Carpal Tunnel Syndrome

Presentation by Dr. Williams

CARPAL TUNNEL SYNDROME

Carpal tunnel syndrome is a painful, numbing, weakening condition of the hand due to compression of the median nerve at the wrist. The median nerve provides sensation to the thumb, index, long and radial half of the ring finger and innervation of the opposing muscles of the thumb. Pressure on this nerve as it enters the hand through the unyielding confines of the carpal tunnel causes the characteristic symptoms of the condition termed by some "the industrial injury of the informed age" or "the new industrial epidemic." Characteristically, the symptoms of carpal tunnel syndrome are insidious, slow and gradual in onset without a history of inciting injury. They usually occur in the dominant hand of middle-aged ladies with paroxysms increased with activities and relieved with rest. They complain of being awakened in the middle of the night with an annoying burning, aching, tingling sensation of the hand. Relief is sought by getting up, shaking the hand, holding it down and running water over it, rubbing it, going to the window and letting air blow over it. Years ago when carpal tunnel syndrome was not a household word, it was misdiagnosed and considered by some doctors to be an hysterical conversion syndrome or occupational neurosis. It was not unusual for an individual with the condition to seek the advice of a psychiatrist. Now the condition is so well known, patients come into my office with any kind of hand pain stating they have discussed the condition with their neighbor and they have carpal tunnel syndrome. Often, instead of consulting a psychiatrist these days they consult an attorney.

Carpal tunnel syndrome was first mentioned in 1731 by Ramazzini, who described disorders of the hand and wrist associated with performances of repetitive manual jobs in clerks and scribes from incessant movements of the hand. In 1860, Sir James Paget described the autopsy findings of median nerve compression of the wrist to the Royal College of Surgeons. A few other small series of cases were reported in the early 1900s but it was not until 1946 that Cannon and Love described 38 cases of median nerve symptoms in the hand which were amenable to surgical decompression by release of the transverse carpal ligament. Large series of carpal tunnel syndrome were reported in the 50s and 60s. The causes of the condition were largely attributable to any metabolic or structural disorder that would increase the pressure in the carpal tunnel either by swelling of the structures in the tunnel or narrowing of the tunnel. The carpal tunnel is formed by the concave arches of the wrist bone and an unyielding non-elastic transverse carpal ligament on the anterior surface of the wrist. The soft median nerve and the nine hard, long thumb and finger flexors pass through the carpal tunnel as they enter the hand. The flexor tendons are lined by a thin slippery stocking-like membrane which allows a slick lubricating gliding surface for the tendons. This membrane is called tenosynovium. When the tenosynovium thickens it increases the content of the unyielding carpal tunnel causing compression on the spaghetti-like soft median nerve. The medical literature initially emphasized any metabolic or structural disorder that would increase the pressure in the carpal tunnel or narrow the tunnel. These included rheumatoid arthritis, tuberculosis, gout, amyloidosis or fractures about the wrist. The majority of cases, however, were considered to be due to "nonspecific tenosynovitis." In these conditions the swollen membrane about the tendons was not due to infection or associated with gout, rheumatoid arthritis or any other known metabolic condition. During the 1970s and 1980s there has been increased awareness that this nonspecific tenosynovitis has an occupational basis. Ergonomics - the study of work, particularly human machine systems, has clearly demonstrated many cases of carpal tunnel syndrome or a result of repetitive strain or cumulative trauma. High force and high repetitive jobs, particularly performed with the wrist extended or flexed or ulnarly deviated, are high risk factors. The tenosynovium response to overuse by an inflammatory reaction is much like when one develops a blister or a callus on the hand from repetitive forceful use of a screwdriver. As the tenosynovium thickens gradually over a period of weeks, months and years, the pain, numbness and weakness in the hand from median nerve compression increases. Studies by Gelberman and co-workers at the University of California demonstrate that with 90 degrees of wrist flexion the pressure in the carpal tunnel increases to 94 mm. of mercury, while with 90 degrees of wrist extension the mean pressure was 110 mm. of mercury. In the neutral position, pressure was 2.5 mm. of mercury. In patients with carpal tunnel syndrome the mean pressure was 32 mm. of mercury at rest, and release of the carpal tunnel brought about immediate reduction in the pressure. The incidence of carpal tunnel syndrome in the general population is unknown, but has been estimated to occur in about 1 to 2 percent of the population. In Annals of Internal Medicine, the March 1990 Editorial, it was stated that The California Occupational Health Program indicated a significant under-reporting of the carpal tunnel syndrome by healthcare providers in Santa Clara County. A survey indicated that there were 7,214 patients with carpal tunnel syndrome in 1987, of which 47 percent were believed to have been work-related. Forceful grasping or pinching, awkward positions of the hand and wrist, direct pressure over the carpal tunnel and the use of vibrating hand tools increased the risk of development of the syndrome. Metabolic risk factors include diabetes, hypothyroidism, and inflammatory-types of arthritis and alcoholism. For many years the occupational factors were overlooked but this is not the case today. The incidence of carpal tunnel syndrome has been reported to be 14.5 percent in certain meat packers and poultry workers, 17 percent in keyboard computer operators, 18 percent among Swedish scissor makers, 56 percent among Swedish packers, and 53 percent among Finnish butchers. A high incidence has been reported in grocery checkers, musicians, typists, housekeepers, cooks, carpenters, dental hygienists, electronic assembly workers and those who use vibratory tools such as chain saws, riveting hammers, percussion drilling machines, and oscillating sanders. The cumulative effect of the biomechanical stress on the hand and wrist is widely accepted in the insurance and medical community today. These previously classified nonspecific tenosynovitis cases are now considered to be a neurological overuse syndrome or from a repetitive strain injury, cumulative trauma disorder. Even the word computeritis has been coined. The diagnosis is made by noting numbness in the thumb, index, long and radial half of the ring finger, weakness in the thumb muscles of opposition, and the characteristic nocturnal tingling paresthesias. A motor nerve conduction of greater than 4.5 milliseconds or sensory nerve conduction greater than 3.5 milliseconds is an objective method of confirming the diagnosis. A positive Tinel's sign, percussion of the nerve at the wrist, or a Phalen's sign, holding the wrist flexed 60 seconds exacerbating the symptoms, are other diagnostic signs. Treatment: From a medical, surgical standpoint, when a patient is seen with numb fingers, a weak thumb and delay in median nerve conduction, relief of pressure on the median nerve must be obtained properly to prevent irreversible damage to the nerve with resultant permanent numbness and weakness of the hand. Conservative measures include splinting of the wrist in the neutral position, resting the fingers, nonsteroidal anti-inflammatory agents or steroid injections in the carpal tunnel. These are directed at reducing the volume of tenosynovium, thereby giving more room for the median nerve in the carpal tunnel. If relief of the symptoms and signs are not obtained, surgical decompression of the carpal tunnel is  indicated. This operation is performed through a thenar crease incision in which the transverse carpal ligament is incised longitudinally, the median nerve freed, and the tenosynovium excised. The transverse carpal ligament is not repaired but allowed to heal with a few millimeter gap which, in essence, enlarges the carpal tunnel. The results of surgery are considered very good by most standards but are often unpredictable in workmens' compensation cases. Surgery in most large series has afforded at least 90 percent or more relief of the symptoms, gradual return of sensory appreciation, sometimes immediately and sometimes over a six month period. Harris, Gelman and Associates reported in The Journal of Hand Surgery in 1989, that grip strength was 28 percent of pre-operative at three weeks, 73 percent at six weeks, and return to the pre-operative level at three months. At six months, grip strength was 116 percent. Pinch strength returned sooner. Two-point sensory discrimination returned to normal in 75 percent, improved in 75 percent and did not change in 8 percent. In about 6 percent of individuals there was a residual painful scar. One percent developed reflex sympathetic dystrophy. Prevention of carpal tunnel syndrome in the workplace is gaining more attention. The National Institute for Occupational Safety and Health has an institute within the Centers for Disease Control and has targeted carpal tunnel syndrome for surveillance in certain states, along with occupational asthma, lead poisoning, noise induced hearing loss and other conditions. The goal is to prevent carpal tunnel syndrome in jobs predisposing workers to repetitive forceful jobs involving certain awkward hand positions, or the use of vibratory hand tools or those with resultant direct external pressure over the carpal tunnel. Prevention includes modification of hand tools and improvement in work-station design and work practices as well as altering the worker's posture. Examples include altering a computer height so that the wrist is in the neutral position rather than the hyperextended position, using the thumb for button control rather than the fingers since the thumb muscles are less prone to fatigue, curving the handle of the knife 90 degrees in a poultry processor so that the cuts can be made with the arm rather than repetitive wrist flexions, keeping knives sharp at all times to reduce the force of meat cutting, the use of protective splints, five minute rest period per hour for computer workers and no more than 70 percent of the workday at the same job. Hopefully, by early recognition of the condition and appropriate prevention methods, the incidence of carpal tunnel syndrome can be greatly reduced. Prevention of carpal tunnel syndrome includes 1) early diagnosis so that a splint/steroid injections may relieve the initial symptoms and avoid the necessity of time lost and costly surgery, 2) a temporary job assignment to reduce the repetitive wrist flexion and extension or relief from a vibratory tool, 3) re-design of tools such as the use of a 19 degree curved handle for chicken processing, which eliminates the need to flex the wrist while cutting the meat. The job must fit the worker which may mean Page 8 changing the height of an assembly line so that the wrist can be at a neutral position, properly re-shaping tools, use of protective splints, padding of the tools and the use of gloves. Carpal tunnel syndrome is a multifactorial condition by timely recognition, appropriate clinical management and analysis of ergonomic factors. Hopefully the occupational risks can be greatly reduced, thereby both benefitting the worker and the employee.

CARPAL TUNNEL SYNDROME

If a 42-year-old data entry clerk in your office reported that, although she had had no injuries and during the day she was okay, but that she had been awakened in the middle of each night for the past two weeks with a numb, aching, burning feeling in her right hand that was relieved by holding her hand down and shaking it, rubbing it and running cold water over it, would you feel she had a work-related problem? What you would be dealing with is a condition called carpal tunnel syndrome. This condition recently has been called "the new industrial epidemic" and "the industrial injury of the informed age." Carpal tunnel syndrome is caused by median nerve compression at the wrist. The median nerve is one of the three major nerves in the upper extremity. On its way to the hand, it gives branches to forearm muscles; then it passes into the hand through the carpal (or wrist) canal where it provides sensation for the thumb, index, long and half of the ring finger, and innervates the thumb opposition muscles. As the median nerve enters the hand through the carpal tunnel, it divides sending branches to the thumb, index, long and half of the ring finger. It is important to appreciate this anatomical fact as seen here in this anatomical specimen. Another nerve supplies sensation to the little finger and half of the ring finger. This ulnar nerve does not go through the carpal tunnel; therefore, in carpal tunnel syndrome, sensation of the little finger is normal. The carpal tunnel is formed by the concave arching wrist bones and a tough unyielding ligament. It contains the nine finger and thumb flexor tendons - hard structures - and the median nerve - a soft structure - plus a thin stocking-like covering of the tendons called tenosynovium; "teno" for tendon and synovium for a thin, slippery membrane that facilitates tendon gliding. In this diagram we see the transverse carpal ligament, the relatively hard flexor tendons in white with their tenosynovium seen in blue, and the median nerve. In this picture the carpal tunnel has been opened by an incision of the transverse carpal ligament. One sees the nine flexor tendons with their surrounding tenosynovium. Carpal tunnel syndrome is caused by any condition which reduces the size of the carpal tunnel, such as a fracture or dislocation of the wrist bone, or much more commonly an increase in the volume of the carpal tunnel by an inflammatory disease process or an occupational problem which thickens the tenosynovium. The onset of carpal tunnel syndrome is usually gradual and insidious over weeks to months with nocturnal exacerbations in which the patient is awakened with a painful, numb feeling. The symptoms are usually in the dominant hand, bilaterally, one-third of the time. It is worse during periods of increased activities and usually relieved on the weekends with rest. The symptoms of pain may extend from the hand and wrist to the forearm, arm and shoulder along the course of the median nerve. At first, the person feels that the whole hand is numb, but with specific questioning the little finger is spared. The weakness involves the muscles which bring the thumb into opposition. The signs of carpal tunnel syndrome are loss of sensory appreciation, except in the little finger, weakness of opposing the thumb, prolonged median nerve conduction which can be measured electronically, a Tinel's sign and Phalen's sign. This demonstrates the way the thumb's strength is tested for opposition. This would be weak in a late case of carpal tunnel. Tapping of the median nerve at the wrist, causing tingling paresthesias, is called a Tinel's sign. Flexing the wrist for 60 seconds, with resultant increase in numbness and pain in the median distribution, is called a Phalen's sign. Carpal tunnel syndrome was originally thought to be due to some disease or metabolic condition of the body such as rheumatoid arthritis or gout, tuberculosis, hypothyroidism and associated with a high incidence of diabetes or alcoholism. The vast majority of cases did not have a definite cause for the tenosynovitis so it was labeled "non-specific." We know now that most cases of carpal tunnel syndrome are caused by thickened tenosynovium, and that repetitive forceful activities cause inflammation of the tenosynovium with resultant thickening of the tenosynovium, which in the carpal tunnel causes compression of the median nerve by an increase in the content of the carpal tunnel. The median nerve is soft - like spaghetti -where the tendons are firm and unyielding. This condition is now called one of the cumulative trauma (disorders) or repetitive strain injuries. C.T.S. is different from most repetitive strains since the median nerve becomes "entraped" in the unyielding carpal tunnel. It has been shown that with the wrist in the neutral position in controlled individuals, the pressure and millimeters of mercury is 2.5 and in those with carpal tunnel syndrome it is 32. With the wrist in flexion the pressure in the carpal tunnel is 31 in controlled and 94 mm. of mercury in a person with carpal tunnel syndrome. With the wrist in extension in normal individuals, the pressure in the carpal tunnel is 30 mm. of mercury and in those with carpal tunnel syndrome it is 110 mm. of mercury. Ergonomic studies have outlined many occupational risk factors for carpal tunnel syndrome. They are summarized here as high repetitive jobs, high force jobs, jobs which require the wrist to be in flexion, extension or ulnar deviation, and the use of vibratory tools or direct pressure over the carpal tunnel. These occupational risk factors are basically repetitive or forceful jobs with the wrist and fingers in the flexed or extended position. The tenosynovium thickens, thereby compressing the median nerve, giving the signs and symptoms of carpal tunnel syndrome. The incidence of carpal tunnel syndrome in the general population is unknown. It has been estimated to be about 1, possibly 2 percent. In meat packers it was found in 14.5 percent, in Swedish scissor makers 18 percent, in Finnish butchers 50 percent, and in computer operators 17 percent. There is also a high incidence in dental hygienists, musicians, grocery checkers, assembly workers, carpenters and those using vibratory tools such as compression hammers and chain saws. Treatment is directed at relieving the pressure on the median nerve. Conservative measures to reduce the tenosynovium include rest, splints and steroid injections. If symptoms persist, surgery is required to open the tunnel. A simple wrist splint often worn at night is helpful in some individuals. Steroid injections into the tenosynovium sometimes reduce the inflammatory swelling, thereby relieving the pressure on the median nerve. A surgical procedure simply opens the carpal tunnel by incising the transverse carpal ligament. Here is a surgical procedure in which the patient had numbness in the median nerve distribution, and slight weakness of the lateral thenar muscles. This is an individual showing the surgical incision over the carpal tunnel. The transverse carpal ligament has been released revealing the thickened yellowish tenosynovium. (This is some of the excised tenosynovium). Here is the freed nerve and some of the flexor tenosynovium removed. This shows the edge of the cut transverse carpal ligament. This is the incision closed. A percutaneous operative technique with two small incisions is now becoming popular. The results of surgery are 90 percent or more improvement and decrease in the symptoms. Usually the nocturnal paresthesias are relieved immediately and the numbness resolves over several weeks to months, but the results are unpredictable in workmens' compensation cases. Most people, however, can return to light work in six weeks or less and heavy duty work in three to four months. This is a typical post-operative scar which is barely visible some years after carpal tunnel release. Prevention is the aim of the industry and the medical profession. Early recognition of the symptoms and signs permits early conservative therapy. The use of a protective splint even at work neutralizes the wrist. Early use of cortisone injections can decrease the tenosynovial inflammation and the tendency for permanent tenosynovial thickening. Also, modifications in the work place would be directed at reducing repetitive wrist flexion. For example, in the poultry industry, reduction of wrist flexion can be done by using a 20 degree angled knife. This allows use of the shoulder and arm for cuts rather than the wrist. Reduction of activities requiring repetitive finger flexion with the wrist in extension is highly desirable. Also, reducing the direct pressure from small handles over the carpal tunnel is desirable by enlarging handles and wearing gloves. Data processors should be encouraged to avoid the wrist hyperextension position. Altering the work place will allow raising and lowering the height of the chair and having wrist supports to keep the wrist in the neutral position. You recall we said the pressure in the carpal tunnel is much less in the neutral position than in flexion or extension. A five minute per hour "break" or rest period, and a 70 percent time limit per work day for a repetitive or forceful job is recommended, particularly if they are developing early carpal tunnel symptoms.

In summary, prevention is the goal to reduce lost time and the need for surgery. This includes reduction in high force, high repetition job activities, the wrist in neutral, protective splints, alter the work posture, alter the workers' tools and reduce vibratory forces as much as possible.