ORIGINAL ARTICLE
Work related and individual predictors for incident neck
pain among office employees working with video display
units
T Korhonen, R Ketola, R Toivonen, R Luukkonen, M Häkkänen, E Viikari-Juntura
.............................................................................................................................
Occup Environ Med
2003;60:475–482
Aims: To investigate work related and individual factors as predictors for incident neck pain among
office employees working with video display units (VDUs).
Methods: Employees in three administrative units of a medium sized city in Finland (n = 515) received
mailed questionnaires in the baseline survey in 1998 and in the follow up survey in 1999. Response
rate for the baseline was 81% (n = 416); respondents who reported neck pain for less than eight days
during the preceding 12 months were included into the study cohort as healthy subjects (n = 232). The
follow up questionnaire 12 months later was completed by 78% (n = 180). Incident neck cases were
those reporting neck pain for at least eight days during the preceding 12 months.
Results: The annual incidence of neck pain was 34.4% (95% CI 25.5 to 41.3). Poor physical work
environment and poor placement of the keyboard increased the risk of neck pain. Among the individual
factors, female sex was a strong predictor. Smoking showed a tendency for an increased risk of neck
pain. There was an interaction between mental stress and physical exercise, those with higher mental
stress and less physical exercise having especially high risk.
Conclusion: In the prevention of neck disorders in office work with a high frequency of VDU tasks,
attention should be given to the work environment in general and to the more specific aspects of VDU
workstation layout. Physical exercise may prevent neck disorders among sedentary employees.
T
he evidence of risk factors for various types of neck disor-
ders is based mostly on cross sectional studies, and a lim-
ited number of longitudinal studies. According to a recent
review
1
and two later prospective studies,
23
a positive relation
has been found between various neck disorders and work
related risk factors, such as static neck and arm postures,
duration of sitting, as well as workplace design. Among other
job characteristics, high quantitative job demands, having
little influence on one’s work situation, and limited rest break
opportunities have been found as predictors of neck pain.
4–7
Among individual factors, the role of psychological factors has
been emphasised.
8
Concer ning video display unit (VDU) work, the evidence of
risk factor s is based mainly on cross sectional studies. Increas-
ing hours of computer use and incomplete work–rest cycle
control, have been associated with musculoskeletal discomfort
in the neck–shoulder area and upper extremities,
9–12
especially
when using input devices, such as a keyboard or a mouse.
13–15
Computer use in sustained non-neutral postures, such as neck
rotation and shoulder abduction, have been identified as risk
factor s for neck–shoulder symptoms.
10
Postural stress caused
by poor workstation ergonomics, such as inappropriate
location of the screen, keyboard, or mouse, have been
associated with musculoskeletal problems.
11 15–19
By ergonomic
interventions, such as supporting the forearm on the tabletop,
a reduction of postural load,
14
discomfort,
20 21
or neck pain
22
has
been achieved. Work organisational factors, such as increasing
work pressure or hurry and lack of job security or decision
making opportunities, as well as problems in work atmos-
phere, may contribute to an increased occurrence of work
related musculoskeletal complaints.
10 12 23
Among individual factors, female gender and older age have
been found to be associated with a more frequent report of
neck pain.
38
Among health behavioural factors, smoking has
been found as a risk f actor,
24–26
whereas the evidence on physi-
cal exercise has been inconsistent. A low frequency of exercise
has been found preventive in some studies.
27 28
Among seden-
tary workers a low physical activity has been a r isk factor in
some studies,
24 29
whereas no effect has been found in some
other studies.
29–31
The role of psychosocial and psychological
factor s, such as stress, tension, depression, and job satisfaction
has been frequently observed in the occurrence of various
neck disorders.
8 32–35
We carried out a prospective study among office workers in
municipal administrative units. The aim was to investigate
work related and individual factors as predictors for incident
neck pain among office employees working with VDUs.
METHODS
Study population
The study was conducted in three municipal administrative
units. The study population was the entire population of those
full time working employees, whose job included VDU work
for more than four hours per week (n = 515). Altogether 416
workers participated in the baseline survey in 1998 (81%).
From the baseline respondents, the subjects of interest were
those who reported local or radiating neck pain for less than
eight days during the preceding 12 months. These subjects
were classified as “healthy” at baseline (n = 232). This cohort
was studied 12 months later, the response rate being 78%
(n = 180). At follow up in 1999 the incident cases were those
workers who reported local neck pain or radiating neck pain
for at least eight days during the preceding 12 months.
Questionnaire
Data were collected via structured mailed questionnaires. The
assessment of the potential risk factor s took into considera-
tion various physical and psychological workload and
ergonomic factors. The questionnaire also included questions
on lifestyle and psychosocial factors.
The incident cases were healthy subjects at the baseline
who reported at follow up local or radiating neck pain for at
See end of article for
authors’ affiliations
.......................
Correspondence to:
Dr R Ketola,
Musculoskeletal Research
Unit, Department of
Physiology, Finnish Institute
of Occupational Health,
Topeliuksenkatu 41 aA,
FIN-00250 Helsinki,
Finland;
Accepted 25 September
2002
.......................
475
www.occenvmed.com
least eight days during the preceding 12 months. The exact
wording of the question for local neck pain was as follows:
“Estimate the total number of days you have had local neck
pain (not radiating) during the preceding 12 months”. The
original question had five categories: 0 days, 1–7 days, 8–30
days, >30 days but not daily, and daily. The wording for radi-
ating pain was as follows: “Estimate the total number of days
you have had neck pain radiating to the upper extremity
(forear m, hand, or fingers) during the preceding 12 months”.
The original question had five categories: 0 days, 1–7 days,
8–30 days, >30 days but not daily, and daily. In the analysis,
we combined the first two categories, because we think that
some days with neck pain does not indicate a disorder. We also
combined the three last categories. Thus, a two category vari-
able was used: 0–7 days (healthy) and 8 or more days (incident
neck pain).
As measured in the 1998 baseline questionnaire, we used 11
work related and 11 individual variables as potential
predictors for the outcome. We selected these factors into our
study based on our hypotheses and earlier evidence as follows.
Work related factors
• Time used for VDU work (self rated proportion of time used
for VDU work as percentage of total work time). The exact
wording for the question was: “Estimate how many percent
of your working time during the preceding month you have
used for each task of the following tasks”. The definition for
VDU work was use of keyboard or other input or control
device, including short thinking periods and checking the
results on the screen. In the analysis, a dichotomy <50%
and >50% was used.
9
• Physical work environment (lighting conditions, tempera-
ture, quality of the air, size of the working room, and acous-
tic conditions in the work environment). The subjects rated
each component by a scale from 1 to 5, where 1 was very
poor and 5 very good. Since all the items were positively
associated with the outcome, for each subject the mean of
the five components was calculated to represent the status
of the physical work environment. In the analysis a
dichotomous variable was used, values higher than 3
denoting good and values from 1 to 3 poor environment.
• Ergonomics of the workstation (work chair, work desk,
screen, keyboard, mouse, and document holder were
considered). The workers rated each component by a scale
from 1 to 5, where 1 was very poor and 5 very good. For each
subject the mean of the six components was calculated to
represent the value of the workstation ergonomics. In the
analysis a dichotomous variable was used, in which values
4 to 5 denoted good ergonomics and values from 1 to 3 poor
ergonomics, because of a positively skewed distribution.
• Viewing distance (distance between the eyes and the mid-
dle point of the screen (cm), measured by the employees
themselves in their own offices). Based on the recommen-
dations of the ISO Standard (Ergonomic requirements for
office work with visual display terminals),
36
two categories
were used, where the distance between 50 and 70 cm was
good and other measures were poor.
• Height of the VDU screen (distance between the upper edge
of the screen and the horizontal level of the eyes, measured
by the employees themselves in their own offices). Based on
the ISO recommendations,
36
two categories were used,
where >10 cm was good and <10 cm poor. As the viewing
distance mostly varied between 50 and 65 cm (mean = 57
cm), poor ver tical location corresponds to a viewing angle of
<20° below the horizontal line.
37
• Distance of the VDU keyboard (distance between the g-h
point of the keyboard and the edge of the desk, measured by
the employees themselves in their own working rooms).
Based on the ISO recommendations,
36
two categories were
used, where >15 cm was good and <15 cm poor. Negative
measurements, such as a separate keyboard holder in use,
were very rare.
• Deviance of the VDU keyboard from the midpoint (deviance
between the g-h point of the keyboard and the middle line
of the body, measured by the employees themselves in their
own working rooms). Based on the ISO
recommendations,
36
two categories were used, where 0 ±2
cm was good and higher deviancies were poor.
• Distance of the VDU mouse (distance between the middle
point of the mouse and the edge of the desk, measured by
the employees themselves in their own working rooms).
Based on the recommendations,
13 18
two categories were
used, where >15 cm was good and <15 cm poor.
• Deviance of the VDU mouse (deviance between the middle
point of the mouse and the middle line of the body,
measured by the employees themselves in their own work-
ing rooms). Based on the recommendations,
13 18
two catego-
ries were used, where the measures between −30 cm and
+30 cm were good, and higher distances were poor.
• Breaks during work (whether there were breaks when
working at the VDU). The scale ranged from “much too
little” to “fully enough”. In the analysis a dichotomous
variable was used, where less than “fully enough” was
studied as potentially involving an increased risk of neck
pain.
• Influence on work load (the extent the subjects were able to
influence their own work load in terms of amount and
tempo of their tasks). The five level variable ranged from
“very little” to “ver y much”. A dichotomous variable was
used, the potential risk associated with having some or very
little influence.
Individual factors
• Sex.
• Age in 1998 (25–43, 44–51, and 52–61 years; data driven
categorisation as tertiles).
• Frequency of physical exercise (times/week, two catego-
ries).
• Smoking (two categories: never smoker and current
smoker/ex-smoker).
• Health status (self rated status of health; two categories:
very good/rather good and average/rather poor/very poor).
• Mental stress. The wording of the question was: “Stress
means the situation when a person feels tense, restless,
nervous, or anxious, or is unable to sleep at night because
his mind is troubled all the time. Do you feel that kind of
stress these days?” (two categories: none/little and some/
fairly much/much).
• Mental strain. Perceived tension was used as an indicator
for this concept (two categories: never/rather seldom and
sometimes/rather often/continually).
• Depression (two categories: never/rather seldom and
sometimes/rather often/continuously).
• Job satisfaction (two categories: very satisfied/rather
satisfied and neutral/rather dissatisfied/very dissatisfied).
• Time used for domestic activities, such as cleaning, child
care, cooking, gardening, home repairs (hours spent on
average during work days; two categories: <1 hour and >1
hour).
• Time used for hobbies including static load on neck shoul-
der area, such as handicrafts, music instrument playing,
computer games (hours spent on average during work days;
two categories: <1 hour and >1 hour).
Table 1 presents a comparison of the baseline variables among
the study cohort (n = 232) between those who participated in
476 Korhonen, Ketola, Toivonen, et al
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the follow up (n = 180) and those who dropped out from the
follow up (n = 52). There were no differences between the
groups regarding the majority of the variables. However, the
respondents were younger and more stressed than the
non-respondents. The respondents also rated the physical
work environment as poorer.
Table 1 Comparison of the baseline variables among the respondents (n=180) and
non-respondents (n=52) of the follow up survey
Respondents Non-respondents
p valuen% n%
Work related variables
VDU working time 0.54
<50% 122 70 34 71
>50% 52 30 14 29
Physical work environment 0.08
Mean score >3 123 70 42 81
Mean score <353301019
Ergonomics of workstation 0.34
Mean score >3 127 72 39 76
Mean score <349281224
Distance of the screen 0.42
Good (50–70 cm) 106 69 29 66
Poor (<50 cm or >70 cm) 48 31 15 34
Height of the screen 0.18
Good (>10 cm) 102 68 33 77
Poor (<10 cm) 48 32 10 23
Distance of the keyboard 0.19
Good (>15 cm) 70 49 14 39
Poor (<15 cm) 73 51 22 61
Deviance of the keyboard 0.07
Good (0±2 cm) 73 51 24 67
Poor (> ±2 cm) 70 49 12 33
Distance of the mouse 0.19
Good (>15 cm) 46 51 10 38
Poor (<15 cm) 45 49 16 62
Deviance of the mouse 0.22
Good (0±30 cm) 38 42 8 31
Poor (> ±30 cm) 53 58 18 69
Breaks during work 0.59
Fully enough 66 63 17 63
Rather enough/rather little/much too little 39 37 10 37
Influence on work load 0.45
Somewhat/rather/very much 93 52 26 50
Very little/rather little 85 48 26 50
Individual variables
Sex 0.29
Female 80 44 26 50
Male 100 56 26 50
Age 0.04
25–43 58 32 11 22
44–51 59 33 12 23
52–61 62 35 28 55
Smoking 0.22
Never smoker 97 55 25 48
Current/ex-smoker 78 45 27 52
Frequency of physical exercise (times/week) 0.34
<154301835
>2 124 70 34 65
Health status 0.27
Very good/rather good 120 68 31 62
Average/rather poor/very poor 57 32 19 38
Mental stress 0.02
None/little 88 50 34 68
Some/fairly much/much 89 50 16 32
Mental strain 0.29
Never/rather seldom 99 56 31 62
Sometimes/rather often/continually 77 44 19 38
Depression 0.37
Never/rather seldom 117 66 35 70
Sometimes/rather often/continually 60 34 15 30
Job satisfaction 0.55
Very satisfied/rather satisfied 135 76 38 76
Neutral/rather/very dissatisfied 42 24 12 24
Time used for domestic activities (hours/day) 0.28
<1 48 27 17 33
>1 128 73 35 67
Time used for hobbies (hours/day) 0.56
<1 139 79 41 79
>137211121
Predictors for neck pain in VDU work 477
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Statistical methods
Cross tabulations and logistic regression models were used as
main methods of analysis for associations between the
outcome variable and the potential risk factors. To construct a
multivariable model a forward selection strategy was used.
38
The inclusion of the variables for the first model was based on
testing the significance of the potential predictors as groups of
variables, adjusting for age, sex, and VDU work time for work
related variables, and for age and sex for individual variables.
Among the work related variables the groups to be tested
were: (1) general work conditions (influence on work load,
breaks during work); (2) general ergonomics (physical work
environment and ergonomics of the workstation); and (3)
VDU specific ergonomics (height and distance of the screen,
distance and deviance of the keyboard, distance and deviance
of the mouse). Among the individual factors the groups were:
(1) general health and health behaviour (perceived health
status, physical exercise, smoking); (2) psychological health
(stress, strain, depression); (3) job satisfaction alone; and (4)
leisure time activities (time used for domestic tasks, time used
for certain hobbies).
From each group of variables, those with p < 0.2 were
selected for further analyses. Based on the first steps of mod-
elling, physical work environment, and distance of keyboard
among the work related factors, and smoking among the indi-
vidual factors were included into the further stages of analy-
sis. Thus, the model with direct effects included these predic-
tors, plus sex, as well as age and VDU working time as possible
confounders. Because of missing values in the explanatory
variables, the final model was based on 138 observations.
Finally, the first level interactions were tested. We were
mainly interested in interactions of age with sex and with
work related risk factors, as well as of stress with the work
related variables and physical exercise. The significant
interactions (sex with age and mental stress with frequency of
physical exercise), were added into the model of the direct
effects. For the direct effect model and the interaction model,
the results were presented as odds ratios (OR), with 95% con-
fidence intervals (CI). The significance of the models was
evaluated by AIC and −2 log L values, whereas the goodness of
fit was tested by the Hosmer and Lemeshow method.
39
The
statistical analyses were performed with the computer
package SAS System for Windows (version 8.1).
40
RESULTS
Fifty six per cent of our subjects were men (n = 100). Age
range was 25–61 years (mean 47 years, median 49 years). The
proportion of the total working time used for VDU tasks
ranged from 2% to 100% (mean 36%, median 30%). Thirty per
cent of the subjects worked actively with VDUs for 50% or
more of their total working time.
The incidence of local neck pain or radiating neck pain was
34.4% (95% CI 25.5 to 41.3). The incidence of local neck pain
only was 13.3% and the incidence of the radiating pain only
was 14.4%. The incidence of combined local and radiating
neck pain was 6.7% (table 2). Table 3 shows the distribution of
subjects in the different categories of neck pain in 1999
according to explanatory variables.
The risk of neck pain was about twofold for those rating the
physical work environment as poor in comparison to those
who rated their work environment as good. Each item of the
score showed a positive association with the outcome as
follows: lighting (OR = 1.4, 95% CI 0.7 to 2.8), temperature
(OR = 1.2, 95% CI 0.6 to 2.4), quality of the air (OR = 1.7, 95%
CI 0.8 to 3.5), size of the working room (OR = 1.5, 95% CI 0.7
to 3.0), and acoustic conditions in the work environment
(OR = 1.4, 95% CI 0.7 to 2.8), but none of the items was sig-
nificant alone. Also poor placement of the VDU keyboard
increased the risk of neck pain. Women had an almost three-
fold risk compared with men. Current or ex-smokers had an
almost twofold, although not significant, risk in comparison
with the never smokers (table 4).
Table 5 shows the multivariable model with significant
interactions. There was an interaction between mental stress
and physical exercise: workers with a higher level of mental
stress and lower frequency of physical exercise had an almost
sevenfold risk compared to those with lower stress level and
higher exercise frequency. The risk associated with the physi-
cal work environment became higher, whereas that for
distance of the keyboard and smoking tur ned out to be lower,
compared with the model with the direct effects only.
Tables 6 and 7 show the interactive effects of sex and age.
Women had a higher risk than men, except in the age group
44–51 years (table 6). The risk of neck pain increased after the
age of 43 among the men, whereas among women the risk was
lower for those aged 44–51 years and increased for those older
than 52 years (table 7).
DISCUSSION
In this cohort study among office employees working with
VDUs, we found that incident neck pain was associated with
both work related and individual factors. Inappropriate physi-
cal work environment and poor VDU related ergonomics,
together with individual factors, such as gender and smoking,
predicted neck pain. In addition, the employees with higher
mental stress and less physical exercise had an especially high
risk.
Concer ning the validity of this study the crucial question
would be related to possible bias caused by low participation
rates. The drop out rates in various longitudinal studies of
musculoskeletal disorders have ranged between 7% and
57%.
41
The response rates of our study were in the baseline
survey 81% and in the follow up 78%, corresponding to drop
out rates between 19% and 22%. In all, our response rates were
among the highest ones in longitudinal studies, resulting in
an overall participation rate of 63%. The non-respondents to
the follow up questionnaire did not differ from the
respondents with regard to most explanatory var iables. How-
ever, the respondents seemed to be more stressed than the
non-respondents.
Table 2 Incidence of neck pain among Finnish office workers in 1998–99 (cohort
of the healthy subjects in 1998, n=180)
Local neck pain
Radiating neck pain
Less than 8 days
(healthy)
8 days or more
(cases) Total
n% n% n%
Less than 8 days (healthy) 118 66 26 14 144 80
8 days or more (cases) 24 13 12 7 36 20
Total 142 79 38 21 180 100
478 Korhonen, Ketola, Toivonen, et al
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In order to take into account the duration of exposure to
VDU work, we adjusted our analyses for the proportion spent
at the computer of the total working time. We found it neces-
sary to control for this factor, since the effects of the various
Table 3 Distributions of the subjects in the different categories of neck pain* in
1999 according to explanatory variables; odds ratios for explanatory variables
Neck pain*
(n=62)
Healthy
(n=118) Crude OR
n % n % OR 95% CI
Work related variables
VDU working time
<50% 41 34 81 66 1.0
>50% 18 35 34 65 1.0 0.6 to 2.9
Physical work environment
Mean score >3 36 29 87 71 1.0
Mean score <3 2445 2955 2.01.0to3.9
Ergonomics of workstation
Mean score >3 42 33 85 67 1.0
Mean score <3 1837 3163 1.20.6to2.3
Height of the screen
Good (>10cm) 3130 7170 1.0
Poor (<10 cm) 19 40 29 60 1.5 0.7 to 3.1
Distance of the screen
Good (50–70 cm) 35 33 71 67 1.0
Poor (<50 cm or >70 cm) 17 35 31 65 1.1 0.5 to 2.3
Distance of the keyboard
Good (>15cm) 1826 5274 1.0
Poor (<15 cm) 29 40 44 60 1.9 0.9 to 3.9
Deviance of the keyboard
Good (0±2 cm) 21 29 52 71 1.0
Poor (> ±2 cm) 26 37 44 63 1.5 0.7 to 3.0
Distance of the mouse
Good (>15cm) 1533 3167 1.0
Poor (<15 cm) 15 33 30 67 1.0 0.4 to 2.5
Deviance of the mouse
Good (0±30cm) 1232 2668 1.0
Poor (> ±30 cm) 18 34 35 66 1.1 0.5 to 2.7
Breaks during work
Fully enough 21 32 45 68 1.0
Rather enough/rather little/much too little 14 36 25 64 1.2 0.5 to 2.8
Influence on work load
Somewhat/rather/very much 26 28 67 72 1.0
Very little/rather little 34 40 51 60 1.7 0.9 to 3.2
Individual variables
Sex
Male 2626 7474 1.0
Female 36 45 44 55 2.3 1.2 to 4.4
Age
25–43 22 38 36 62 1.0
44–51 17 29 42 71 0.7 0.3 to 1.5
52–61 23 37 39 63 1.0 0.5 to 2.1
Smoking
Never smoker 31 32 66 68 1.0
Current/ex-smoker 29 37 49 63 1.3 0.7 to 2.4
Frequency of physical exercise (times/week)
>2 3931 8569 1.0
<1 2139 3361 1.40.7to2.7
Health status
Very good/rather good 43 36 77 64 1.0
Average/rather poor/very poor 18 32 39 68 0.8 0.4 to 1.6
Mental stress
None/little 30 34 58 66 1.0
Some/fairly much/much 30 34 59 66 1.0 0.5 to 1.8
Mental strain
Never/rather seldom 33 33 66 67 1.0
Sometimes/rather often/continually 27 35 50 65 1.1 0.6 to 2.0
Depression
Never/rather seldom 37 32 80 68 1.0
Sometimes/rather often/continually 23 38 37 62 1.3 0.7 to 2.6
Job satisfaction
Very satisfied/rather satisfied 45 33 90 67 1.0
Neutral/rather/very dissatisfied 15 36 27 64 1.1 0.5 to 2.3
Time used for domestic activities (hours/day)
<1 12 25 36 75 1.0
>1 4837 8063 1.80.8to3.7
Time used for hobbies (hours/day)
<1 45 32 94 68 1.0
>1 1541 2259 1.40.7to3.0
*Local or radiating neck pain, or both.
Predictors for neck pain in VDU work 479
www.occenvmed.com
risk f actors have been dependent on the duration of VDU
work.
942
The time used for VDU work was measured as self
reported proportion of total working time during the preced-
ing month. In a study among newspaper workers it was found
that the workers overestimated their time working with the
VDU when compared with that based on observation.
43
How-
ever, these validations concerned typing only, whereas in our
study the definition for VDU work was use of keyboard or
other input or control device, including short thinking periods
and checking the results on the screen. The preliminary results
of our own validation among a sample of workers support the
findings of Bernard et al in that the workers tend to overesti-
mate their VDU working time (data not shown).
Our data suggest that poor placement of the keyboard is a
predictor for neck pain. Our finding is supported by the study
of Aarås and colleagues
17
who found that supporting the fore-
ar ms on the tabletop in front of the operator reduced signifi-
cantly the load on both right and left trapezius. Also, the
review of Bergqvist and colleagues
16
and that of Tittiranonda
and colleagues
10
give evidence of associations between various
aspects of keyboard use and symptoms in the neck–shoulder
area and in the upper extremities.
Most of the evidence concerning placement of the mouse
has been related to hand/wrist disorders.
9
A few studies have
reported an association between mouse location and neck
pain.
18 44
In our study, placement of the mouse was not a
significant risk factor. Because of missing values for many of
the subjects (n = 89) we did not include this variable into the
final models. Most of the subjects who did not give the
requested measure for the VDU mouse location either did not
use mouse at all, or used it for less than half of their VDU
working time.
Among other VDU specific ergonomic factors, the location
of the screen did not reach significance and was not included
in the final models. However, based on the univariate analysis,
high location of the screen (<10 cm below the horizontal level
of the eyes or <20° below the horizontal sight line) showed a
tendency for being a risk factor. It has been shown that visual
discomfort and musculoskeletal strain, particularly in the
neck and shoulders, are associated with computer screen
height.
45 46
Among the subjects with presbyopia, higher moni-
tor placement has been associated with neck extension caused
by visual demands when using bifocals.
37
On the other hand,
an extreme low location is often associated with musculo-
skeletal stress caused by neck flexion.
47 48
However, the benefit
of a lower placement is reduction of eye irritation, when the
open surface of the eyes is smaller and the lachrymation is
better.
49
Finally, the results of a recent field study support the
midlevel (∼20°) or somewhat higher placement.
19
The subjects
Table 4 Odds ratios for predictors of neck pain
among Finnish office workers in 1998–99 (logistic
regression model, adjusted for age and time used for
VDU work, n=138)
Predictors
Neck pain
OR 95% CI
Work related predictors
Physical work environment
Mean score >3 1.0
Mean score <3 2.1 0.9to4.9
Distance of the keyboard from the edge of the table
Good (>15 cm) 1.0
Poor (<15 cm) 2.1 1.0 to 4.5
Individual predictors
Sex
Male 1.0
Female 2.9 1.3 to 6.7
Smoking
Never smoker 1.0
Current/ex-smoker 1.9 0.8 to 4.3
AIC = 174.94.
−2 log L = 158.94 (df=7).
Hosmer and Lemeshow goodness of fit test: p=0.23.
Table 5 Odds ratios for predictors of neck pain
among Finnish office workers in 1998–99 (logistic
regression model with interactions, adjusted for time
used for VDU work; n=137)
Predictors
Neck pain
OR 95% CI
Work related predictors
Physical work environment
Mean score >3 1.0
Mean score <3 2.4 1.0to6.0
Distance of the keyboard from the edge of the table
Good (>15 cm) 1.0
Poor (<15 cm) 1.9 0.8 to 4.3
Individual predictors
Sex
Male 1.0
Female 6.7 1.4 to 30.9
Age
25–43 1.0
44–51 2.7 0.6 to 12.5
52–61 2.5 0.5 to 12.1
Smoking
Never smoker 1.0
Current/ex-smoker 1.5 0.6 to 3.6
Mental stress
None/little 1.0
Some/fairly much/much 0.5 0.2 to 1.4
Frequency of physical exercise (times/week)
>21.0
<1 0.8 0.2to2.7
Interactions
Age × sex
25–43 × male 1.0
44–51 × female 0.1 0.0 to 0.7
52–61 × female 1.1 0.1 to 10.3
Mental stress × frequency of physical exercise
None/little × >21.0
Some/fairly much/much × <1 6.7 1.0 to 43.6
AIC = 171.91.
−2 log L = 145.91 (df=12).
Compared with the main effects model: 158.94–145.91 = 13.04
(df=5), p<0.05.
Hosmer and Lemeshow goodness of fit test: p=0.32.
Table 6 Effect (odds ratio) of sex on
neck pain in different age groups
Sex
Age (y)
25–43 44–51 52–61
Male (reference) 1.0 1.0 1.0
Female 6.7 0.6 7.3
Table 7 Effect (odds ratio) of age on
neck pain according to sex
Age (y)
Sex
Male Female
25–43 (reference) 1.0 1.0
44–51 2.7 0.2
52–61 2.5 2.8
480 Korhonen, Ketola, Toivonen, et al
www.occenvmed.com
of this study were younger (mean 37 years) and did not use
bifocals. According to our criterion, the midlevel location or
any placement lower was regarded as acceptable. This
criterion was thought to be reasonable in our study, as the
subjects were relatively old (mean 47 years), commonly used
bifocals, and therefore may have benefited from a relatively
lower location of the screen.
14 42
The VDU specific measures, such as location of the screen,
keyboard, and mouse, were based on the measurements done
by the subjects themselves. This might be a source of error if
there were low agreement between self assessed locations and
direct measurements. An earlier validation study has found a
good agreement between self reported locations and direct
measurements.
13
However, the keyboard and the mouse are
used in parallel, their placements being dependent on each
other. The design of the keyboard affects the location of the
mouse and the location of the mouse affects the shoulder and
ar m posture.
18 44
For example, mouse users may benefit from a
shorter keyboard without a number pad.
50
We measured the
placements of only three components of the VDU workstation.
It should be noted that the actual work posture is not
exclusively affected by these workstation dimensions.
51
The physical work environment was a significant predictor
in our data. This variable included five aspects: lighting, tem-
perature, quality of the air, size of the working room, and
acoustic conditions in the work environment. For each subject
the mean of the five components was calculated to represent
the status of the physical work environment. All items of the
score showed a positive association with the outcome. It has
been suggested that, especially, lighting conditions are impor-
tant for the reduction of visual discomfort in VDU work.
Visual discomfort, in turn, correlates highly with neck
pain.
14 22
Of thermal conditions in VDU work, draught has
been reported as a problem in connection with discomfort in
the neck–shoulder area.
52
In our study the quality of indoor air
was also associated with neck pain.
The variables of the physical work environment were self
reported. Although this assessment preceded incident neck
pain, there is a possibility of bias, if those who in the follow up
reported neck pain had a different perception of their work
environment at baseline.
The risk for neck pain was significantly higher for the
women than for the men. This agrees with earlier studies.
Smaller stature and lower strength of the shoulder muscles
have been suggested to partly explain the sex
difference.
3151853
Concer ning VDU work in particular, gender
differences have been found, for example, in the use of a com-
puter mouse. Women are working with higher relative
musculoskeletal load, for instance, applying higher forces to
the mouse and using greater range of motion, than are men.
54
On the other hand, female sex may entail risk factors which
were not measured in the study.
55
Concer ning the present
study, different types of work tasks may be one explanation for
the sex effect in the results. Among our subjects, the women
worked in more monotonous tasks, such as assisting and sec-
retarial.
The men showed a tendency for increasing neck pain after
the age of 40 years. Among the women there was a U shaped
association. The youngest (aged 25–43) and the oldest (aged
52–61) workers had higher incidence than the middle aged
(44–51) workers. The higher incidence among our oldest
group is in line with earlier incidence studies.
3
The high inci-
dence among the youngest group was somewhat unexpected.
One could ask whether the youngest workers do the most
monotonous tasks and have the least influence on their work.
Concer ning leisure time activities, women in this age group
are often involved with a considerable amount of homework
and childcare. We tested the effect of hours spent on domestic
activities, but it did not turn out as a significant predictor in
our data.
In the model with direct effects only, mental stress was not
a significant predictor. However, stress had an interaction with
physical activity. Among those whose stress level was higher
and who exercised less frequently, the risk for neck pain was
especially high. There is consistent evidence that stress is
associated with neck pain in cross sectional studies,
16 32 34
yet
there are only few longitudinal studies suggesting stress as a
predictor of neck pain.
38
Results concerning the relation of
physical exercise and musculoskeletal pain are less
consistent.
27–29 31
However, it should be noted that among sed-
entary workers, exercise has been shown as beneficial.
24 29
For
the sedentary workers with a low frequency of leisure time
physical exercise, other leisure time activities may play a role,
especially if they impose on musculoskeletal organs as the
work does. We tested the effect of hours spent with hobbies,
such as computer games, handicrafts, and musical instrument
playing, but this variable was not a significant predictor in our
data.
We conclude that in the prevention of neck disorders in
office work with a high frequency of VDU tasks, attention
should be given to the work environment in general and to the
more specific aspects of VDU workstation layout. In addition,
our study provided further evidence that physical exercise
may be preventive of neck disorders among sedentary
employees.
ACKNOWLEDGEMENT
We acknowledge the Finnish Work Environment Fund for financial
support.
.....................
Authors’ affiliations
T Korhonen, R Ketola, R Toivonen, R Luukkonen, M Häkkänen,
E Viikari-Juntura, Finnish Institute of Occupational Health, Helsinki,
Finland
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