Objectives: This study aimed to estimate the prevalence, magnitude, and direction of the associations among disability, pain intensity, number of pain sites, and health-related quality of life (HRQoL) in patients reporting low back pain (LBP) as their primary pain. Methods: In January 2009, an Internet survey was performed for randomly selected adults aged 20-79 years who were registered as Internet research volunteers. Of 20 044 respondents, individuals with LBP as the primary pain were analyzed for associations among disability, number of pain sites, and HRQoL. Factors associated with low HRQoL were examined using multiple logistic regression modeling. Results: Of the 20 044 respondents, 25.2 % (n = 5060) reported LBP and 13.5 % (n = 2696) reported LBP as their primary pain. Among those with LBP as the primary pain, HRQoL decreased with increase in disability and number of pain sites. In multivariate analyses, disability [adjusted odds ratio (aOR), 2.93-4.58], number of pain sites (aOR, 1.42-6.12), pain intensity ≥7 (aOR, 1.88), and age ≥60 years (aOR, 1.55) were associated with low HRQoL. Conclusions: Approximately 13.5 % of patients reported LBP as their primary pain. Disability with absence from social activity and ≥7 pain sites were strongly associated with low HRQoL.
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