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Cumulative Trauma Disorders aka Repetitive Strain Injury

Why are They Important? 

Between 1991 and 1994 the yearly rate of Cumulative Trauma Disorders (CTD) increased by a factor of four to 332,000 cases. According to the Bureau of Labor Statistics (BLS) the total cost to business for that year for the condition was $10.8 billion. They claim that in 1997 over 150,000 cases were reported. At present, it affects 2.5 million computer users and according to the BLS the incidence of all types of CTDs make up to 60% of all occupational illnesses.  

The incidence has been increasing at such a rate that the National Institute of Occupational Safety and Health (NIOSH) had predicted that 50% of the national workforce would be affected with a CTD injury by the year 2000. Of all the different types of Cumulative Trauma Disorders, Carpal Tunnel Syndrome (CTS) alone is the second most common surgical procedure in the United States with an overall price tag of up to $60,000 per case. Back injuries rate second to CTS in costs.       

Currently, according to the U.S Department of Labor, when added up the direct and indirect costs of CTDs may total as much as $100 billion. 

What are Cumulative Trauma Disorders?  

The disorder describes a mechanism of injury resulting in a variety of musculoskeletal conditions depending on the particular muscles, tendons or ligaments involved. The condition is also referred to as Repetitive Strain Injury (RSI), Occupational Overuse Syndrome (OOS) and Repetitive Motion Syndrome (RMS).  The repetitive movements of muscles and associated support structures cause the tissues to become injured when there is insufficient recovery time.

As is similar to static muscle contractions the small blood vessels constrict as the muscles contract thereby preventing a sufficient amount of oxygen from reaching the muscle cells. Metabolic waste products build up in the tissues, because they are unable to be flushed out of the area. The repetitive nature of the activity causes the muscle to become fatigued and the rest cycle is inadequate for the muscle to recover. There may be inflammation involved especially when tendon and ligament structures are affected i.e. tendonitis. The risk of injury increases when such factors as intensity, frequency and duration of the activity exceed the physical ability of the worker to tolerate the work.  

Who is at Risk for Developing CTD and Why is the Incidence Increasing?  

Especially at risk are computer users, manufacturing and assembly-line workers, data entry workers and programmers, secretarial workers and transcriptionists, painters, musicians, carpenters and construction workers. Athletes are also susceptible due to the repetition and forces involved in their activity.  

Many of these jobs have been around for some time but there has been a change toward increased specialization in the workplace in which workers perform less variety of functions and work in limited, awkward and sustained postures using highly repetitive movements. These movements may be highly specialized while concentrating the work into small muscle groups. With keyboard and production line work it is the weaker muscles in the wrists and forearms that take on bulk of the work. 

Even with minimal forces involved, the lack of general physical conditioning of workers combined with this repetitious activity and overspecialization is a prescription for injury. It is no wonder that people who sit in chairs all day and work at computers make up such a large group of CTD sufferers.  

Women are more vulnerable to these injuries due to fluctuations in hormonal levels. These changes cause fluid retention, which reduces blood flow to muscles. There is increasing pressure on single mothers to take on jobs in high-risk categories that are characterized by repetitive tasks involving small muscle groups.  

How is CTD Prevented and Treated? 

Due to poor circulation into tendons, ligament and connective tissues, repetitive type injuries are resistant to treatment. Therefore it is much more desirable to prevent the conditions in the first place. In activities and tasks requiring a lot of repetition the workplace should be modified with injury prevention as a primary goal. In fact, ergonomic modification itself becomes part of the treatment.  

Much of the ergonomic modifications to computer workstations are geared towards the prevention of CTD type injuries. The advent of adjustable chairs, computer monitor arms, keyboards and footrests are all designed and intended for the purpose of avoiding sustained awkward postures. Particular attention must be paid to correct positioning of the wrists to avoid conditions like Carpal Tunnel Syndrome and tendonitis. When doing keyboard work it is best to elevate the wrists and avoid the habit of wresting them while typing. This prevents having to raise the hands into hyperextension and provides the freedom of movement of the hands to reach keys without having to stretch the fingers. As flat screens become more affordable and therefore accessible the computer user will have more desk room in order to rest the forearms during pauses. Similarly, these workstation modifications will help to avoid forward head positioning and slouching of the shoulders. These positions are primary culprits in developing neck and upper back pain and contributors to CTDs.  

Computer Vision Syndrome (CVS) is also considered a CTD involving a constant attempt of the eyes to focus on computer images. Shorter blocks of time spent at the computer, frequent breaks, appropriate lighting and the avoidance of glare all play a role in preventing this condition. With LCD technology we may see a decrease in vision problems as the computer images become clearer. 

A significant finding by NIOSH was that injury susceptibility tended to be a function of the amount of time spent at the computer. This finding speaks to the importance of using short rest pauses or “micro breaks” and these are most beneficial when coupled with stretches or exercises. The purpose of these micro breaks is to augment the regularly scheduled breaks and should be taken as frequently as necessary depending on the extent of the forces required by the work. In general, micro breaks of 20 to 180 seconds should be taken for every 10 to 15 minutes of continuous work.  

The idea of exercise is to stretch muscles that have been contracted for a prolonged period of time and contract muscles that have been stretched for a period of time. Stretches should be done at least every 2-3 hours throughout the work shift. Job rotation puts variety in the work routine and allows for postural changes and the normalization of blood flow to tissues. Jobs with high force or repetitive requirements should be rotated with jobs with low force or static requirements. Similarly, jobs that require standing should be rotated with jobs that require sitting. 

The manual handling of materials as is required in many occupations poses a particular hazard to the low back. Risk of cumulative trauma to the low back increases when lifting is done more than every 5 minutes and there are repeated lifts of objects over 30 pounds from a position below the level of the hands. Any lifting below this level necessitates bending at the waist, which leaves the worker vulnerable to low back injury. Lifting and carrying should be done with carts and mechanical devices whenever possible and, if done manually, the material should be lifted and carried as close to the body as possible to reduce the concentration of forces at the lumbar facets and discs. 

Tools and machine controls should be operable without having to bend the wrists while applying high pressures. Soft handle grips reduce pressure points in the hand and by increasing the surface area of the grip the grip strength is maximized. Powered tools tend to reduce work time and require less pressure but can produce vibration, which can cause nerve damage. In addition, with working temperatures below 70 degrees F. grip strength is decreased and there is an increased risk of cumulative trauma. 

In the realm of manufacturing and assembly type jobs work surface heights should be adjustable to elbow height in order that correct postures can be maintained. Sit/stand stools are helpful because they allow for changes in body position, which tends to dissipate stresses in the legs and back. Work surfaces and seats should be padded at potential pressure points. Work should be done with the hands at a comfortable distance from the body with the most frequently handled objects placed closest to the worker. This is important because fatigue increases the more the arms become extended. Illumination levels should comply with standards set for the specific tasks being performed. Anti-fatigue mats should be available to reduce fatigue for standing tasks.  

Ergonomic survey checklists are useful for job and workstation analysis and they can identify the cumulative trauma susceptibilities that workers may have for particular jobs. By identifying deficiencies in the workplace modifications can be implemented to significantly reduce the incidence of CTDs. 

1) Anderson, David. “RSI can Strain the Bottom Line.” Business and Health, January  1998
2) “RSI FAQ.” - ""
3) “The RSI Epidemic.” - ""
4) “Reducing RSI.” - ""

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