138 Chapter 6 DISCUSSION The current study aimed to investigate the presence of groups of patients with distinct trajectories of adherence to HBE recommendations among people with LBP and to identify differences in baseline characteristics between groups. Three groups with distinct trajectories were identified. The “low declining adherence” group started with moderate adherence and declined to almost no adherence over the course of treatment. The “low increasing adherence” group started at around the same level of moderate adherence as the “low declining adherence” group, but adherence increased over time to almost 80 points on the EXAS. The “high stable adherence” group started with the highest adherence, and adherence declined slowly to approximately the same level as the “low increasing adherence” group at the end of the trajectory. None of the baseline characteristics showed statistically significant differences between the identified trajectory classes, including treatment group allocation in the intervention study. It is noteworthy that the width of the confidence intervals of the trajectories increases sharply as the number of treatments increases. This is because the number of patients still receiving treatment declines quickly after 6 treatment sessions reducing the precision of estimated trajectories past this point. To our knowledge, the current study is the first to measure adherence trajectories to HBE recommendations in patients with LBP during treatment by a physical therapist, making direct comparison of our results with similar studies in patients with LBP difficult. However, trajectories of adherence were previously investigated in patients with osteoarthritis of the knee and/or hip (17). The authors found 3 distinct trajectories of adherence over time, similar to the current study. A major difference with the current study, however, is the development of the identified trajectories over time. In patients with osteoarthritis of the knee and/or hip, the trajectories either declined gradually or rapidly, or adherence was low for the entire trajectory. This contrasts with the trajectories found in the current study, which started either around the 40-point mark or at the 80-point mark with a gradual change over time and only the trajectory for the smallest group (12.1% of the participants) showed a large decrease in adherence over time. The patients belonging to the other groups reported either increasing adherence or very slowly decreasing adherence over the course of treatment, with both groups ending up at roughly the same level of adherence after 10 treatment sessions. A possible explanation for this difference between the trajectories of adherence found in both studies is the time period over which the measurements were taken. In our study, all treatments ended within 12 weeks and measurements were only taken while the patient was still being treated by their therapist, whereas in the other study results were included from studies where treatment lasted from 12 weeks to 6 months and adherence was measured for 36 to 78 weeks. As a result, patients in our study most likely had far more opportunities to receive support from their therapist during the period in which adherence was measured,
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