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Forces and Moments: Modern Biomechanics and Engineering Terminology for the Podiatrist

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Feb 26, 2015.

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    For those interested, I recently published a short video on YouTube discussing the concept of forces and moments for podiatrists interested in learning more about biomechanics that is also listed on my FaceBook page.

    Last edited by a moderator: Sep 22, 2016
  2. Nice succinct presentation.
  3. drhunt1

    drhunt1 Well-Known Member

    Actually...not a bad presentation. I'll be much more constructive here towards your video than many were towards mine. But that being written, it's nice to see you perhaps being inspired by my video contributions to create your own.

    First...pick up the pace of your presentation, especially early in the presentation. If this video was created for patients, that would be one thing, but creating a video for other Podiatrists whom are already familiar with anatomy...speak at a faster pace. Second, you don't need to bring up your credentials. Everyone knows who you are, so that's not only redundant, but unnecessary. Third, of all the "moments" to discuss in the physics of the foot, comparing distal vs. proximal bunion correction procedures seems the least likely. The real problem with CBWO is not the lever arm that could disrupt the fixation technique. It's getting the bone cuts exactly right, ie., making the cuts parallel from dorsal to plantar, and then making the green-stick closure prior to fixation. There's much more "fudge factor" available in the distal osteotomies. While I realize Dale Austin designed the Chevron to be non-fixated and allow for early ambulation, I don't know too many Podiatrists that have the patient ambulate in the first few days after surgery even with adequate fixation. Post-op edema is a real problem.

    Imagine using animation to show some of the more salient points you're trying to make. I believe it's the wave of the near future in Podiatric education in particular, and anatomy in general. Just my two cents.
  4. Ian Linane

    Ian Linane Well-Known Member

    Actually drHunt1 I have disagree with you on the pace.

    As someone who has small level hearing problems, part natural, part industrial caused (few years working in the weaving industry before ear protectors), the slower pace works fine for me. It allows me to pick up the beginning and ending of words ( often important consonants) which then allows me to grasp the word better and still have time to hear the next one and make sense of the sentence.

    There is nothing irritates me more than professionals assuming an audience can hear them.

    Equally, and perhaps to my shame, physics has not always been a thing I grasp easily so again the pace allowed me to grasp the words, assimilate them in a context and worked for me.
  5. drhunt1

    drhunt1 Well-Known Member

    Ian-I have more than just a "small level of hearing problems", (a consequence of years of shot gunning). In fact, I need to use head phones with the volume turned up in order to catch much of what is being said in lectures or on the net. What's great about creating videos is the fact that the information can be viewed multiple times. If the information is "iconic", the creator of the video WANTS the viewer to watch it several times in order to absorb the details and substance. Those viewers that aren't hearing impaired, such as you and I, may not have to, unless the information is simplistic or rudimentary. More substantive videos will need to be watched multiple times regardless of the ability, (or lack thereof), to hear the content. It's the melding of voice and video with more complex ideas that should create the need to watch the video several times. It's how we learn.

    I like the following video. A lot there...a lot not discussed. But you get the point.

  6. J.R. Dobbs

    J.R. Dobbs Active Member

    But then you would, since it is your video and you come across to the observer as being very, very ego-centric. A cursory glance: does the first metatarsal head sit higher than the lesser metatarsals because of a metatarsus primus elevatus as you state, or is it simply that the first metarsal head has a much greater diameter than the lesser metatarsals and a sesamoid apparatus beneath it? I think you could take any foot type and the dorsal surface of the 1st metatarsal would sit higher compared to the lesser metatarsal heads, but you seem convinced that this is due to a metarsus primus elevatus. IS this because it fits with your pet theory?

    Video's are all well and good, flashy graphics are cool, but the message being put across? That has to be accurate. I'm not convinced that yours is, Dr Hunt. I think you are more interested in how good you think you are. Viewed from a watchers point of view.
  7. drhunt1

    drhunt1 Well-Known Member

    J.R.-Plain film radiographs, clinical observation and a cursory knowledge of foot types will lead one to acknowledge this patients' structural deformity. MPE, by definition, is not as you have written. There should be a normal parabola in the frontal plane of the met heads. Here's a good article on this:


    Also, did you happen to notice her great toes? Remind you of a thumb, as the IPJ's ROM needs to compensate?

    Not a word about the animated overlays on the feet. Hmmmm...interesting. Considering I've never seen that performed before anywhere by anyone, I find that rather telling. Egocentric?
  8. J.R. Dobbs

    J.R. Dobbs Active Member

    Have you read Demp? Clearly not, or you would not refer to a parabolic curve as being normal.

    Demp, PH: A mathematical model for the study of metatarsal length patterns. JAPA 54:2 1964 p.107-110

    Demp PH: Mathematical medicine. JAPA 60:9 1970 p352-353

    Demp PH: The metatarsal hyperbola and the pathomechanical forefoot. Currrent Podiatry 20:3 1971 p15-17

    Demp PH: A numerical taxonomy for evaluating the angular biomechanics of the human metatarsus. Current Podiatry 24:5 1975 p.9-11

    Demp PH: Biomechanical optimality and the mathematical measurement of diagnostic patterns in the human foot. Arch Pod Med Foot Surg 3:1 1976 p.11-21

    Demp PH: Biomechanical foot roentgenometry. Yearbook of podiatry 1978-1979. Ed: TH Clarke. Futura Publ. Co. New York 1978 p. 64-70

    Demp PH: An anthropometric index for screening foot dysfunction. Current Podiatry. 28:6 1979a p.11-13

    Demp PH: A mathematical taxonomy to evaluate the biomechanical quality of the human foot. M.S. Thesis (unpublished) Polytechnic Institute of New York, USA June 1979b

    Demp PH: A correlation of length, width, height and pathomechanical quality in the human foot. Current Podiatry 31:8 1982 p23

    Demp PH: Biomechanical profile analysis of the foot radiograph based on mathematical modelling. Current Podiatry 32:10 1983a p15-17

    Demp PH:Mathematical modelling in podiatric surgery. A new approach to biomechanical evaluation. J Acad Amb Foot Surg 1:1 1983b p72-73

    Demp PH: A mathematical taxonomy to evaluate the biomechanical quality of the human foot. Mathl Comput Modelling 11 1988 p341-345

    Demp PH: A mathematical taxonomy to evaluate the biomechanical quality of the human foot. Mathl Comput Modelling 12 1989 p777-790

    Demp PH: Using conic curves to classify pathomechanical biostructure of the metatarsus. Mathl Comput Modelling 14 1990a p668-673

    Demp PH: Pathomechanical metatarsal arc: radiographic evaluation of its geometric configuration. Clin Pod Med Surg 7:4 1990b p765-776

    Demp PH: Numerical diagnosis of pathoanatomy in the human forefoot: A pilot study. The Lower Extremity 1:2 1994 p133-138

    Demp PH: Geometric models that classify structural variation of the foot. JAPMA 88:9 1998 437-441

    In other words, it's a hyperbolic curve.

    Didn't get as far as any animation yet, was interested in your frontal plane observation of how the 1st MTPJ is more dorsally situated and stopped at that point as it wasn't too engaging. Lets take it point by point for now. Can you provide counter to my criticism, before shifting planes to the transverse projection:

    Does the 1st metatarsal head have a much greater diameter than the lesser metatarsal heads, yes or no? If it has a much greater diameter and a sesamoid apparatus beneath it, and it does, can you give me a foot type in which the dorsal surface of the first metatarsal head would not be further from than the supporting surface in the frontal plane than the lesser metatarsal heads from forefoot loading through midstance? Your video suggested that this was due to metatarsus primus elevatus. This is may or may not be true, it could simply be due to the fact that the first metarsal head is bigger and has the sesamoids beneath it. Can you counter this argument? Yes or no will suffice.

    Yes, you might do well to reflect on the fact that this is how you come across, yet I doubt your ego will let you.
  9. drhunt1

    drhunt1 Well-Known Member

    Heavy on Demp! In normal lateral radiographs, as the article I posted suggests, the first met head does not rise above the second. I will include a lateral view of the patient's foot for another view...but one that can be seen in the video presentation. Yes, the first met is bigger than the lesser mets. Yes, there's a sesamoid apparatus. But I suggest you revisit Merton Root's description beginning on page 48 in Volume 2, where he discusses 1st met ROM and plantarflexed vs. dorsiflexed 1st mets.

    I come across as egotistical? Perhaps my online "demeanor" is bolstered by the fact that, at least in my mind, I have resolved a medical issue that is almost 200 years old. Forgive my passion for what is that I have discovered. I also urge you to view the entire video sequence. Never before have I witnessed anyone producing the animated overlays. Think of what could be produced with a bigger budget. The money I spent on this animation alone is equal to the reimbursement of ~10 bunion surgeries...certainly not chicken feed. There's more to come, however...I don't want to give anyone here the impression that I'm a "one-hit wonder".
  10. J.R. Dobbs

    J.R. Dobbs Active Member

    But you didn't answer my questions nor address my points. Is there a reason why you are avoiding these? Your video, up to the point that I watched it, did not show any lateral radiographs, rather it showed a frontal plane video of a foot on a treadmill and stated that the reason that the dorsal surface of the 1st MTPJ was further from the supporting surface than the lesser MTPJ's was due to a metarsus primus elevatus. This patient may have had a metatarsus primus elevatus, but your video intimated that any person in which the dorsal surface of the first MTPJ was further from the supporting surface than the lesser MTPJ's has a metatarsus primus elevatus. This just isn't true is it, Dr Hunt? In defense, you then put up a sagittal plane radiograph of someone with a metatarsus primus varus??? Maybe some frontal plane radiographs of patients without a metatarsus primus elevatus might be more supportive of your point.

    No change there then, nor in my opinion.
  11. drhunt1

    drhunt1 Well-Known Member

    Wow...I can't really believe I'm having this discussion with you. I'm also surprised that Kevin hasn't weighed in to tell you how "unprofessional" you are for using an alias. And yes...I did answer your question; I didn't avoid them. Are you suggesting that ALL feet have a 1st met that appears higher then the lesser mets because of the sesamoid apparatus and the size of the first met in comparison? Then explain the following pic shown below.

    The lateral view I submitted previously was of the same patient you saw in the video...I didn't just submit any X-ray, as you suggest, showing a MPE. But then, one could determine the elevatus just by looking at the video, right? And yes, if the patient presents with a glaring difference between the first and lesser mets, I do consider it either a structural or functional MPE. Why did you avoid mentioning her great toe looking like a thumb? Why did you not comment on her abducted gait pattern while transferring from propulsion into swing phase? Are you avoiding these issues?

    Why don't you post some of your contributions to the profession of Podiatry...what problems you have solved while using Demp or any of your own theories and what means of elaboration you have paid handsomely for to achieve these goals. I won't accuse you of being egocentric, but that might be a good start...or a decided finish point.
  12. Rob Kidd

    Rob Kidd Well-Known Member

    While (one of my) biological heroes, Steve Gould hated the expression, the term "pre-adaption" jumps to the fore when I read the above arguments. Often when looking at what something is, so to speak, you really need to consider what it was. That is what was the first metatarsal morphology before it became the major weight bearing unit of a half dome? Have any of the above literature taken into account the non-human metatarsal morphology? I am not familiar with the list above, but that is the question I would be asking. All over the body, parts of morphology are not pointing to what they do now - they are pointing to what they did in a previous life. Happy Saturday.
  13. J.R. Dobbs

    J.R. Dobbs Active Member

    DrHunt, you can put up as many lateral x-rays as you want, the fact remains that when we view a foot from the frontal plane in walking gait, from forefoot loading through midstance, the dorsal surface of the 1st metarsal head will always be higher from the supporting surface (you call this a height differential) than the lesser metatarsal heads because the first metatarsal head has a greater vertical diameter in the frontal plane than the lesser metarsal heads and also has the sesamoid apparatus beneath it.

    Attached Files:

  14. drhunt1

    drhunt1 Well-Known Member

    I will counter your statements above, by telling you this: you are flat out wrong. Your demeanor and tact remind me suspiciously of a telephone conversation I had recently with a Podiatrist on the East Coast.

    You STILL won't acknowledge the fact that you were wrong about my "throwing any x-ray up" to prove the point, when, in fact, it was a lateral view of THE SAME patient shown in the video. You still haven't addressed the second x-ray I posted which I pulled off the net, showing the bisection of the talus traveling through the middle of the head of the first met...in a NORMAL foot. Is that 1st met head glaringly elevated over the second? You confuse frontal plane parabolas with normal lesser met alignment, citing one author in your attempts to do so...obviously avoiding what you should be witnessing in your own practice. Have you ever done surgery, J.R.? If you did, then you would know that the plantar plate elevates the lesser met heads like the sesamoid apparatus of the first, which you deem as contributory to the first met head ALWAYS being elevated. Let's have some fun...shall we? I will post a pic of my youngest son's foot. Explain what you see here.

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