Carpal tunnel syndrome (CTS) is a disorder that causes pain and weakness in the hand and wrist. CTS develops from problems in a nerve in the wrist — not the muscles, as some people believe. The symptoms of CTS can range from mild to incapacitating.
To understand how carpal tunnel syndrome arises, it is important to know the parts of the hand and wrist that are involved.
The Carpal Tunnel. The carpal tunnel is a passageway that forms beneath the strong, broad transverse ligament. This ligament is a bridge that extends across the lower palm and connects the bones of the wrist (carpals) that form an arch below the tunnel.
The Median Nerve and Flexor Tendons. The median nerve and nine flexor tendons pass under the ligament bridge and through the carpal tunnel (similar to a river). They extend from the forearm up into the hand:
The median nerve travels through a compartment in the wrist called the carpal tunnel. The ligaments that traverse the nerve are not very flexible. Any swelling within the wrist compartment can put excessive pressure on structures such as the blood vessels and the median nerve. Excessive pressure can constrict blood flow and cause nerve damage. The symptoms from the compression cause pain, loss of sensation, and decreased function in the hand.
It is not completely known how the process leading to carpal tunnel syndrome actually evolves, and how nerve conduction (the transmission of the nerve signal) through the wrist changes. In general, carpal tunnel syndrome develops when the tissues around the median nerve swell and press on the nerve. Early in the disorder, the process is reversible. Over time, however, the insulation on the nerves may wear away, and permanent nerve damage may develop.
The following events have been observed in the hands of people with carpal tunnel syndrome:
The result of these processes is pain, numbness, and tingling in the wrist, hand, and fingers. Only the little finger is unaffected by the median nerve.
Symptoms of carpal tunnel syndrome usually progress gradually over weeks and months, or sometimes years. Anyone with recurrent or persistent pain, numbness and tingling, or weakness of the hand should consult a doctor for a diagnosis. Symptoms often develop as follows:
Symptoms may occur not only when the hand is being used but also at night when the patient is at rest. Even in cases where work is the suspected cause, symptoms typically first occur outside of work. In fact, the disorder may be distinguished from similar conditions by pain that occurs at night after going to bed.
Biological Causes. Carpal tunnel syndrome is considered an inflammatory disorder caused by repetitive stress, physical injury, or a medical condition. It is often very difficult, however, to determine the precise cause of carpal tunnel syndrome. No tests are available to identify a specific cause. Except in patients with certain underlying diseases, the biological mechanisms leading to carpal tunnel syndrome are unknown.
Working Conditions versus Medical Problems. Although some studies suggest that more than half of CTS cases are associated with workplace factors, there is no strong evidence of a cause-and-effect relationship. In fact, most studies now strongly suggest that carpal tunnel syndrome is primarily associated with medical or physical conditions such as diabetes, osteoarthritis, hypothyroidism, and rheumatoid arthritis.
CTS also tends to occur in people with certain genetic or environmental risk factors. These risk factors include obesity, smoking, alcohol abuse, or significant mental stress. CTS sometimes runs in families, which suggests that it has some type of genetic origin. When people who are susceptible to CTS are subjected to repetitive hand or wrist work, the risk for CTS can become significant. CTS, then, is very likely to be due to a combination of factors that lead to nerve damage in the hand.
High Force and Vibration. Even though medical and physical conditions may be the initial culprits leading to CTS, certain working conditions may be linked to nerve damage. Work that involves high force or vibration is particularly hazardous, as is repetitive hand and wrist work in cold temperatures.
In addition to CTS, other disorders of the hand and wrist result from these work-related movements. They include the following:
All of these problems are generally associated with repetitive and forceful use of the hands, resulting in damaged muscles and bones of the upper arms.