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Biomechanics and foot orthoses

Discussion in 'Biomechanics, Sports and Foot orthoses' started by biomech, Jun 29, 2006.

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  1. Boris "Biomech" Karloff:

    You need to go to the internet, type in "cheap arch supports" into the search engine of your choice, and buy any one of the ones that come up so you can be satisfied with your choices. And if you want to get educated, it would help if you actually did some work on your own, and didn't expect us to do all the work for you. By the way, both Boris Karloff and Albert Einstein worked hard at their professions. What is your profession???
     
  2. Dieter Fellner

    Dieter Fellner Well-Known Member

    Kevin - congratulations , great news for you!

    PS may we now refer to you as gramps/grandpa etc? :D
     
  3. Finally, we are getting somewhere. It would have been a lot easier for you to have just come out with this in the first place.

    I suspect this has been a nightmare for you because you have no idea what kinematics and kinetics are and probably don't know the first thing about what we have been saying.

    I guess the moral of this story is: if you don't understand what your podiatrist is saying to you- ASK, rather than coming onto a professional forum anonymously and insulting respected members of the community when you don't understand the answers that they give to you.
     
  4. Thanks Dieter......as they say in the southern USA....you can call me anything you want, as long as you don't call me "late for dinner". ;)
     
  5. Heather J Bassett

    Heather J Bassett Well-Known Member

    Way To Go Simon***!!
     
  6. sedkoal

    sedkoal Welcome New Poster

    How orthoses affect lower extremity

    Hello!

    I'm presently studying Podiatry in Canada, more precisly in Quebec, and i have a job for the summer in a biomechanic lab. The objective of our study is actually foot orthoses and postural stability. I guess i have like 20 research that talk about that. I think the most interesting is certainly the one conducted by A. Mündermann & al., named Foot orthoses affect frequency components of muscle activity in lower extremity (Gait & Posture, 2006). They have actually discovered that orthoses seems to affect lower extremity by changing the muscular activity, which is in turn influencing kinetics and kinematics. Were now talking about intrinsec forces over the foot, and the whole body as well, which is very interesting. So, since i'm just finished my 1st year, you should check it out yourself! If you want other infos about the other researchs ive read or what we have ourselves discovered throughout our experiment at the lab, just email me at sedkoal@hotmail.com.

    Have a good day!
     
  7. You will find that there are other orthosis research studies that specifically have looked at the effects of foot orthoses on balance (Guskiewicz KM, Perrin DH: Effects of orthotics on postural sway following inversion ankle sprain. J Orthop Sp Phys Ther, 23:326-331, 1996; Hertel J, Denegar CR, Buckley WE, Sharkey NA, Stokes WL: Effect of rearfoot orthotics on postural control in healthy subjects. J Sport Rehabil, 10:36-47, 2001; Rome K, Brown CL: Randomized clinical trial into the impact of rigid foot orthoses on balance parameters in excessively pronated feet. Clin Rehab, 18:624-630, 2004).


    The study by Mundermann et al done at the University of Calgary(Mundermann A, Wakeling JM, Nigg BM, Humble RN, Stefanyshyn DJ: Foot orthoses affect frequency components of muscle activity in the lower extremity. Gait and Posture, 23:295-302, 2006), did not look at balance parameters but, rather, looked at changes in electromyographic activity with running in orthoses.

    Are you planning on carrying out research on balance with orthoses, or are you just reviewing the literature?
     
  8. sedkoal

    sedkoal Welcome New Poster

    Hello,

    Indeed, we will do a research about orthoses and postural stability. But first, I had to do a research in litterature, that's why i know pretty much of the articles you mentionned. We're acutally defining what our protocole will be. We're trying several conditions and analyses the data to see if it matches with the litterature. Our goal is to find, precisely, how orthoses affect lower limb and to discover something new and interesting that could be clinically relevent. From what i saw in litterature, there are many interpretations and it's not a piece of cake. Maybe was my post not all coherent, but please, keep in mind that i'm in a learning process and that some concepts are not that clear for me! Anyway, that's what my vision of the whole thing is.

    Sincerly

    Jason
     
  9. Jason:

    Please let me know if you need any help, ideas or assistance with your research since I would be glad to help if I can. In addition, there are many other members of Podiatry Arena that are very experienced researchers that could probably lend a helping hand if you need one.

    Good luck with your research.
     
  10. Atlas

    Atlas Well-Known Member

    It is unfair that some of us, including me, remain anonymous and exchange in debate with some that have the courage to do otherwise.
    However, it is a good question.

    I think Craig has mentioned add/abd moments in relation to knee pain.

    Simon, I think we can extrapolate on the kinetics/kinematics answer, which would help the students of the profession understand clearer.
     
  11. Ron,

    The problem with anonymity is that it denies accountability.

    So ...
    Normally, the effects of external forces and moments on the body are resisted or controlled by forces generated internally either in passive tissues, such as joint capsules, ligaments or articular cartilage, or in active tissues such as muscles. In this way a functional static posture or pattern of motion is generated. In a body segment in which injury or disease is present, one or more of these tissues is unable to produce appropriate force. For example, a ligament may be stretched or torn, joint cartilage may have lost it's structural integrity, or a muscles may have rerduced or increased tone. In all of these cases a more "normal" function may be restored by modifying the system of external forces and moments acting across one or more of the joints of the body by using an orthoses.

    According to Bowker (Bowker, P.: The biomechanics of orthoses. In Bowker, P. et al: Biomechanical Basis of Orthotic Management. Butterworth Heinemann 1993) there are four ways in which an orthosis may modify the system of external forces and moments acting across a joint. He terms the first three of these as "direct" in that the orthosis actually surrounds the joint being influenced. The fourth he terms "indirect" as the orthosis modifies the external force system beyond its physical boundaries.

    1. An orthosis may modify moments acting about a joint. In doing so it may restrict either partially or totally, the rotational motion at the joint. In partially restricting motion, the orthosis may limit the RoM available about any particular axis, or may limit the number of axes about which motion may occur.

    2. An orthosis may modify the normal forces acting about a joint and thereby restrict translational motion at the joint.

    3. The orthosis may reduce the axial forces carried across a joint. this is achieved by sharing the loads between anatomical structures and orthosis.

    4. The fourth "indirect" approach is probably most applicable to foot orthoses and involves modifying the point of application and line of action of the ground reaction force (GRF) during either static or dynamic weightbearing. This approach can, in theory, result in a modification of both normal and axial forces and moments about a joint.

    As the foot contacts the floor during gait, it is subjected to ground reaction force which has components in all three body planes (X, Y, Z). As stance phase progresses from heel-strike through toe-off, the relative values of these three components change, so that the direction of the resultant GRF also changes. In addition, its precise point of application on the plantar surface moves progressively forwards from proximal to distal.

    Thus, at any instant during the gait cycle the GRF has a particular line of action which, in general, will lie at some distance from the centre of rotation of each of the joints of the lower limb. The GRF will thus create moments about each of these joints, the effect of the moment being determined by whether the GRF passes anteriorly or posteriorly (or medially or laterally) to the joint, and its magnitude being determined by the perpendicular distance between the joint axis and the line of action of the force.

    Now, if we look at an orthoses with all it's curves very, very closely we can break it down to a series of inclined planes. These inclined planes modify the point of application and line of action of the GRF, which in the presence of an orthosis we can term Orthosis Reaction Force (ORF) by trigonometrical functions.

    See the attached image.

    Here we have a slice through an orthosis. There are four examples of possible points of application for the ORF (a, b, c, and d) the ORF vectors at these points are represented by the four coloured lines (for simplicity, these are drawn normal to the incline of the orthosis at this point). There are also three possible axis positions (1, 2, 3). Note how for a given magnitude of ORF the inclination of the orthosis shell at the point of contact can have dramatic effects on the moment produced about any given axis position. Note also how change in axial position also influences the moment produced.

    Although this is a very simplistic model, I hope that it demonstrate one of the ways in which orthoses may work and helps the "students" to better understand the complexities of this problem. However, for those who want a more complete picture, look up some of the experiments performed using mechanical stimuli on the foot, where they have elicited phase of gait dependent motor responses from the stimulation of cutaneous nerves. Try googling H-reflexes sural nerve. Interesting how cutaneous stimulation (which we must get from orthotic shells) can influence muscular contraction. Also interesting how a past colleague of mine found that a reduction in sural nerve conduction was one of the first things to be lost in diabetic neuropathy.
     

    Attached Files:

    Last edited: Jul 10, 2006
  12. Dave Smith,

    Please draw us all a proper diagram with the forces in the right place and labelled correctly etc..

    Thanks. ;)
     
  13. Ron,

    You said "we", and then referred to "students of the profession", are you a qualified podiatrist now?

    Perhaps, you could hold up your half of the "we" thing and "extrapolate" for the students :p
     
  14. Nicely said Simon. From now on, unless I know the real name of the person asking the question on Podiatry Arena, I will either not respond or I will give a minimal response. I suppose if the person doesn't think it is important that we know what their name is, then I don't think it is important that I answer their question!!

    One thing that must be emphasized when attempting a mechanical analysis of how foot orthoses exert their effects on the foot: for each discrete location where the orthosis mechanically interacts with the plantar foot, there will be a discrete orthosis reaction force (ORF) vector that will have the four components of a force vector: point of application, direction, line of action and magnitude.

    Therefore, if we divided the surface of the plantar foot that contacts the orthosis into 1,000 discrete points of equal surface area, then each of these discrete areas on the plantar foot will have an ORF vector that can be thought to act at the center of that discrete area, with a certain line of action, with a certain magntitude and a direction that would produce a compression force between the orthosis and the foot [unless, of course, the orthosis is sticky which will then cause the orthosis to exert a tension force on the plantar foot when the foot attempts to lift from the orthosis].

    So, when we are analyzing the mechanical effects of a medial heel skive, for example, we must not just assume that the forces are "normal" (i.e. perpendicular) to the orthosis plate surface at the medial cup of the orthosis since there may also be frictional forces present at that point on the orthosis plate that are "tangent" (i.e. parallel) to the orthosis plate surface. In addition, the addition of a medial heel skive may cause an increase in medially-directed lateral heel cup pressure from the orthosis that may also contribute to increasing the STJ supination moments along with the changes due solely to modifications in medial heel cup shape. Daryl Phillips drew a similar analysis to Simon's analysis about a decade ago at one of the Root/Weed Seminars to "disprove" how the medial heel skive worked. Unfortunately, he totally ignored the contributions from frictional forces from the orthosis which I pointed out with great delight to the podiatrists attending the meeting. These frictional forces may be a significant component of the forces an orthosis exerts on the foot.

    By the way, Simon, you need to get CorelDraw or some other similar program. Dave Smith got the program and it has greatly improved his capability to produce illustrations for electronic and print distribution.
     
  15. Agreed. In fact as the angle of inclination increases these frictional components become increasingly important to prevent the overall vector becoming increasingly "horizontal". Here is a thought though, it seems theoretically plausable to have a vector who's point of application is medial to the STJ axis, but due to it's line of action, creates pronatory moment about the joint axis. Kind of questions the simple transverse plane "where is the axis and where is the force" analysis.

    Kevin, first I need to get Dave Smith's head for physics ;)
     
  16. Yes, certainly as we get further more into the depths of what makes a foot pronate and supinate then we must get more complicated and detailed in our mechanical analyses. In order to simplify the concepts sufficiently to be useful for most clinicians, I have often used gross oversimplification of the "if the force is medial to the STJ axis this causes STJ supination moment" explanation. However, I have repeatedly used this simplified mechanical explanation just so that most of my non-engineer, non-biomechanics PhD clinical audience will be able to learn step by step, before it gets so complicated that they become totally lost in precise biomechanics analysis.

    Like I said earlier, consider not only line of action but also direction of force vector from the orthosis. It could also be theoretically possible to make the orthosis lateral heel cup adhere to the plantar-lateral heel so that the tension force from the orthosis at heel off would create a STJ supination moment. Will call it the "super-glue orthosis". :p
     
  17. Atlas

    Atlas Well-Known Member


    When do we stop being a student of the profession Simon? When we graduate as a podiatrist?

    No, I am not a qualified podiatrist. So perhaps I am not qualified enough to state how an orthotic (and what additions/modifications) could assist:
    - a recalcitrant lateral(or medial) collateral ligament pathology of the knee?
    - a recalcitrant lateral(or medial) meniscal pathology of the knee?
    - tib ant or post overuse
    - a recalcitrant lateral(or medial) ligamentous strain-type pathology of the ankle
    - a recalcitrant lateral(or medial) impingement pathology of the ankle.


    But I think, if orthotic therapy and influence are explained in the context of the above conditions then several positives result.
    1. Rather than giving the students/clinicians two words (kinetics and kinematics) or complex physics, we can actually give them clinically relevant tools to use on the next session. When their patient complains of medial ankle pain or lateral knee pain, clinical reasoning can 'hit the ground running'.

    2. A basic understanding of compressive and tensile forces can guide them to diagnose lower-limb musculo-skeletal conditions more accurately and quicker.
    3. It allows one to prognosticate whether an orthotic device will be effective in assisting the condition.
    4. It also allows the student/clinician to understand why the orthotic is making the condition better or indeed worse.
    5. If the device is making the condition worse, it allows the practitioner to alter the impact that the orthotic is making on the pathology, via way of additions/subtractions to the device.
    6. It compliments "Gardiner's rule", which although not supported by research evidence (yet), is a fantastic and simple clinical teaching tool.




    I would be interested to know what style of device+/- modification you would lean to when confronted with clinically diagnosed cases set out above.



    Ron
     
    Last edited: Jul 12, 2006
  18. Ron,
    You're clearly not qualified enough to hold up your part of the "we" thing, since you haven't even attempted to.

    Personally, I use a patient centred approach to treatment, so it is really unwise to try and give a formula or recipe for a device to treat "conditions", since without details of the individual it is somewhat blind judgement. However, understanding the function of each tissue and understanding the physics of orthoses can allow you to construct devices which may help off-load the tissues. I've already explained this.

    So rather than getting stroppy with me Ron because I made fun of you, perhaps a better educational approach to this to help the "students" is to adopt a Socratic style to lead "the students" to the answer's they seek. I could have just given you the bird and said: off you go then, explain to the "students" and show everyone how clever you are... but this way is actually better from an educational stand-point. I used to be a teacher you know ;)


    So in order to answer Ron's Question we must first know the answer to the following questions (and others):

    How is each tissue type most commonly injured? In tension, compression, torsion etc?

    What is the mechanical function of each of the tissues listed?

    When during the gait cycle are each of the tissues under load and in their "stress position"

    What are the options in terms of casting?

    What are the options in terms of posting?

    What are the mechanical effects of the posts?

    What are the options in terms of shell geometry?

    What are the mechanical effects of the shell?

    That'll do for now, there is more to it than that, but answer those questions first and we'll be on our way to designing the right orthoses.
     
    Last edited: Jul 12, 2006
  19. I make no apologies for explaining how orthotics alter kinematics and kinetics by "giving" what Ron terms "complex physics"- (forces and moments were on the ordinary level syllabus when I went to school- hardly complex) since by it's very nature, biomechaincs is applied physics- sorry, but it's true, if you want to understand biomechanics, you better start understanding physics. And Ron, speaking from a position of some educational experience. I think the approach to empowerment of students taken here by explaining the principles so they can apply it to any mechanically induced pathology is far better in the long term than providing a recipe to treat specific conditions. But hey you probably have more knowledge of educational theory than me. I just bet your lecturers love you.

    One other thing: Bold in text messages is considered as shouting, so I'd appreciate it if you'd stop shouting. We used to use this kind of respect.
     
    Last edited: Jul 12, 2006
  20. Prognosticate (is there really any need for such words? Probably an inverse correlation there somewhere) on this. How do you explain how orthoses work when a patient comes back for review 6 weeks post dispensation and reports a 50% improvement in symptoms when on examination you find they have been wearing the left device under the right foot and vice versa? Experienced that one yet? Happens frequently, happened to me today.

    Everyone is selling something. "Sell me a God, it's love time..."- Eat
     
  21. Atlas

    Atlas Well-Known Member

    Sort of. Even though it is a formula or a recipe, I wouldn't recommend an inverted rearfoot device for recalcitrant lateral ligament pathology in the ankle or knee.

    Being made fun of is half the fun. And who is getting stroppy over bold text?



    There is a lot of merit in empowerment, but if this is going to be done via complex physics, that I would guess 20% of musculo-skeletal practitioners/students understand at best, then perhaps "we" should recommend half a physics degree before entry.

    You're kidding aren't you? Where are the rules pertaining to implied use of bold, italics, underline etc. All I was trying to do was emphasise the crux of my long-winded post. If the bold hurt you, what did the big red writing do on the 1st page?

    Maybe lateral column support is underrated.

    I re-iterate my question. What do "we" do to devices that make your patient's condition worse?





    Don't you like Gardiner's rule? What is wrong with it?






    Ron
     
  22. I still can't agree that this is complex physics. If you can't multiply two numbers together you shouldn't be doing a degree.


    Maybe it's the way I prescribe and make my devices, but you know, I can't recall the last time that one of my patients condition got worse after receiving an orthosis from me. What do you do when your devices make your patients condition worse Ron?
     
    Last edited: Jul 13, 2006
  23. Atlas

    Atlas Well-Known Member

    As musculoskeletal practitioners, 'we' all like to think that 'we' have a 100% success rate and never exacerbate the condition of our patients. Sell me a god?
     
  24. admin

    admin Administrator Staff Member

    This thread is locked until I can find the time over the next few days to remove posts or parts of posts that contribute nothing to the substance of the thread.
     
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