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There are eight small bones called carpal bones in the wrist. A ligament (also called retinaculum) lies across the front of the wrist. Between this ligament and the carpal bones is a space called the carpal tunnel. The tendons that attach the forearm muscles to the fingers pass through the carpal tunnel. A main nerve to the hand (median nerve) also goes through this tunnel before dividing into smaller branches in the palm.

The median nerve gives feeling to the thumb, index and middle fingers, and half of the ring finger. It also controls the movement of the small muscles at the base of the thumb.

  • Pins and needles. This is tingling or burning in part or all of the shaded area shown above. This is typically the first symptom to develop. The index and middle fingers are usually first to be affected.
  • Pain in the same fingers may then develop. The pain may travel up the forearm and even to the shoulder.
  • Numbness of the same finger(s), or in part of the palm, may develop if the condition becomes worse.
  • Dryness of the skin may develop in the same fingers.
  • Weakness of some muscles in the fingers and/or thumb occurs in severe cases. This may cause poor grip and eventually lead to muscle wasting at the base of the thumb.
  • In most cases it is not clear why it occurs. It is thought that some minor changes occur in the tendons and/or other structures going through the carpal tunnel. This may cause an increase in pressure within the tunnel. The increase in pressure is thought to squash (compress) and restrict the blood supply to the median nerve. As a result, the function of the median nerve is affected causing the symptoms.
  • Your genes may play a part. There seems to be some inherited (genetic) factor. About 1 in 4 people with carpal tunnel syndrome have a close family member (father, mother, brother, sister) who also has or had the condition.
  • Bone or arthritic conditions of the wrist such as rheumatoid arthritis or wrist fractures may lead to carpal tunnel syndrome.
  • Various other conditions are associated with carpal tunnel syndrome. For example: pregnancy, obesity, an underactive thyroid, diabetes, the menopause, other rare diseases, and a side-effect of some medicines. Some of these conditions cause water retention (oedema) which may affect the wrist and cause carpal tunnel syndrome.
  • Rare causes include cysts, growths, and swellings coming from the tendons or blood vessels passing through the carpal tunnel.