ABSTRACT: BACKGROUND CONTEXT:The STarT Back Screening Tool (SBST) categorizes risk of future disability in patients with low back pain (LBP). Previous studies evaluating the use of SBST in physical therapy (PT) populations do not reflect the ethnic and socioeconomic diversity occurring in clinical practice and lack statistical power to evaluate factors associated with outcomes within each SBST risk category. PURPOSE:The purpose of this study is to further refine SBST risk categorization for predicting improvements in functional disability with attention toward patient level factors that might guide SBST use in routine outpatient physical therapy practice. STUDY DESIGN/SETTING:This was a retrospective cohort study that took place within a large academic, tertiary-care health system. PATIENT SAMPLE:The study cohort consisted of 1,169 patients with LBP who completed a course of outpatient physical therapy from June 1, 2014 to May 31, 2015 and who completed the patient-reported SBST and modified low back pain disability questionnaire (MDQ) questionnaires as part of standard of care. OUTCOME MEASURES:Improvement in functional disability defined as decrease in 10 or more points in the MDQ. METHODS:Multivariable logistic regression was performed to evaluate independent predictors of improvement after PT, which included SBST risk category, baseline MDQ, a two-way interaction term between SBST category and baseline MDQ, prior level of function (independent vs. required assistance), demographic characteristics, number of completed PT visits, and duration of PT episode of care. In exploratory analyses, additional two-way interaction terms between SBST category and the significant predictors were added to the regression model. RESULTS:Mean age of patients in the study cohort was 55.1 years (SD 16.1); 657 (56.2%) were female, 117 (10.0%) were black race, 127 (10.9%) had Medicaid insurance, and 353 (30.2%) had previously received PT for back pain. In all, 35.8% (n=419) patients categorized as low risk SBST category, 40.7% (n=476) medium risk SBST category, and 23.4% (n=274) high risk SBST category. There was an interaction between baseline MDQ and SBST risk category and improvement with PT. For all three SBST categories, higher baseline MDQ was associated with higher probability of improvement, but the effect was less pronounced as SBST risk category increased. Additional factors independently associated with reduced odds of improvement after PT included black race (odds ratio [OR] 0.44, 95% confidence interval [CI] 0.28-0.72), Medicaid insurance (OR=0.58, 95% CI 0.36-0.95), and prior PT (OR=0.48, 95% CI 0.34-0.67). In exploratory analyses, there was a significant interaction between insurance type and SBST risk category in predicting functional improvement after PT. Patients with Medicare and Medicaid insurance had similar rates of improvement in low and high risk SBST categories but different rates of improvement in the medium risk categories. CONCLUSIONS:The SBST tool predicts outcomes of PT in a cohort of patients receiving outpatient PT for LBP. The odds of improvement varied according to baseline disability and SBST risk status. Race, insurance type, and history of previous PT influenced prediction independent of SBST risk status. Incorporating these variables and the interaction between SBST and baseline disability in outcome models has the potential to refine prediction of outcomes after PT.
