Gluteal Tendinopathy – Is psychological all that matters?

Over the last few weeks there’s been a paper circulating in reference to gluteal tendinopathy and psychological factors. Link to article:

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This is an excellent study that has a great methodology, comparing a wide range of topics, and gives us some great information to discuss that has not previously been examined.

As the title states: “Psychological factors not strength deficits are associated with severity of gluteal tendinopathy: a cross-sectional study” - psychological factors are more important that strength – at least that is how many are interpreting this paper. Much like most things in science, it’s not that simple.

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For those who didn’t read the paper, here is a quick synopsis:

What did they do?

The authors recruited 204 participants, ranging from 36-71 years of age, 82% females, and examined standardized outcome measures from the participants for pain catastrophizing, pain self-efficacy, depression, quality of life, and amount of physical activity. Additionally, the participants were evaluated for waist and hip circumferences, BMI, hip abductor strength, and pain inhibition. From there, an independent research performed the statistical analysis to sub-group these people into having either mild, moderate, or severe pain and disability. These groups were then compared by the results of outcomes and evaluations.

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What did they find?

The severe group had significantly “worse” results for all psychological factors – higher pain catastrophizing, lower pain self-efficacy, and higher depression - compared to the mild group. Quality of life and physical activity also showed this same relationship where the severe group had lower quality of life and less physical activity weekly than the mild group. Waist to hip ratio was significantly greater in the severe group, particularly for women. BMI was significantly different across each group as well, with the severe group having the highest mean BMI. The one that stands out is the hip abductor muscle strength as the groups showed no significant difference between them.

As you can see in the above paragraph, what most people are pounding their chests on from this study is that psychological factors (and everything else) were significantly different between the mild and severe group, but hip abductor strength was not.

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It is important that we do not jump to conclusions though from only a cursory evaluation of the evidence. There is much more to consider when we evaluate the information in this paper.

The first thing we should consider is that there has been a connection demonstrated between hip abductor strength and gluteal tendinopathy – the paper even mentions this. If we are to presume (which we will get into more soon) that hip abductor strength does not distinguish between severity of groups, it is still very relevant to the condition itself. This is one of my primary concerns with how most people are interpreting this paper.

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Our second point to address is that this information is ground breaking for this specific topic, but for most people who keep up to date with current literature on the topic of pain, it is likely not much of a surprise. When it comes to most musculoskeletal conditions, especially those that are chronic like this condition, we have seen a similar trend. The severity of many of these conditions will be correlated to the severity of catastrophizing, depression, self-efficacy, or quality of life.

It is great that we now have evidence to support this for this specific condition, but it doesn't mean that we should start to throw the baby out with the bath water. Knowing these are important for this condition does not mean that we should start to eliminate all of the things we previously considered to be of value.

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The third point that is critical to address is the hip abductor muscle strength relationship to body weight. When we compare the groups, we see the hip abductor muscle strength was similar between groups. However, the body mass index of the groups did change as the severity changed – more severe presentations were from heavier individuals. This information is important to consider in context.

In general, cross sectional area correlates with strength level. In contrast, in this population we are not seeing that, instead we are seeing the opposite trend.* This should be alarming for a few reasons. When the cross sectional area increases, the internal moment arm of the muscle is at a greater mechanical advantage, indicating that if it applied the same amount of force it should be stronger. In this situation we are not seeing that, indicating that these people are not able to create the same amount of force as the others.

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Where this becomes a more significant problem is these same individuals who are unable to create the same amount of force, actually require more force. In order for someone to be able to produce the same kinematic motion as the others, but that someone has greater mass, that person needs to be able to produce more force - which they aren't able to.

Our current body of evidence points in the direction that gluteal tendinopathy will generally present in those with lower hip abduction strength, but it may be important for us to also look at it in relation to body weight (strength relative to body weight). As well, it is fairly rare that people truly use hip abduction in the form of raising a leg laying on their side, but instead needing it control their pelvis during gait, stepping up stairs, etc. This is why the body weight relation is specifically important to consider in this context.

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Shout out to Scot Morrison of Physio Praxis for the above image - follow him to be smarter

Whenever we have evidence that presents with something “contrary” or “challenging” to what we have previously learnt, it is important that we fully appraise it!

In summary, when working with gluteal tendinopathy, we absolutely should be evaluating the psychological factors, but we also need to examine other things such as body mass index and hip abductor strength. An ideal treatment sceanrio is where we work to address all of these as needed by the respective patient.

*=Addressing this point, we are making an assumption that cross sectional area increased as BMI increased, which is not necessarily accurate, but we are supported to a degree that hip measurements also increased similarly to the BMI changes. As the hip circumference increases, the gluteal region would also increase (which may be due to fat, muscle, or other soft tissue

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