MUSCULOSKELETAL DISORDERS (MSDS)-CONSEQUENCES OF PROLONGED

STATIC POSTURES

Introduction

The World Health Organization defines MSD as “a

disorder of the muscles, tendons, joints, intervertebral

discs, peripheral nerves and vascular system, not directly

resulting from an acute or instantaneous event but

installing gradually and chronically”.

There are many types of factors responsible for MSD:

occupational factors, medical factors (physical disorders,

genetic predisposition, and age) and life style factors.

Usually two or more factors trigger MSD. Work in

dentistry is characterized by some body postures with

different degrees of distortion. In this case the

professional factors are represented by: prolonged static

postures, repetitive movements, inadequate lighting, the

excessive exertion of the small muscles, and the

instrument tight grip, raised arms, static exertion of the

muscles on long term, vibrations.

Working tasks in dentistry have an intellectual and a

physical component - the result of the muscular effort.

The muscular effort can be either static – the length of the

167

Journal of Experimental Medical & Surgical Research

Cercetãri Experimentale & Medico-Chirurgicale

Year XIV · Nr.4/2007 · Pag.167-172C e r c e t a r ie x p e r i m e n ta le &

m edico-chirurgicale

)

1 - UMF”Victor Babeº” Timiºoara, University of Dentistry, Department of Oral-Dental Diagnosis.2 - UPTimiºoara, Faculty of Mechanics.

3 - UMF”Victor Babeº” Timiºoara, Department of Medical Informatics

SUMMARY:Musculoskeletal disorders (MSDs) are progressively installed. In dentistry prolonged staticpostures, repetitive movements, excessive contraction of short muscles could causemusculoskeletal disorders. Even when the sitting posture is the one recommended by ISO11226 – Ergonomics-Evaluation of static working postures, there is a high risk of developing musculoskeletal disorders. Each member of the dental team is predisposed to pain or injuryin different areas of the body, depending on their tasks and position in relation to the patient. This presentation shows the causes and the mechanisms that lead to musculoskeletaldisorders and some methods for prevention.

Key Words: dentists, musculoskeletal disorders, static working postures

AFECTIUNI MUSCULO-SCHELETALE – CONSECINTE ALE POSTURII ORTOSTATICEPRELUNGITE

REZUMAT:Afectiunile musculo-scheletale se instaleaza progresiv. In stomatologie cele mai frecventecauze sunt reprezentate de posturi statice prelungite, miscari repetitive, folosirea in exces amuschilor scurti. Chiar daca pozitia sezanda este cea recomandata de ISO 11226 –Evaluarea ergonomica a pozitiilor statice de munca, exista un risc crescut de aparitie aacestor afectiuni. Fiecare membru al echipelor stomatologice este predispus la dureri sileziuni in diferite zone ale corpului in functie de posturile pe care le adopta la locul demunca. Aceasta lucrare prezinta cauzele si mecanismele ce conduc la afectiunilemusculo-scheletale si citeva metode pentru prevenirea lor.

Mirella Anghel1

Veronica Argeºanu2

Cristina Talpoº-Niculescu1

Diana Lungeanu3

Received for publication: 19.07.2007

Revised: 11.09.2007

Correspondence to: Mirella Anghel, e- mail: ergonomie@umft.ro

E x p e r i m e n t a l

M e d i c a l S u r g i c a l

R E S E A R C H

J O U R N A L o f

muscle remains unchanged (isometric contraction) or

dynamic - rhythmic changes of alternations and

shortenings of the muscles (isotonic contraction). The

physical expressions of the muscles are characterized by

gesture - the direct relation between man and working

means by repeated movements and posture – the static

posture.

The posture is the complex term used as reference for

a number of movements and posture concepts. The

posture was defined in various ways: a posture or a body

position, the relative postures of the body parts for a

specific activity.

The static posture implies the followings:

l isometric muscular contractions with acid

lactic accumulation,

l compression of the blood vessels,

l vicious static postures and non physiological

moments: of the spine (resulting in

discopathia) and of the arms (resulting in

tendinitis, epicondylitis).

l repetitive disorders – that have a cumulative

effect, affecting the joints, ligaments and

tendons.

All these factors contribute to the occurrence of MSDs

and affect the personnel involved in static activities

(dentists, PC operators, tailors). Pain, fatigue and

disorders of the musculoskeletal system may result from

sustained inadequate working postures and poor

working conditions. Musculoskeletal pain and fatigue

may influence posture control which can increase the

risk of errors and may result in low work efficiency. Good

ergonomic design of the workplace is a basic

requirement for improving musculoskeletal health.

Working posture in the dental surgery

Despite that since 1958 (as the result of the study

“Time and Motion”) the sitting postures have been

recommended as the healthiest and the most correct

ones, the findings of a research done in Timisoara proved

that more than 50% of the dentists that are over 45 work

in dental surgery in orthostatic postures, while those

168

Fig.1 Sample

Fig. 2 Orthostatic posture

aged between 24 and 35 exclusively prefer the sitting

postures. The aim of the survey, performed with the help

of Medical Informatics, is to show to what extent the

dentists’ working manner (posture, habits, schedule etc)

affects their health. 70 dentists were selected (figure1)

out of 850, women and men and all age categories

(between 24 and 75 years old). Most of them had a

upright working posture and those adopting sitting

postures chose wrong, incorrect postures. A

questionnaire with several topics was filled in and the

data analysis used SPSS v. 13. The results proved that

60% of the dentists worked in orthostatic position.

Orthostatics. Although there is manual work that can

be performed only in orthostatic posture (the

determination of occlusion, some extractions), but still

the inconveniences of this posture should be mentioned

(fig.2):

- it is more tiring due to a heavier blood flow

- the body weight is distributed on a smaller surface,

fact that negatively influences the equilibrium,

- when the pedal is used, the support is only on one

leg,

- movements accuracy is diminished.

The effects of a prolonged orthostatic posture upon

health are the followings:

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Fig. 3 Symmetrical postures

FIG. 4 ISO 11226 – Ergonomics-Evaluation of static workingpostures

FIG. 5 Back support

- the energy consumption is10% higher than in sitting

postures,

- the heart rate gets higher,

- the static effort is higher than sitting effort,

- the osteoarticular system is affected,

- the peripheral venous circulation is affected

- pains in the lower members occur associated with

the feeling of burden and cramps of the calf.

The sitting postures. The correct working postures in

the dental surgery are the sitting postures that conform to

the following requirements:

- symmetrical postures (fig.3),

- all horizontal axes should be parallel,

- the legs should be slightly apart (a 30º-45º angle),

- the shank should be perpendicular on the floor,

- the upper part of the body should be perpendicular on

the chair – forward movements should be made

without curving the spine,

- the head could bend 20º-25º

- the arms should be close to the body

- the forearms should be nearly horizontal (max. 25%

raised)

- the shank / thigh should be at 115º

- the soles should be on the floor (fig.4)

When working in sitting postures a chair is required to

support the seat and back (fig.5). In this situation one

should alternate active and passive sitting postures.

The active posture (figure 6) could be defined as the

correct body posture that is maintained by the muscles

of the back, the back being leaned forward. This posture

can not be maintained for a very long time. The passive

posture is the one in which the back is sustained by the

dentists’ back of the chair. There are certain moments

when the wrong postures can not be avoided. In wrong

postures the oxygen supply in muscles is altered and it is

essential to maintain it for a very short time. The supply

is determined by the alternative contraction of the

muscles, while the blood with residue is removed the

muscles relax, and are supplied with oxygenated blood.

The muscular pump can function at its best if there is a

continuous movement of the muscles that consists in

contractions and relaxations. The static postures do not

allow consecutive contractions and relaxations. That is

why in correct static postures various posture

movements should be made in order to determine

alternative contraction and relaxation of different

muscular groups. If a wrong posture is adopted sooner

than 3 or 4 seconds the muscular pump will start its

restrictions so that the muscles could not be supplied

with the optimum amount of oxygenated blood. This

stress can result in ischemia and pain in the overexerted

170

FIG.6 Dentist (at 10) and dental assistent (at 3) postures

and patient position.

FIG.7 Relaxed body posture of a dentist (at 12) and of dentalassistant (at 3).

muscles and that is why at that specific moment an

adequate muscular relaxation is necessary for the

normal functioning of the muscles (figure 7).

It is a fact that in time, the wrong working habits of the

dentist lead to an accumulation of traumas that cause

physical stress and MSDs.

MSDs ONSET AND DEVELOPMENT

MSDs occur due to the biomechanical and

physiological changes happened in time. Prolonged static

postures trigger this mechanism, which induces these

biomechanical and physiological modifications. Due to

non physiological and non balanced postures, bending

and rotations of the head, neck or body muscles there is a

lack of balance. In this case, the muscles responsible for

these movements get stronger and shorter and exert

asymmetrical forces while the opposite muscles relax

and get weaker. During the static muscular effort the

isometric contraction of the muscles is being exerted and

thus, the unchanged length of muscles induces a higher

tension and vessels compression. As a result the blood

flow decreases and implicitly the amount of oxygen and

nutrient contribution is diminished and ischemia occurs,

the lactic acid accumulates in muscles and causes

muscular pains and fatigue. If muscles relax on these

specific moments, the affected tissue is recovered; but

necrosis still occurs if the recovery extent is smaller than

the affected one. To counterbalance the function of the

affected muscles that are out of use, other muscles take

over their function and thus the muscular substitution

takes place.

The result of all these processes is deterioration of

joints, ligaments and tendons, accompanied by joint

hypermobility, nerve compression and damage of

intervertebral discs.

MSDs CLASSIFICATION

1. Nerve Entrapment Disorders: carpal tunnel

syndrome, ulnar neuropathy.

2. Occupational Disorders of the Neck and Brachial

Plexus (figure 8): tension neck syndrome, cervical

spondylosis, cervical disc disease, brachial plexus

compression.

3. Shoulder disorders (figure 9): trapezius myalgia,

rotator cuff tendonitis, rotator cuff tears, and

adhesive capsulitis.

4. Tendonitis of the Elbow, Forearm and Wrist: de

Quervain´s disease, tendonitis, tenosynovitis,

epicondylitis

5. Hand-Arm Vibration Syndrome: Raynaud’s disease.

6. Low Back Disorders: chronic low back pain.

In conclusion, pain, injury or MSDs are consequences

of the working process in dentistry and represent

important causes of morbidity and work inefficiency.

Research put into evidence the high incidence of

disorders resulted from wrong postures. Thus in a survey

of 1200 patients, 38% had disorders of the hands, 14%

had disorders of the arms, 44% had disorders of the

shoulder, 61% had disorders of the neck and cervical

171

FIG. 8 Occupational Disorders of the Neck and Brachial Plexus - disk pressure C4 – C5 - lateral osteofitis

FIG. 9 Shoulder disorders

- osteoporosis - internal, external or posterior joint calcification

spine, 43% had disorders of the thoraces spine, 61% had

disorders of the lumbar spine and 10% had disorders of

the legs.

MSDs reduce work capacity; patients need recovery,

which is often expensive, and sometimes patients can

not fully recover and have to end up their professional

career. Dentistry is a profession with high risk of

developing MSDs.

Prevention methods

1. Adopting a correct working posture

2. Use of adequate light

3. Good planning of dental care sessions

4. Alternative planning of long and short sessions

5. Alternating the body postures – sitting and upright

6. Having short breaks after each care session and long

coffee or lunch breaks, the sink should be installed at

distance.

7. The working day should not be longer than 7 hours.

8. Every 6 weeks a journey should be planned.

9. Sports activities should be practised for about 45

minutes three times a week.

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