Two small bones in the wrist, along the lower edge of the palm, called the pisiform and the hamate form a canal of sorts through which the ulnar nerve passes. This is called Guyon’s canal, and any obstruction or narrowing of this canal can result initially in sensitivity, and numbness or pain in the ring and pinky finger and the wrist. When something obstructs or compresses the ulnar nerve in this location, it is called Guyon's canal syndrome.

Causes of Guyon's canal syndrome are variable. They can include injury or fracture of either the pisiform or hamate bones. Tiny tumors can also form near the nerve obstructing it. Constant pressure on the site, as when someone holds onto the handlebars of a bike can result in Guyon's canal syndrome. It is sometimes called handlebar palsy. Arthritis in the wrist bones may also create Guyon's canal syndrome.

Early symptoms of Guyon's canal syndrome include “pins and needles” feelings in the ring and little finger of the affected hand. When this is ignored, Guyon's canal syndrome may progress to a very painful and “burning” sensation in the wrist. The condition also may result in continual numbness of the pinky and ring finger.

The condition worsens with lack of medical intervention, and eventually will result in difficulty controlling the muscles in the hands. Spreading the fingers may be difficult and even thumb movements can be challenging. Pain in the wrist often increases.

Usually, the pain and numbness signals a problem. Most people with the condition assume they have carpal tunnel syndrome. It’s actually easy to differentiate between Guyon's canal syndrome and carpal tunnel, because carpal tunnel initially causes numbness in the thumb, index and middle finger, while Guyon's canal syndrome first affects the pinky and ring finger.

Diagnosis of the condition is made by taking a thorough medical history and determining what activities the patient engages in. X-rays may be taken if the doctor suspects a broken or fractured bone. Another common test is called nerve conduction velocity (NCV), which measures the speed of nerve impulses and allows the doctor to definitively diagnose where the nerve is working more slowly.

If Guyon's canal syndrome is diagnosed in its early stages, refraining from the activities that created the situation can sometimes treat it. Patients may wear a brace at night and during the day to keep the wrist in a stable position. If a fracture is the cause, patients may wear a cast. Some doctors also prescribe physical therapy to help patients practice better body alignment and arm and hand positioning to release pressure on the nerve.

When early intervention don’t resolve Guyon's canal syndrome, surgery may be performed to remove obstruction to the ulnar nerve and rebuild a stable “canal” for it. This is frequently an outpatient surgery, and patients usually can go home the day they have the surgery. They will have their hand heavily bandaged for several weeks, and may work with physical therapists after the surgery. Outcome of surgery is usually good, especially when a physical therapy regime is followed.