The Clinical Course of Low Back Pain
Well-conducted randomised clinical trials (RCTs) generally provide the strongest evidence for the effectiveness of treatments. RCTs on the effectiveness of treatments for non-specific low back pain have not found evidence for a clear superiority of any treatment. Yet, low back pain symptoms tend to improve in RCTs regardless of the treatment provided. Such improvement seems to follow a pattern common to all treatment arms, of rapid early improvement within the first 6 weeks reaching a plateau over the following 12 months. This is explained at least partly by the 'natural history' (i.e. the propensity for symptoms to improve without treatment). With the use of treatment this is referred to as the 'clinical course' of symptoms. The clinical course of back pain has been assessed in observational (cohort) studies. It was also found to follow a pattern of general improvement that starts rapidly and plateaus over time. Although this suggests a similarity between RCTs and cohort studies, there is no clear evidence for this from direct comparison. More importantly, it is not clear whether the size of overall symptom improvement is the same in these two groups of studies. There is only a limited evidence for a direct comparison, mainly comparing RCTs with non-randomised trials and observational studies that included comparator groups.
There is an assumption that the course of symptoms in RCTs is different from that in cohort studies. It has been suggested that the mere participation in a trial influences the course of symptoms. This might be explained by benefits perceived by participants and assumed to be related to the intensive assessment and monitoring. The so called 'Hawthorne effect' was quoted as an example of how individuals change behaviour due to the attention they receive from researchers.. Although this is expected to apply to all studies, it might be relatively more pronounced in RCTs compared with cohort studies.
Another issue is whether participants in RCTs are in some way different from the average person presenting for care in usual clinical practice. Whether their willingness to be randomly allocated to a treatment or a placebo makes these individuals different from the average patient to whom the results of RCTs will be applied. If true, this raises the issue of whether participants in RCTs are less representative of the average patients compared with participants in observational studies in which patients are not randomised.
It is therefore important to establish the evidence for the similarity or otherwise, in the pattern and the size of back pain symptom improvement in these two types of studies. This would test the assumption that mere willingness to enrol in RCTs and be randomised to treatments would influence the clinical course of symptoms. This would have potentially important implications on interpreting the results of RCTs and their generalizability in clinical practice.
The aim of this systematic review and meta-analysis was to compare changes in low back pain symptoms over time in RCT participants with those of participants in observational cohort studies.
Background
Well-conducted randomised clinical trials (RCTs) generally provide the strongest evidence for the effectiveness of treatments. RCTs on the effectiveness of treatments for non-specific low back pain have not found evidence for a clear superiority of any treatment. Yet, low back pain symptoms tend to improve in RCTs regardless of the treatment provided. Such improvement seems to follow a pattern common to all treatment arms, of rapid early improvement within the first 6 weeks reaching a plateau over the following 12 months. This is explained at least partly by the 'natural history' (i.e. the propensity for symptoms to improve without treatment). With the use of treatment this is referred to as the 'clinical course' of symptoms. The clinical course of back pain has been assessed in observational (cohort) studies. It was also found to follow a pattern of general improvement that starts rapidly and plateaus over time. Although this suggests a similarity between RCTs and cohort studies, there is no clear evidence for this from direct comparison. More importantly, it is not clear whether the size of overall symptom improvement is the same in these two groups of studies. There is only a limited evidence for a direct comparison, mainly comparing RCTs with non-randomised trials and observational studies that included comparator groups.
There is an assumption that the course of symptoms in RCTs is different from that in cohort studies. It has been suggested that the mere participation in a trial influences the course of symptoms. This might be explained by benefits perceived by participants and assumed to be related to the intensive assessment and monitoring. The so called 'Hawthorne effect' was quoted as an example of how individuals change behaviour due to the attention they receive from researchers.. Although this is expected to apply to all studies, it might be relatively more pronounced in RCTs compared with cohort studies.
Another issue is whether participants in RCTs are in some way different from the average person presenting for care in usual clinical practice. Whether their willingness to be randomly allocated to a treatment or a placebo makes these individuals different from the average patient to whom the results of RCTs will be applied. If true, this raises the issue of whether participants in RCTs are less representative of the average patients compared with participants in observational studies in which patients are not randomised.
It is therefore important to establish the evidence for the similarity or otherwise, in the pattern and the size of back pain symptom improvement in these two types of studies. This would test the assumption that mere willingness to enrol in RCTs and be randomised to treatments would influence the clinical course of symptoms. This would have potentially important implications on interpreting the results of RCTs and their generalizability in clinical practice.
The aim of this systematic review and meta-analysis was to compare changes in low back pain symptoms over time in RCT participants with those of participants in observational cohort studies.
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