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ideal foot-footware interaction

Discussion in 'Biomechanics, Sports and Foot orthoses' started by markjohconley, May 2, 2016.

  1. markjohconley

    markjohconley Well-Known Member


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    Is it ideal for the foot to move in relation to the footwear?
    Would it not be more desirable for the footwear to move where and when to transmit / exert the required forces to the foot; is it better to have the footwear as part of the surface complex or as part of the foot complex?
    mark
     
  2. Boots n all

    Boots n all Well-Known Member

    "Is it ideal for the foot to move in relation to the footwear?"

    Depends on the clinical needs, some parts of the shoe move in relation to the foot and other areas move the foot.

    Diabetic Charco, we design the forefoot sole and TCO to go where the mechanics drive the foot with least resistance, but the upper, stiffeners and rear sole control the foot where we want it.
     
  3. markjohconley

    markjohconley Well-Known Member

    ..the sole and TCO being a major factor in the external 'mechanics' applied to the foot

    'control'?; and aren't they also factors in producing the external 'mechanics'

    I realise it's very easy to misunderstand someone else's post.
    The reason for the OP was that I never put a 4 degree midstance grind into the rearfoot post of orthoses; there was only the Rootian paradigm when I started. It didn't make common sense to have the foot moving so much within the shoe, do podiatrists still prescribe the 4 degree rearfoot grind? (not aware of the correct terminology for it), mark
     
  4. efuller

    efuller MVP

    This question made me think of basketball shoes, soccer cleats and blisters. The ideal shoe would make it so that there is no slip between shoe and surface, and shoe and foot without causing damage to the foot. That is probably true up to a point. For example, ski bindings, need to allow slip when the forces get too high.

    Eric
     
  5. efuller

    efuller MVP

    I doubt that a 4 degree bevel in the rearfoot post of an orthotic ever had that much effect on rearfoot motion. The inside of the shoe conformed to the shape of the rearfoot post pretty quickly in most cases. Although, you could make the case that the bevel caused a medial shift in the center of pressure under the heel of the foot.

    Eric
     
  6. markjohconley

    markjohconley Well-Known Member

    Goodaye Dr Fuller, I seemed to recall the 4 deg bevel was on the anterior medial aspect of the rearfoot post? if so wouldn't it shift the CoP laterally?
    If the foot doesn't move that much in a shoe then why do we have heel stiffeners?
    Why I'm asking i suppose is the shoe is regarded mechanically as part of the surface and yet it's attached to the foot, unlike, obviously, the surface.
    I get the feeling that this may be a silly thread?, thanks, mark
     
  7. efuller

    efuller MVP

    The anterior medial part of the post is parallel with the anterior edge of the orthotic. The posterior lateral portion is angled upward so at the most lateral Posterior edge the bottom of the post is farther off of the ground. (Up until the time the post sinks into the midsole of the shoe.) So, with the shoe flat on the ground the bevel would tend to shift the center of pressure medially. Conversely, if the shoe is inverted at heel contact (it quite often is) the lateral part of the rearfoot post, even with the bevel, will tend to provide a better connection of ground reaction from the shoe through the post to the orthotic to the heel. That is when comparing an orthotic with a rearfoot post to one without.

    The purpose of heel stiffeners is to prevent motion of the foot relative to the shoe. They are part of the reason that foot does not move much relative to the shoe. Have you ever tried playing basketball in running shoes. Running shoes are much worse at preventing medial to lateral slide of the foot inside the shoe. The ideal shoe will prevent movement of the foot relative to the shoe. Different activities will require different shoe design features to prevent that movement.

    Eric
     
  8. markjohconley

    markjohconley Well-Known Member

    Thanks for trying Eric.
    When I was made to grind the 4 degree (talking 87-88) we did so into a flat rear-foot posted (thermoplastic) orthosis with the grinder removing material from the flat post at its most anterior medial 'corner', with most material removed at that corner and less as you ground the more lateral and posterior section of the grind itself. Is this what you're saying? or the opposite? If the former surely you would reduce the ORF plantar to that grind, and wouldn't that mean the CoP would be shifted laterally?


    Exactly, or should that be, 'lessen' or 'impede'?


    Thanks Eric, again
     
  9. efuller

    efuller MVP

    It sounds like we are talking about different posts. When I was taught to make rearfoot posts out of methyl methacrylate a posting elevator was used that had the bevel in it. The anterior end of the orthotic shell rested on one level and the heel cup rested on a 4mm thick platform that had 4 degree bend in it. The elevated platform was meant to accommodate for heel forefoot height difference in shoes. So a perfectly made rearfoot post with post motion (bevel) when placed on flat table top would contact at the anterior edge of the shell and the posterior edge of the rearfoot post. The underside of the post would be higher off of the table laterally as opposed to medially. It is quite amazing that they went this far in the geometry of rearfoot post and ignored the fact that the post sinks into the midsole of the shoe and the shoe will hit inverted.

    There are many ways to make a rearfoot post with a bevel. I heard one way where they inverted the orthotic when they put the post on. Then they ground off the medial plantar side of the post so when they were finished the medial underside of the post was parallel to the anterior edge and lateral side was beveled upward. This would, when finished, look the same as what I described above. Mark, that still sounds different to what you were describing.

    Eric
     
  10. markjohconley

    markjohconley Well-Known Member

    Yes Eric, definitely this one, you're right; so CoP medially shifted both at contact and thereafter?; thus, an unwanted inversion of the rear-foot on heel contact, thanks to the 'lateral' grind; which wouldn't help the integrity of the lateral heel stiffener, and again, why would you want movement within the footwear?, let the footwear do it .... and yep we, as in a few in my group, used to query the deformation of the midsole and subsequent alteration in anticipated effect of the orthoses, thanks, mark
     
  11. Petcu Daniel

    Petcu Daniel Well-Known Member

    I don't think so ! My believe is the footwear's potential is underestimated. The simplest explanation is that the process of design and manufacture of a footwear is more complex, time consuming, boring and unpaid compared with that of a foot orthotics, more people being implied in this process. I can't imagine a podiatrist, who can design and manufacture foot orthotics, designing shoe upper....

    I remember a Kirby's Newsletter ('Goals of foot orthotics therapy') quoting Nigg's answer to the question: 'how a clinician should decide what specific type of foot orthotics would be best for an individual?' The answer wasn't 'a long list of biomechanical parameters' but: ' the podiatrist must decide first what the goal of the foot orthosis for the patient before the most effective foot orthosis can be designed for that patient'

    Now, thinking that the concept of 'ideal' is very challenged in this field (see Root's ideal physical relationship...) I'll try to answer changing 'foot orthotics' with 'footwear' in Nigg's answer.

    Daniel
     
  12. Petcu Daniel

    Petcu Daniel Well-Known Member

    I think both above described rearfoot posts are designed for the same theoretically purpose: facilitating normal pronation. In my opinion the lateral rearfoot post motion is an example of not considering the footwear geometry. If you look at a shoe last you'll see it's frontal plantar sections being convex on the entire surface (last bottom part). This will increase the degree of rearfoot post motion as this was designed based on a flat platform. In the case of the first ray cut out the same shoe last bottom curvature has the potential to reduce the desired effect as it will rise the first metatarsal head.

    Daniel
     
  13. Petcu Daniel

    Petcu Daniel Well-Known Member

    I'm not sure about this, let's say, definition of the ideal shoe. One of the best arguments come from the article 'Rotational stiffness of football shoes influences talus motion during external rotation of the foot' ( http://www.ncbi.nlm.nih.gov/pubmed/22667677 ). On the other hand the movement relative to the shoe's upper is different by the foot's movement relative to shoe sole so what means 'movement relative to the shoe' ?

    Daniel
     
  14. Boots n all

    Boots n all Well-Known Member

    Not all footwear Last have a convex forefoot, this Last feature/design is not found in Veldscheon production Lasts for example.
    It is a little strange that runners have this feature as it is not relevant to any force Lasted production, the feature was introduced to assist in the manufacturing process when pneumatic toe Laster's were used.
    You can see that process on our school shoe production video, not on force Lasted runners.
     
  15. markjohconley

    markjohconley Well-Known Member

    Definitely, maybe TooMoon. 30 years ago, I did a 6/12 post-grad ?Footwear Appreciation Course? with the Bespoke Prescription Bootmaking teaching staff. We had to make a pair of ?Oxford? shoes (Balmoral (US)) including b/heel leather flares; nothing like the modern athletic footwear



    Daniel, I'm not sure. Wouldn't the in-shoe inferiorly-directed pressure from the forefoot keep the anterior edge of the orthoses against the insole throughout stance?, and if so, the lateral heel grind would never contact the insole, the rearfoot post would be constantly contacting with the medial side unground surface, yes?

    Good Point, considering Boots'n'All's qualifications
     
  16. Petcu Daniel

    Petcu Daniel Well-Known Member

    Another reason is an esthetically one in order to create the illusion of a tight/small foot appearance because a convex shape in the forefoot area will create a reduced width of the foot in the ball area. The question is how much allowance is permitted between foot and last ball girth in order to create a ideal (?!) foot-footwear interaction. Think at the diabetic foot !
    I've seen at IVO 2015 many custom made lasts without this convex area. I think one reason because it is more easily to manufacture it manually without this curvature.

    I'm not sure I understood well ! I don't see a reason for which both type of posts be designed on the same rearfoot post. I think for the medial one it will keep the anterior wedge against the insole as a function of shell stiffness. But till to be in contact, this type of post should permit some bending of the shell in the arch area in the midstance, isn't it ?

    Daniel
     
  17. Glen Willey

    Glen Willey Member

    The other benefit of a convex curve on a last's forefoot is to ensure, as weight is delivered on the 1st and 5th met during ambulation, the medial and lateral top-line of the footwear is tightened as these areas are forced down. This is particularly important in court shoes and flat ladies shoes where no fasteners are part of the design. The sole needs flexibility for this to occur.
    Platform soled footwear should have nil transverse curve as with quality men's leather soled footwear.
    Footwear requiring buildups for LLD should also have this convex curve reduced, before modification as not to force the foot base into similar convex position.
     
  18. Boots n all

    Boots n all Well-Known Member

    Daniel you make some good points.

    But how much do you think a convex forefoot Last reduces the width of the forefoot, 3%? Is it worth it?

    Pedorthic Lasts dont have the convex forefoot because they dont need it, custom made footwear are normally hand made and not court shoes.

    How much allowance is permitted between forefoot and Last? l dont know what is "permitted" but we allow nothing in the ball area. For me it should be a snug fit not allowing for any movement, if we allow extra room we get forefoot movement = shear at the planta aspect and we may also get folds in the leather upper that will rub.

    We commercially produce custom Lasts for Pedorthist, if you want the convex forefoot just order it, but l dont think it will serve any client that needs custom footwear?
     
  19. Boots n all

    Boots n all Well-Known Member

    Glen, Good point about the build up.
    l saw a 1/2 pair last week that had been built up 35mm by a shoe repairer and the sole was convex, the poor bloke could hardly walk
     
  20. Petcu Daniel

    Petcu Daniel Well-Known Member


    Yes, but the upper assembly (leather + textile) is viscoelastic which means that a remanent deformation will be produced in time. This will lead to a movement of the foot's ball area relative to the footwear which will create shear.
    How do you take foot measurement, taking into account the girth difference between loaded-unloaded foot ? Thanks !
    Some data regarding the allowances values you can find in this old text: https://kclpure.kcl.ac.uk/portal/en...ar(524b98f3-e92f-434b-be0e-c4379dc25d04).html
    Daniel
     
  21. markjohconley

    markjohconley Well-Known Member

    Originally Posted by markjohconley
    Daniel, I'm not sure. Wouldn't the in-shoe inferiorly-directed pressure from the forefoot keep the anterior edge of the orthoses against the insole throughout stance?, and if so, the lateral heel grind would never contact the insole, the rearfoot post would be constantly contacting with the medial side unground surface, yes?...



    Daniel I was referring to these orthoses
    Originally Posted by efuller
    ?.. a posting elevator was used .... The anterior end of the orthotic shell rested on one level and the heel cup rested on a 4mm thick platform .. The elevated platform was meant to accommodate for heel forefoot height difference in shoes. .... ignored the fact that the post sinks into the midsole of the shoe .... they inverted the orthotic when they put the post on. Then they ground off the medial plantar side of the post so when they were finished the medial underside of the post was parallel to the anterior edge and lateral side was beveled upward. ..?
     
  22. markjohconley

    markjohconley Well-Known Member

    Does this confirm that the orthoses in question would only contact the insole on the medial side?
     
  23. Petcu Daniel

    Petcu Daniel Well-Known Member

    Now I've understood! I think no matter are the manufacture methods the lateral grind post should look similar. You have right but only for midstance+terminal stance phases (Perry). In theory, this post motion is related to the STJ's axis pitch and should act in the initial contact+loading response (Perry) phases and not through all stance. In practice, I think this modification is not considering the footwear sole geometry so I don't understand how it could work !
    Daniel
     
  24. Petcu Daniel

    Petcu Daniel Well-Known Member

    I don't think so - I've tried to explain in a previous post !
    Daniel
     
  25. Boots n all

    Boots n all Well-Known Member

    We use a 3D laser scanner, weight baring for most, see image for more detail, the STL file generated is then used so we can add, if wanted, heel pitch, toe spring and extra depth for an orthoses and a toe box for toe wriggle room. It depends on what is ordered and what the client may need...e.g Charcot rocker bottom foot with a fused STJ may be best with no heel pitch at all.
    We then send the new file to the other end of our factory were another of the minions use a 4 axis mill to mill the new Last.

    The vamp lining and upper leather are bonded together, should be cut from the butt, with the grain heel to toe, our footwear is "heat set", the lasted footwear is without sole and is heated to 85 degrees for 15min, this takes out any other remaining stretch that might still be there, the heel stiffener is long the rigid and mostly MGF have a very stiff sole so "stretch" is not so much an issue, but if it is, we can fix it by refitting to the Last and...if l tell you the others Pedorthist will put the boot into me...
     

    Attached Files:

  26. markjohconley

    markjohconley Well-Known Member

    Sorry Daniel, this is how 'we' used to have to do it 30 years ago; didn't make sense then
     
  27. efuller

    efuller MVP

    It is really hard to figure out what a beveled post will do at heel contact. For most people the whole shoe, and the orthotic inside the shoe, is inverted at heel contact. When you read what the designers of the beveled post, you see that they believed that the post caused the heel bisection to be 4 degrees inverted at heel contact. This notion is ridiculous for many reasons starting with the whole shoe is inverted at that time. The beveled post may still be useful, but not for the reasons that were given. If you do a frontal plane free body diagram analysis of the shoe orthotic and foot at heel contact you would see that there would be a more solid connection between ground reaction force located at the lateral heel of the shoe and the lateral aspect of the heel if there was a flat post opposed to a beveled post as opposed to no post. Looking at the free body diagram, if you wanted to shift the center of pressure the farthest medial, for a longer period of time, you would use a rearfoot post only on the medial side of the heel cup.

    Eric
     
  28. markjohconley

    markjohconley Well-Known Member

    I thought it was 'in the past' however just read this, 'The inserts ... a four degree intrinsic rearfoot grind, and balanced forefoot intrinsic and maximum arch congruency',
    in, 'The Role of Arch Compression and Metatarsophalangeal Joint Dynamics in Modulating Plantar Fascia Strain in Running'

    I'm relatively new at perusing the 'articles', I expect it's still used a lot in research from non-up-to-date biomechanists?
     
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