Repetitive Stress Injury (RSI) is attributed to a number of overlying
biomedical factors. Repetitive activities performed at work or leisure over an
extended period of time, constant excessive load or effort and poor body mechanics
are suggested as causes of RSI. In addition, medical conditions such as pregnancy,
rheumatoid arthritis, and diabetes can also contribute to RSI. When RSI occurs at
the wrist and/or fingers, persons complain of numbness, tingling and pain in the area
of the thumb, index, and middle fingers. The pain often increases at night and can
radiate to the forearm, upper arm and neck. Eventually the affected person loses
strength in the affected hand and can no longer easily move the fingers.
The term given for this set of symptoms is carpal tunnel syndrome (CTS), which is the narrowing of the anatomical tunnel formed by the wrist (carpal) bones through which the median nerve travels. The compression of the median nerve influences its sensory and motor innervations to the thumb, index, and middle fingers causing tingling, numbness, burning sensation, weakness and clumsiness.
The U.S. Department of Labor (DoL) concluded that the CTS is the “Chief occupational hazard of the 90’s”, affecting around eight million Americans and accounting for 41% of all work-related injuries. It is estimated that 25% of all computer operators have CTS, and by the year 2000 the DoL estimates over 50% of the workforce may be affected. Approximately 20,000 medical procedures are performed every year to correct various aspects of CTS; however, only 23% of all CTS patients are able to return to their previous professions after surgery.
Women are twice as likely to develop CTS as their male counterparts. Although they comprise 45% of the work force, they experience 66% of all work- related repetitive stress injuries. The Occupational Safety and Health Administration (OSHA) estimates that by the year 2000, cumulative trauma syndromes will account for 50 cents of each dollar spent on medical care. The American Academy of Orthopedic Surgeons estimates that CTS cost 1 billion dollars annually in medial treatment. Each worker compensation claim for repetitive stress injuries can cost from $20-100K.
Keyboard usage exacerbates other repetitive actions that are associated with CTS. Carpal Tunnel Syndrome, and its associated pathologies, is common among persons who use keyboards or fretboards as well as flute and string players. Treatment options for CTS vary widely, they include; surgery, Yoga, wrist splints that minimize wrist movements, specialized exercise equipment that strengthen the muscles of the forearm and fingers, and psychological support after the injury. The rationale for Yoga is that stretching and relaxing the wrist and forearm musculature can minimize CTS. Wrist splints can often help, especially within three months of the onset of symptoms. Their use reduces the latency of the evoked electromyogram (EMG) of the median nerve. The latency measurement of the median EMG is considered the criterion standard for the diagnosis of CTS. Various exercise devices have also been reported to be effective. Flextend is an example of such a device designed to correct the imbalance between the flexor and extensor muscles of the wrist. Flexor muscles of the forearm are more powerful than the extensor muscles and may contribute to the onset and progression of CTS.
The diagnosis of carpal tunnel syndrome is difficult. The classic procedure used to detect CTS via latency times of the median nerve and/or clinical evaluations have indicated that these two methods are not adequate to identify all patients who have the symptoms of CTS. Another method commonly used by the clinician is to evaluate the grip strength of the patient. This procedure requires the patient to maintain a constant amount of force for a minute or to rapidly grip and release a force-measuring device (dynamometer). This procedure does not mimic the real world, and its value as a diagnostic tool is questionable.
At present there is no objective measurement of the force that the fingers can produce when they are sequentially generating force on a keyboard while controlling the wrist angle. Although CTS is a major problem facing the work force and recreational groups in the United States, there is no reported method that quantifies pre- and post-finger force values after clinical intervention. In addition, there are no standards (e.g.: databases) of how much force one or all the fingers can generate while typing in a controlled situation. To develop such a database, a system is needed to collect and analyze finger-force data.
At present the diagnosis of CTS remains controversial. Atcheson, Ward and
Lowe evaluated 297 patients of whom 38% were diagnosed with CTS and studied
whether there were any underlying pathologies that may contribute to the diagnosis
of CTS. They concluded that a person with CTS is one who complains only of pain
in his/her upper limb.
The subjective criteria for diagnosis CTS consisted of the following:
The purpose of this project is to describe a force-measuring device that records single- and multiple-fingers force profiles. This system will incorporate individual force sensors on an ergonomically designed and commercially available computer keyboard. In addition, software will be developed to record the subject's depression and release of single and multiple keys and the force profile of each finger-force level.