Causes and Risk Factors of Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) occurs when the median nerve, one of the large nerves in the wrist, is pinched as it passes through the tight carpal tunnel. The resulting pressure can develop due to many reasons. The chief factors are the structure of your wrist, injury, and conditions that lead to inflammation and swelling. Stress due to repetitive motion or using vibrating tools is a minor risk factor, while computer use is an unproven risk.

The carpal tunnel is formed by the small wrist bones on the bottom and a tight ligament on top. If pressure builds up in the carpal tunnel, the nerve is pinched and begins to function abnormally. When this happens, patients experience the typical symptoms of carpal tunnel, including pain, tingling, and numbness.

The pressure in the carpal tunnel is increased with certain positions of the wrist. Many people complain of carpal tunnel symptoms at night which is due to the fact that they sleep with their wrists folded under their body. This position can increase carpal tunnel pressure, exacerbating symptoms.

Most of the time there is no one cause that can be found for carpal tunnel syndrome, and often there are multiple risk factors that may be contributing.

The the most significant risk factors include:

• Wrist injury: A dislocation, fracture, burn, or severe bruise on the wrist or lower arm can cause swelling in the carpal tunnel.
• Anatomic factors: You may have been born with a small carpal tunnel, tiny wrists, or a bone arrangement that impinges on the carpal tunnel. Deformity can also develop due to inflammatory arthritis.
• Sex: Women are more likely to have carpal tunnel syndrome, perhaps because they have smaller wrists than men.
• Age: The biggest age risk group is 40 to 60.
• Inflammatory conditions including rheumatoid arthritis increase the risk.
• Conditions that damage nerves, including diabetes, may affect the median nerve.
• Conditions that lead to fluid retention, including pregnancy, menopause, and kidney failure
• Hypothyroidism: The mechanism isn't understood, but the condition can cause fluid retention and might lead to deposits on the median nerve.
• Acromegaly (overactive pituitary gland) increases the size of the median nerve, which raises the risk of compression.
• Repetitive use due to flexing the wrist, most often seen on an industrial assembly line in industries such as manufacturing, sewing, cleaning, and food processing

Controversy Over Computer Use as a Cause

There is a longstanding debate about the use of keyboards (or other technologies such as a computer mouse or smartphone) leading to the development of carpal tunnel syndrome. Despite many large and well-designed scientific studies, it has not been shown that carpal tunnel is caused by repetitive work activities such as typing or using a computer mouse.

Most of the data pointing to occupation as a risk factor for developing CTS comes from studies investigating the use of vibratory heavy machinery (including jackhammers), or the type of repetitive or forceful wrist use seen in some industrial jobs.

Sleeping with your wrists flexed, especially if they are under your body, increases the risk. Some activities, both at home and at work, can potentially cause repetitive increases in pressure in the carpal tunnel. Poorly designed work spaces can result in holding the wrist in a position that irritates the nerve. You may spend long periods doing the same motion or gripping an object, such as a pen, tightly. Poor posture with your shoulders rolled forward can compress the nerves in your neck and affect your arm and hand. A cold environment can also lead to hand pain and stiffness.

Obesity is also a risk factor. A BMI of 30 or more increases the risk of carpal tunnel, although why it does is not clear.