0:03 [Music]
0:05 This is a tricky one because what I want
0:08 to do because I've been marking hundreds
0:11 of exam papers and I see how some
0:12 students are struggling with this. What
0:16 I want to do is describe
0:19 the loss of motor function that occurs
0:22 when major nerves of the upper limb are injured.
0:24 injured.
0:27 But there is so much dexterity, so much
0:30 complexity here that I want to simplify it,
0:32 it,
0:34 but often you get pulled into that complexity.
0:36 complexity.
0:38 Um, and it just makes it harder to
0:40 remember and learn. Okay, so middle of
0:42 the road. I'm going to simplify a little
0:44 bit, but I'm not going to oversimplify.
0:46 But we're going to look at the major
0:48 nerves of the upper limb from proximal
0:52 to distal and we'll talk about injuries
0:55 at classical sites and the loss of motor
0:57 function as a result. See, I'm already
0:59 I'm already skipping the sensory bits to
1:04 make it a little bit simpler. [Music]
1:11 [Music]
1:12 exam questions often have a little bit
1:14 of a clinical vignette, a clinical
1:18 leadin. So, nerves can be injured by
1:20 penetrating trauma that cuts the nerve,
1:26 by uh compression, by um crushing. They
1:30 can be injured by a joint dislocating
1:32 and then stretching a nerve because
1:34 nerves are not stretchy. If you stretch
1:37 it, you damage the nerve. They can be
1:40 injured by a bony fracture by the sharp
1:43 pointy bits of the fracture itself or by
1:46 the surgical repair of that fracture or
1:49 by bony growths as a result of that
1:53 fracture repair process. Um so there are
1:55 a number of ways in which nerves can be
1:59 injured and then um in real life we're
2:01 not doing real life today we're doing
2:03 hypotheticals but in real life nerves
2:05 can be injured to a different degree.
2:07 You know a nerve is a collection of
2:08 thousands or tens of thousands or
2:10 hundreds of thousands of individual
2:12 neurons. So how much of the nerve has
2:14 been injured and which part of the nerve
2:16 has been injured which is going to
2:18 innovate which muscles which can give
2:20 you slightly different signs and
2:22 symptoms. But we're going to we're going
2:25 to distill it down.
2:27 Um oh dear, this already isn't starting
2:29 well. Um because if we're going to start
2:32 proximally, well, we've got the brachial plexus.
2:34 plexus.
2:35 Okay, number one. Um so the brachial
2:37 plexus, I'm not going to describe the
2:39 anatomy of the brachial plexus. Don't do
2:41 that, Sam. That's in another video. Um
2:43 but in terms of injuries to the brachial
2:47 plexus um of the most common injuries
2:49 are an injury to the upper trunk and the
2:51 lower trunk back here. Now the upper
2:54 trunk will injure
2:59 nerves formed from the C5 and C6 spinal
3:01 nerve roots. If you're going to damage
3:03 the upper trunk of the brachio plexus,
3:05 the shoulder gets pulled away from the
3:08 head. Somebody lands on their head and
3:10 it pushes it away from the shoulder. So
3:12 you you stretch these nerves. Like I
3:14 say, nerves don't do stretching. So you
3:17 tear um nerves associated with the upper
3:18 trunk either before the upper trunk or
3:22 during the upper trunk. Now those nerves
3:25 are going to form the suprcapular nerve,
3:26 the auxiliary nerve and the
3:29 muscularcutaneous nerve. There's the
3:31 auxiliary nerve. There's the
3:33 musculutaneous nerve. We haven't got a
3:34 supracapular nerve, but you can guess
3:37 where it goes, right? Supracapular.
3:39 So the supracapular nerve is going to innovate
3:41 innovate
3:43 suppinatus and infraspinanatus. So two
3:54 uh one of them up here we um
3:57 that means that if the supcapular nerve
4:01 has been injured you will struggle to start
4:03 start
4:05 abduction of the upper limb at the
4:09 shoulder and there will be weakness of
4:12 lateral rotation of the humorris at the
4:14 shoulder. If the auxiliary nerve has
4:17 been damaged, well, that innovates
4:19 the deltoid muscle. So likewise, the
4:23 deltoid muscle is also involved in
4:24 abduction. Okay? So we've lost
4:26 abduction. Um, and if the muscular
4:29 cutaneous nerve is injured, that goes to
4:32 the muscles of the anterior arm, the
4:34 anterior brachium, and these muscles
4:37 flex the elbow. The thing to remember
4:40 here is that biceps brachi also is a
4:42 powerful sinator.
4:44 Um don't worry I'm going to sum
4:45 summarize this in a moment. So a sinator.
4:47 sinator.
4:51 So herbs pausy, upper brachial plexus,
4:55 upper trunk brachio plexus injury. We've
4:58 lost suprcapular nerve, auxiliary nerve
5:00 and muscularcutaneous nerve function.
5:02 And if you can't abduct, the arm will be
5:04 hanging to the side. It will be adducted.
5:06 adducted.
5:10 The arm will be medially rotated because
5:12 the medial rotators will be working and
5:14 the lateral rotators won't be working.
5:16 The elbow will be extended because the
5:19 elbow flexors have been paralyzed. And
5:21 because biceps brachi is a powerful
5:23 supenator, that means the pronators will
5:27 win and the forearm will be pronated. So
5:31 with an upper trunk or superior trunk
5:33 brachio plexus nerve injury, the arm
5:35 will be at the side, the elbow will be
5:37 extended and the forearm will be
5:41 pronated. Herbs pulsey.
5:44 One more brachio plexus one.
5:48 A clumpkey's pausy describes an injury
5:52 to the lower trunk way in there of the
5:56 brachial plexus. Now this is involving
6:00 uh the roots C8 and T1 and this will go
6:03 on and contribute to the uh ulna nerve
6:06 and the median nerve.
6:08 M and this one's
6:12 particularly awkward depending upon
6:14 how affected everything is. So a clum
6:16 keys pulsey is caused in the opposite
6:19 direction. So the arm being pulled up
6:21 like that, it's an obstetric injury
6:23 during birth. Well, it isn't anymore
6:24 because everybody knows their anatomy
6:27 and nobody does this. Um but if you
6:30 stretch the brachial plexus through the
6:32 axilla, again, nerves don't stretch.
6:34 That damages the lower trunk that gives
6:36 a clumps pulsey. Now we'll talk about
6:40 these nerves more but the ulna nerve is
6:43 responsible for innovating almost all of
6:44 the small muscles of the hand the
6:47 intrinsic muscles of the hand. Um the
6:49 median nerve is responsible for
6:51 innovating u most of the muscles of the
6:54 anterior forearm but the ulna nerve um
6:57 innovates the ulna side of plexodum
7:00 profundus the deep flexor of the fingers
7:04 and also um flexor karpy ulnaris the
7:09 flexor of the wrist on the ulna side.
7:12 So in clumpies Pauly the most common
7:19 sign is a form of claw hand. Um often
7:23 digits four and five are hyperextended
7:25 at the metacarpoalleneal
7:30 joint and flexed at the interfallengeal
7:33 joints like this. Um and this is
7:35 ascribed to the lumbricals. The
7:37 lumbercles are some fun muscles that
7:39 hardly any students ever understand. But
7:41 the lumbercles are
7:45 important in properly extending and
7:49 controlling extension of the fingers uh
7:52 extension of the um interfallenal joints
7:54 particularly because they pull on uh a
7:58 dorsal hood. You see how
8:00 I get sucked into this and it ends up
8:02 being too complicated. Okay. Clumkeyy's
8:05 pausy, lower brachial plexus injury.
8:08 Look at the hand. Look at digits four
8:11 and five. Look at that hyper extension
8:14 of the metacarpoaleneeal joint and
8:16 flexion of the interfallengeal joints
8:19 giving that claw position because the
8:20 lumbercles on this side of the hand
8:22 innovated by the ulna nerve are
8:24 paralyzed whereas many other muscles are
8:26 kind of working. Now if the if the
8:28 median nerve has also been affected then
8:31 you'll see that across the hand. Um you
8:32 the reason I'm doing that is that you
8:35 may well see extension of the wrist if
8:38 that flexor of the wrist has um been
8:41 paralyzed but because there's quite a
8:43 bit of overlap often the wrist is in an
8:46 okay position. It's that bit it's that
8:47 position of the fingers that you're
8:50 concerned about. Clumpkey's py that's
8:52 all we'll say about it. I've done
8:54 another video about it properly. Okay,
8:57 we can move on to the simpler stuff. The
9:00 auxiliary nerve which we can see here
9:03 runs around the humorris. So the
9:05 auxiliary nerve can be damaged by
9:07 dislocation of the shoulder. It can be
9:11 injured by a fracture at the neck of the
9:13 humorris and subse subsequent repair and
9:16 what have you. The auxiliary nerve
9:18 innovates the deltoid muscle. The
9:21 deltoid muscle is responsible for
9:24 abduction as well as um flexion and
9:27 extension of the humorous at the
9:30 glenoumeral joint of the shoulder. Um but
9:32 but
9:34 if the auxiliary nerve is injured,
9:36 deltoid is paralyzed. Um the thing you
9:39 will notice is um a loss of abduction of
9:42 the upper limb. Supraspinatus will still
9:43 be intact. So you can start off
9:45 abduction but you need deltoid to get
9:47 the arm up here. So auxiliary nerve
9:51 injury up
9:53 at the proximal humorous,
9:57 loss of abduction, loss of deltoid.
10:00 The muscularcutaneous nerve here running
10:02 on the anterior humorous. The
10:04 muscularcutaneous nerve
10:08 is the nerve running to the muscles of
10:11 the anterior compartment of the arm. So
10:13 biceps, brachi and brachiialis and what
10:16 have you. These muscles are flexors of
10:18 the elbow. So if the musculutaneous
10:22 nerve is injured up here, you lose
10:24 flexion of the elbow.
10:26 The other nerve that's up here in the
10:30 axilla is the radial nerve. And see
10:33 where it is there. So the radial nerve
10:34 gets injured in something called
10:38 Saturday night pausy which is um
10:40 somebody drinks a lot of alcohol become
10:42 very inebriated and they put their arm
10:44 over the back of the chair and they fall
10:46 asleep for a long period of time very
10:48 very heavy sleep and they don't move and
10:49 because of where that nerve is that
10:51 means the nerve gets compressed. This is
10:54 why we don't when somebody's got a a
10:56 lower limb fracture and they're using a
10:59 um a crutch. This is why crutches don't
11:01 go up into your armpits anymore because
11:05 they crush the radial nerve. So if the
11:07 radial nerve is injured at this level up
11:09 at the axilla, well the radial nerve
11:11 innovates the muscles of the posterior
11:13 compartment of the arm and the posterior
11:15 compartment of the forearm. So you will
11:17 lose uh innovation of triceps, you'll
11:20 lose innovation of all of these guys,
11:22 which means that if you injure the
11:25 radial nerve at the axilla, you lose
11:28 elbow extension and you lose wrist
11:33 extension and you lose finger extension. Okay,
11:35 Okay,
11:37 another fun exam question. Um it was in
11:40 one of my exams actually and students
11:43 were very good at it. um the radial nerve
11:49 winds around
11:53 the humorris. So a mid humorous fracture
11:55 is likely to damage the radial nerve at
11:57 this point. And likewise uh orthopedic
12:00 repair at this point needs to be careful
12:02 not to damage the radial nerve. And then
12:04 of course bony growths as a result of
12:05 that fracture can also damage the radial
12:07 nerve. If you damage the radial nerve at
12:10 this point, um, elbow flexion may still
12:12 be functioning because you've innovated
12:14 some of the triceps, but hey,
12:16 elbow flexion is probably not going to
12:17 be happening if this bone's fractured
12:20 anyway. So, if if the radial nerve is
12:23 injured at this point, you'll certainly
12:27 lose um wrist extension and finger
12:29 extension. So you'll get, you know,
12:31 wrist drop same as before, but we got to
12:34 think about the nerve traveling down the
12:36 arm. If it's injured at different points
12:38 along the arm, if it's already innovated
12:40 stuff, that stuff's still going to work.
12:42 It's the stuff it hasn't got to yet
12:44 that's going to lose its innovation,
12:46 lose its motor function, and be
12:51 paralyzed. So radial nerve mid humorris
12:53 uh median nerve
12:57 we see the median nerve
13:01 at the elbow anterior to the elbow. So
13:02 this can be damaged so it's right up
13:04 against the bone here. So this can be
13:06 damaged by a supraondila hummeral
13:08 fracture. It can be damaged by a
13:10 penetrating injury. It could be damaged
13:13 by elbow fracture, elbow dislocation.
13:16 The media nerve is going to innovate the
13:18 muscles of the anterior forearm and the
13:20 muscles of the thear eminence and the
13:23 lumbricals on this side. So if the media
13:29 nerve is injured here, you will lose
13:32 finger flexion, wrist flexion. Um
13:34 Um
13:36 you'll lose the thumb's complicated.
13:38 You'll lose opposition of the thumb.
13:42 You'll lose flexion of the thumb.
13:45 Abduction of the thumb. Careful with the
13:46 thumb. There's a lot going on with the
13:48 thumb. Median nerve injured at the
13:50 elbow. You lose opposition of the thumb.
13:52 That's a good one. Opposition because
13:55 it's weird. Um, and the media nerve also
13:58 innovates the um pronator muscle. So,
14:00 you lose pronation. So, if the media
14:02 nerve is injured at the elbow, you lose
14:05 pronation, you lose wrist flexion, you
14:07 lose finger flexion. At least that's
14:09 part of the story. Remember how I said
14:13 the ulna nerve also innovates the ulna
14:16 part of flexor digtorum profundus the
14:19 deep flexor muscle of the fingers and it
14:22 also innovates um flexor cararpi naris
14:24 the wrist flexor on this side.
14:27 So that complicates things. So because
14:29 of that overlap of medial nerve doing
14:31 most of the work in the forearm nerve
14:34 doing a little bit on the ner side. If a
14:36 patient has a medial nerve injury at the
14:40 elbow and you ask them to make a fist, um
14:42 um
14:45 they won't be able to flex their fingers
14:48 normally, but the bit of the flex
14:50 digtorum profundus muscle that's
14:52 innovated by the ulna nerve and still
14:55 works will flex the little fingers. So
14:58 you might get that sort of position. So
15:01 flexodum superficialis in innovates will
15:04 flex all the fingers that's gone. Flex
15:06 digtor and profundus. The median nerve
15:08 bit will innovate those fi will flex
15:10 those fingers. Flex digtor and profundus
15:12 will flex those fingers. Dab is gone.
15:16 Dab it still works. You see how I so
15:19 quickly go off topic.
15:21 Somebody has a median nerve injury at
15:23 the elbow. You ask them to flex their
15:27 fingers. Fingers four and five will
15:29 flex. The others won't because the
15:31 muscles in the forearm innovated by the
15:34 median nerve are now paralyzed. And that
15:37 gives the hand of benediction. The hand
15:39 of benediction only occurs because you
15:41 have asked the patient to make a fist
15:44 and they're unable to. That's as good as
15:46 they can do.
15:50 Moving on, the media nerve then
15:52 runs down the forearm, innovates almost
15:54 all of these muscles, and then it's
15:55 going to run through the carpal tunnel
15:57 here to get into the hand. when it gets
15:58 into the hand, it's going to innovate
16:01 the muscles of the thear eminence at the
16:02 base of the thumb and it's going to
16:06 innovate a couple of lumbles here. So if
16:08 the if the median nerve is injured at
16:13 the wrist, which could occur with a
16:15 fracture of the distal radius, a collie
16:17 fracture, it could occur with carpal
16:20 tunnel syndrome. It could occur with a
16:22 fracture of the wrist. It could occur
16:24 with a a penetrating injury to the
16:26 wrist. If the median nerve is injured at
16:28 the wrist, well, these muscles have
16:31 already been innovated. So, they work fine.
16:32 fine.
16:35 But these nerves distal to the injury
16:37 point in the base of the thumb, they
16:40 don't work. So, if a median nerve at the
16:42 wrist, a median nerve injury at the
16:45 wrist has occurred,
16:48 opposition will be weak or impossible
16:50 and and flexion and abduction. But
16:52 opposition, stick with opposition.
16:57 That's the the one you can remember.
16:59 Stop there. Okay. Well, you know, stop
17:01 with the median nerve. We'll move on to
17:05 the NA nerve. Final nerve for today.
17:07 Uh the ulna nerve. Now, you know, the
17:10 era nerve runs around
17:12 uh the medial epicondile of the humorus.
17:14 It's your funny bone. That's where
17:16 that's where you always bang it, right?
17:18 So the ulna nerve can be damaged by
17:21 elbow fracture, elbow dislocation, elbow
17:25 injury. Um and the key thing here that
17:27 we said is that the ulna nerve is going
17:28 to innovate almost all of the intrinsic
17:31 muscles of the hand. So if the ulna
17:33 nerve is injured at the elbow
17:35 in the hand,
17:43 abduction and adduction of the fingers.
17:44 That's what you're looking for because
17:46 those intrinsic muscles, the interosius
17:48 muscles that are innovated by the on the
17:50 nerve are paralyzed.
17:52 So abduction and adduction of the
17:56 fingers are lost. Also um this muscle in here
17:58 here
18:00 adductor pelicus will also be um
18:02 paralyzed because that's innovated by
18:05 the ulna nerve. So adduction of the
18:10 thumb will also be lost. Um
18:14 yes, the ulna nerve also innovates flex
18:17 digital and profundus or part of it and
18:20 flex carpial narus which means there
18:24 might be some changes to wrist flexion
18:28 and changes to finger flexion but really
18:30 nerve injury at the elbow. look to the
18:33 hand and test those intrinsic muscles of
18:36 the hand by testing for abduction and
18:39 adduction of the fingers.
18:41 Let's summarize.
18:44 Okay, so you got to remember all this.
18:47 Um let's go back to the top. So brachial
18:50 plexus upper trunk if the upper trunk is
18:53 injured which occurs when the head is
18:55 pushed away from the shoulder. The
18:57 presentation is that the the arm is
19:01 hanging by the side. Um the the whole
19:03 upper limb is medially rotated. The
19:06 elbow is extended. The forearm is
19:09 pronated and that's herbs pulsey.
19:12 Whereas clumsy's pulsey
19:15 is that side of the brachial plexus is
19:19 stretched. So the lower trunk has been
19:23 injured and with clumpkey's pulsey go to
19:26 the hand and we're thinking about the
19:27 ulna nerve largely but we're thinking
19:29 about the position of these fingers
19:33 hyperextension of the metacarpal joints
19:35 and flexion of the interfallengeal joints.
19:37 joints. Um
19:38 Um
19:42 auxiliary nerve
19:45 to deltoid. So if the auxiliary nerve is
19:48 injured, you lose deltoid, can't do
19:51 abduction. If the musccutaneous nerve is
19:55 injured, that means you can't do elbow
19:59 flexion. If the median nerve is injured
20:01 at the forearm, you can't do wrist
20:04 flexion, finger flexion, opposition of
20:07 the thumb. If the radial nerve is
20:10 injured at the axilla, you can't do
20:12 extension of the elbow, extension of the
20:15 wrist, extension of the fingers. If the
20:17 media nerve is injured at the wrist, you
20:19 can't do opposition, but everything else
20:22 is okay. If the owner nerve is injured
20:25 at the elbow, you go to the hand and you
20:27 test the intrinsic muscles of the hand
20:31 for abduction and adduction.
20:32 That's the stuff you got to know to pass
20:35 my exams. That's the stuff you got to
20:38 know. All right, those I mean, if you
20:39 want to find out more about the nerves
20:41 and the movements and all that sort of
20:42 stuff, just search YouTube for my name
20:44 and whatever it is you're interested in
20:46 anatomy wise, and if I've done it, it'll
20:50 pop up. But that's a summary of the
20:53 major injuries at the major joints,
20:54 which is where they often occur, to
20:57 major nerves, and loss of motor
20:59 function. Oh, I hope that helps you
21:00 remember. I'm sorry. Is it just is
21:02 complicated. There is more detail to
21:04 this, but you can grow from that and add
21:06 the detail with experience if you need
21:07 it. Otherwise, that might be all you
21:09 need. Stop talking, Sam. Okay, let's go
