Carpal tunnel syndrome

Carpal tunnel syndrome is a nerve entrapment disorder that results from compression of the median nerve which winds its way through the wrist through a narrow passageway called the carpal tunnel.

This compression typically causes pain, numbness, and tingling in the thumb, index finger, middle finger, and the thumb side of the ring finger, which are the areas of skin innervated by the median nerve.

Now taking a cross section of the wrist, we’ll see a bony arch known as a carpal arch on the dorsal side of the hand which forms the floor of the carpal tunnel, and a sheath of connective tissue called the flexor retinaculum or transverse carpal ligament, which is on the palmar side of the hand forms the roof of the carpal tunnel.

Also there are nine flexor tendons, which go to the fingers and thumb, as well as one nerve—the median nerve—which travels down the forearm and go through the carpal tunnel.

The skin of the hand served by the median nerve includes the thumb, the index finger, and middle finger, as well as half of the ring finger that’s on the thumb side.

The other side of the ring finger and pinky are served by the ulnar nerve, and the back of the hand’s served by the radial nerve, only the median nerve goes through the carpal tunnel.

Carpal tunnel syndrome is caused by compression of the median nerve, and that typically happens as a result of inflammation of the nearby tendons and tissues, which creates local edema or swelling which increases the amount of fluid in a very tight space, and essentially puts pressure on the median nerve.

Initially that pressure can cause a dull ache or discomfort in any of the areas of the hand that are innervated by the median nerve.

Eventually this discomfort can lead to sharp, pins-and-needles-like pain, called paresthesia, which can extend up the forearm.

People might also have muscle weakness which can cause clumsiness with tasks like holding small objects, turning doorknobs and keys, or fine motor tasks like buttoning up a shirt.

In severe situations, the thenar muscles at the base of the thumb can start to waste away.

This happens because those muscles are innervated by the recurrent branch of the median nerve which arises from the median nerve after it passes through the carpal tunnel.

Basically, in a nutshell, any structure innervated by the median nerve downstream of the point of compression can be affected.

Interestingly, a superficial sensory branch of the median nerve, called the palmar branch, provides sensation to the central base of the palm.