The Relationship of the Therapeutic Alliance to Patient Characteristics and Functional Outcome During an Episode of Physical Therapy Care for Patients With Low Back Pain: An Observational Study

Objective. Research supports the relevance of the therapeutic alliance (TA) between patients and physical therapists on outcomes, but the impact of TA during routine physical therapist practice has not been quantified. The primary objective of this study was to examine the relationship between TA assessed during a physical therapy episode of care for patients with low back pain and functional outcome at the conclusion of care. The secondary objective was to examine psychometric properties of the Working Alliance Inventory-Short Revised (WAI-SR) form, a patient-reported TA measure. Methods. This study was a retrospective analysis of prospectively collected data from 676 patients (mean [SD] age = 55.6 [16.1] y; 55.9% female) receiving physical therapy for low back pain in 45 outpatient clinics from 1 health system in the United States. Participating clinics routinely collect patient-reported data at initial, interim, and final visits. The lumbar computer-adapted test (LCAT) was used to evaluate functional outcome. The TA was assessed from the patient's perspective at interim assessments using the WAI-SR, bivariate correlations were examined, and regression models were examined if interim WAI-SR scores explained outcome variance beyond a previously validated multivariate prediction model. Internal consistency and ceiling effects for the WAI-SR were examined. Results. Interim WAI-SR scores were not correlated with patient characteristics or initial LCAT, but they were correlated with final LCAT and LCAT change from initial to final assessment. WAI-SR total score (adjusted R-2 = 0.36), and Task (adjusted R-2 = 0.38) and Goal subscales (adjusted R-2 = 0.35) explained additional variance in outcome beyond the base model (adjusted R-2 = 0.33). Internal consistency was higher for WAI-SR total score (alpha = .88) than for subscales (alpha = .76-.82). Substantial ceiling effects were observed for all WAI-SR scores (27.2%-63.6%). Conclusion. Findings support the importance of TA in physical therapist practice. Measurement challenges were identified, most notably ceiling effects. Impact. This study supports the impact of the patient-physical therapist alliance on functional outcome. Results extend similar findings from controlled studies into a typical physical therapist practice setting. Better understanding of the role of contextual factors including the therapeutic alliance might be key to improving the magnitude of treatment effect for discrete physical therapist interventions and enhancing clinical outcomes of physical therapy episodes of care.