Is Low Back Pain Associated With Worse
Health-related Quality of Life 6 Months Later?This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to: Frankp@chiro.org
FROM: 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,
pnolet@rogers.com
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:
Introduction
Globally, low back pain (LBP) is the leading cause of years lived with disability and has been so over the last 20 years. [1] 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. [2] The economic burden of LBP has substantial direct and indirect costs. [3] LBP in the general population is a common condition marked by a chronic or recurring course with the majority of cases being mild. [4] Many with mild LBP do not seek care and most have a good prognosis. [5] 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. [6] The prevalence of LBP tends to be higher in females and in those aged 40–80 [7]. The point, 1 month, and 1 year prevalence is 18.3, 30.8, and 38 %, respectively. [7]
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. [8] HRQoL is an important indicator for incident musculoskeletal disorders. [9] 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 surgery. [10]
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. [15] 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.
Discussion
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 confounding.
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. [31] 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. [10] 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 important difference.
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. [14] 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. [15]
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. [16] Further, the differences between respondents and nonrespondents in the initial wave of the survey would suggest no selective response bias due to LBP. [16] 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.
Conclusions
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.
Acknowledgments
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.
Conflict of interest
None.
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