Prognostic factors for low back pain in patients referred for physiotherapy: comparing outcomes and varying modeling techniques.

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.