Guyon's canal syndrome, sometimes referred to as Handlebar palsy, is caused by entrapment of the ulnar nerve

Ulnar nerve entrapment

Ulnar nerve entrapment is a condition where the ulnar nerve becomes trapped or pinched due to some physiological abnormalities. -Classification:...

 in the Guyon canal

Ulnar canal

The ulnar canal or ulnar tunnel, also called Guyon's canal, is a space at the wrist between the pisiform bone and the hamate bone through which the ulnar artery and the ulnar nerve travel into the hand.-Eponym:...

 as it passes through the wrist.

Symptoms usually begin with a feeling of pins and needles

Pins and Needles

Pins and Needles is a musical revue with a book by Arthur Arent, Marc Blitzstein, Emmanuel Eisenberg, Charles Friedman, David Gregory, Joseph Schrank, Arnold B. Horwitt, John Latouche, and Harold Rome and music and lyrics by Rome...

 in the ring and little fingers before progressing to a loss of sensation and/or impaired motor function of the intrinsic muscles of the hand which are innervated by the ulnar nerve

Ulnar nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...

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Guyon's canal syndrome is commonly seen in regular cyclists due to prolonged pressure of the Guyon canal against bicycle handlebars.

Pathology

There are 3 types of Guyon's canal syndrome, characterised by the location within the Guyon canal at which the ulnar nerve is compressed:

Type I

Proximal compression in Guyon's canal leads to motor weakness in all of the intrinsic muscles of the hand which are innervated by the ulnar nerve

Ulnar nerve

In human anatomy, the ulnar nerve is a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve. The nerve is the largest unprotected nerve in the human body , so injury is common...

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There is also sensory loss in the territory of the hand served by the ulnar nerve.

Type II

This is the most common type of Guyon's canal syndrome, and is caused by compression of the ulnar nerve at the lower wrist. This results in symptoms associated with Type I (above), however the sensory branch to the dorsal part of the hand and the motor supply to the muscles of the base of the palm are unaffected. Therefore Type II involves an impairment in motor function of the hand, with sensory innervation unaffected.

Type III

This is the least common type of Guyon's canal syndrome, and is caused by compression of the superficial branch of the ulnar nerve at the distal portion of Guyon's canal. Type III results in a loss of sensation from the cutaneous territory of the hand which is served by the ulnar nerve. There is no motor function impairment.

Treatment

Initial line of treatment is with anti-inflammatory drugs or cortisone injections. There have been trials with gloves which help protect the ulnar nerve from compression. The most radical treatment option is surgery to relieve tension in the Volar carpal ligament which forms the roof of Guyon's canal, thereby reducing compression on the ulnar nerve.