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Foot Orthosis Biomechanics

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Feb 21, 2015.


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    Dieter Fellner and I are currently having a good discussion on foot orthosis biomechanics and theory on Present Podiatry e-Talk. I thought I would include the latest part of our current discussion since I thought it would be of potential interest to many Podiatry Arena contributors and lurkers.

     
  2. ayrtonsenna

    ayrtonsenna Member

  3. David Smith

    David Smith Well-Known Member

    It is very easy to demonstrate the kinetic changes afforded by an orthosis even with no kinematic change.

    Take a 5litre container of water hold it waist high at arms length and wait 2 minutes, how are your muscles? - feel the burn.

    Now take the same container place it on a convenient work bench - assume the same position as you were when previously holding the 5 litre container of water - no burn, even if you stood there for and hour. Same kinematics whole different set of forces.
     
  4. Dieter Fellner

    Dieter Fellner Well-Known Member

    Kevin,

    It may be worth to add, the seed for the discussion, and much of the interpretation arises from Dr. Shavelson's blog and his Foot Centring / Vaulting concept. For those unfamiliar with Dr. Shav, (apologies to those who are), Dr. Shav believes he can return foot posture to an optimal position (we are not sure what he means by that), by vaulting the foot (we are not sure what he means by that either) So that function follows form, i.e. kinetics is a product of kinematics. I like to entertain the concept, from time to time, if for no other reason that I get a good debate from Kevin and Eric, as to why it isn't so. I am rarely disappointed!
     
  5. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha Dieter,

    We have done some orthotics research for the US Department of Defense on utilizing dynamic composite (carbon fiber) spring-lever plates within our othotics systems to help reduce heel strike peak impulse, improve balance and improve overall energy efficiency of the system.

    Which may help the foot better "ultilize" Gravity

    "Gravity, and that pesky and difficult to manage amalgam of tissue known as the foot, is not so easy to control by simply applying a bent piece of plastic within a "foam" shoe.

    Furthermore, how can we tweak our orthotic design to squeeze out more kinematic change, to translate into a more efficient kinetic effect. We deploy additional design features into the orthosis. We add the Kirby skive, or ask for the Blake inverted design modification, or deeper, wider heel cups, maybe medial / lateral flanges." or maybe composite spring lever midsoles...?

    Are we done designing orthotic modifications or is there a future for composites in our footwear/orthotic systems?

    The last few Olympics seem to prove that their is a vast fast future...

    A Hui Hou,
    Steve

    American Society of Testing Materials voting member for committees,
    E54.04 Homeland Security Applications and Personal Protective Equipment
    F13 Footwear Safety and Traction

    Co-PI SBIR A11-109 "Advanced Composite Insoles for the Reduction of Stress Fractures." US Dept. of Defense and Army Medical Research and Materials Command.

    DoD final report link posted here, please review and respond.
    http://kingetics.com/store/wp-conte...-Phase-1-Final-Report-2012-Public-Release.pdf
     
  6. Dananberg

    Dananberg Active Member

    Kevin’s points on modeling very important, but the basic model must be accurate for the structures being evaluated.

    Heel strike to forefoot contact GOES WITH GRAVITY! It is the period of heel unweighting followed by heel lift-off which goes AGAINST GRAVITY. Fighting the effects of gravity therefore is NOT adding improved cushioning, better rearfoot control, or improved “vaulting” in and of themselves. To visualize the effects of “fighting gravity” observe the ability to raise one’s heel prior to the opposite heel striking the ground.

    As an example, think of a patient with a rocker bottom foot. Since we know that FORM FOLLOWS FUNCTION, something in the way this person walks is contributing to the appearance of the foot. Assuming a flat walking surface, it is impossible to “shape” the foot to be rounded on the plantar surface. Instead, if the heel raises but the forefoot (at the MTP joints) remains stationary, and the plantar ligaments are lax, the foot can and will deform into the shape we fully recognize.

    I am not trying to suggest that issues of rearfoot control or firm foot orthotics are incorrect. I am suggesting that to properly model the foot and provide for the appropriate treatment options, we need to recognize that fighting gravity is a heel lift issue, and not one associated with heel strike.

    Howard
     
  7. Surely the muscular activity of the pretibial muscles from heel strike to forefoot loading is an example of the body "fighting gravity" too? Or have I missed the point?
     
  8. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha,

    I think you guys are missing the point.

    When we start building dynamic energy returning levered "rocker bottom" orthotics we can change kinematics of heel lift, dramatically.

    Howard sorry but I must disagree with you.
    "- it is impossible to “shape” the foot to be rounded on the plantar surface."

    If an orthotic is mechanically bonded to a foot it becomes part of the foot and functions with the foot (as an addition the foot),, if it is part of the same closed kinetic chain.

    We are building and testing cantilevered orthotics that function as a rounded surface, why else can I walk up hill using less energy? Probably because the spring plate has least a 2:1 mechanical advantage of the forefoot to help lift-vault the rearfoot-heel.

    You may have not have researched our new advanced composite simple machine based orthotic technology, but that is no reason we should be excluded from this professional conversation nor your future learned comments.

    Our scientific poster board on this technology was submitted and presented at last years APMA's national scientific meeting, PFA national meeting and last year's AOPA national meeting. Our US Department of Defense research results have been posted on my last post on this thread. Our scientific abstract was accepted for the past Dynamic Walking Conference, International Running Symposium, APMA and AOPA national meetings.

    Someone please prove to me (give me a bone here) that the mechanical engineering of biomechanics is not totally falling on dead heads...

    https://www.youtube.com/watch?v=Sh9SyiQUfg0



    Mahalo,
    Steve


    Dare You to Move...San Diego Style
    https://www.youtube.com/watch?v=hBmAOTZZiPc
     
  9. Dananberg

    Dananberg Active Member

    Steven,

    You wrote "Howard sorry but I must disagree with you.
    "- it is impossible to “shape” the foot to be rounded on the plantar surface.""

    I believe it is not me who missed the point. I was discussing ROCKER BOTTOM feet in my post, and not the reverse.. I know you can change arch height positively, but that was not my point nor was it at all related to the concepts I tried to convey.

    I was discussing form vs. function and was trying to point out how a model must reflect what Stephen J. Gould referred to as "the exception proving the rule". If rocker shaped feet function in such a way to develop their concave form, the model must be capable of describing this or it is likely incorrect. If the rocker shape were purely a contact related issue, it could not be concave as the ground is flat, hence its form would have to be flat. However, in the sagittal plane facilitation (SPF) model, heel lift without sagittal plane metatarsal rotation (failure of the bases to pivot about the heads), is a concept in which the form and function co-exist. The SPF model would also predict that with normal (and most importantly timely) sagittal plane rotation, arch height would increase over time.

    Howard
     
  10. Dananberg

    Dananberg Active Member

    Simon,

    Yeah, you missed the point....but raised a rather import issue. I was actually referring to the idea of modeling "pronation" and how the tough time in the bearing phase is to "step up", not necessarily to heel strike.

    A US robotic engineer, Tad McGeer, found that the energy cost associated with toe off of the trailing limb is equivalent to the resistance of foot slap at heel strike by the pre-tibial muscles in the forward limb. It just makes me marvel at the level of sophistication of human anatomy. Glad you brought this up.

    Howard
     
  11. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha Howard,

    Please understand I have the deepest respect for your past research and leadership in our profession.

    This string started just as another Dennis bashing, but it has potential. Even though poor Dennis is sitting on the outside of Podiatry Arena looking in right now.

    I am not talking about arch height I am talking about rocker bottom/levers in our closed kinetic chains regardless if they are feet or the orthotics or prosthetics we use to influence the shape and kinematics of our feet and lower limbs.

    When we build gait systems that lift the heel at the right time of gait with the right frequency and with significant enough force to make a physical change (Biomechanics of Sports Shoes, Nigg et all) we may need to change your concept of initial heel lift which will make the follow statement incorrect,

    "Heel strike to forefoot contact GOES WITH GRAVITY! It is the period of heel unweighting followed by heel lift-off which goes AGAINST GRAVITY"

    This is not correct when the cradle and spring plate of the orthotic lift the heel off the flat ground during this period of "unweighting". If the orthotic is working against gravity and the foot benefits from this work does the foot still have to work the same against gravity? I would say not as much with a more efficient dynamic system.

    and these are the systems we should be researching and developing and teaching...

    Mahalo,
    Steve

    Only through change can we change for the better...
     
  12. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha Howard,

    You brought up another good point.

    If the anterior section of the foot and spring plate is supported by the cantilevered force of the rearfoot contacting the ground we should also be able to influence and reduce the energy expended for the mitigation of foot slap,

    "US robotic engineer, Tad McGeer, found that the energy cost associated with toe off of the trailing limb is equivalent to the resistance of foot slap at heel strike by the pre-tibial muscles in the forward limb"

    We also know that most energy is lost during gait at the MPJ's and if we can stiffen the shoe/orthotic we can reduce some of that energy loss. Drs. Nigg and Stefanyshyn have previously published on this. Why have we not taken advantage of this and incorporated this concept into our gait systems yet?

    Carbon fiber spring plates are the future of our orthotic constructions and treatments. We just need to make them comfortable and functional.

    And yes, we need to lower the price of composites Kevin but that will come with economies of scale.

    Happy Friday!
    Steve

    The only thing we have to fear is frail shoes stepping on sharp glass and nails...
     
  13. Dananberg

    Dananberg Active Member

    Steven,

    You wrote "We also know that most energy is lost during gait at the MPJ's and if we can stiffen the shoe/orthotic we can reduce some of that energy loss. Drs. Nigg and Stefanyshyn have previously published on this. Why have we not taken advantage of this and incorporated this concept into our gait systems yet? "

    This is the story of my life; making MTP joint motion function in a timely fashion so as to minimize energy loss during gait. The entire fascia network has its distal insertion into the bases of all 5 phalanges. They are important! Even though we think of dorsiflexion and plantarflexion as movement of the toes, this is only true NWB. During WB, the toes, once in ground contact, are stationary, and everything (ie, the entire body) moves around them! With heel lift, the fascia automatically tightens and exerts this tension through the entire body. This provides the musculature with a resistive covering against which they can press. This in turn causes a postural tension which becomes an integral part of the supportive system. Without MTP joint flexion, there is no fascia tightening.

    This is not to say that rockers cannot reduce the stress of heel off, but there is just more to it than that. Rockers can have flex lines added, and therefore provide the best of both worlds. I have had considerable success with this approach for decades....

    Howard
     
  14. Dr. Steven King

    Dr. Steven King Well-Known Member

    Aloha Howard,

    Your truly are a "Master of the First Ray".

    Can we not reinforce the mpj's with composite plating thereby reducing the work/strain on the plantar fascia?

    Would that not help reduce the pathologies suffered from excessive repetitive loads to these tissues?

    "With heel lift, the fascia automatically tightens and exerts this tension through the entire body. This provides the musculature with a resistive covering against which they can press. This in turn causes a postural tension which becomes an integral part of the supportive system. Without MTP joint flexion, there is no fascia tightening."

    Why must we rotate around the toes?

    Why can't we rotate over an orthotic or other gait system that we devise to off load those structures?

    "During WB, the toes, once in ground contact, are stationary, and everything (ie, the entire body) moves around them!"

    Thanks for the discourse,
    Steve
     
  15. Dananberg

    Dananberg Active Member

    Matt,

    Skiing is way too good to spend much more time with this topic. From your questions, it seems as though you haven't read anything I wrote.

    The key to understanding foot and postural support involves making sure that the motion occurs when it is supposed to occur. Feet support themselves quite adequately when allowed to move thru a normal range of motion. Creating an orthotic form which is perceived as ideal, and then basically attaching it to the foot, regardless of the material from which it is made, is doomed to failure, and mostly from discomfort.

    During my practice years, I saw many, many patients who presented with AFO's which extended to either the sulcus or toes. THEY WERE INTOLERABLE. Cutting them back to behind the met heads and adding a 1st ray cut created MIRACLES for each one of them. The better the foot moves, even with a concurrent disability, the more comfortable that patient becomes. I can't be locked in place.

    From a balmy 23F, crystal clear beautiful ski day in Stowe, Vermont.

    Howard
     
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