Comprehensiveness and validity of a multidimensional assessment in patients with chronic low back pain: a prospective cohort study

BACKGROUND: Chronic low back pain is a multidimensional syndrome affecting physical activity and function, health-related quality of life and employment status. The aim of the study was to quantify the cross-sectional and longitudinal validity of single measurement scales in specific construct domains and to examine how they combine to build a comprehensive outcome, covering the complex construct of chronic low back pain before and after a standardized interdisciplinary pain program. METHODS: This prospective cohort study assessed 177 patients using the Short Form 36 (SF-36), the Multidimensional Pain Inventory (MPI), the Symptom Checklist-90-Revised (SCL-90-R), the Oswestry Disability Index (ODI), and 2 functional performance tests, the Back Performance Scale (BPS) and the 6-Minute Walking Distance (6MWD). The comprehensiveness and overlap of the constructs used were quantified cross-sectionally and longitudinally by bivariate correlations, exploratory factor analysis, and effect sizes. RESULTS: The mean age of the participants was 48.0 years (+/− 12.7); 59.3% were female. Correlations of baseline scores ranged from r = − 0.01 (BPS with MPI Life control) to r = 0.76 (SF-36 Mental health with MPI Negative mood). SF-36 Physical functioning correlated highest with the functional performance tests (r = 0.58 BPS, 0.67 6MWD) and ODI (0.56). Correlations of change scores (difference of follow-up – baseline score) were consistent but weaker. Factor analysis revealed 2 factors: “psychosocial” and “pain & function” (totally explained variance 44.0–60.9%). Psychosocial factors loaded strongest (up to 0.89 SCL-90-R) on the first factor, covering 2/3 of the explained variance. Pain and function (ing) loaded more strongly on the second factor (up to 0.81 SF-36 Physical functioning at follow-up). All scales showed improvements, with effect sizes ranging from 0.16–0.67. CONCLUSIONS: Our results confirm previous findings that the chronic low back pain syndrome is highly multifactorial and comprises many more dimensions of health and quality of life than merely back-related functioning. A comprehensive outcome measurement should include the predominant psychosocial domain and a broad spectrum of measurement constructs in order to assess the full complexity of the chronic low back syndrome. Convergence and divergence of the scales capture the overlapping contents and nuances within the constructs.