116 Chapter 5 Nevertheless, this study also had a few limitations. First, the results seem to suggest that patients’ risk of developing persistent LBP could be an effect modifier of the betweengroup differences on the primary outcome. Especially in the highest risk group, consistent between-group differences were seen in both the primary and secondary outcomes, supporting the rationale for stratified blended physiotherapy. As it was not the primary aim of this study, the sample size calculation did not take interaction into account, the numbers were small, and therefore, the results should be interpreted with caution. Second, as we conducted a pragmatic study, the experiences of physiotherapists in either using web-based applications or treating patients with nonspecific LBP were not considered inclusion criteria for physiotherapy practices. However, given both the complexity of blended care (17) and the complexity of treating patients with nonspecific LBP (4), it can be expected that more experienced physiotherapists are able to deliver better treatment than less experienced physiotherapists. Therefore, experience might have influenced our analysis. Finally, 4 included patients were excluded from the analysis after being diagnosed with specific LBP. As this number is low and occurred equally in both treatment groups (2 in each group), we expect that this has not influenced the results (64). CONCLUSIONS The stratified blended physiotherapy intervention e-Exercise LBP is not more effective than face-to-face physiotherapy in patients with nonspecific LBP in improving physical functioning in the short term. For both stratified blended physiotherapy and face-to-face physiotherapy, within-group improvements were clinically relevant. To be able to decide whether e-Exercise LBP should be implemented in daily physiotherapy practice, future research should focus on the long-term cost-effectiveness and determine which patients benefit most from stratified blended physiotherapy. Acknowledgments This study was cofunded by the Taskforce for Applied Research SIA (RAAK.PRO02.063), part of the Dutch Research Council. The funder had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors are grateful for the invaluable help provided by Loes Kolenberg in the analysis of the physical activity data. Authors’ Contributions TK participated in the development of the design of the study, conducted the study, performed the statistical analyses, and drafted and revised the manuscript. MFP was the principal investigator, developed the design of the study, and participated in the writing and revision of the manuscript. CJJK participated in the development of the design of the
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