Anatomy clinical correlates: Median, ulnar and radial nerves

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Introduction0:00–0:23

The median ulnar and radial nerves course through the forearm and wrist and may help coordinate the movement of her forearms and hands.
These nerves however, are prone to injury because of various causes and depending on which one of them is injured, that will result in characteristic symptoms that can help us recognize and identify it for the median nerve.

Median nerve injuries0:23–3:05

The clinical manifestations depend on whether the lesion has occurred distally as in carpal tunnel syndrome or approximately as in an anterior displaced portion of a medial supracondylar humerus fracture.
The most common cause of median nerve injury is carpal tunnel syndrome, which is when the tunnel in the wrist through which the median nerve passes becomes narrower and compresses the median nerve.
This can happen due to repetitive use like typing on a keyboard injuries like an anterior lunate dislocation. Or it can be associated with conditions such as hypothyroidism, diabetes or in pregnancy.
Symptoms of median nerve injury would be pain and paresthesia in the radial 3.5 digits, weakness of the 1st and 2nd, lumbrical thenar atrophy and weakness of thumb, abduction and opposition of the affected hand.
Specifically the recurrent branch of the median nerve is what provides motor innervation to the thenar muscles of the hand which are responsible for abduction, flexion and opposition.
So with injuries, people may have issues opposing the thumb and it may be difficult to perform actions like buttoning up a shirt damage to the recurrent branch of the median nerve alone causes what is known as a hand, which refers to atrophy of the thenar eminence and inability to oppose the thumb.
Damage to the entire median nerve at the level of the wrist presents clinically as a median claw. Let's break this down quickly.
So the 1st and 2nd lumbrical are innervated by the median nerve. And the lumbrical normally flex the metacarpophalangeal joints and extend the distal and proximal interphalangeal joints.
If the median nerve is injured, the opposite occurs. So at rest or when the patient tries to extend all the fingers, the index and middle fingers stay extended at the MCP and the D IP and P IP stay flexed, especially since the finger flexors are unopposed, resulting in the median claw.
Now, in a proximal lesion to the median nerve, as in a supracondylar fracture, we have all of the same deficits as in a distal lesion.
But now all of the finger flexors of the 2nd and 3rd digit are also affected such as the flexor digitorum superficialis and the lateral half of flexor digitorum profundus.
So when an individual is asked to make a fist, they can only flex the 4th and 5th digit. And this presentation or claw is referred to as Pope's blessing or hand of benediction.
And it is indicative of a proximal median nerve injury. Ok.

Ulnar nerve injuries3:05–4:58

Next, there's ulnar nerve injuries which can occur anywhere between its origin from the brachial plexus to the ulnar canal or Guillain canal in the wrist.
Most commonly, it's associated with elbow injuries such as fracture of the medial epicondyle of the humerus in a distal ulnar nerve injury, like a fracture to the hook of the hamate bone.
Or when cyclists compress the hook of the hamate bone. When holding onto handlebars, there's numbness and sensory loss to the medial 1.5 digits, weakness in abduction and adduction in digits, 2 to 5 weakness in the abduction of the thumb, weakness in flection of the 4th and 5th digits and opposition of the fifth digit as well as hypothenar eminence atrophy.
It also manifests clinically as an ulnar claw. This is the exact opposite of the median claw where this time we have paralysis of the medial two lumbrical.
So at rest or when the patient tries to extend their hand, the ring and pinky finger stay extended at the MCP and the D IP and P IP stay flexed and the finger flexors are once again unopposed.
Ok. So in a proximal lesion to the ulnar nerve, as in a medial epicondyle fracture, trauma or prolonged leaning or sleeping on your elbow, we have all of the same deficits as in a distal lesion.
But now there is the additional problem that we have lost function of the flexor digitorum profundus on the medial side.
So when a patient is asked to make a fist, they can only close their 2nd and 3rd digits or fingers. And this is called an OK gesture.
Additionally, there is a loss of flexor carpi ulnaris resulting in risk adduction deficits. So when they try to flex their wrist, it deviates radially.

Radial nerve injuries4:58–6:42

Finally, radial nerve injury can happen a few different ways. First off, it can occur by repetitive pronation and supination of the forearm.
For example, when using a screwdriver. In this case, it manifests clinically as finger drop.
This occurs because the deep branch of the radial nerve pierces, the supinator muscle as it travels distally and overuse of supination can cause impingement here.
After the supinator muscle, this branch goes on to innervate the extensor indices. So, reduced function of this muscle can result in a finger drop due to weakness of the finger extensors and unopposed action of the finger flexors.
Radial nerve injury can also occur because of a midshaft fracture of the humerus or because of a lateral deviation of a displaced supracondylar fracture of the humerus.
This manifests clinically as weakness of the supinator and extensor muscles of the wrist and fingers as well as sensory loss to the posterior forearm, dorsal lateral hand and dorsal thumb.
The classic clinical finding is wrist drop, which is when the wrist hangs in a partly flexed position. On account of unopposed wrist and finger flexors.
Finally, it can occur due to compression of the brachial plexus. For example, when using crutches or sleeping with your arm hanging over a chair.
Hence the term Saturday night palsy, since this injury occurs superior to the branches of the triceps, brachii. This also causes paralysis of the triceps leading to loss of elbow extension.
In addition to loss of wrist and finger extension, there will also be loss of sensation over the dorsal hand and thumb as well as the posterior forearm or arm.
Depending on how high up the nerve damage is. All right, is a quick recap.

Review6:42–8:26

The median nerve specifically, its recurrent branch can be injured at the level of the wrist, resulting in atrophy of the thumb and an inability to oppose the thumb called an ap hand injury to the entire nerve of the wrist results in a median claw, which is when the index and middle fingers stay extended at the metacarpophalangeal joints.
While the distal and proximal interphalangeal joints stay flexed when trying to open the hand from rest. Due to weakness of the lateral two lumbrical proximal median nerve injuries have the same deficits as distal injuries, plus additional weakness of the forearm muscles innervated by the median nerve.
This results in a clinical finding called Pope's blessing or the hand of benediction. When an individual's ask to make a fist and they can only close their medial two fingers, ulnar nerve injuries distally at the wrist, result in numbness and sensory loss to the medial 1.5 digits, weakness in abduction and abduction in digits, 2 to 5, weakness in abduction of the thumb, weakness in flection of the 4th and 5th digits and opposition of the fifth digit, as well as hypothenar eminence atrophy plus the characteristic ulnar claw, which is the exact opposite of a median claw.
Approximal ulnar injury has the same deficits as the distal injury as well as weakness of wrist adduction and flexion of the medial two digits and also results in the ok, gesture.
Finally, radial nerve injury may result in either finger drop, wrist drop or Saturday night, palsy, as well as sensory deficits to the dorsal hand and thumb, forearm and arm depending on the mechanism and location of the injury.