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Prognostic Factors for Low Back Pain in Patients Referred for Physiotherapy: Comparing Outcomes and Varying Modeling Techniques

Bekkering, Geertruida E., PhD*†; Hendriks, Henricus J. M., PhD; van Tulder, Maurits W., PhD†‡; Knol, Dirk L., PhD†‡; Simmonds, Maureen J., PhD; Oostendorp, Rob A. B., PhD*∥**; Bouter, Lex M., PhD

doi: 10.1097/01.brs.0000173901.64181.db

Study Design. Data were derived from a randomized controlled trial on the (cost-) effectiveness of the implementation of the clinical guidelines on physiotherapy for low back pain in primary care.

Objectives. To describe the course of low back pain in patients who are referred to physiotherapy, to identify clinically important prognostic factors on different outcomes, and to evaluate the influence of different statistical techniques in developing a prognostic model.

Summary of Background Data. Several studies have aimed to identify prognostic factors for low back pain in primary care. These studies focused on different outcome measures and used various statistical techniques.

Methods. Primary outcomes were perceived recovery, improvement in pain, improvement in functioning, and presence of disabling low back pain at 3 and 12 months follow-up. Multivariate logistic regression analyses were performed for each outcome variable. Two cut-off points were used to determine significance with respect to the univariate analysis, and two selection methods were used to build the final multivariate models. The resulting prognostic models were compared.

Results. A total of 500 patients were included. Pain and disability reduced considerably in the first 3 months, but further reduction was only modest. Prognostic factors varied for different outcomes, but the duration of the current episode was included in all models generated. Varying the statistical techniques also resulted in a different prognostic model with some change to the amount of variance explained.

Conclusions. A substantial proportion of patients still experienced some pain and disability at 12 months follow-up. The most stable predictor of prognosis in low back pain was the duration of the current episode. The choice of statistical method influenced the final model; however, changes in the explained variance were small.

We described the course of low back pain in patients referred to the physiotherapist, identified prognostic factors for recovery, and evaluated the influence of various outcomes and statistical techniques in developing a prognostic model.

From the *Dutch Institute of Allied Health Care, Amersfoort, The Netherlands; † Institute for Research in Extramural Medicine and the ‡Department of Clinical Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, The Netherlands; §Department of Epidemiology, Maastricht University, The Netherlands; the ¶School of Health Professions and Rehabilitation Sciences, University of Southampton, Highfield, Southampton, Hants, United Kingdom; the ∥Centre of Quality of Care Research, University Medical Center, Nijmegen, The Netherlands; and **the Department of Medicine and Pharmacology, Free University of Brussels, Brussels, Belgium.

Acknowledgment date: December 23, 2003. First revision date: June 6, 2004. Second revision date: August 29, 2004. Acceptance date: September 17, 2004.

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

Federal funds were received to support 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 ad requests for reprints to Henricus J.M. Hendriks, Dutch Institute of Allied Health Care, PO Box 1161, 3800 BD, Amersfoort, the Netherlands; E-mail:

© 2005 Lippincott Williams & Wilkins, Inc.