European Spine Journal 2015 Mar; 24 (3): 458–466
Paul S. Nolet, Vicki L. Kristman, Pierre Cotem, Linda J. Carrollm J. David Cassidy
Department of Graduate Education and Research,
Canadian Memorial Chiropractic College,
Toronto, ON, Canada,
PURPOSE: The purpose of this study was to investigate the impact of low back pain (LBP) on future health-related quality of life (HRQoL). Current evidence suggests that individuals with LBP have poorer HRQoL than those without LBP. However, most of the evidence comes from cross-sectional studies where LBP and HRQoL are determined at the same time. One prospective study examined the association between days with LBP and HRQoL but did not account for the intensity of LBP. Therefore, this association needs to be tested in a large prospective population-based sample with a valid measure of LBP and adequate control of known confounders.
METHODS: We formed a cohort of 1,110 randomly sampled Saskatchewan adults in September 1995. LBP at baseline was measured with the chronic pain questionnaire. The SF-36 questionnaire was used to measure physical and mental HRQoL at 6 months follow-up. Multivariable linear regression was used to estimate the association between graded LBP at baseline and HRQoL at 6 months while controlling for the effects of confounding.
RESULTS: The 6–month follow-up rate was 70.7 % (785/1,110). LBP had a dose-response relationship with worsening physical HRQoL at 6 months, after controlling for age, income, arthritis, neck pain, and kidney disorders: grade III-IV LBP (β = –10.23; 95 % CI –12.46, –7.99), grade II LBP (β = –6.72, 95 % CI –8.79, –4.65), and grade I LBP (β = –1.77; 95 % CI –3.18, –0.36). There was no dose-response relationship between LBP and mental HRQoL at 6 months.
CONCLUSIONS: Low back pain has an impact on future physical health-related quality of life (HRQoL). Strategies for reducing the effects of LBP on HRQoL should be an important focus for clinicians, researchers, and health policy makers.
Keywords: Low back pain, Quality of life, Risk, Cohort study
The Full-Text Article:
Globally, low back pain (LBP) is the leading cause of years
lived with disability and has been so over the last 20 years.  LBP has moved from a rank of eleventh spot globally
in 2000 as a cause of disability adjusted life years (DALY)
to sixth place in 2010, putting LBP just behind HIV/AIDS
in the absolute measure of health loss.  The economic
burden of LBP has substantial direct and indirect costs. 
LBP in the general population is a common condition
marked by a chronic or recurring course with the majority
of cases being mild.  Many with mild LBP do not seek
care and most have a good prognosis.  A systematic
review of 11 studies, including those seeking primary care
for LBP, found that only one-third had recovered at the
12–week mark with 65 % still reporting LBP 1 year later.  The prevalence of LBP tends to be higher in females
and in those aged 40–80 . The point, 1 month, and
1 year prevalence is 18.3, 30.8, and 38 %, respectively. 
Low back pain is common in the most productive years
of life and can impact a person’s health-related quality of
life (HRQoL). HRQoL includes physical, social, and psychological
functioning, work role functioning, and vitality
in a global construct.  HRQoL is an important indicator
for incident musculoskeletal disorders.  HRQoL can
help inform clinicians, researchers, and health policy
makers on the impact of LBP on individuals. Clinically
meaningful changes in physical HRQoL have been found
in patients with degenerative LBP 1 year after undergoing
Several cross-sectional studies have found a positive
association between LBP and HRQoL in adults. [11–14]
One longitudinal study followed 2,358 Japanese adults
over 1 month.  Linear regression models were used to
measure the association between the number of days with
LBP over the month and the 1–month change in HRQoL
using the Short Form 8–item Health Survey. There was a
positive association between the number of days with LBP
and physical HRQoL after controlling for age, comorbidities,
income, employment status, and baseline PCS. This
study measured the number of days with LBP, but did not
account for the intensity of LBP.
The purpose of this study was to test the hypothesis that
in the general population, those with prevalent LBP
experience a decrease in future HRQoL, in comparison to
those without LBP. We used a population-based cohort
from the general population of Saskatchewan to measure
the association between baseline graded LBP and HRQoL
measured in the 6–month follow-up survey while controlling
for known confounders.
The purpose of this study was to determine the impact of
LBP on future HRQoL. Clinically significant associations
were found between grades III–IV and grade II LBP and
a worsening physical HRQoL at 6 months, even after
adjusting for confounding. Controlling for baseline PCS
reduced the strength of the association in the final PCS
model. No association was found between graded LBP
and 6–month mental HRQoL after adjusting for
Not controlling for baseline PCS in the final PCS model
strengthened the association with LBP grade by reducing
PCS scores a further 7.66 points in grade III–IV LBP and
4.38 points in grade II LBP. In the PCS model not adjusting
for baseline PCS, the observed association may have been
over-estimated, if baseline PCS were, in fact, a confounder.
Conversely, controlling for baseline differences in PCS
may have led to over-adjustment as PCS may be on the
causal pathway.  That is, baseline PCS may mediate
the association between baseline graded LBP and 6 months
PCS because six of the seven questions that form the CPQ
ask about LBP in the last 6 months. In the SF-36 PCS,
questions relate to HRQoL at present and over the prior
4 weeks. If baseline PCS is a mediator, then it should not
be treated as a confounder. On the other hand, not controlling
for baseline differences in PCS may over-estimate
associations. The true association likely lies somewhere
between the final model including baseline PCS and the
final model without baseline PCS.
The PCS results in this study for grade II–IV LBP
were clinically significant and were of a greater magnitude
than the substantial clinical benefit threshold found
in 357 patients 1 year after having lumbar spine
arthrodesis for the treatment of degenerative spine conditions.  Glassman et al. found the threshold for
substantial clinical benefit in the PCS of the SF-36
questionnaire to be a 6.2 point improvement and a 4.9
point improvement for the minimal clinically important
difference. In the PCS final model that controlled for
baseline PCS HRQoL, the association with grade II and
grade III–IV LBP were below the minimal clinically
The results of this cohort study elaborate on the findings
of cross-sectional studies on adult populations reporting an
association between LBP and health status. [11–14] Only
one cross-sectional study used multivariable regression
analysis and controlled for potential confounding factors.
Yamada et al. reported reductions in HRQoL in the EQ-5D
in LBP patients that were significantly lower than the study
population.  One study examined the association
between LBP and HRQoL prospectively. Ono et al.
examined the change in HRQoL over 1 month in 617
subjects who reported at least 1 day of LBP. In the multivariable
regression model, after adjusting for age,
comorbidities, income, employment status, and baseline
PCS scores, an increase in one LBP day during the month
was associated with a 0.72 point reduction in PCS for
males and 0.29 point reduction for females. Reduction in
the MCS was not statistically significant for either gender. 
There are several strengths to our study. First, we used
data from a prospective, population-based random sample
of Saskatchewan adults. Second, we used valid and reliable
measures of LBP and HRQoL. Third, we used a multivariable
regression model to control for the confounding
effects of baseline socio-economic status, general health,
and comorbidity while considering the baseline differences
in PCS and MCS.
Our study has some limitations. The attrition analysis
suggests that respondents were older (4.8 years) than nonrespondents.
Baseline differences in PCS and MCS
HRQoL were similar between responders and nonresponders,
so it was unlikely that attrition influenced our
findings to any great degree. Secondly, the Saskatchewan
Health and Back Pain Survey had a 55 % response rate in
the first wave of the survey. This may introduce selection
bias and decrease the generalizability of our findings. We
are confident that this had little influence on our results
because the Saskatchewan Health and Back Pain Survey
used an accurate and complete sampling frame and a random
sample of adults selected from the population. 
Further, the differences between respondents and nonrespondents
in the initial wave of the survey would suggest
no selective response bias due to LBP.  Finally, we
cannot rule out the presence of residual confounding.
Baseline PCS HRQoL was responsible for a marked
reduction in the association between graded LBP and
physical HRQoL at 6 months. We do not know if baseline
PCS HRQoL is both a mediator and confounder of this
association. Our study design did not allow us to examine
these complex pathways.
The results suggest that LBP has a clinically significant
impact on future health-related quality of life (HRQoL). Further, this analysis advances
the understanding of confounding influences of the association
between LBP and PCS HRQoL. This may be of
interest to clinicians, researchers, and health policy makers.
To improve the HRQoL in a population, it will be important
to prevent and treat disabling LBP of greater pain
intensity. Future research should examine the association
between LBP and future HRQoL using more advanced
statistical techniques, such as structural equation modeling,
to assess the direct and indirect effects of baseline HRQoL.
The authors would like to acknowledge the
Chiropractors’ Association of Saskatchewan for funding the Saskatchewan
Health and Back Pain Survey and the assistance of Saskatchewan
Health in sampling the Saskatchewan population.
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