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Archives for Biomechanics

Severs Disease in Adults?

3rd February 2023 by under Biomechanics     

This is an interesting one. According to a search engine keyword tool, the phrase ‘severs disease in adults‘ is searched for up to 700 times a month! That is 700 people looking for information on Server’s disease (Calcaneal apophysitis) occurring in adults. It is impossible for Severs disease to occur in adults, so I am not so sure what they are actually looking for.

Severs disease is a disorder of the growth plate at the back of the calcaneus. That growth plate merges with the rest of the calcaneus about the mid-teenage years. There is no growth plate there after that time, so it is impossible for Severs disease to be a problem in adults.

It could be that people are searching for information if the Severs disease that children get can continue to be a problem as they become adults (it doesn’t).

It could be that they have heard that Severs disease is common in children and they want to know if it could be the cause of there heel pain as an adults (its not). Heel pain is reasonably common in adults and it has many causes. Severs disease is just not one of them.

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“Too many toes” or “all the toes”

9th April 2022 by under Biomechanics     

I think most of us have heard of the ‘too many toes sign’. This is when there are more than a few of the toes are visible on the lateral side due to an abduction of the forefoot when standing or walking.

This image from a screen grab of video that I did of a case I talk about during the Clinical Biomechanics Boot Camp could just about be considered as the “too many toes” sign:

Below is a screen grab of the video of the other foot. I like to call that one the “all the toes” sign rather than just the “too many toes” sign as all of the toes are visible laterally.

The key point in talking about this case was that it was the right foot that was the painful one and the left one with that severe “overpronation” was not the problem one. This means that the “too many toes” sign is not something to be necessarily worried about. What you need to be worried about is the forces behind the foot posture and be worried about them if they are high.

The “too many toes” sign is not really good terminology and is just something that clinicians may say to patient as part of a conversation. It is not a diagnosis. It is probably better to use the components of the Foot Posture index to put a number on the amount of forefoot abduction rather than just say too many toes.

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Inhibition of the peroneal muscles

4th January 2022 by under Biomechanics     

The concept of peroneal muscle inhibition has both intrigued me and confused me, yet I do see it clinically and see the results, but the lack of objective data does trouble me. I started this discussion to get a better understanding of it. I am not sure it did.

The concept is that there is some sort of inhibition of the peroneal muscles, particularly the peroneus longus and the muscle does not work as it should. This “weakness” can lead to a range of symptoms from functional hallux limitus (and its compensations), increased risk for ankle sprains, lateral foot pain and maybe Achilles tendon pain. Muscle testing will show a significantly weaker peroneus longus. Its not clear what it is that leads to this inhibition which without objective data to consider that is a problem.

Typically with a mobilization of the proximal and distal tibiofibular joint, you can see an almost immediate return to the strength of the peroneus longus. I have certainly seen that plenty of times clinically and have no doubt about its clinical usefulness. However, I really struggle to come up with a coherent explanation of how the inhibition was  caused and how the mobilization overcomes it. It you have something to contribute, please head over to Podiatry Arena and contribute your ideas in the thread on this topic.

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Posterior tibial tendon dysfunction or adult acquired flat foot or progressive collapsing foot deformity?

3rd July 2021 by under Biomechanics     

What should it be called? I have long been part of the school that thinks we should be sticking with the posterior tibial tendon dysfunction name as that is the one that has mostly stuck and the problem was considered one of the posterior tibial muscle no longer being able to do its job – it just made sense. Two things are starting to change my mind:

  1. The pathomechanical and other studies have shown there is a lot more to it than just the posterior tibial tendon.
  2. The confusion between posterior tibial tendon dysfunction and posterior tibial tendonitis is too common and leading to wrong treatment choices (especially in runners).

It is the later point that is getting more and more attention. They are not the same thing. Posterior tibial tendonitis is an overuse injury in active healthy people. Posterior tibial tendon dysfunction is a progressive flatfoot deformity in older, often overweight adults. Two totally different sets of symptoms; two totally different populations; two totally different sets of clinical features …. yet some think they are the same thing on a continuum and some mix the two up and use the same treatment interventions. Nope.

I now think we should be calling posterior tibial tendon dysfunction either adult acquired flatfoot or progressive collapsing foot deformity to avoid the confusion and better reflect the underpinning pathological process. This terminology of progressive collapsing foot deformity is the name that seems to be being used more frequently in the most recent literature on this problem.

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Peroneal Tendinopathy is easy!

29th June 2021 by under Biomechanics     

In my hands peroneal tendinopathy or tendonitis used to be a challenge. In the past I reckon I was close to a 100% failure rate in managing it. In the last 10 or so years I think I am now close to a 100% success in managing it. What changed? It was based on our research evidence. I talked about that in this blog post: Peroneal Tendonitis in Runners on my running research blog. It was pretty clear that almost everyone with peroneal tendinopathy had a lower than average supination resistance. That means the force needed to supinate the foot was low and as a consequence the peroneal tendons have to work harder, increasing the risk for tendinopathy. This also means that those with it need lateral wedging under the heel to decrease the loads in the tendon. That wedging actually leads to a substantial reduction in the forces that the tendon is subjected to, so hence the lateral wedging is a very and often is dramatically effective to manage peroneal tendonitis.

Yes, lateral wedges do try to pronate the foot more, but never had a problem with doing that. It did take a mindset change to get confident to start doing this 10 or more years ago, but I have not looked back. This is a perfect example of research informing and changing clinical practice.

This also means that a typically arch supporting medially wedged foot orthotic is going to increase the load on the peroneal tendon and is not going to be indicated. This also explains why I had almost a 100% failure on managing this in the past.

Also, of course, we do the usual load management approaches to this tendon once that reduction in load on the tendon with the wedge is done.

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“Overpronation” …. oh no!

26th June 2021 by under Biomechanics     

In social media, everyone is an expert on this. Opinions vary, but facts don’t, but all so often those opinions are being stated in the ignorance of the actual research evidence.

I have written so many times about this in so many places (eg here, here and here), so lets type it slowly and make it clear:

Firstly, there is no clear definition of “overpronation” which is why I generally put it in the “x”, but we all know it when we see it. Yes, pronation is normal, but we generally lack a clear definition of when that normal becomes too much. However, we do have normative data on the foot posture index (FPI), so there is some consensus as to what is normal and abnormal. I am pretty sure most of those posting in social media about “overpronation” have no clue what this normative data is or even what the FPI is that its based on is. This is also probably complicated that the division between normal and abnormal is most likely to be subject specific and mediated by many other factors, such as tissue capacity.

Secondly, yes there is something wrong with “overpronation”. Too many in social media keep saying that it is not a problem. Yes, there are studies that show its not and yes, there are studies showing that it is a problem. This also has to be interpreted in the context of how each study actually measured “overpronation”. When you get conflicting evidence you then need to turn to the systematic reviews and meta-analyses which assess the quality of studies and how much weight to give each of those studies. All those most recent reviews of the preponderance of that evidence have shown the same thing: “overpronation” is a problem; it is a risk factor for running injury. However, it is only a small risk factor, but it is still a statistically significant risk factor.

Thirdly, just becasue someone can show an example of someone who massively “overpronates” and does not have a problem is not evidence that it is not a problem. The video of Haille Gebrselassie (“the truth”) come to mind. This is no different to showing someone who has smoked cigarettes their whole life who did not develop lung cancer. Does that mean smoking does not cause lung cancer? People who use examples like that video of Haille Gebrselassie to support their case really should know better and are just showing their ignorance of causation and the actual scientific evidence and just what a risk factor is and how it works.

Fourthly, there are multiple causes of “overpronation” and if it needs to be dealt with, it is dealt with by dealing with that cause in that individual. Anyone who is advocating one particular treatment for “overpronation” really have no clue what they are talking about. There are multiple options, but the option that will only work is the one that is directed at the specific cause in each individual. You can tell how much someone in social media knows about this based on what they say you need to do to deal with it. One hit wonders are clueless, so ignore them.

Enough said … again.

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The Clinical Importance of Navicular Drop and Navicular Drift

24th June 2021 by under Biomechanics     

I am a big fan of teaching people how to measure the navicular drift and drop. However, the evidence is that for clinical use they are not that reliable, so that does limit the usefulness of these clinical tests in clinical practice.

Having said that, I still think we should be teaching how to do it, but in the context of the unreliability of them. The reason for this is that the concept behind navicular drift and drop does have implications for foot orthotic prescribing. What learning how to do the tests gives clinicians is an appreciation of the relative movements of the midfoot in the sagittal and transverse planes. Navicular drop measures the sagittal plane motion of the midfoot and navicular drift measures the transverse plane motion of the midfoot. Learning how to do the measurement of these two gives an appreciation of the relative motion of that midfoot in the sagittal and transverse plane. Once that appreciation and understanding is grasped, then there is probably no need to do the measurements on a routine basis in clinical practice. You can just observe it and note how much drop there is compared to how much drift there is. Are the about the same or is there more of one compared to the other?

My impression is that the amount of navicular drift should be about the same as navicular drop. If drop is greater, then that means that there is more movement in the sagittal place compared to the transverse plane. This means there is more arch collapse, when means that the foot orthotics need to have more support in the midfoot. If the drift is greater, then that means there is more movement in the transverse plane compared to the sagittal plane. This means that there is more movement of the midfoot medially rather than arch collapse. This means that foot orthotics need more medial and lateral support to control that midfoot transverse plane motion.

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The Lunge Test Should be Done in Footwear

20th June 2021 by under Biomechanics     

I think we all know that the range of motion of the ankle joint is important for normal function. I have made no secret of how useful I think the lunge test is in evaluating that ankle joint range of motion. While there is some discussion as to what is the normal value for the lunge test (I think its around 35-38 degrees) or even if the ankle joint range of motion must be done in subtalar joint neutral (I don’t think it doesn’t need to be), the lunge test is still proving useful and being widely used in clinical practice.

In the early days of running the Clinical Biomechanics Boot Camps we used to do a lot of practicals on the lunge test. Participants would practice on each other and I would go around the room to check how they were going. It was surprising just how many would be considered tight on the lunge test. I would then use my hand as a “heel raise” and get then to stand on that. Almost always they then had a normal range of motion using the lunge test. I soon come to realise that the “heel raise” of my hand was doing what the shoe did, in that all shoes typically have a higher stack height in the heel than the forefoot (the drop). People function and walk in shoes, so the lunge test (and probably as many clinical tests as possible) should be done in the shoes. When we started doing the lunge test barefoot and then in the shoes at the Clinical Biomechanics Boot Camps, almost everyone who was under what was considered normal, was within normal limits when the test was repeated in their footwear. This has implications of the nature of the intervention and if the calf muscles were really limited or not.

There is a whole lesson in the online version of the Clinical Biomechanics Boot Camp devoted to this.

Please consider doing the lunge test in the patients shoes.

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The Entity that is “Functional Hallux Limitus”

15th June 2021 by under Biomechanics     

Functional hallux limitus is a theoretical construct. There is no doubt that the phenomenon that is functional hallux limitus exists, but that can often be as far any any agreement or consensus gets with this. There is no doubt that there are some feet when the foot is up in the air that there is a full range of motion available at the the first metatarsophalangeal joint yet when that foot is weightbearing during gait, that joint just does not want to move. That is the definition of what functional hallux limitus is.

I have written about this a lot, speculating that functional hallux limitus has many possible causes and that it may be better to conceptualize it as a nothing more that each person having a variable stiffness range of motion at the first metatarsophalangeal joint and that this may be related to the windlass mechanism. If this is the case then what we typically considered to be a functional hallux limitus is really the extreme of this variable stiffness and that functional hallux limitus probably exists as a continuum and not as an either/or entity.

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Abductory twist or medial heel whip?

20th May 2021 by under Biomechanics     

The abductory twist is an observation that is frequently made during a gait analysis. Just recently I have started to notice a common terminology issue and I am somewhat confused if they are the same thing or separate things. Most people seem to use the term ‘abductory twist‘ as the same thing as a ‘medial heel whip‘. I believe they are probably different things and they get confused as to what the entity actually is.

I consider an abductory twist to be that sudden medial or abductory movement of the heel just as the heel come off the ground. I wrote here about the possible reasons for this, one being an ‘overpronation’ and the other being a functional hallux limitus. I do not consider that this comes from a more proximal problem like others do. Some people also call this a medial heel whip. They only way to help this is to deal with the ‘overpronation’ or functional hallux limitus. Exercises can not help this.

However, when you listen to or read about what some people consider to be a medial heel whip they are talking about the heel being whipped medially, especially in runners, after the foot has come off the ground. That is something different to the abductory twist that has been previously described. I do consider that this medial heel whip could be due to a proximal problem around the hip and pelvis. The only way to deal with this is deal with the proximal causes and exercises may be very helpful.

If you hear or read someone talking about an abductory twist and/or medial heel whip try to ascertain which one of the two entities they are talking or writing about and just when in the gait cycle that they are observed.

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