/little).

Median nerve for digits 2 and 3; Ulnar nerve for digits 4 and 5.

Birth trauma, specifically forceful separation of the head from the shoulder during delivery.

Claw hand involving digits 4 and 5 (Ulnar claw).

Wrist drop.

Axillary nerve; Loss of abduction and external rotation (SABER).

Median claw affects digits 2-3; Ulnar claw affects digits 4-5.

Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (all supplied by the median nerve).

Triceps extension/wrist and finger extension (leading to wrist drop).

Cubital tunnel syndrome (compression at the medial epicondyle of the humerus).

Loss of thumb flexion (due to paralysis of both Flexor Pollicis Longus and Flexor Pollicis Brevis), in addition to loss of opposition.

At the wrist (Carpal Tunnel Syndrome) and at the elbow.

Median claw affects digits 2-3; Ulnar claw affects digits 4-5.

Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis (all supplied by the median nerve).

Triceps extension/wrist and finger extension (leading to wrist drop).

Cubital tunnel syndrome (compression at the medial epicondyle of the humerus).

Loss of thumb flexion (due to paralysis of both Flexor Pollicis Longus and Flexor Pollicis Brevis), in addition to loss of opposition.

At the wrist (Carpal Tunnel Syndrome) and at the elbow.