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What works best for whom? An exploratory, subgroup analysis in a randomized, controlled trial on the effectiveness of a workplace intervention in low back pain patients on return to work

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Author: Steenstra, I.A. · Knol, D.L. · Bongers, P.M. · Anema, J.R. · Mechelen, W. van · Vet, H.C.W. de
Type:article
Date:2009
Institution: TNO Kwaliteit van Leven
Source:Spine, 12, 34, 1243-1249
Identifier: 241542
doi: doi:10.1097/BRS.0b013e3181a09631
Keywords: Workplace · Veilig en Gezond Werken · Low back pain · Moderators · Return to work · Subgroups · Workers · Workplace intervention · Activities of Daily Living · Adult · Age Distribution · Age Factors · Cohort Studies · Disability Evaluation · Female · Health Promotion · Human Engineering · Humans · Intervention Studies · Low Back Pain · Male · Middle Aged · Occupational Diseases · Occupational Exposure · Occupational Health · Outcome Assessment (Health Care) · Pain Measurement · Program Development · Sex Factors · Sick Leave · Single-Blind Method · Work Capacity Evaluation · Work Schedule Tolerance · Workplace · Young Adult

Abstract

STUDY DESIGN. Exploratory subgroup analysis in a randomized controlled trial (RCT). OBJECTIVE. To detect possible moderators in the effectiveness of a workplace intervention in a population of workers with sick leave due to sub acute nonspecific low back pain. SUMMARY OF BACKGROUND DATA. In a recently published RCT, a workplace intervention was effective on return to work, compared to usual care. Examining the heterogeneity of effect sizes within the population in this RCT (n = 196) can lead to information on the effectiveness of the intervention in subgroups of patients. METHODS. A subgroup analysis was performed by adding interaction terms to the statistical model. Before analysis the following possible moderators for treatment were identified: age, gender, pain, functional status, heavy work, and sick leave in the previous 12 months. Cox regression analyses were performed and survival curves were plotted. RESULTS. The interaction (P = 0.02) between age (dichotomized at the median value) and the workplace intervention indicates a modifying effect. The workplaceintervention is more effective for workers <44 years (HR, 95% CI = 2.5, [1.6, 4.1] vs. 1.2 [0.8, 1.8] for workers <44 years old). The interaction between sick leave in the previous 12 months and the workplace intervention is significant (P = 0.02). The intervention is more effective for workers with previous sick leave (HR, 95% CI = 2.8 [1.7, 4.9] vs. 1.3 [0.8, 2.0]). A modifying effect of gender, heavy work, and pain score and functional status on the effectiveness of this intervention was not found. CONCLUSION. The findings from these exploratory analyses should be tested in future RCTs. This workplace intervention seems very suitable for return to work of older workers and workers with previous sick leave. Gender, perceived heavy work, and baseline scores in pain and functional status should not be a basis for assignment to this intervention. © 2009 Lippincott Williams & Wilkins, Inc.