Radial Nerve

00:01 So, now, let's have a look at the radial nerve.

00:04 The radial nerve is a direct continuation of the posterior cord.

00:07 And we can see the radial nerve now passing here.

00:10 It passes into the posterior aspect of the arm through the triangular interval and don't forget that it then runs down in the radial groove, separating the lateral and medial heads of triceps.

00:22 It gives rise to a number of cutaneous branches.

00:25 Here, we've got the posterior brachial cutaneous nerve.

00:28 So, as the posterior aspect of the arm and the posterior aspect of the forearm, the posterior antebrachial cutaneous nerve.

00:36 So, that's important to remember when we look at the sensory loss.

00:40 We can also see the radial nerve as it descends down in the posterior aspect of the arm.

00:45 Here, we're looking at on a lateral view, it penetrates the lateral intermuscular septum.

00:50 And then, it runs all the way down into the forearm.

00:53 We can see it enters the anterior compartment of the arm, closely associated with brachioradialis.

00:59 And here, we can see brachialis muscle as well. Here, it's entering into the forearm.

01:05 The radial nerve then continues down within the forearm.

01:07 It's giving rise to a deep branch here and a superficial branch.

01:12 The superficial branch then courses along the lateral aspect of the forearm to go and supply the skin around the hand.

01:20 Here, we can see the superficial branch is supplying the dorsal aspect of the palm and the lateral three digits.

01:28 Where the other median and ulnar nerves were supplying the other aspect of the surface of the skin, here, we've got the radial nerves sensory innervation supplying the dorsal lateral aspect of the palm and dorsal aspects of the lateral three digits.

01:43 A lot of the time, you have traumatic injury within the axilla.

01:46 We spoke about that with the muscular cutaneous nerve.

01:49 If this happens within the axilla and impacts the radial nerve, then, we have paralysis of all the muscles innervated by the radial nerve.

01:58 So, we're going to have widespread paralysis of various muscles.

02:01 It could also happen if you fracture the humerus at the level of the radial groove.

02:05 Remember, that's where the radial nerve is running alongside the humerus, separating the medial and lateral heads of triceps.

02:12 Here we have a fracture damaging the radial groove, impacting on the radial nerve.

02:17 Depending on where the branches two triceps have come off, if they've come off proximal to this fracture, then, triceps may be spared.

02:25 But if they haven't yet come off and they're still to come off, then, fracture at the level of the radial groove could impact the triceps.

02:34 Everything else distal though will be impacted.

02:38 As most of the radial nerve impacts the extensors of the wrist, wrist drop due to paralysis of extensor and unopposed tonic contraction of the flexors will mean we have wrist drop here.

02:50 So, essentially, what's happening, you've got no counterbalance now to the flexors of the forearm.

02:55 Usually, what happens is there's an interplay between the extensors and the flexors of the forearm to allow your hand to assume a mid-position.

03:03 But if you've got no extensor muscles counteracting the flexors, then, the flexors completely override it and you end up with wrist drop.

03:13 Due to the posterior cutaneous supply of the hand and the forearm and the arm which we can see here, the posterior brachial cutaneous nerve, the posterior antebrachial cutaneous nerve and the sensory distribution around the dorsal aspect of the hand.

03:28 We can see damage to the radial nerve will lead to a loss of sensation coming from these regions.

03:34 Here, we can show the sensory loss when the radial nerve is damaged high up.