Using the Quebec Task Force Classification to subgroup low back pain patients in primary care: an analysis of longitudinal clinical data from chiropractic and general practice

Background Low back pain (LBP) patients with related leg pain and signs of nerve root involvement (NRI) are considered to have a worse prognosis than patients with LBP alone. However, knowledge is limited about the importance of distinguishing between leg pain above or below the knee and leg pain with and without NRI. The objectives of this study were 1) to investigate whether patients in the four QTF categories (LPB alone, LBP + leg pain above knee, LBP + leg pain below knee, and LBP + NRI) differ on baseline characteristics; 2) to investigate the relationship between QTF categories and global perceived effect (GPE) and activity limitation after 2 weeks, 3 months, and 1 year as well as one-year-trajectories of LBP intensity; including whether there is a hierarchy of the four groups in terms of severity in outcome measures, and to what extent QTF categories predict these outcomes; and 3) to describe whether this relationship is similar chiropractic practice (CP) and general practice (GP). Method This is a prospective observational cohort study of adult patients seeking care for LBP in CP or GP. Patients completed an extensive baseline questionnaire and were classified into the four QTF categories by the practitioner. Associations between QTF categories and outcomes were tested using univariate regression models and models adjusted for demographic factors . Predictive capacity was quantified in terms of R-squared and Area Under the ROC Curve (AUC). Results The study comprised 1271 (947 from CP and 324 from GP) patients. Compared with patients with LBP alone, patients with leg pain and patients with NRI were more severely affected across baseline characteristics and outcome measures in both CP and GP. QTF categories were associated with activity limitation at all follow-up time-points in both CP and GP (p<0.001). Patients with LBP alone had the least activity limitation at all time points and LBP + NRI had the most activity limitation with the exception of GP patients at 2 weeks. In both cohorts, QTF-categories were associated with 2 of 5 trajectories of LBP intensity (p< 0.05) and with GPE at two weeks (p< 0.05) but not 3 months and 1 year. Nearly twice as many patients with LBP alone compared with patients with LBP + NRI were improved at 2 weeks in both cohorts. None of the outcomes were accurately predicted by the QTF (R2 range: 0.05-0.14); AUC range: 0.53-0.65). Conclusions The QTF classification differentiated between distinctly different patient subgroups. Local LBP was on all parameters the least severe condition. Although less clear-cut, distribution of leg pain and clinical signs of NRI differentiated between patient groups with different clinical presentation and course; generally with increasing severity across categories from LBP alone, over LBP + above knee and LBP + below knee to LBP + NRI.