Carpal tunnel syndrome is an entrapment neuropathy of the wrist. It occurs when the median nerve, which runs through the wrist and enervates the thumb, pointer finger, middle finger and the thumb side of the ring finger, is aggravated because of compression. Symptoms include numbness, tingling and pain in the fingers the median nerve sensitizes. Some people have difficulty grasping items and may have pain radiating up the arm. Carpal tunnel syndrome is common in people who work on assembly lines, doing heavy lifting and packing involving repetitive motions. Other repetitive movements such as typing are often implicated in cause carpal tunnel syndrome, however some clinical evidence contradicts this association. Additional causes of the syndrome include pregnancy, diabetes, obesity or simply wrist anatomy in which the carpal tunnel is narrow. Treatment includes immobilization with a splint or in severe cases surgery to release the compression of the median nerve.
Description
Carpal tunnel syndrome (CTS) is caused by a compression of the median nerve in the wrist, a condition known as nerve entrapment. Nerve entrapments occur when a nerve that travels through a passage between bones and cartilage becomes irritated because a hard edge presses against it. In almost every case of nerve entrapment, one side of the passage is moveable and the repetitive rubbing exacerbates the injury.
Three sides of the carpal tunnel are made up of three bones that form a semicircle around the back of the wrist. The fourth side of the carpal tunnel is made up of the transverse carpal tunnel ligament also called the palmar carpal ligament, which runs across the wrist on the same side as the palm. This ligament is made of tissue that cannot stretch or contract, making the cross sectional area of the carpal tunnel a fixed size. Running through the carpal tunnel are nine tendons that assist the muscles that move the hand and the median nerve. The median nerve enervates the thumb, forefinger, middle finger, and the thumb side of the ring finger. The ulnar nerve that serves the little finger side of the ring finger and the little finger runs outside of the transverse carpal tunnel ligament and is therefore less likely to become entrapped in the wrist.
The tendons that run through the carpal tunnel are encased in a lubricating substance called tensynovium. This substance can become swollen when the tendons rub quickly against one another, as occurs when the finger muscles are used repeatedly. When this happens, there is less space within the carpal tunnel for the median nerve and it becomes compressed or pinched.
When a nerve is compressed, the blood supply to the nerve is interrupted. In an attempt to alleviate the problem, the body's immune system sends new cells called fibroblasts to the area to try to build new tissue. This eventually results in scar tissue around the nerve. In an area that cannot expand this only worsens the situation and puts more pressure on the nerve. A compressed nerve can be likened to an electrical wire that has been crimped. It cannot transmit electrical signals to the brain properly and the result is a feeling of numbness, tingling or pain in the areas that the nerve enervates.
Compression of the median nerve causes tingling and numbness in the thumb, forefinger, middle finger and on the thumb-side of the fourth finger. It may also cause pain in the forearm and occasionally into the shoulder. Some persons have a difficult time gripping and making a fist.
People who suffer from CTS range from those who are mildly inconvenienced and must wear a splint at night to relieve pressure on the median nerve to those who are severely debilitated and lose use of their hands. Problems associated with CTS can invade a person's life making even simple tasks such as answering the phone, reading a book or opening a door extremely difficult. In severe cases, surgery to release the median nerve is often suggested by an orthopedist. The carpal tunnel ligament is cut, relieving the pressure within the carpal tunnel. Rates of success are quite high with the surgical procedure.
Demographics
Carpal tunnel syndrome is more common in women than in men, perhaps because the carpal tunnel generally has a smaller cross section in women than in men. The ratio of women to men who suffer from CTS is about three to one. CTS is most often diagnosed in people who are between 30 and 50 years old. It is more likely to occur in people whose professions require heavy lifting and repetitive movements of the hands such as manufacturing, packing, cleaning and finishing work on textiles.
Causes and symptoms
Carpal tunnel syndrome may occur when anything causes the size of the carpal tunnel to decreases or when anything puts pressure on the median nerve. Often the cause is simply the result of an individual's anatomy; some people have smaller carpal tunnels than others. Trauma or injury to the wrist, such as bone breakage or dislocation can cause CTS if the carpal tunnel is narrowed either by the new position of the bones or by associated swelling. Development of a cyst or tumor in the carpal tunnel will also result in increased pressure on the median nerve and likely CTS. Systemic problems that result in swelling may also cause CTS such as hypothyroidism, problems with the pituitary gland, and the hormonal imbalances that occur during pregnancy and menopause. Arthritis, especially rheumatoid arthritis, may also cause CTS. Some patients with diabetes may be more susceptible to CTS because they already suffer from nerve damage. Obesity and cigarette smoking are thought to aggravate symptoms of CTS.
Much evidence suggests that one of the more common causes of CTS involves performing repetitive motions such as opening and closing of the hands or bending of the wrists or holding vibrating tools. Motions that involve weights or force are thought to be particularly damaging. For example, the types of motions that assembly line workers perform such as packing meat, poultry or fish, sewing and finishing textiles and garments, cleaning, and manufacturing are clearly associated with CTS. Other repetitive injury disorders such as data entry while working on computers are also implicated in CTS. However, some clinical data contradicts this finding. These studies show that computer use can result in bursitis and tendonitis, but not CTS. In fact, a 2001 study by the Mayo Clinic found that people who used the computer up to seven hours a day were no more likely to develop CTS than someone who did not perform the type of repetitive motions required to operate a keyboard.
The two major symptoms of carpal tunnel syndrome include numbness and tingling in the thumb, forefinger, middle finger and the thumb side of the fourth finger and a dull aching pain extending from the wrist through the shoulder. The pain often worsens at night because most people sleep with flexed wrists, which puts additional pressure on the median nerve. Eventually the muscles in the hands will weaken, in particular, the thumb will tend to lose strength. In severe cases, persons suffering from CTS are unable to differentiate between hot and cold temperatures with their hands.
Diagnosis
Diagnosis of carpal tunnel syndrome begins with a physical exam of the hands, wrists and arms. The physician will note any swelling or discoloration of the skin and the muscles of the hand will be tested for strength. If the patient reports symptoms in the first four fingers, but not the little finger, then CTS is indicated. Two special tests are used to reproduce symptoms of CTS: the Tinel test and the Phalen test. The Tinel test involves a physician taping on the median nerve. If the patient feels a shock or a tingling in the fingers, then he or she likely has carpal tunnel syndrome. In the Phalen test, the patient is asked to flex his or her wrists and push the backs of the hands together. If the patient feels tingling or numbness in the hands within one minute, then carpal tunnel syndrome is the likely cause.
A variety of electronic tests are used to confirm CTS. Nerve conduction velocity studies (NCV) are used to measure the speed with which an electrical signal is transferred along the nerve. If the speed is slowed relative to normal, it is likely that the nerve is compressed. Electromyography involves inserting a needle into the muscles of the hand and converting the muscle activity to electrical signals. These signals are interpreted to indicate the type and severity of damage to the median nerve. Ultrasound imaging can also be used to visualize the movement of the median nerve within the carpal tunnel. X rays can be used to detect fractures in the wrist that may be the cause of carpal tunnel syndrome. Magnetic resonance imaging (MRI) is also a useful tool for visualizing injury to the median nerve.
Treatment team
Treatment for carpal tunnel syndrome usually involves a physician specializing in the bones and joints (orthopedist) or a neurologist, along with physical and occupational therapists, and if necessary, a surgeon.
Treatment
Lifestyle changes are often the first type of treatment prescribed for carpal tunnel syndrome. Avoiding activities that aggravate symptoms is one of the primary ways to manage CTS. These activities include weight-bearing repetitive hand movements and holding vibrating tools. Physical or occupational therapy is also used to relieve symptoms of CTS. The therapist will usually train the patient to use exercises to reduce irritation in the carpal tunnel and instruct the patient on proper posture and wrist positions. Often a doctor or therapist will suggest that a patient wear a brace that holds the arm in a resting position, especially at night. Many people tend to sleep with their wrists flexed, which decreases the space for the median nerve within the carpal tunnel. The brace keeps the wrist in a position that maximizes the space for the nerve.
Doctors may prescribe non-steroidal anti-inflammatory medications to reduce the swelling in the wrist and relieve pressure on the median nerve. Oral steroids are also useful for decreasing swelling. Some studies have shown that large quantities of vitamin B-6 can reduce symptoms of CTS, but this has not been confirmed. Injections of corticosteroids into the carpal tunnel may also be used to reduce swelling and temporarily provide some extra room for the median nerve.
Surgery can be used as a final step to relieve pressure on the median nerve and relieve the symptoms of CTS. There are two major procedures in use, both of which involve cutting the transverse carpal tunnel ligament. Dividing this ligament relieves pressure on the median nerve and allows blood flow to the nerve to increase. With time,
the nerve heals and as it does so, the numbness and pain in the arm are reduced.
Open release surgery is the standard for severe CTS. In this procedure, a surgeon will open the skin down the front of the palm and wrist. The incision will be about two inches long stretching towards the fingers from the lowest fold line on the wrist. Then next incision is through the palmar fascia, which is a thin connective tissue layer just below the skin, but above the transverse carpal ligament. Finally, being careful to avoid the median nerve and the tendons that pass through the carpal tunnel, the surgeon carefully cuts the transverse carpal ligament. This releases pressure on the median nerve.
Once the transverse carpal tunnel ligament is divided, the surgeon stitches up the palma fascia and the skin, leaving the ends of the ligament loose. Over time, the space between the ends of the ligament will be joined with scar tissue. The resulting space, which studies indicate is approximately 26% greater than prior to the surgery, is enlarged enough so that the median nerve is no longer compressed.
A second surgical method for treatment of CTS is endoscopic carpal tunnel release. In this newer technique, a surgeon makes a very small incision below the crease of the wrist just below the carpal ligament. Some physicians will make another small incision in the palm of the hand, but the single incision technique is more commonly used. The incision just below the carpal ligament allows the surgeon to access the carpal tunnel. He or she will then insert a plastic tube with a slot along one side, called a cannula, into the carpal tunnel along the median nerve just underneath the carpal ligament. Next an endoscope, which is a small fiber-optic cable that relays images of the internal structures of the wrist to a television screen, is fed through the cannula. Using the endoscope, the surgeon checks that the nerves, blood vessels and tendons that run through the carpal tunnel are not in the way of the cannula. A specialized scalpel is fed through the cannula. This knife is equipped with a hook on the end that allows the surgeon to cut as he or she pulls the knife backward. The surgeon positions this knife so that it will divide the carpal ligament as he pulls it out of the cannula. Once the knife is pulled through the cannula, the carpal ligament is severed, but the palma fascia and the skin are not cut. Just as in the open release surgery, cutting the carpal ligament releases the pressure on the median nerve. Over time, scar tissue will form between the ends of the carpal ligament. After the cannula is removed from the carpal tunnel, the surgeon will stitch the small incision in patient's wrist and the small incision in the palm if one was made.
The two different surgical techniques for treating CTS have both positive and negative attributes and the technique used depends on the individual case. In open release, the surgeon has a clear view of the anatomy of the wrist and can make sure that the division of the transverse ligament is complete. He or she can also see exactly which structures to avoid while making the incision. On the other hand, because the incision to the exterior is much larger than in endoscopic release, recovery time is usually longer. While the symptoms of CTS usually improve rapidly, the pain associated with the incision may last for several months. Many physicians feel that the recovery time associated with endoscopic release is faster than that for open release because the incision in the skin and palma fascia are so much smaller. On the other hand, endoscopic surgery is more expensive and requires training in the use of more technologic equipment. Some believe that are also risks that the carpal ligament may not be completely released and the median nerve may be damaged by the cannula, or the specialized hooked knife. Research is ongoing in an attempt to determine whether open or endoscopic release provides the safest and most successful results.
Success rates of release surgery for carpal tunnel syndrome are extremely high, with a 70–90% rate of improvement in median nerve function. There are complications associated with the surgery, although they are generally rare. These include incomplete division of the carpal ligament, pain along the incisions and weakness in the hand. Both the pain and the weakness are usually temporary. Infections following surgery for CTS are reported in less than 5% of all patients.
Recovery and rehabilitation
One day following surgery for carpal tunnel syndrome, a patient should begin to move his or her fingers, however gripping and pinching heavy items should be avoided for a month and a half to prevent the tendons that run through the carpal tunnel from disrupting the formation of scar tissue between the ends of the carpal ligament.
After about a month and a half, a patient can begin to see an occupational or physical therapist. Exercises, massage and stretching will all be used to increase wrist strength and range of motion. Eventually, the therapist will prescribe exercises to improve the ability of the tendons within the carpal tunnel to slide easily and to increase dexterity of the fingers. The therapist will also teach the patient techniques to avoid a recurrence of carpal tunnel syndrome in the future.
Clinical trials
There are a variety of clinical trials underway that are searching for ways to prevent and treat carpal tunnel syndrome. The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) supports this research on CTS. Their website is <http://clinicaltrials.gov/search/term=Carpal+Tunnel+Syndrome>.
One trial seeks to determine which patients will benefit from surgical treatments compared to non-surgical treatments using a new magnetic resonance technique. The study is seeking patients with early, mild to moderate carpal tunnel syndrome. Contact Brook I. Martin at the University of Washington for more information. The phone number is (206) 616–0982 and the email is bim@u.washington.edu.
A second trial compares the effects of the medication amitriptyline, acupuncture, and placebos for treating repetitive stress disorders such as carpal tunnel syndrome. The study is located at Harvard University. For information contact Ted Kaptchuk at (617) 665–2174 or tkaptchu@caregroup.harvard.edu.
A third study is evaluating the effects of a protective brace for preventing carpal tunnel syndrome in people who use tools that vibrate in the workplace. The brace is designed to absorb the energy of the vibrations while remaining unobtrusive. For information on this study contact Prosper Benhaim at the UCLA Hand Center. The phone number is (310) 206–4468 and the email address is pbenhaim@mednet.ucla.edu.
Prognosis
Persons with carpal tunnel syndrome can usually expect to gain significant relief from prescribed surgery, treatments, exercises, and positioning devices.
BOOKS
Johansson, Phillip. Carpal Tunnel Syndrome and Other Repetitive Strain Injuries. Brookshire, TX: Enslow Publishers, Inc. 1999.
Shinn, Robert, and Ruth Aleskovsky. The Repetitive Strain Injury Handbook. New York: Henry Holt and Company. 2000.
American Chronic Pain Association (ACPA). P.O. Box 850, Rocklin, CA 95677. (916) 632-0922 or (800) 533-3231. ACPA@pacbell.net. <http://www.theacpa.org>.
National Chronic Pain Outreach Association (NCPOA). P.O. Box 274, Millboro, VA 24460. (540) 862-9437; Fax: (540) 862-9485. ncpoa@cfw.com. <http://www.chronicpain.org>.
National Institute of Arthritis and Musculoskeletal and Skin Dieseases (NIAMS). National Institutes of Health, Bldg. 31, Rm. 4C05, Bethesda, MD 20892. (301) 496-8188; Fax: (540) 862-9485. ncpoa@cfw.com. <http://www.niams.nih.gov/index.htm>.
