Median Nerve – Nerve Lesion of Upper Limb

00:01 Now let’s turn to the median nerve. Now, there is a number of places the median nerve can be damaged. It could be damaged in the arm, at the elbow, and at the carpal tunnel.

00:10 Remember, the median nerve doesn’t supply anything in the arm, but it supplies considerable amounts of muscles in the anterior compartment of the forearm and in the hand. So damage to the nerve, to the median nerve, again via maybe traumatic injury to the median nerve, principally at the elbow joint is a common place. But again, you can have damage up in the arm or down, as we’ll see in the wrist region.

00:34 But damage at the elbow can lead to paralysis of FDS, flexor digitorum superficialis, and the lateral two tendons of flexor digitorum profundus. So these muscles will be paralyzed.

00:49 You’ll also have paralysis of the thenar muscles working on the thumb, and lumbricals 1 and 2, those laterally positioned lumbricals. The effect, well again, if you appreciate what these muscles do, then the effect of damage to the median nerve is going to be an inability to flex the proximal interphalangeal joints of digits 1 to 3, and weakened flexion of digits 4 and 5. You’re also going to have an inability to flex the distal interphalangeal joints of digits 2 and 3. So you can see paralysis of the median nerve leads to quite some substantial inabilities of the contractile abilities of these muscles leading to quite a significant functional deficit. You’ll also be able to see that there’s going to be flexion still be possible at the distal joints of digits 4 and 5 due to the flexor digitorum profundus having the ulnar innervation. So because the tendons that pass the digits 4 and 5, from flexor digitorum profundus, are from the ulnar nerve, then these are going to be spared. You’re also going to have inability to flex the metacarpophalangeal joints of digits 2 to 3. And due to loss of the lumbricals, you won’t be able to extend the interphalangeal joints of digits 1 and 2.

02:19 So this means that when a patient is asked to form a fist, digits 2 and 3 essentially remain extended. And this is what we can see here. Due to a loss of the flexor digitorum profundus and the flexor digitorum superficialis and the various other muscles I’ve mentioned like the lumbricals, because these are effectively paralyzed that when someone is asked to form a fist, then the function of the flexor digitorum profundus that is supplied by the ulnar nerve is still intact, these digits can flex, but the remaining digits remain extended.

02:56 And this is known as hand of benediction. And we can see that here on the picture.

03:00 We can see digits 4 and 5 have flexed, but digits 2 and 3 remain extended. And this is indicative of median nerve damage. If the median nerve was damaged in the carpal tunnel, then you wouldn’t have that problem because the median nerve would have already given off the branches to the muscles in the anterior compartment of the forearm.

03:26 So the muscular branches already have come off here. So the function of these muscles will be preserved.

03:34 However, as the nerve passes through the carpal tunnel, it can be due to carpal tunnel syndrome that you could have this problem, or if you try to lacerate if there’s a laceration of your wrists, then perhaps the median nerve could be damaged. And this could lead to paralysis of the thenar muscles and lumbricals 1 and 2.

03:56 So these are supplied by the recurrent branch of the median nerve that passes through the carpal tunnel, and therefore, it’s likely to be damaged. Because of that, you have an inability to oppose the thumb, and you lose the fine motor movement that is possible via the lumbricals with digits 2 to 3. So loss of fine motor movements of the lumbricals, and we can see that here. We see the lumbricals will be damaged, and we see the thenar eminence here will be damaged due to damage to the recurrent branch of the median nerve.

04:33 Sensory loss, well, you’ll have tingling or reduced, loss of sensation over the lateral three and a half fingers. We can see that here, sensory loss over fingers 1, 2, 3, and the lateral surface of finger 4 due to sensory branches from the median nerve emerging distal to the carpal tunnel. So these branches, these sensory branches coming from the medial nerve that supply these fingers are coming once it has pass the carpal tunnel. So they will be damaged, and you’ll have that tingling, reduced sensation.

05:07 However, sensation of the central palm will be preserved because the branch that supplies the central palm, this palmar branch here, actually comes off the median nerve before it passes through the carpal tunnel. So because of that, it’s not going to be damaged. So if there is sensory loss of the 1, 2, 3 and a half fingers but with carpal tunnel damage, the central palm sensation remains intact.