Carpal Tunnel Syndrome.

Last updated Thursday, February 10, 2005

Figure 2 - Pressure on the median nerve

Causes and effects

Causes

The numbness, tingling, and weakness from CTS are due to pressure on the median nerve (see figure 2). This nerve carries signals between the hand and brain. In the wrist, the median nerve and several tendons that allow the fingers and thumb to bend pass through the carpal tunnel, a "tunnel" created by the carpal (wrist) bone and other tissue. The most common cause of CTS is swelling or inflammation around the tendons and nerve, which increases the pressure within the carpal tunnel. This increased pressure affects median nerve function, causing the symptoms of CTS.

In most patients with CTS, the cause is not known. However, anything that causes swelling on the tendons or produces repeated pressure on the median nerve can lead to CTS or make it worse if the condition already exists.

Possible causes of pressure on the median nerve include:

1. Injuries, such as a blow to the wrist. This may break one or more of the carpal bones and damage the median nerve.
2. Arthritis-related diseases, such as rheumatoid arthritis. These diseases cause pain and swelling in joints and other parts of the body. They can cause swelling of tissues in the carpal tunnel, resulting in pressure on the median nerve.
3. Work activities and hobbies that require highly repetitive wrist or finger motion, especially in combination with forceful pinching or gripping or activities involving vibrating hand tools or instruments that put pressure at the base of the palm. Some examples are:
   • meat, fish, and poultry processing
   • construction and carpentry
   • electronics assembly
   • logging and sawmill operations
   • supermarket cashiering and scanning
   • activities of hairdressers, factory and farm workers, and mechanics
   • needlework or knitting
   • typing or working at a computer keyboard

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