A Prospective Study
of Back Belts for Prevention of Back Pain and Injury
|
|
James T. Wassell,
PhD
Lytt I. Gardner, PhD
Douglas P. Landsittel, PhD
Janet J. Johnston, PhD
Janet M. Johnston, PhD
Journal of the American Medical
Association
Context Despite
scientific uncertainties about effectiveness, wearing back belts in the
hopes of preventing costly and disabling low back injury in employees
is becoming common in the workplace.
Objective To evaluate the effectiveness of using back belts in
reducing back injury claims and low back pain.
Design and Setting Prospective cohort study. From April 1996 through
April 1998, we identified material-handling employees in 160 new retail
merchandise stores (89 required back belt use; 71 had voluntary back belt
use) in 30 states (from New Hampshire to Michigan in the north and from
Florida to Texas in the south); data collection ended December 1998, median
follow-up was 6 1 /2 months.
Participants A referred sample of 13873 material handling employees
provided 9377 baseline interviews and 6311 (67%) follow-up interviews;
206 (1.4%) refused baseline interview.
Main Outcome Measures Incidence rate of material-handling back
injury workers compensation claims and 6-month incidence rate of
self-reported low back pain.
Results Neither frequent back belt use nor a belt-requirement store
policy was significantly associated with back injury claim rates or self-reported
back pain. Rate ratios comparing back injury claims of those who reported
wearing back belts usually every day and once or twice a week Vs those
who reported wearing belts never or once or twice a month were 1.22 (95%
confidence interval [CI], 0.87-1.70) and 0.95 (95% CI, 0.56-1.59), respectively.
The respective odds ratios for low back pain incidence were 0.97 (95%
CI, 0.83-1.13) and 0.92 (95% CI, 0.73-1.16).
Conclusions In the largest prospective cohort study of back belt
use, adjusted for multiple
individual risk factors, neither frequent back belt use nor a store policy
that required belt use was associated with reduced incidence of back injury
claims or low back pain.
JAMA. 2000;284:2727-2732
Back injuries have
been the leading cause of disability in the United States for people younger
than 45 years and have been the most expensive health care problem for
the 30- to 50-year-old age group.1 Low back pain accounted for 23% ($8.8
billion) of total workers compensation payments in 1995. 2 The Annual
Survey of Occupational Injuries and Illnesses conducted by the Bureau
of Labor Statistics indicates that in 1998 there were 279507 back injuries
due to overexertion that resulted in lost work days (89% in material-handling).
3 In response to the increasing human and economic costs of back injury,
employers have attempted preventive measures; specifically, the widespread
use of industrial back belts, approximately 4 million of which were purchased
in 1995. 4 This study was designed to address 2 objectives: (1) to examine
the effect of store policy by comparing a belt-use requirement policy
with a voluntary belt-use policy and (2) to compare employees who reported
wearing back belts usually every day with those reported wearing the belt
less frequently, based on interview responses.
Study Design
Between April 1996 and April 1998, 50 new stores and 110 newly expanded
stores (combination supermarket and merchandise) of a single corporation
were enrolled on the date they first opened for regular business. A prospective
cohort study was conducted following sequential assignment (according
to store opening date) of groups of stores to either the traditional belt-requirement
policy or voluntary belt use. Employees were required to wear back belts
during material-handling activities in the belt-requirement stores, while
belts were made available only by request in the voluntary belt-use stores.
Of the 160 stores
in the study, 89 required back-belt use and 71 had voluntary belt use.
The original goals of introducing stores with voluntary belt use were
to create an environment in which employees were free not to wear back
belts without violating store policy and to compare the back injury rate
with stores that required belt use. The main focus of this study is on
interview data: determining employee characteristics and belt wearing
habits from a baseline interview for comparison of injury rates and a
follow-up interview to determine the incidence of self-reported low back
pain.
Study stores were
distributed across 30 states from New Hampshire to Michigan in the north
and from Florida to Texas in the south; most states included both belt-requirement
and voluntary belt-use stores. We obtained payroll records of hours worked
and workers' compensation injury reports for all stores for calculation
of injury incidence rates. The National Institute for Occupational Safety
and Health (NIOSH) Human Subjects Review Board formally approved the study's
design and data collection instruments in August 1995, following a public
peer review meeting in April 1995.
Data Collection
A survey contractor conducted telephone interviews using trained interviewers.
Participants completed an informed consent form either in a prestudy employee
meeting or at the beginning of the telephone interview. Telephone calls
were placed to employees while working at the store during regular working
hours. For each store, interviews were attempted for a period of at least
30 calendar days (excluding weekends). Follow- up interviews were attempted
for all employees who had a baseline interview. Interviews were not conducted
from mid-December to mid-January due to the holiday shopping season.
Both the baseline and follow-up interviews consisted of questions covering
work history, lifestyle habits, medical history, job activities, psychosocial
factors, belt wearing habits, and demographic information. Participants
were asked 4 job satisfaction questions from the Quality of Employment
Survey developed by the US Department of Labor and NIOSH.5 The sum of
the responses for these 4 items were used to create a dichotomous measure
of job satisfaction using the median cut point.
Job Titles
The job title receiver/unloader identified workers with the greatest
exposure to physical work unloading freight trucks; stocker was used to
designate employees with responsibility for moving stock to the merchandise
floor. Department managers were employees whose physical work mostly
involved arranging stock on shelves and other less strenuous activities,
and the group designated as others were employees with various other jobs
involving material handling. In a separate study 6 receiver/ unloaders
had the highest exposure to manual material handling (based on lifting
heavier loads more frequently), followed by department managers, then
stockers. Job title was determined from an employees first baseline
interview response and consistency in reporting job title was evaluated
from the follow-up interview: 85% of department managers, 75% of stock-ERs,
71% of receiver/unloaders, and 31% of the others were working in the same
job title that they reported during the baseline interview.
Self-reported
Back Belt Use
Self-reported belt wearing was determined from the response to the question:
During the past month, how many days per week did you wear the back
belt? Response categories were: never, once or
twice a month, once or twice a week, or usually
every day. The never and once or twice month
categories were combined and are referred to herein as never. Consistency
was evaluated from the follow- up interview with 75% reporting usually
every day, 81% reporting never, and 31% reporting once or twice per week
in the same baseline category.
Back Belt
The back belt provided by the corporation is designed to fit around the
waist without shoulder straps. The belt is constructed of stretchable
nylon material with Velcro ends and mesh in back. Tightness is adjusted
by choosing the location to attach the Velcro and tightening side panels
when lifting. This same back belt was used in human subjects laboratory
studies of biomechanics (Rebecca J. Giorcell, Ph.D., et al, unpublished
data, 1998) and physiology effects (Thomas G. Bobick, Ph.D., et al, unpublished
data, 1998). All employees, when first hired and regardless of the store
policy, received a short introductory information and training session
on proper lifting and belt use via videotape or interactive computer-based
learning.
Back Pain Data
Self-reported low back pain (hereafter back pain) was defined as a positive
response to a question asking if respondents experienced any low back
pain in the 6 months preceding the follow-up interview, with a frequency
of 4 or more episodes (median). A history of previous back injury was
determined by a positive response to questions about back pain (with the
addition of a reported severity 7 on a 10-point scale) at the baseline
interview; had previous back surgery; had ever been told by a doctor
that he/she had arthritis of back joints, degenerative joint disease of
the back, lupus erythematosus, ankylosing spondylitis, or spondylolisthesis;
or had seen a doctor, nurse, physical therapist, or chiropractor
for a strain or sprain of the lower back or ruptured disk in the back.
Injury Claims
Data
The data consisted of the dates of occurrence and characteristics of work-related
material-handling back injuries requiring medical care recorded in the
companys own workers compensation reporting system. The data
consisted of all claims received by the corporation, regardless of whether
the claim was accepted or rejected for compensation. Although compensation
rules vary among states, corporation procedures and policies regarding
which injuries are included in their corporate database do not vary among
states. Material-handling compensation claims for back injuries consisted
of those with an external cause code containing strain or
sprain followed by lifting, pushing,
pulling, reaching, holding, or carrying.
Back injuries unrelated to material handling (such as fall,
caught by, caught between, struck by,
slip, or trip without fall) were excluded.
Statistical Methods
The regression models used to investigate the effects of belt wearing
and store policy were selected to control for type of store (new stores
or newly expanded stores that are a combination of supermarket and merchandise),
demographic risk factors (age, race, and sex), work exposure (job title
and lifting frequency), variables found important in previous studies
(history of previous back injury and job satisfaction), and a standard
health-risk factor (smoking). These 11 covariates were investigated using
Poisson regression to model the incidence rate of back injury claims,
taking account of the variable work-hours of follow-up for each employee.
Logistic regression was used to model the incidence of back pain as a
binary outcome in which employees had similar length of follow-up. Potential
effect modification was investigated using interaction terms and separate
analysis of subgroups of data. Subgroup analyses were conducted for those
who were concordant for belt wearing at both the baseline and follow-
up interviews and for employees with the most strenuous job tasks. Regression
analyses and confidence intervals (CIs) for odds ratios (ORs) and rate
ratios (RRs) were calculated using SAS statistical software.7
Other CIs were calculated using StatXact.8
There were a total
of 144469 employees who worked in the 160 stores during the study period.
Of these, 13873 (10%) were identified by store management as involved
in material handling tasks prior to the interview process (FIGURE).
For the 6311 employees who completed both a baseline and a follow-up interview,
the median (and mode) of the length of time between baseline and follow-up
interview was 6 1 /2 months. Payroll and workers' compensation data collection
ended December 1998.
TABLE
1 shows employee characteristics from the baseline interview by store-belt
policy and belt wearing. There was a lack of compliance with the store
belt-wearing policy. In the stores requiring belt use, 58% of employees
reported wearing belts usually every day; 14%, once or twice a week; and
28%, never. In the stores with voluntary belt-use, 33% of employees reported
wearing belts usually every day; 11%, once or twice a week; and 56%, never.
There was a slight difference in the proportions who completed a follow-up
interview, worked in new stores, or had a history of previous back injury
by frequency of belt wearing. Employees who reported belt wearing usually
every day were more likely to be receivers/unloaders or stockers and were
less likely to be department managers or others, and were also more likely
to report lifting more than 9 kg (20 lb) at work usually every day.
Among the 9377 who
completed a baseline interview and were matched to payroll data, there
were 195 back injury claims (12.9 million work-hours) for a crude incidence
rate of 3.03 per 100 full-time equivalent (FTE) (95% CI, 2.62-3.48). Among
the 6311 who completed a baseline and follow-up interview, there were
1088 cases of back pain (17%; 95% CI, 16%-18%). There were no statistically
significant protective effects comparing employees who wore belts usually
every day with employees who never wore belts for either back injury claims
(RR, 1.22; 95% CI, 0.87-1.70) or low back pain (OR, 0.97; 95% CI, 0.83-
1.13). There were no statistically significant protective effects comparing
employees who wore belts once or twice a week with employees who never
wore belts for either back injury claims (RR, 0.95; 95% CI, 0.56-1.59)
or back pain (OR, 0.92; 95% CI, 0.73-1.16). TABLE 2 presents
percentages reporting back-pain and back injury claim rates, stratified
by risk factors. Table 2 also presents multivariate regression
estimates with each variable adjusted for all other variables listed.
Among the other risk
factors in the models, a history of previous back injury was the strongest
risk factor for both outcomes. Frequent lifting of heavier than 9 kg (20
LB) at work was associated with significantly increased odds of back pain
but not for back injury claims. Women had significantly more back pain
than men, but they did not have a higher back injury claim rate. Other
races did not differ significantly from white persons for back pain but
persons of other races had a higher back injury claim rate. Similarly,
results for job satisfaction and smoking differed by outcomes. Poor job
satisfaction was significantly associated with increased risk of back
pain but not with a higher back injury claim rate. Current smokers had
higher risk for back injury claims and former smokers had higher risk
for back pain.
Table
1. Characteristics of the Study Population by Self-reported Belt
Wearing at Baseline Interview* |
|
|
Self-Reported
Belt Wearing
|
|
|
Required
Belt-Use Store
|
Voluntary
Belt-Use Form
|
|
|
|
|
|
|
|
|
Characteristics |
Usually
Every Day
|
1
to 2 times a week
|
<1
or 2 times a Month
|
Usually
Every Day
|
1
to 2 times a week
|
<1
or 2 times a Month
|
|
|
|
|
|
|
|
|
No.
of baseline interviews
|
3004
|
700
|
1474
|
1361
|
471
|
2349
|
|
|
|
|
|
|
|
|
Mean
age, y
|
36
|
36
|
35
|
36
|
36
|
35
|
|
|
|
|
|
|
|
|
New
store type
|
728
(24)
|
161
(23)
|
434
(29)
|
352
(26)
|
109
(23)
|
616
(26)
|
|
|
|
|
|
|
|
|
History
of back injuries
|
430
(14)
|
99
(15)
|
217
(14)
|
216
(16)
|
92
(20)
|
315
(13)
|
|
|
|
|
|
|
|
|
Lifting
> 9 kg
|
1873
(62)
|
384
(55)
|
469
(32)
|
888
(64)
|
268
(57)
|
1328
(57)
|
|
|
|
|
|
|
|
|
Job
Titles |
|
|
|
|
|
|
Department
Manager
|
644
(21)
|
260
(37)
|
|
262
(19)
|
149
(32)
|
776
(33)
|
Receiver
or Unloader
|
795
(26)
|
112
(16)
|
278
(19)
|
394
(29)
|
76
(16)
|
442
(19)
|
Others
|
258
(9)
|
77
(11)
|
188
(13)
|
133
(10)
|
60
(13)
|
289
(12)
|
|
|
|
|
|
|
|
|
Good
job satisfaction |
1702
(57)
|
344
(49)
|
735
(50)
|
773
(57)
|
244
(52)
|
1226
(52)
|
Current
Smokers
|
1075
(36)
|
209
(30)
|
492(33)
|
477
(35)
|
149
(32)
|
807
(34)
|
|
|
|
|
|
|
|
|
White
|
2334
(78)
|
585
(84)
|
1285
(87)
|
988
(73)
|
360
(77)
|
2003
(85)
|
|
|
|
|
|
|
|
|
Women
|
1490
(50)
|
387
(55)
|
799
(54)
|
611
(45)
|
264
(56)
|
1277
(54)
|
|
|
|
|
|
|
|
|
Follow-up
Interviews f1
|
1998
(66)
|
456
(65)
|
968
(66)
|
950
(70)
|
303
(64)
|
1633
(70)
|
____________________________________________________
* Data are presented as number (percentage) of subjects in each column
unless otherwise indicated. Row categories are not mutually exclusive.
Row total of 8358 is less
than the number of completed interviews (n=8377) because of missing values.
New stores vs newly expanded
stores (see "Methods" section).
To convert to pounds divide
by 0.45.
f1 Row total of 6299 is less than the number of completed interviews (n
= 6311) because of missing values.
____________________________________________________
There was no statistically
significant difference for the preplanned comparison of back injury claim
rates among the 13873 employees identified by store management as involved
in material-handling tasks prior to the interview process. Stores with
a belt requirement had 236 material-handling back injury claims among
16.1 million work-hours for a crude incidence rate of 2.94 per 100 FTEs.
Stores with voluntary belt use had 203 material-handling back injury claims
among 12.5 million work-hours for a crude incidence rate of 3.26 per 100
FTE (RR, 0.90; 95% CI, 0.75-1.09). Additionally, we found no effect of
the belt-requirement store policy among those interviewed for either back
injury claims (RR, 0.94; 95% CI, 0.70-1.28) or back pain (OR, 1.06; 95%
CI, 0.92-1.22).
No statistically
significant effects of back belts were found among the subgroup of employees
who had no history of previous back injury, using regressions with the
same covariates shown in Table 2. Back pain was not different
between those who reported belt wearing usually every day and those who
reported never wearing a belt (OR, 0.98; 95% CI, 0.82-1.17), and the back
injury claim rate was not different for these groups (RR, 1.34; 95% CI,
0.91-1.98). Among the subgroup who had a previous history of back injury,
there were no effects of belt wearing on back pain (OR, 0.90; 95% CI,
0.65- 1.25), or back injury claim rate (RR, 0.92; 95% CI, 0.47-1.79).
Back belt use may
be considered as a measure of compliance with store policy, so an interaction
term between belt wearing and store policy was examined for the models
shown in Table 2. This interaction term shows that there
is no effect of back belts when comparing employees who reported belt
wearing usually every day in stores that required belt use with those
employees who reported never wearing a belt in voluntary belt-use stores
for back pain (OR, 1.07; 95% CI, 0.89-1.29) or for back injury claims
(RR, 1.19; 95% CI, 0.79-1.78).
Back belt use is
affected by store policy, so to assess the possibility that a model including
both covariates might introduce excess error, the store policy covariate
was removed from the regression models shown in Table 2.
Back pain was not different between those who reported belt wearing usually
every day compared with those who reported never wearing a belt (OR, 0.99;
95% CI, 0.85-1.14), and the back injury claim rate was not different for
these groups (RR, 1.20; 95% CI, 0.87- 1.65) after removing the store policy
covariate.
No statistically
significant effects of belt wearing were found among a subgroup who reported
consistent belt wearing habits on both the baseline and follow-up interviews.
Using the same co-variates shown in Table 2, regressions
were used to compare employees who reported in both interviews wearing
belts usually every day with those who reported in both interviews never
wearing a belt. There was no evidence that wearing back belts reduced
back pain (OR, 0.88; 95% CI, 0.73-1.07) or back injury claims (RR, 1.57;
95% CI, 0.98- 2.50) in these groups that reported consistent belt-wearing
habits.
To focus on those
employees who frequently lifted heavier loads, regressions were restricted
to the subgroup of employees with the most strenuous job. Using the same
covariates as shown in Table 2, for an analysis restricted
to receiver/unloaders, back pain was not different between those who reported
belt wearing usually every day compared with those who reported never
wearing a belt (OR, 0.81; 95% CI, 0.58-1.14), and the back injury claim
rates appeared to be the same for these groups (RR, 1.53; 95% CI, 0.82-2.84).
Table
2. Risk Estimates and Regression Results for Low Back Pain
and Back Injury Claims and Material Handlers |
|
|
>
4 Self reported Episodes of Low Back Pain (1088 Cases)
|
Back
Injury Workers Compensation Claims (195 Claims)
|
|
|
|
|
Variable
|
No.
of Events/No. Interviewed(%)*
|
Adjusted
Odds Ratio (95% CI)
|
No.
of Claims/Million Worker Hours (Rate per FTE)
|
Adjusted
Rate Ratio (95% CCI)
|
|
|
|
|
|
Belt
Wearing |
|
|
|
|
< 1-2 times per month
|
455/2601
(17.5)
|
1.00
|
70/5.08
(2.76)
|
1.00
|
|
|
|
|
|
1-2
times per week
|
130/759
(17.1)
|
0.92
(0.73-1.16)
|
21/1.61
(2.61)
|
0.95
(0.56-1.59)
|
Usually
Every Day
|
502/2939
(17.1)
|
0.97
(0.83-1.13)
|
104/6.16
(3.38)
|
1.22
(0.87-1.70)
|
|
|
|
|
|
|
Store
policy
|
|
|
|
|
Voluntary
belt use
|
486/2893
(16.8)
|
1.00
|
86/6.58
(3.08)
|
1.00
|
Belt
use required
|
602/3418
(17.6)
|
1.06
(0.92-1.22)
|
109/7.30
(2.98)
|
0.94
(0.70-1.28)
|
|
|
|
|
|
|
Store
type
|
|
|
|
|
Newly
opened
|
256/1585
(16.2)
|
1.00
|
66/3.23
(4.09)
|
1.00
|
Newly
expanded
|
832/4726
(17.6)
|
1.11
(0.94-1.31)
|
129/9.65
(2.67)
|
0.69
(0.51-0.95)
|
|
|
|
|
|
|
Previous
back injury |
|
|
|
|
No
|
770/5427
(14.2)
|
1.00
|
148/11.05
(2.68)
|
1.00
|
Yes
|
318/884
(36.0)
|
3.24
(2.75-3.82)
|
47/1.83
(5.14)
|
2.03
(1.45-2.86)
|
|
|
|
|
|
Frequency
of lifting > 9 kg
|
|
|
|
|
Almost
never
|
131/948
(13.8)
|
1.00
|
29/1.97
(2.95)
|
1.00
|
1-2
times per week
|
218/1413
(15.4)
|
1.29
(1.01-1.65)
|
42/2.89
(2.89)
|
0.88
(0.54-1.42)
|
Usually
everyday
|
706/3689(19.1)
|
1.71
(1.38-2.13)
|
11.3/7.45
(3.03)
|
0.87
(0.57-1.35)
|
|
|
|
|
|
Job
Title |
|
|
|
|
Department
Manager
|
328/1896
(17.3)
|
1.00
|
56/3.86
(2.90)
|
1.00
|
Stocker
|
439/2419
(18.1)
|
1.01
(0.85-1.20)
|
62/4.96
(2.50)
|
0.98
(0.67-1.44)
|
Receiver
or Unloader
|
220/1379
(16.0)
|
0.95
(0.78-1.17)
|
59/2.65
(4.45)
|
1.50
(1.01-2.23
|
Other
|
99/607
(16.3)
|
1.04
(0.79-1.38)
|
18/1.39
(2.59)
|
0.93
(0.49-1.75)
|
|
|
|
|
|
Job
Satisfaction |
|
|
|
|
Good
|
487/3493
(13.9)
|
1.00
|
108/7.09
(3.04)
|
1.00
|
Bad
|
600/2814
(21.3)
|
1.60
(1.39-1.84)
|
87/5.77
(3.01)
|
0.94
(0.70-1.26)
|
|
|
|
|
|
Smoking
Status |
|
|
|
|
Never
|
537/3328
(16.1)
|
1.00
|
83/6.90
(2.40)
|
1.00
|
Former
|
165/850
(19.4)
|
1.26
(1.03-1.56)
|
29/1.75
(3.31)
|
1.56
(0.99-2.45)
|
Current
|
383/2113
(18.1)
|
1.10
(0.94-1.28)
|
83/4.19
(3.96)
|
1.64
(1.19-2.26)
|
|
|
|
|
|
Race
|
|
|
|
|
White
|
923/5213
(17.7)
|
1.00
|
149/10.64
(2.80)
|
1.00
|
Other
|
165/1097
(15.0)
|
0.89
(0.73-1.08)
|
46/2.23
(4.12)
|
1.46
(1.02-2.08)
|
|
|
|
|
|
Sex |
|
|
|
|
Man
|
429/2861
(15.0)
|
1.00
|
94/5.89
(3.19)
|
1.00
|
Woman
|
659/3450
(19.1)
|
1.56
(1.34-1.82)
|
101/6.99
(2.88)
|
1.10
(0.80-1.52)
|
|
|
|
|
|
Age,
y |
|
|
|
|
<25
|
219/1232
(17.8)
|
1.00
|
43/2.40
(3.58)
|
1.00
|
25-39
|
459/2740
(16.8)
|
0.87
(0.72-1.06)
|
103/5.62
(3.67)
|
0.96
(0.66-1.41)
|
40-54
|
319/1834
(17.4)
|
0.79
(0.64-0.97)
|
46/3.83
(2.40)
|
0.61
(0.39-0.96)
|
55
|
91/503
(18.1)
|
0.84
(0.63-1.13)
|
3/1.05
(0.57)
|
0.15(0.05-0.47)
|
____________________________________________________
* Interview responses are based on 6311 total follow-up interviews. Some
respondents did not answer all the questions.
Logistic regression model
with binary response outcome of pain reported at follow-up interview among
6311 employees. Estimates are adjusted for all other variables in this
Table. Because of missing covariate values, 6011 observations were used
for the multivariate model 'CI' indicated confidence intervals.
Denominators in million
worker-hours exposure are rounded to 2 decimal places. Rate per 100 full-time
equivalents (FTEs) is per 200000 work hours.
Poisson regression model
using back injury counts and work-hours among 9377 employees with a baseline
interview, estimates adjusted for all other variables in this Table.
f1 To convert to pounds divide by 0.45.
____________________________________________________
To assess the potential
for selection bias, the effects of belt wearing on back injury claim rates
were compared among employees who completed a follow-up interview and
those who did not complete a follow-up interview. The crude back injury
claim rate among the 3066 employees who completed a baseline interview
but did not complete a follow-up interview (5.04 per 100 FTE; 95% CI,
3.88-6.44) was nearly twice the crude back injury claim rate compared
with the 6311 employees who completed both interviews (2.61 per 100 FTE;
95% CI, 2.19-3.09). However, there was no significant difference in back
injury claim rates comparing those who reported wearing belts usually
every day with those who reported never wearing them among those who did
not complete a follow- up interview (RR, 0.97; 95% CI, 0.53-1.85) and
among those who completed a follow-up interview (RR, 1.37; 95% CI, 0.91-2.05)
in multivariable Poisson regressions. In another evaluation of potential
selection bias, the effects of belt wearing on the prevalence of back
pain were estimated using the baseline interview data as in a cross-sectional
study. In a multivariable logistic regression there was no difference
in the prevalence of back pain at baseline comparing those who reported
wearing belts usually every day with those who reported never wearing
them (OR, 1.07; 95% CI, 0.94-1.21).
The NIOSH prospective
cohort study of back pain and back injury claims in 9377 employees, controlling
for multiple individual risk factors, found no evidence to support the
use of back belts as a preventive measure. We found no effects of belt
wearing in various subgroups: employees with and without a history of
previous back injury, employees with consistent self-reported belt wearing
habits from baseline to follow-up interviews, and employees with the most
strenuous job. Among 13873 material-handling employees in 160 stores,
we found no difference in unadjusted back injury claim rates comparing
a belt-requirement store policy to a voluntary belt-use store policy.
Previous studies
have relied on worker compliance to a store policy to determine belt-wearing
habits.9-11 Accurate determination of workers actual workplace belt-wearing
habits is a recognized limitation of these studies. By directly interviewing
employees about their belt-wearing habits, our study more closely measures
typical belt use in the workplace rather than implied belt use based on
store policy.
A recent study in
California over a 6-year period found a higher injury rate during the
months preceding the implementation of a mandatory back belt-use policy
than during the months after the policy was implemented (RR, 1.52; 95%
CI, 1.36-1.69).12,13 In this historical cohort study, estimates of back-belt
effects were based on aggregate back injury claim rates without controlling
for multiple individual risk factors. The NIOSH study was prospective
with concurrent comparison groups, evaluated both back injury claim rates
and self-reported low back pain and controlled for well-known back injury
risk factors.
The potential effects
of selection bias on the back pain results, due to the inability to complete
follow-up interviews on all employees who had a baseline interview, is
a limitation of our study. Ancillary analyses do not demonstrate that
selection biases alter the main conclusions of this study. Other analyses
of subgroups of employees and interaction effects attempted to discover
belt effects among groups of employees who were most likely to be affected
by belt wearing. However, even these comparisons failed to find any back-belt
effects.
Our study evaluates
back belts using a prospective design in new stores distributed over a
wide geographic region, concurrent comparison groups, comprehensive individual
interviews, detailed exposure information, a job satisfaction measure,
multivariable regression analysis, and sufficient sample size. This study
considered 2 outcomes: the incidence of back pain and workers compensation
claims for material-handling back injury requiring medical care. Adjustment
for multiple risk factors was incorporated in our investigation, especially
a history of previous back injury and lifting frequency, which has been
lacking in some previous studies on the effects of back belts. This is
the largest prospective study to date of material-handling workers with
individual data on back-belt use, back pain, and important confounders.
Results based on these multiple analyses of data all converge to a common
conclusion: back-belt use is not associated with reduced incidence of
back injury claims or low back pain in material handlers.
Author Affiliations:
Centers for Disease Control and Prevention, National Institute for Occupational
Safety and Health, Division of Safety Research, Morgantown, WVa. Dr. Gardner
is now with National Center for HIV, STD and TB Prevention. Dr. Landsittel
is now with the National Institute for Occupational Safety and Health,
Health Effects Laboratory Division. Dr. Janet M. Johnston is now with
the University of Pittsburgh, Graduate School of Public Health, Pittsburgh,
Pa.
Corresponding Author and Reprints: James T. Wassell, PhD, Centers
for Disease Control and Prevention, National Institute for Occupational
Safety and Health, Division of Safety Research, 1095 Willowdale Rd, Morgantown,
WV 26505. (e-mail: jtw2@cdc.gov).
Acknowledgment: We thank the efforts of Jennifer L. Bell, PhD,
Guang X. Chen, MD, and David K. Hilling for analytical support; William
Halperin, MD, Roslyn A. Stone, PhD, Lawrence J. Fine, MD, Kyle Steenland,
PhD, Nancy A. Stout, EdD, and James W. Collins, PhD, for administrative
and/or scientific contributions; Thomas K. Hodous, MD, Harvey Checkoway,
PhD, Barbara Silverstein, PhD, Ellen Eisen, ScD, and Laura Punnett, ScD,
for critical review; Nancy J. Roder, MS, Louis D. Smith, MSEE, Linda L.
Morton, MS, Martin S. Forde, ScD, Susan Moir, MS, and Ninica L. Howard,
MS, for other support.
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