Anatomy clinical correlates: Median, ulnar and radial nerves

The median, ulnar and radial nerves course through the forearm and wrist, and they help coordinate the movement of our 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, the clinical manifestations depend on whether the lesion has occurred distally, as in carpal tunnel syndrome, or proximally, as in an anteriorly 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 associated with conditions such as hypothyroidism, diabetes, or in pregnancy.

Symptoms of median nerve injury would be pain and paraesthesia in the radial 3 and a half digits, weakness of the first and second 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 ‘ape hand’, which refers to atrophy of the thenar eminence and inability to oppose the thumb..

Damage to the entire median nerve at the level or the wrist, or distal median nerve, presents clinically as a “median claw”.

Let’s break this down quickly.

So, the first and second lumbricals are innervated by the median nerve, and the lumbricals normally flex the metacarpophalangeal joints and extend the distal and proximal interphalangeal joints.