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Beyond Minimally Important Change: Defining a Successful Outcome of Physical Therapy for Patients With Low Back Pain

Fritz, Julie M. PhD, PT, ATC*†; Hebert, Jeff DC; Koppenhaver, Shane PhD, PT; Parent, Eric PhD, PT§

doi: 10.1097/BRS.0b013e3181ae2bd4
Health Services Research

Study Design. Prospective, longitudinal cohort study

Objective. To examine the validity of a threshold that has been used to define a successful outcome for patients with low back pain (LBP), undergoing nonsurgical rehabilitation based on a 50% improvement on the Modified Oswestry disability index (ODI).

Summary of Background Data. Making research findings interpretable is a goal of evidence-based practice. One attempt to improve interpretability is reporting treatment results as the percentage of patients achieving a threshold level of improvement within treatment groups along with mean between-group differences. The most recommended threshold is the minimum clinically important difference of the outcome tool. For clinical conditions with favorable natural histories such as LBP, thresholds requiring more than minimal improvement may be preferable for defining success.

Methods. Patients with LBP receiving 4 weeks of physical therapy were examined. The ODI and measures of pain, fear-avoidance beliefs, and demographic characteristics were recorded at baseline and after treatment. A 15-point global rating of change was also completed after treatment. The percent ODI change with treatment was computed and compared between groups known to have different prognoses. The percent ODI change was compared to the global rating of change to determine the accuracy of various thresholds of success based on the percent ODI change.

Results. A total of 243 subjects (mean age 37.2 ± 11.4 years, 44.9% female) were included. Mean percent ODI change was 43.1% (±40.5), and 109 subjects (44.9%) had a successful outcome (≥50% ODI improvement). As hypothesized, baseline factors with known prognostic importance were less likely to be present in subjects with a successful outcome. The 50% ODI improvement threshold for success had high sensitivity (0.84; 95% CI: 0.79, 0.88) and specificity (0.89; 95% CI: 0.85, 0.93) when compared with success based on the global rating of change. No other percent improvement threshold for the ODI had a higher accuracy than the 50% threshold when compared to the global rating of change.

Conclusion. A threshold of 50% improvement on the ODI may be a valid measure for defining a successful outcome for patients with LBP.

The results of clinical research may be more interpretable if results are reported as a percentage of patients achieving a “successful” outcome. This study found that achieving at least 50% improvement on the Oswestry was a valid definition of a successful treatment outcome.

From the *Department of Physical Therapy, University of Utah, Salt Lake City, UT; †Intermountain Health Care, Salt Lake City, UT; ‡College of Health, University of Utah, Salt Lake City, UT; and §Department of Physical Therapy/Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada.

Acknowledgment date: July 3, 2008. First revision date: September 6, 2008. Second revision date: November 1, 2008. Acceptance date: March 22, 2009.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Dr. Fritz, PhD, PT, ATC, Department of Physical Therapy, University of Utah, 520 Wakara Way, Salt Lake City, UT 84108; E-mail: julie.fritz@hsc.utah.edu.

© 2009 Lippincott Williams & Wilkins, Inc.