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