Work Related Musculoskeletal Disorders

Physical Factors in Work Place and Ergonomics

Prof. Dr. Selma KARABEY

• Work-related musculoskeletal disorders (WMSDs) are a group of painful disorders of muscles, tendons, and nerves.

low back pain, neck pain carpal tunnel syndrome, tendonitis, thoracic outlet syndrome, tension neck syndrome,

• WMSDs are very difficult to define within traditional disease classifications. These disorders have received many names, such as:

Repetitive motion injuries. Repetitive strain injuries. Cumulative trauma disorders. Occupational cervicobrachial disorders. Overuse syndrome. Regional musculoskeletal disorders. Soft tissue disorders.

• MSDs are the single largest category of work-related illness,

• representing a third or more of all registered occupational diseases in the United States, the Nordic countries, and Japan.

• MSDs occur in certain industries and occupations with rates up to three or four times higher than the overall frequency.

What are the risk factors for WMSDs?

• WMSDs arise from arm and hand movements such as bending, straightening, gripping, holding, twisting, clenching and reaching.

• These common movements are not particularly harmful in the ordinary activities of daily life.

• WMSDs are associated with work patterns that include:

Fixed or constrained body positions. Continual repetition of movements. Force concentrated on small parts of the body, such as the hand or wrist. A pace of work that does not allow sufficient recovery between movements.

High-risk sectors include • nursing facilities;• air transportation; • mining; • food processing;• leather tanning; and • heavy and light manufacturing(vehicles, furniture,

appliances, electrical and electronic products, textiles, apparel and shoes)

• Upper extremity musculoskeletal disorders are also highly prevalent in manual-intensive occupations, such as

• clerical work, • postal service, • cleaning, • industrial inspection• and packaging.

• Back and lower limb disorders occur disproportionately among

• truck drivers, • Warehouse workers, • airplane baggage handlers, • Construction trades, • nurses, nursing aides and other patient-care workers,• operators of cranes and other large vehicles

LOW BACK PAİN

• The best predictor of low back pain is a history of low back pain.

• First episodes occur among persons in the age range 20-39 years.

• But the proportion of the population is relatively uniform across the working years.

• It is seen more frequently among males than females in Western countries

• But in surveys in the general population, males and females are affected with equal frequency.

• Persons in lower social classes are more likely to report low back pain than those in higher classes,

• Probably because of their tendency to have jobs requiring heavy physical labour.

• Worldwide at least 37 percent of low back pain has been attributed to occupational factors (Punnett et al.2005)

• The prevalence of low back pain is also high in low income areas of the world.

• In a community based study in rural China , the percentage having low back pain during the course of a year was 65 per cent

(Barrero et al. 2006) • It was 61 per cent for tannery workers in India (Öry et al. 1997)• 56 per cent in steel industry in South Africa (Van Vuuren et al. 2005)• 36 per cent in an urban population in Turkey (Gilgil et al. 2005)

• Lifting objects of 25 Ib or more • Lifting of heavy objects while bending and twisting the

body• Holding heavy objects from the body while lifting• Failing to bend the knees while lifting.• Driving motor vehicles either on or of the job• Exposure to whole-body vibration increase the risk for

the low back pain

• Sitting in combination with other exposures such as whole body vibration and awkward posture increases the risk for low back pain

• Cigarette smoking has been found in many studies to be associated with low back pain

• Psychological attributes such as low social support in the workplace and low job satisfaction may increase risk.

• Many risk factors in middle and low income countries are similar to those high income countries.

• In rural China, having been a farmer , reporting moderate or heavy physical stress and

• Being exposed to vibration were associated with low back pain

(Barrero et al.2006)• In urban Turkey, cigarette smoking was related to the

occurrence of low back pain. (Gilgil et al. 2005)

Estimating the global burden of low back pain attributable to combined occupational exposures. Punnett L., Prüss-Üstün A., Nelson D.I., et al.

American Journal of Industrial Medicine,2005;48:459-69

Occupational category Relative risk

Managers and professionals

1(referent)

Clerical and sales workers 1,38

Production workers 2,39

Service workers 2,67

Farmers 5,17

Relative risk for low back pain by selected occupational category

NECK PAİN

• In high-income countries, about 60-70 per cent of adults report having experienced neck pain at same time

• Some studies report that males and females are affected with equal frequency whereas

• Others show a female excess.• Chronic neck pain and disability from neck pain occur

more often in females than males.

• Neck pain occurs most frequently in young adulthood, and some evidence suggests that its prevelence decreases with age

Risk factors for either general neck pain or herniated cervical disc are

• Heavy lifting,• Cigarette smoking,• Driving motor vehicles,• Exposure to whole body vibration• Psychological distress• Psychosomatic problems• Headaches

Work Related Injuries

• WMSDs include three types of injuries:

Muscle injury. Tendon injury. Nerve injury.

Muscle Injury

• When muscles contract, they use chemical energy from sugars and produce by-products such as lactic acid which are removed by the blood.

• A muscle contraction that lasts a long time reduces the blood flow.

• Consequently, the substances produced by the muscles are not removed fast enough, and they accumulate in the muscles.

Muscle Injury-2

• The accumulation of these substances irritates muscles and causes pain.

• The severity of the pain depends on the duration of the muscle contractions and the amount of time between activities for the muscles to get rid of those irritating substances

Tendon Injury

• Tendons consist of numerous bundles of fibres that attach muscles to bones.

• Tendon disorders related to repetitive or frequent work activities and awkward postures

• Occur in two major categories --tendons with sheaths found mainly in the hand and wrist; and tendons without sheaths, generally found around the shoulder, elbow, and forearm.

Tendon Injury-2

• The inner walls of the sheaths contain cells that produce a slippery fluid to lubricate the tendon.

• With repetitive or excessive movement of the hand, the lubrication system may malfunction.

• It may not produce enough fluid, or it may produce a fluid with poor lubricating qualities.

• Failure of the lubricating system creates friction between the tendon and its sheath, causing inflammation and swelling of the tendon area.

Tendon Injury-3

• Repeated episodes of inflammation cause fibrous tissue to form.

• The fibrous tissue thickens the tendon sheath, and hinders tendon movement.

• Inflammation of the tendon sheath is known as tenosynovitis.

• When inflamed, a tendon sheath may swell up with lubricating fluid and cause a bump under the skin.

• This is referred to as a ganglion cyst.

Nerve Injury

• Nerves carry signals from the brain to control activities of muscles.• They also carry information about temperature, pain and touch from

the body to the brain, and control bodily functions such as sweating and salivation.

• Nerves are surrounded by muscles, tendons, and ligaments. • With repetitive motions and awkward postures, the tissues

surrounding nerves become swollen, and squeeze or compress nerves .

Nerve Injury-2

Identified disorders, occupational risk factors and symptoms

Disorders Occupational risk factors Symptoms

Tendonitis/tenosynovitis Repetitive wrist motions Repetitive shoulder motions Sustained hyper extension of armsProlonged load on shoulders

Pain, weakness, swelling, burning sensation or dull ache over affected area

Epicondylitis (elbow tendonitis)

Repeated or forceful rotation of the forearm and bending of the wrist at the same time

Same symptoms as tendonitis

Carpal tunnel syndrome Repetitive wrist motions Pain, numbness, tingling, burning sensations, wasting of muscles at base of thumb, dry palm

DeQuervain's disease Repetitive hand twisting and forceful gripping

Pain at the base of thumb

Thoracic outlet syndrome Prolonged shoulder flexion Extending arms above shoulder height Carrying loads on the shoulder

Pain, numbness, swelling of the hands

Tension neck syndrome Prolonged restricted posture Pain

• When parts of the body are near the extremes of their range of movements, stretching and compression of tendons and nerves occur.

• The longer a fixed or awkward body position is used, the more likely we are to develop WMSDs.

• For example, working with the torso bent forward, backward or twisted can place too much stress on the low back.

reaching above shoulder level

reaching behind the body

Rotating the arms  Bending the wrist

• Reaching forward too far out in front of the body

How are WMSDs treated?

• The treatment of WMSDs involves several approaches including the following:

Restriction of movement. Application of heat or cold. Exercise. Medication and surgery.

How can we prevent WMSDs?

• Hazards are best eliminated at the source; this is a fundamental principle of occupational health and safety.

• In the case of WMSDs, the prime source of hazard is the repetitiveness of work.

• Other components of work such as the applied force, fixed body positions, and the pace of work are also contributing factors.

Human factors and ergonomics (HF&E)

• a multidisciplinary field incorporating contributions from psychology, engineering, biomechanics, mechanobiology, industrial design, physiology and anthropometry.

• it is the study of designing equipment and devices that fit the human body and its cognitive abilities.

Definition of the International Ergonomics Association

• Ergonomics (or human factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data and methods to design in order to optimize human well-being and overall system performance.

• .

• Proper ergonomic design is necessary to prevent repetitive strain injuries and other musculoskeletal disorders, which can develop over time and can lead to long-term disability.

• Human factors and ergonomics is concerned with the "fit" between the user, equipment and their environments.

• HF&E is employed to fulfill the goals of occupational health and safety and productivity.

• It is relevant in the design of such things as safe furniture and easy-to-use interfaces to machines and equipment.

• It takes account of the user's capabilities and limitations in seeking to ensure that tasks, functions, information and the environment suit each user.

• To assess the fit between a person and the used technology, human factors specialists or ergonomists consider the job (activity) being done and the demands on the user; the equipment used (its size, shape, and how appropriate it is for the task), and the information used (how it is presented, accessed, and changed).

• Mechanization• One way to eliminate repetitive tasks is to mechanize the job. • Where mechanization is not feasible or appropriate, other

alternatives are available.• Job Enlargement and Enrichment• This increases the variety of tasks built into the job. • It breaks the monotony of the job and avoids overloading one part of

the body. • Job enrichment involves more autonomy and control for the worker.

• Job Rotation• It requires workers to move between different tasks, at fixed or

irregular periods of time. • But it must be a rotation where workers do something completely

different. • Different tasks must engage different muscle groups in order to

allow recovery for those already strained.

• Team Work• Team work can provide greater variety and more evenly distributed

muscular work. • The whole team is involved in the planning and allocation of the

work. • Each team member carries out a set of operations to complete the

whole product, • allowing the worker to alternate between tasks, hence, reducing the

risk of WMSDs.

• Workplace Design• The guiding principle in workplace design is to fit the workplace to

the worker. • Evaluation of the workplace can identify the source or sources of

WMSD. • Proper design of the workstation decreases the effort required of the

worker to maintain a working position. • Ideally, the workstation should be fully adjustable, providing a

worker with the options to work in standing, sitting or sitting-standing positions, as well as fitting the worker's body size and shape.

• Tools and Equipment Design

• Proper design of tools and equipment significantly decreases the force needed to complete the task.

• Providing the worker with the proper jigs or fixtures for tasks that require holding elements saves a lot of muscular effort in awkward positions.

• Good tools, maintained carefully and where necessary frequently changed, can also save a lot of muscle strain.

• Work Practices• A well-designed job, supported by a well-designed workplace and

proper tools, allows the worker to avoid unnecessary motion of the neck, shoulders and upper limbs.

• Training should be provided for workers who are involved in jobs that include repetitive tasks.

• Workers need to know how to adjust workstations to fit the tasks and their individual needs.

Hand Tool ErgonomicsHow should one design the workstation for precision work?

For a fixed-height workbench:• provide work platforms to

accommodate shorter workers;• raise the work surface for taller

workers.• Provide sufficient leg clearance to

allow the worker to get close to the work object, thereby reducing the need to bend the torso.

• Provide a foot rest as foot support that will improve body balance and minimize the static load on the workers back.

• Anti-fatigue matting reduces lower back and leg discomfort and minimizes fatigue.

Hand Tool Ergonomics-2How should one design the workstation for precision work?

• Consider using chairs or stools to allow work in a sitting or standing position.

• Where feasible provide the worker with a tilted workstation.

• This reduces static load on the back and upper body.

Hand Tool Ergonomics-3How should one design the workstation for precision work?

• Use jigs or vices to hold the work object steady and secure at the proper height and position for optimum comfort

• Use vices to minimize pinching and gripping forces.

Hand Tool Ergonomics-4How should one design the workstation for assembly work?

• In assembly work, static load, awkward postures and forceful movements are major risk factors for WMSDs.

• Prolonged standing and the fatigue resulting from it additionally contribute to WMSDs.

• Use jigs and vices to hold the work object steady at the right height and position for optimum comfort.

Hand Tool Ergonomics-5How should one design the workstation for assembly work?

• Use tool balancers to reduce the effort of holding and operating the tool

• If possible use the lightest tool that can get the job done properly, preferably one weighing less than 1 kg (2 lbs).

• Anti-fatigue matting reduces lower back and leg discomfort and minimizes fatigue.

What is an example of a workstation for sitting/standing?

• Continuous standing or sitting while working is a common source of discomfort and fatigue.

• Frequent changes of body positions, including alternating between sitting and standing, helps to avoid fatigue.

• Adjust the workstation to the proper height.• Use a swivel chair with an adjustable seat

height.• Adjust the chair seat height to 25-35 cm

(about 10 - 14 in.) below the work surface.• Use a footrest with a height of 40-50 cm

(about 16 - 20 in.)

• How does job design/redesign reduce the risk for back injury due to Manual Material Handling (MMH)?

• The design or redesign of jobs involving MMH should be approached in the following stages:

eliminate heavy MMH decrease MMH demands reduce stressful body movements pace of work and rest breaks improve environmental conditions

What is an example of a semi-circular workstation?

• Arrange work in a semi-circle.• Use a swivel chair to reduce

body twisting, to allow easy movements, and to reduce side-to-side motions.

• Use sloping work tables whenever possible to reduce bending, and to encourage an upright position while sitting or standing.

Why isn't the most common placement of the computer mouse the best?

• Typically we position the mouse at the right (or left) of the keyboard.

• This is not the easiest place to reach, however.

• Having 'extra keys' to the right of the letter and number keys (for example, arrow keys, insert, page down and the number pad) do not allow users to place the mouse more directly in line with their arm and shoulder.

• Reaching your arm forward or sideways beyond an "easy reach" zone can lead to these discomfort and even injury.

Computer Mouse - Location - Beside Keyboard

What is an ergonomic chair?

• Ergonomic chairs are designed to suit a range of people; however, there is no guarantee that they will suit any one person in particular.

• Chairs may not suit every task or arrangement at the workstation.

• A chair becomes ergonomic only when it specifically suits a worker's size (body dimensions), his or her particular workstation, and the tasks that must be performed there.

References and Web Sources

• Centers for Disease and Prevention, Work-Related Musculoskeletal Disorders (WMSD) Prevention

• http://www.cdc.gov/workplacehealthpromotion/implementation/topics/disorders.html

• Canadian Centre for Occupational Health and Safety, Work-related Musculoskeletal Disorders (WMSDs)

• http://www.ccohs.ca/oshanswers/diseases/rmirsi.html

• ELEMENTS OF ERGONOMICS PROGRAMS, Centers for Disease and Prevention, ,1997

• http://www.cdc.gov/niosh/docs/97-117/pdfs/97-117.pdf• Making the best use of lifting and handling aids,Health and Safety• http://www.hse.gov.uk/pubns/indg398.pdf

References and Web Sources

• Oxford Textbook of Public Health, Musculoskeletal Diseases,Roger Detels, Robert Beaglehole, Mary Ann Lnsang, Martin Gulliford,2009, vol 3

• Health and Safety Executive, Musculoskeleteal Disorders• http://www.hse.gov.uk/msd/resources.htm

• Work-related musculoskeletal disorders: the epidemiologic evidence and the debate, Laura Punnett, David H. Wegman,, Journal of Electromyography and Kinesiology 14 (2004) 13–23

• Work-related Musculoskeletal Disorders Guide and Tools for Modified Work,Susan Stock, Raymond Baril, Colette Dion-Hubert, Claire Lapointe, Sonia Paquette, Josée Sauvage, Serge Simoneau, Claude Vaillancourt, 2005• http://www.irsst.qc.ca/media/documents/PubIRSST/OMRT-En.pdf