Mellor et al. (2022)

Mediators and moderators of education plus exercise on perceived improvement in gluteal tendinopathy

Exercises causes improvements in pain self-efficacy and patient-reported functioning and causes the pain to be less constant

There was no mediating effect of corticosteroids over wait-and-see, thus exercise is favored

None of the selected moderators influenced the observed treatment effects

Introduction

Deciding what treatment to offer a patient presenting with a musculoskeletal pathology is something you’re doing everyday when working as a physio. Ideally, you choose a treatment plan based on the knowledge that you achieved in school, through internships, practice, (continuing) education and clinical experience and reasoning. But practice is not only about deciding what treatment to give someone. You’ll get confronted with patients asking for the why’s and how’s of a treatment. Knowing what mechanisms lead to better outcomes may be valuable to your practice. Mediators of treatment explain how a treatment works to achieve a certain outcome. This way you get to inform your client better about the underlying drivers for improvement. On the other hand, knowing which characteristics of your patient influence his or her outcomes of treatment (moderators) allows you to select certain types of treatment to tailor the intervention individually. This study tried to seek out what the mediators and moderators of gluteal tendinopathy outcomes are.

Methods

This research was an exploratory analysis of a previously published RCT. In this RCT, published in 2018, 3 arms were compared against one another. The RCT compared an 8-week education and exercise (14 sessions) to one single corticosteroid injection to a wait-and-see approach in gluteal tendinopathy. Individuals of 35-70 years of age with lateral hip pain for more than 3 months in whom gluteal tendinopathy was confirmed were included. At 8 weeks and at 1 year, global rating of change (GROC) was the chosen outcome measure and results indicated that education and exercise was the preferred treatment. 

 

Education plus exercise and corticosteroid injection use resulted in higher rates of patient reported global improvement and lower pain intensity than no treatment at eight weeks. Education plus exercise performed better than corticosteroid injection use. At 52 week follow-up, education plus exercise led to better global improvement”.

 

To reveal mediators and moderators of gluteal tendinopathy outcomes following education plus exercise, this post-hoc analysis was performed. The outcome of interest was global rating of change at 52 weeks, rated on an 11-point scale ranging from “very much better” to “very much worse”. The outcomes were transformed to a dichotomous scale and the responses “moderately better” to “very much better” were defined as successful outcomes. 

Results

The following table illustrates the mediators in each group at baseline and at 8 weeks. Significant mediators at 8 weeks are hip torque, higher patient specific function, higher self-efficacy and lower levels of constant pain when we look at the education plus exercise versus wait-and-see. This means that the education plus exercise group had, on average, higher levels of pain self-efficacy and patient-specific function than the wait-and-see and lower levels of constant pain at eight weeks. The education plus exercise group also had higher values of gluteal muscle torque than the wait- and-see group.

When comparing the education plus exercise group and the corticosteroid group, we see that the exercise group had higher self-efficacy and functioning and less constant pain at 8 weeks. With corticosteroid injections, higher pain self-efficacy and functioning was seen at 8 weeks compared to the wait-and-see group.

 

mediators and moderators of gluteal tendinopathy outcomes
From: Mellor et al., J Orthop Sports Phys Ther. (2022)

 

The effect of education plus exercise versus wait-and-see on global rating of change is mediated by patient specific function, pain constancy, and pain self-efficacy. When comparing education plus exercise and corticosteroid injection the same is seen. This means that higher patient specific function and self-efficacy and less constant pain cause the improvements in the GROC outcome. Thus education and exercise exerts its effects on GROC through improvements in function, self-efficacy and pain levels, but not through improvements in active abduction or hip torque. 

Results of the moderation analysis indicate that there was no evidence that menopausal status, symptom duration and VISA-G (pain and disability) moderated the GROC outcome at 1 year. Thus these variables did not influence the observed treatment effects.

 

“Education plus exercise does not improve a patient’s perception of their condition by strengthening muscle or improving active hip abduction movement – implicit targets of exercise. Instead, it seems education plus exercise influences patient perception of improvement through lessening how frequently they experience pain, increasing their ability to do tasks that were important to them or had been previously compromised, and allowing them to do more when in pain”

Questions and thoughts

Mediators and moderators of gluteal tendinopathy outcomes were selected by the authors and a rationale for each was provided. The authors defined the following potential mediators: active abduction range, abductor muscle torque, pain self-efficacy, pain constancy and patient-specific function. The mediation analysis revealed that the positive effects of education and exercise were mediated (=caused) by improvements in self-efficacy, and patient-specific functioning and by less constant pain. Thus contrary to commonly thought, this exercise program did not exert its effects by increasing the hip muscle strength or abduction ROM. By participating in this exercise program, patients did not achieve improvements by strengthening or by regaining movement range, but rather the program led to improvements through lessening how frequently they experience pain (less pain constancy), increasing their ability to do tasks that were important to them or had been previously compromised (better patient-specific functioning), and allowing them to do more when in pain (improved pain self-efficacy). 

The selected potential moderators did not influence the treatment effects. Thus, gluteal tendinopathy disability, menopausal status, symptom duration, the severity of tendon pathology as determined by MRI and pain catastrophizing did not alter the observed treatment effects of exercise plus education at 1 year. 

Talk nerdy to me

This study gives an overview of the mechanisms that lead to improvements in GROC outcomes at 1 year. However, the present study was a post-hoc analysis of data from an RCT where the sample size was calculated to detect differences in GROC, but not to identify potential mediators and moderators of gluteal tendinopathy outcomes. This should be kept in mind because the possibility to find false negative results is increased this way. 

Only a select number of variables was selected, but there may have been many more that influence the effects of education plus exercise on GROC. However, these types of analyses have been performed in other conditions like in low back pain and osteoarthritis. Here the mediation effect of self–efficacy and aspects of the pain experience on the effects of a variety of treatments (most involving some element of physical activity/exercise and education/information) is also seen. The mediators from this study may therefore be accepted as potential true mediators. The sensitivity analysis further reveals that the results for pain constancy were relatively insensitive to change due to confounding. However, the patient-specific functioning was more sensitive to changes due to confounding variables and as such, this should be cautiously interpreted.

Take home messages

Improved function, self-efficacy and less constant pain levels through education and exercise cause the improvements in GROC rather than improvements in strength and range of motion. The menopausal status, symptom duration and gluteal tendinopathy disability did not influence the improvements in GROC. It should be kept in mind that the sample size was calculated for another purpose than studied here and that this was a post-hoc analysis.

 

Reference

Mellor R, Kasza J, Grimaldi A, Hodges P, Bennell K, Vicenzino B. Mediators and moderators of education plus exercise on perceived improvement in individuals with gluteal tendinopathy: an exploratory analysis of a three-arm randomised trial. J Orthop Sports Phys Ther. 2022 Oct 28:1-25. doi: 10.2519/jospt.2022.11261. Epub ahead of print. PMID: 36306175. https://pubmed.ncbi.nlm.nih.gov/36306175/

 

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