"Wring Theory" of foot function - The Missing Link?

And what would have happened if you had twisted your hands the other way? The necklace would have tightened- right? So, is it a good analogy for the ligaments of the foot?

I still don't like the argument you build suggesting Sarrafian's model is two-dimensional, it is not. Last week, we had a little delve into whether the foot can be modelled as a tensegrity structure, with the weight of evidence suggesting that it cannot. And, you still haven't answered the questions regarding the existing research on midfoot biomechanics which I posted previously, Clint. Can you?

 

I wonder......if Sarrafian signed onto Podiatry Arena......would he sign on as DrTwistedPlate?.....highly unlikely....

 

Kevin,
I understand it is presumptive to place the sign in name as Dr Wring. Perhaps Sarafian would have signed in as DrTwistedPlate, but as I said in my first post, I am new to this blog and dont know all the ins and out of how to use it. Maybe he was thinking about something exactly like I have presented, but the fact that we continue to try and further develop it, shows that not everything has been yet explained.
I used that name, from the beginning, to maintain consistency from my blog at drwring.wordpress.com. I saw that as a problem, and I have been trying, for a week, to figure out how to change it on Podiatry-Arena. It signs my name as Paul Clint Jones, DPM, but how do I change the Gravatar to say the same?
I am glad to see this thread has, obviously, been keeping you thinking.

 

Clint:

How to change a name on Podiatry Arena is beyond me. Maybe one of the moderators can do it for you?

 

In this "overly simplified" example, if my hands were physically capable of rotating a negative 180 degrees, the same thing would happen. That is astute of you to see. It, also, would be a relatively weak joint position because all the stability of twisting would be on the strength of the ligaments themselves. The example is of a joint axis located with in the joint space itself. The motion is 3D in all three planes at once. My paper refers to past descriptions as having legitimacy, but infers that they are missing something. "Old biomechanics with a new twist" When one wrings a joint, as seen in a foot, you have to try and see what 3D geometry it is creating. Kind of like making a snow angel. We look stupid, flailing around on the ground, but went we stand up, we see a beautiful angel left as a sum of the total motion. In the case of the snow angel, if we look too close, we can't see the beauty of it. I am not a NASA scientist. I am a sculpture, with a background in physics. I am a finish carpenter if you will.
In the case of the twisting example this is too simplified. Most joints are more than a twisting ball in socket. In the foot, many of the joints are a helical twist. This creates a translational component. For example, the 1st met cuneiform joint described axis is outside the defined joint surfaces. The first met plantarflexes and everts relative to the medial cuneiform with supination of the foot. As a triplanar motion, at the same time, it is translating proximal relative to the medial cuneiform. (See anecdotal observation in the anatomy portion of my paper) This is the Helical Wringing effect. The plantar tubercle of the insertion of the peroneus longus is being wedged into the "pangea" of the plantar midfoot. This is the "Mechanical Advantage" spoken of the peroneus longus when foot is in the supinated position. I never understood how this tiny tendon could support so much force, without rupture, when the achilles, with its massive size, is constantly having to be repaired. This lends itself to the thought that it is not all the force into the peroneal longus, but that the tension the tendon creates an osseous meshing that in turn takes the force placed on the first ray.
There is a building in Utah built on the unsettled plains of the 1800s. http://en.wikipedia.org/wiki/Salt_Lake_Tabernacle. Its expansive, unsupported roof was massive, for the time, and was unheard of. It was made of wood, doweled together. Some of the wood was green, when put together, and ended up splitting. Rather than tear the whole thing apart, they used green rawhide and banded the splits, so that when the rawhide dried, it held the boards together, as if they had not split. 100 years later they were still holding. Now was the roof held up by the raw hide? No. The rawhide held the boards in position to allow the boards to take the force. Should the rawhide fail, the boards would eventually fail, in theory.
This is what I mean by the simple machine of a screw(helix). It allows two physical objects to occupy the same, effective space, at the same time. This creates a mechanical stabilizing effect. Doesn't take much to cause this to happen. This helical motion, also, creates a lengthening or induces a simultaneous slack, in the surrounding ligaments, as the helical motion moves in one given direction, while creating an accelerated, shortening of the surround ligaments, in the other direction. Almost a gearing effect. In the case of the 1st met cuneiform the joint induced axis, is outside the joint itself and further modifies how the osseous and ligament components of the joint interplay. The necklace is a good basis to help people to understand the basic concept of the wringing of a joint, but if you stop there it falls far short of what the foot is doing. This concept of a joint being helical vs ball in socket may also, help explain why one joint may fail, while another does not.

This is where my sculpture background comes into play. If you look at Sarafians paper Fig. 2 as he twists the "plate," you can see the distortion of the material. That is caused by the stretching of the material as it was heated and manipulated. Should you measure the material, you will find the dimensions of the material are no longer the same. This is because, not only did was the material twisted, but it was, also, stretched. This happens because a plate is the two dimensions, not 3 dimensions. It has to stretch to fit the new position. Sarafian didnt even take into account the conical form of the foot with the convergence of the medial and lateral columns. Had he done so, he would have had better luck. Just and take a piece of paper (flat plate) and twist it end to end. It does not arch up nicely. It can't because the sides of the plate cannot change in length required to take on the 3 dimensions now placed upon it. Therefore this requires a new geometry that can. I believe this is a conical double helix. I postulate, this is important, as it now can accurately be tested and can yield consistent results.
As for your insistance of answering tensegrity, my theory does not hinge on tensegrity to be functional and viable. The foot is obviously an interplay of tension and compression. There are, obviously, both schools of thought. My inclusion is a reflection that microbiology has shown biotensegrity to be at play in the make up of the cell. Whether or not it proves out in the macro scale is to be seen. Your insights are appreciated and for now, I will leave it in the paper.
I believe that the more important part is that the foot has more than one windlass.
It has the ability to adjust/fine tune itself to achieve this geometry of the conical double helix.
I will try answer your questions regarding the midfoot as I have time.
Clint
Reference to my QUOTE=Simon Spooner;281209]And what would have happened if you had twisted your hands the other way? The necklace would have tightened- right? So, is it a good analogy for the ligaments of the foot?

I still don't like the argument you build suggesting Sarrafian's model is two-dimensional, it is not. Last week, we had a little delve into whether the foot can be modelled as a tensegrity structure, with the weight of evidence suggesting that it cannot. And, you still haven't answered the questions regarding the existing research on midfoot biomechanics which I posted previously, Clint. Can you?[/QUOTE]

 

Clint, just quickly (I'll come back to the rest later). Take a ruler out of your pencil case and hold it in your hand. Is the ruler a 2-dimensional object, or a 3-dimensional object? :bang:

 

By grace of a physical object, it is 3 dimensional, I get that. As far as application to the foot by twisting it, it doesn't work. It doesn't function as the foot does, therefore, there must be more. That is why I am not buying the argument. The foot is far more dynamic than what the twisted plate can describe. It doesn't fit. Even a square peg can fit in a round hole if it is small enough or pushed hard enough. Hicks, MacConnail, and Sarafian were so close, but did not complete the picture.

 

I'm not arguing whether it functions as the foot does, I'm just pointing out that throughout your "paper" you keep describing Sarrafian's model as 2-dimensional and clearly it is not. Which makes the reader think that you do not understand the difference between 3-dimensional objects and 2-dimensional objects. If your paper came to me for review, this is the first thing I would suggest you change, the second thing would be to take the tensegrity section out because it doesn't add anything to the paper and at the level of modelling you are discussing here, the foot does not act as a tensegrity structure. The next thing I'd ask you to think about is the potential conflicts which may exist between your theory and the published literature pertaining to midtarsal joint function...

Remember too, that you haven't validated your model yet either, so perhaps you are pushing a square peg into a round hole as well.

 

who do I talk to????

 

Thank you. Will take under advisement, but the foot is not a plate, twisted or not. It is far more.

 

Craig Payne http://www.podiatry-arena.com/podiatry-forum/member.php?u=3

follow the above link, then on the right hand side of the page under contact info, click on: send a private message

Hope that helps.

 

Some might argue that it's not a double helix either, Clint. It's not, it's a human foot. It's important to keep in-sight that what you are trying to build is a model, a simplification of reality which helps us to understand some function. Sarrafian built a model, his model has it's uses in that it describes the change in 2nd moment of area which occurs as the forefoot moves on the hind foot, it also has it's limitations. Kevin presented a model a couple of pages back in this thread. He'd modelled the plantar arch structures as a coiled spring. In reality, the plantar arch structures are not a coiled spring, but the model is useful in helping us to understand a function of these structures.

Your model may have uses too, it will certainly have limitations. But then, it's just a model. I think it might be useful if you took a step back and worked out exactly and precisely which function/ functions of the foot it is that you are trying to model. Is it forefoot to rearfoot motion; is it modulation of midfoot stiffness; etc? While similar, these two functions may be best represented by two different models, not one all encompassing model of "foot function" because there are an awful lot of "foot functions".

I guess it's no secret that pretty much every podiarist with an interest in biomechanics at one time or another harbours the desire to find some form of single, unified theory of foot function. History is littered with them (Kevin gave an excellent presentation on the history of biomechanical theories in Belgium earlier this year). But to quote my favourite singer, "it's no secret that ambition, bites the nails of success", too.

 

These are excellent comments, Simon.

Clint, as Simon suggested, one must understand that a model will always have limitations since a model attempts to simplify a complex system so that the behavior of the system can be better appreciated and/or predicted. Making a model more complex doesn't always make it a better model. In fact, some of the best mechanical models are quite simplified but still help explain a basic concept that otherwise would be difficult to explain or understand.

I think it would be best to take Simon's advice, take a step back and before you further try to develop or modify your model, try and decide what part of foot function you want to explain. As for me, whatever that is worth, Sarrafian's Twisted Plate model is better than your "Wring Model" for the simple reason it is simpler, easier to understand, less convoluted and a more elegant way of describing a certain functional characteristic of the foot.

Clint, the foot is just as much a twisted plate as it is a double helix and unless you have some data to suggest otherwise, you will probably be spinning your wheels here on Podiatry Arena with most of us. So far, I have seen nothing n reading your "paper" or in your responses to our comments on your model to convince me that:

1) your model is "far more" than the Twisted Plate,
2) your model is 3D and the Twisted Plate is not 3D
3) tensegrity should be an integral of any foot model, including yours, and
4) your model is any better than Sarrafian's or MacConnaill's models from decades ago.

Good luck with your future projects.:drinks

 

That is the nicest thing you've ever said to me. Thank you.

Clint

 

In all honesty, I am trying to help you with everything I write.:empathy: But thus far, I've only said about half a dozen things to you...