The Effect of Patient Financial Liability on Physical Therapy Utilization and Patient Reported Outcomes for Patients With Low Back Pain: An Instrumental Variable Analysis

Low back pain (LBP) is the most common orthopedic complaint managed by physical therapists in the United States. Insurance plans that require greater patient financial liability per physical therapy visit are thought to disincentivize participation in recommended physical therapy plans of care. The primary purpose of this investigation was to use instrumental variable regression to investigate the effect of insurancemediated patient financial liability per visit on physical therapy visit count and functional patient reported outcomes. The secondary purpose of the study was to examine the generalizability of results to the broader excluded patient population—and beyond to patients that seek physical therapy for LBP. Insurance-mediated patient financial liability per visit was a poor instrument with an inconsistent effect that trended against the hypothesized direction. The instrument had no statistically or clinically important effect on visit count, and no subsequent clinically important change in patient reported outcome. A comparison of baseline patient information and “index” values for predicted visit count and change in patient reported outcome identified few potential clinically important differences, yielding the conclusion that results of the primary investigation are likely generalizable to a broader patient population with LBP. These results suggest patient financial liability per visit is a poor instrument with currently available data; however, any results from large observational analyses would likely generalize to a larger patient population with LBP