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Foot orthoses outcomes and kinematic changes

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Dec 11, 2004.

  1. Craig Payne

    Craig Payne Moderator

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    A reduction in the force to do that test when standing on orthoses (static test) appears to be more predictive of clincial outcomes than changes in the pattern of rearfoot motion (a dynamic test) ---- we starting the RCT to further test and refine this next week.

    (Sorry about short sharp answers ---- too many deadlines, too many confernece abstracts due, too many grants to write .... and the students due back Monday :eek:

    HINT TO STUDENTS IF YOU WANT TO PASS = don't ask me how the holiday went
    :cool:
     
  2. Lawrence Bevan

    Lawrence Bevan Active Member

    Dynamic Rearfoot position

    I would have to agree that in walking most orthotics dont influence rearfoot position hugely or consistently so. Changes one may see are often related to the MTJ not STJ, if one can draw an artificial anatomical line between them.

    Less bulging of the midfoot medially under the malleolus, less abductory twist, less knee rotation, longer stride etc are the things you do see and are related to MTJ position. Through altering MTJ position can one alter moments in the STJ? Yes. Does altering the MTJ postion change the ability of the 1st MTP to dorsiflex? Yes. I find although orthotics may not change heel eversion one iota it is unsual to have a successful one that does not alter MTJ pronation and this then facilitates the 1st MTP.
    Using the f-Scan when trying to deal with FnHL or windlassy problems very rarely does just using say a 3mm pad under the 2-5 MTPs make any difference but use somthing moulded to the foot that supported the arch and suddenly its all TONS easier. Hang on a minute am I saying ..."lock the MTJ".... ????!!!! Hmmm whats that a stump? you look familiar, I feel the urge to go around you.....

    Running however I find "clinically" or empirically that heel eversion is tied to symptoms and is useful to use as a marker for orthotic effect. My theory is that the MTJ pathology is still occuring but because of running limb varus and increased lateral to medial and posterior to anterior directed force the heel everts much more significantly with it.


    Ramble, ramble, ramble, burble, burble.

    Lawrence Bevan
    Staff Podiatrist
    Gracelands, Memphis Tennessee
    and Area 51
     
  3. Craig - It would be great if there were static markers/tests that could determine (to some extent) the success or otherwise of foot orthoses. I've been using the Hubscher for a while now, and then F-scanning, and find that a substantial improvement in Hubscher does correlate with improved in-shoe gait parameters. I await your results!

    I'm in the process number crunching some research on the reliability of the Hubscher, Max pronation and supination resistance tests. Good sample size, inter and intra groups. Just getting my head around the stats, but initial results show poor to moderate on most tests, max pronation being the least reliable.

    Lawrence - great points, but reduce the coffee intake maybe? 'locking' the MTJ, whatever next? I've lost the key to that one.

    I think our main issue is the fact that I certainly was taught 'Rootian' theory, very much joint position and motion and supplying orthotics to change rearfoot motion / position. However, when qualified I prescribed these orthotics and people got better. The same year we read the 'normal foot' does not 'work in neutral' and now orthotics may not even change rearfoot motion / position. However (and this is where the thread came from...i know craig!) rootian orthotics can work for many people, but were they putting the foot in STJN (probably not then)?, reducing moments across the STJ reducing symptom related moments?, or reducing tension in the medial band of the plantar fascia and reducing 1st ray dorsiflexory moments allowing windlass etc?. I think I'll go for all three, cover my bases and join Lawrence in podiatry area 51.

    regards to all.

    Paul
     
  4. Lawrence Bevan

    Lawrence Bevan Active Member

    Mtj

    I'll get u a new key cut
     
  5. Mtj

    I think it's available at the 'axes obliquity' store. I have looked there myself a while ago but could not find it
     
  6. Paul and Craig:

    I am not that interested in changes in changes in rearfoot position in relaxed bipedal stance, since they don't often change. However, I am very interested in changes in gait function and symptom improvement. Very often the changes with foot orthoses are seen to occur at the midtarsal joint level, which rearfoot measurements won't necessarily show. However, foot orthoses often do change rearfoot motion in gait.

    The treatment goal for my patients receiving foot orthoses are as follows:

    1. Reduce pathological loading forces on injured structural components.

    2. Optimize gait function.

    3. Not cause other pathologies or symptoms in accomplishing goals #1 and #2.

    Nice discussion, Paul.
     
  7. Thanks Kevin

    I'm glad you said that. I often see alterations in rearfoot motion with foot orthoses. Worried it was just me and Lawrence seeing this! Of course it may be the caseloads we are seeing. With your three step treatment goals , would you expect to see a change in rearfoot motion more in a running orthoses prescrition (for example, designed for the type of runner who is maximally pronating but still maintaining an arch, with post tibial tendonitis?).

    Have a good weekend

    Paul
     
    Last edited by a moderator: Feb 25, 2005
  8. Craig Payne

    Craig Payne Moderator

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    We do see rearfoot motion changes in some patients, we don't see them in others ---- what I am saying is that we have shown that there is no prospective correlation with changes in rearfoot motion and symptom changes.
     
  9. Atlas

    Atlas Well-Known Member

    I don't read much research, I just skim the take-home-message...if I am lucky.


    If we are to believe that rearfoot changes don't always occur despite aggressive rearfoot 'correcting' devices, is this measured by getting the subject to stand on the orthotic? Without the heel counter of a shoe holding the heel on the orthotic? Or is the orthotic strapped to the foot?

    Has some research been done with subjects in plastic tranparent shoes?
     
  10. Craig Payne

    Craig Payne Moderator

    Articles:
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    We did it by measuring frontal plane translation of malleoli relative to a reference point on shoe with and without othoses (within subject design - used digital video frames at several ponts in the stance phase) - ie if the horizontal distance between the reference point and lateral malleolus increases and the horizontal distance between the reference point and medial malleolus decreases --> more inverted rearfoot (and vice versa)

    Irene McClay's group that showed some people pronate more in inverted orthoses, used a cluster marker design attached to the calc via small hole in heel counter (she did tell me how much it weakened te heel counter, but can't recall - it was not much)

    Our current work is using running sandals, so we can attach a comprehensive marker set to the bony landmarks -- but that suffers as there is no heel counter... its all about trade offs in this business.
     
    Last edited: Feb 26, 2005
  11. Paul, I like your questions. Keep them coming.

    Rearfoot motion is often difficult to observe clinically since the changes that occur are hidden by the heel counter of the shoe. However, orthoses commonly affect transverse plane knee position, stride length, relative percentage of stance phase that is propulsion, and midtarsal joint motion.

    The more inverted the orthosis, with the more medial heel skive, then the more likely rearfoot changes will occur. I use this type of orthosis prescription for runners with pathology cause by excessive subtalar joint (STJ) pronation moments (e.g. medial tibial stress syndrome) or walkers with pathology caused by excessive STJ pronation moments (e.g. posterior tibial dyfunction). These orthoses very definitely alter the kinematics of the rearfoot and lower extremity during both walking and running.

    However, the orthoses that I make for patients with a condition that may be caused by excessive rearfoot plantarflexion and forefoot dorsiflexion moments (e.g. plantar fasciitis) will often show little change in rearfoot kinematics since I don't necessarily invert or add a medial heel skive to these orthoses.
     
  12. Lawrence:

    Excellent observations. Addition of a 3 mm pad under the 2nd-5th metatarsal heads adds a subtalar joint (STJ) pronation moment which will tend to cause the foot to often have more late midstance pronation. However, if you use the same forefoot pad with a medial heel varus wedge and a medial longitudinal arch pad, the foot shows dramatic increases in stride length, gait stability and foot comfort. But why??

    The medial heel varus wedge and medial longitudinal arch pad add a STJ supination moment in early stance phase to help decelerate STJ pronation which then, during the latter half of stance phase, works with the 2-5 pad ( that causes a STJ pronation moment) to stabilize the rearfoot. Counteropposing moments on the STJ is one of the keys of this type of "padding" therapy which I have been using in my lecture demonstrations for the past 20 years.

    This idea of counteropposing moments has been used by structural engineers for years in stabilizing tall antennaes by placing cables under tension on opposite ends of the antenne, attached to the ground, to create counteropposing moments to create structural stability of the antenna. A rearfoot varus wedge and forefoot valgus wedge accomplish this same mechanical effect on many feet by applying counteropposing moments across the STJ axis.
     
  13. Hi Kevin, thanks again for the reply

    This is the problem I have with the idea that first ray dysfunction / windlass dysfunction is resonsible for all foot related ills ( i know criag may not have been saying this, but sometimes it seemed that way!). I understand that a FnHL can theoretically 'cause pronation'. And sometimes maybe it does....but in cases when there is a 10 degree tibial varum? Would the large degrees (and velocity) of STJ pronation seen in these patients at contact phase be due to a FnHL? In these cases would we expect, and prescribe, to 'improve' rearfoot kinematics? If this patient was a runner, and had MTSS, would we only expect good results if we did improve this rearfoot motion? Although this tibial varum may result in increased tension in the medial band of the plantar fascia etc, could it possible be the initial pronation velocity / tibial loading responsible for symptoms?

    Cheers again

    Paul
     
  14. Craig Payne

    Craig Payne Moderator

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    The way I explain it to students is like this:

    Imagine a foot that has pronated to end range of motion at the STJ with a huge amount of force. There will be bone on bone contact, that will hurt due to the compressive forces. The post tib will have to work hard (--> maybe MTSS, post tib dysfunction).

    You then put an orthotic under the foot and watch them walk --- imagine there is no difference in the way they walk (ie the kinematics have not changed) - they come back 2 weeks later and the symptoms are gone.

    The question then, is why did they get better even when there is no improvement in the pattern of rearfoot motion (ie kinematics) (which is what our research showed)

    What has happened is this - the STJ has still gone to end range of motion and there is bone on bone contact, but the joint surfaces are only just touching each other and there are not the huge compressive forces that were previously hurting ... ie the foot orthoses have altered the kinetics (ie forces). The post tib will not have to work as hard (symptoms their reduce), as the kinetics have changed.

    To get symptom relief, the kinetics (forces, work) have to be altered --- it does not seem to matter if the kinematics (motion, position) are altered or not.

    Motion and position do not damage tissues (..yet the profession is very hung up on this). Forces damage tissues.

    The force to establish the windlass being lowered with foot orthoses is just one measure of what is happening to the forces. Our research has shown that this lowering of that force is probably related to outcomes.
     
  15. Paul:

    I really don't believe that functional hallux limitus (FnHL) is a cause of pronation, but is a result of a multitude of factors, with excessive subtalar joint (STJ) pronation moments being one of them. Other causes of FnHL can include a long first metatarsal, decreased medial longitudinal arch (MLA) height, a short hallux proximal phalanx and a larger radius of curvature of the first metatarsal head in the sagittal plane. By using a wooden model in a couple of demonstrations I performed at the PFOLA meeting in Boston a few months ago, I was able to show just how changes in MLA height can cause FnHL. Pronation and MLA collapse comes first, FnHL comes second, in my opinion.

    Eric Fuller made a good case for the plantar fascia being one of the structures that can resist STJ pronation moments which, in turn, can be used to suggest how STJ pronation moments affect FnHL (Fuller, Eric A: Center of pressure and its theoretical relationship to foot pathology. JAPMA, 89 (6):278-291, 1999; Fuller, Eric A: The windlass mechanism of the foot: A mechanical model to explain pathology. JAPMA, 90:35-46, 2000).

    In Craig Payne's excellent reply, he discusses how he teaches the concept of interosseous compression forces within the sinus tarsi as a method to help in understanding how the posterior tibial may be affected by STJ pronation moments. I very much like Craig's approach. I introduced this concept of interosseous compression forces within the sinus tarsi and how it may affect posterior tibial contractile activity to cause STJ supination in my first paper on STJ rotational equilbrium (Kirby, KA.: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989).

    Tibial varum does not cause a particularly strong STJ pronation moment since large degrees of tibial varum may cause a STJ supination moment. I can think of many other types of structural deformities that will cause more STJ pronation moment than increased tibial varum.
     
  16. Craig Payne

    Craig Payne Moderator

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    I think a lot of people miss that last point. Also a tibial valgum and/or genu valgum provide a supinatory moment to the STJ. How often do you read in the podiatric literature about them pronating the foot.
    If someone has a tibial varum, yes the foot has to pronate to get flat on the ground, but since when has the "motion" of pronation or the "position" of pronated been pathologic - it never has (hence my comment above about the profession being hung up on motion and position. If a foot pronates excessively, it is still winthin the "range of motion" of the posterior tibial tendon - so how does pronation damage the posterior tibial tendon? It will only damage the post tib of the FORCES are high, so the muscle has to work harder. If the forces pronating in a foot in those with tibial varum are low, whats the problem?

    I gotta go - off now to give the 2nd years their first biomech lecture for the semester - its the "half of what we teach you this semseter is wrong, but we don't know which half it is" lecture...
     
    Last edited by a moderator: Mar 1, 2005
  17. In a paper soon to be published in JAPMA, Bart Van Gheluwe, Friso Hagman and I studied the effects of simulated genu valgum and genu varum on a group of normal subjects walking over a force plate and pressure mat with some very interesting results. We calculated that genu valgum does indeed cause a STJ supination moment in late midstance.

    Until podiatry students and podiatrists fully understand the concepts of moments, rotational equilibrium and external and internal forces acting on the foot and lower extremity, motion and position will still be regarded as being the cause of injuries by the podiatry profession. It has been and it will be a long, hard intellectual battle, but we have made significant progress in this regard within the past 15 years. These efforts to keep us more in line with the thought processes and work from the international biomechanics community will allow podiatric biomechanics stay at the forefront of mechanical and surgical treatment of foot and lower extremity mechanically-based pathologies.

    Personally, I'm very optimistic and glad that we aren't still languishing under the influence of vertically balanced foot orthoses, compensations for forefoot deformities, subtalar joint neutral theory and the two-axis model of the midtarsal joint, even though I am sure that many "podiatric biomechanics experts" still teach these concepts. Thanks, Craig, for your research efforts in this regard.
     
  18. Hi Craig and Kevin

    I've lost the thread here I think, I've just read back over previous messages. I don't think we are disagreeing. I was saying that in certain cases i like to see an improvement in rearfoot motion. In cases of a maximally pronated runner, maintaining and arch, with post-tib tendonits, these patients only significantly seem to get better if I see such an improvement. This obviously links in to forces.

    I've quoted it in some of my papers: 'its not pronation that hurts, but the structures stopping the pronation'.....

    Regards

    Paul


    To put my point more concisely, STJ pronation (motion) lowers the arch and increases tension in the medial band of the plantar fascia (force?). This, is itself, can cause problems related to an FnHL. Due to the nature of tissue loading etc, I often see cases where I would expect to see
     
  19. Whoops!

    sorry about the junk after my name on the last bit. Meant to be to another thread!
     
  20. Craig Payne

    Craig Payne Moderator

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    Jumping from a tall building (motion) does not kill you. Hitting the ground (forces) does.
     
  21. Or put another way, it's not the acceleration that causes injury, it's the deceleration.
     
  22. Atlas

    Atlas Well-Known Member

    Forces and motion.

    Another analogy I would throw in, is that motion is the tired old saggy housewife, and force is the new sleek gravity-defying mistress. But lets not forget who would be more reliable at cooking the roast and picking up the kids.


    I have two problems with its 100% force and 0% motion.
    1. How can these 2 phenomena be independent of each-other?
    2. Awareness of pathological motion and the ability to alter it is a powerful clinical tool.


    1. How can these 2 phenomena be independent of each-other? How can the fellow who splatters himself on concrete do so without plummeting from a height. What else can provide such a FORCE?

    What about the analogy of a baseball catcher or cricket wicket-keeper. When catching a ball at speed, the keeper wisely accepts the ball out in front of his body, but finishes the 'catch' behind him. The motion of his hands in the same direction as the ball gradualises the deceleration. How can motion be completely irrelevant here? No motion equals bruised hands.


    2. Awareness of pathological motion and the ability to alter it is a powerful clinical tool.

    Lets take a posterior impingement of the ankle for instance; for example a clinical os trigonum. End-range plantar-flexion is pathological and symptomatic. Restrict that range to short-of-its-limitation, and the patient is happy. (Restrict it for days and perhaps one has an impact on adjacent secondary soft-tissue inflammation if it existed concurrently). Yes a plantar-flexion moment around the ankle could be aggravating, but only at the end of (PF) range. Limit end-range plantar-flexion with an strapping technique, and the plantar-flexion moment provided by kicking a football or kneeling on your heels becomes tolerable.
    Critics may suggest that the strapping is providing a neutralising dorsi-flexion moment, but how then can one extrapolate and suggest that motion is entirely irrelevant?

    What about an unstable ankle? An ankle with a sloppy mobile anterior-drawer? An ankle that is multi-directionally hypermobile is an inevitable accident that will progressively happen. Osteoarthritis in the talo-crural joint is inevitable. Surrounding musculo-tendinous structures are then 'called up' to function in a manner that they were not intended; to remain hyper-tonically overactive to provide some motion check and joint stability. Stop the extraneous motion (albeit with stabilising FORCES), and reduce signs and symptoms.

    Turning your head to do a head check in a car involves everyday movement and presumably everyday forces. But what happens if we sustain the position? Why the signs and symptoms. The forces haven't suddenly become pathological. They haven't increased. The forces have been sustained/prolonged. In terms of motion, this suddenly hasn't become pathological, nor increased; but the limit of motion has been sustained. In this limit of motion, agonists have shortened, antagonists lengthened, some passive tissues have stretched (tensile forces), while others are impinging (compressive forces).


    If I was a post-tib musculotendinous structure, I would not want to be 'connected to' a foot that's motion permits my insertion to drift/drop further and further away. If you want me to jump from a building, give me the 1st floor, not the 6th. In the early part of stance, the navicular drop/drift is lengthening the unit. At the same time it is contracting eccentrically to control/decelerate/oppose this. IMO, low-dye taping has a significant impact (short-term at least) on tib-post dysfunction. The force crowd will suggest that the low-dye taping provides a sufficient force to counter-act this pathology. The motion person may suggest that it keeps the origin and insertion of tib-post closer together. Limit motion = limit length = reducing tensile stress.

    Take motion out of the equation, and you don't get impingement and sprains etc. I could take one of Ali's punches if he was only allowed 20 degrees elbow extension. His force capacity (musculature) would be the same; but motion augments momentum and hence the force to floor me.



    All the force talk makes sense and can be justified. But I have a problem with 100% force and 0% motion as contributing factors to injury. Despite what the latest research suggests, we need health clinicians (especially students) thinking about forces and motion…not just the former.




    Ron.
     
  23. Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on the object and inversely proportoinal to the mass of the object. F = ma.

    Because of this interrelationship of motion and force, then you are correct, Ron, that one can not say that injury is caused only by force and not by motion. Acceleration is the change of velocity over time or for those that have had calculus, acceleration is the first derivative of velocity. Velocity is the change of displacement of an object over time. Therefore, accleleration is the second derivative of displacement. Therefore, force and motion are directly interrelated by using Newton's Second Law of Motion.


    Helpful here is the Principle of Conservation of Linear Momentum. Here we should use the concept of the impulse-momentum theorem where:
    impulse = change in momentum. Impulse of a force is a product of the average force and the time interval during which the force acts: Impulse = F x t.

    Momentum of an object is the product of the object's masss and velocity: Momentum = m x v.

    Using the Principle of Conservation of Linear Momentum, it can be said that the total linear momentum of an isolated system remains constant (i.e. is conserved). Therefore, for the baseball catcher, the average velocity of the decelerating baseball times its mass will equal the average velocity of the catcher's hand and mitt times its mass. The faster the ball is thrown and the greater the mass of the ball, then the more momentum, so that the catcher will need to absorb more momentum during catching the ball due to conservation of momentum.

    I would agree that we should not say that it is 100% force and 0% motion, since force and motion are tightly interrelated. But I would say that clinicians and students need to know about forces, motion, mass, moment of inertia, moments, moment arms, linear and rotational equilibrium, stress, strain, elastic modulus, and all the other basic mechanical concepts that affect the structural components of the human body. However, it is unlikely that all podiatrists or podiatry students will have a firm grasp on these concepts during my lifetime. Because of this, for many years to come, these important topics of biomechanics will be thought of as "advanced concepts" for podiatrists and will not be considered as basic concepts as first year engineering students consider them.
     
  24. Fallacies:

    Applying a linear equation to a number of joints that move in three axes of motion, thereby oversimplifying the issue so it does not consider angular impulse

    Oversimplifying forces that act on the stance foot as an average force that is then applied to the linear equation; ignoring the fact that the swinging limb contributes momentum (constantly changing in a fashion that is unrepresentative by being averaged) to the stance limb.

    Attempting to apply these Newtonian “concepts” to a system that is clearly neither closed nor isolated.

    Current and past methods in empirical Biomechanics (with and without podiatric input) cannot discern statistically significant differences with and without CFO intervention. However, therein lies numerous clinical significances, which makes these practices successful.

    Perhaps in future, as methodologies and apparatus evolve, such clinical success, "may" be empirically explained.

    I for one look forward to such prospects.

    -Kerry
     
  25. davidh

    davidh Podiatry Arena Veteran

    Hi Kerry,
    You missed out diurnal variation as it applies to the human lower limb.

    I have to point out that applying Newtonian concepts to a system that is clearly neither closed nor isolated is not an activity exclusive to podiatriy.

    Newtonian concepts are widely used in bioengineering - when designing replacement joints for example, and by orthopaedic surgeons, when replacing worn joints.
    Regards,
    David :cool:
    David Holland BSc(Hons) Pod Med, MSc(Bioeng).
     
  26. It is true that other professions use this approach during Finite Element Analysis. Currently initial research and testing by companies such as Smith and Nephew use simulators for data pertaining to joint kinematics and durability. Based on trial data presented at academic conferences this is an apparently rigorous process.

    Eventually, as dialogue between patients and practitioners makes its way back to the drawing board (bioengineers), refining the model indirectly makes the model less finite and more real. Which (relating back to the original topic of discussion posted by Dr. Payne) may account for more clinical versus statistical significance. Again this is a product of research methodologies.

    I have noticed less gait "noise" in those with only a knee arthoplasty rather than the hip. Perhaps this may be due to the fact that during stance the knee mainly flexes and extends through the sagittal plane (medio-lateral axis), i.e. mainly one degree of freedom rather than three of the hip.

    While this curent approach with the hip may never return patients back to their previous state (of 100%), postoperatively their quality of life is mostly better….a great thing!

    Data from my last research what suggested (within subject) significant differences between CFO conditions. However statistical differences were not noted after ensemble averaging of data (a common practice in empirical research).
     
  27. Craig Payne

    Craig Payne Moderator

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    Kerry - thanks for the input...
    The approach we are trying to take is to measure using different "models" what actually happens to the patient mechanically and correlate that to outcomes --- not outcomes as a change in the biomechanical parameters, but outcomes in terms of symptom reduction (using validated measures, such as the FHSQ) .... the ultimate aim to to find predictors of outcomes. from the study I mentioned in the first post, changes in the pattern of rearfoot motion was not related to clinical outcomes ---- some things are getting clearer. We have just started recruiting for a couple of RCT's to test what we found.

    Kerry - thanks for those abstracts of a few weeks ago. Also, I will be in Ottawa in November.
     
  28. Kerry, I have found that in my 20 years of teaching podiatrists and podiatry students biomechanical concepts there must be some simplification of concepts so that they can grasp the basics. As they become more knowledgeable, they can more easily understand more complex concepts. In biomechanical modelling, using uniplanar, simplified models are acceptable as long as you understand their inherent limitations.

    Both internal and external forces acting on the stance phase foot need to be considered when determining the forces acting internally within the foot. Of course the swing limb needs to be included if one is interested in the energetics of locomotion. However, if one is interested in something such as the direction and magnitude of moments acting across the subtalar joint axis at any instant in time, the mechanical contributions of the swing phase limb may be ignored as long as the spatial location of the subtalar joint axis is known, the center or pressure is known and the direction, magitude and line of action of the ground reaction force vector is also known.

    Newtonian concepts are still used in physics, engineering and biomechanics, to this day. I agree with David Holland that they are widely used in many fields. I don't understand which of Sir Isaac Newton's concepts you don't like??

    Have you read the papers by Mundermann et al and Williams et al?(1. Mündermann, A, Nigg BM, Humble, RN, Stefanyshyn, DJ: Foot orthotics affect lower extremity kinematics and kinetics during running. Clin Biomechanics, 18(3):254-262, 2003. 2. Williams, D.S., McClay-Davis, I., Baitch, S.P.: Effect of inverted orthoses on lower extremity mechanics in runners. Med. Sci. Sports Exerc. 35:2060-2068, 2003.) These researchers were able to discern statistically significant biomechanical differences with and without custom foot orthoses. As I have been lecturing for years, orthoses affect moments more than motion.
    [/QUOTE]

    I enjoy your input and criticisms, Kerry. You are obviously very knowledgable in biomechanics. I am interested in your research at Ottawa Hospital if you could let us know more about it, it would be greatly appreciated. We are always looking for new lecturers on biomechanics here in the States. Have you published any of your research yet?
     
  29. Ahh, good. I think it is important to acknowledge the inherent limitations of applying linear physical equations to the foot.

    With respect to the two research articles by Mundermann et al. and Williams et al., both discussed kinematic parameters of the whole foot (i.e. one segment models).

    The Kinetic parameters discussed by Mundermann et al. included peak vertical loading rates (whole foot). Significant differences were found up the kinetic chain including the foot.

    Conversely, Williams et al. kinematic found no significant differences in ankle eversion / inversion, however, peak rear foot inversion moments and work were significantly reduced during inverted CFO trials. The methodology used by this paper still analyses the foot as a single segment, due to limitations. is this acceptable? Perhaps for now.

    This is the paradox:
    1.To better understand the foot and ankle, dynamic, rather than static physical measurements are necessary (methodological limitations).
    2.To better understand the both internal and external forces (both are important) that act on the foot and ankle we need to move towards a more fluid model that encompasses more than two segments (a team at Penn State is currently working on that).

    Looking at the GRF with respect to the STJ is acceptable when looking at instances during stance. What methodologies can we use to the question is how does one take several of these instances and put them together to get a better understanding of foot function (normal or pathological).

    If we look at GRF or CoP with respect to the STJ at best we can view the foot a two segment model. Again is this an appropriate approach?

    -Kerry
     
  30. Atlas

    Atlas Well-Known Member

    I will not even dare to enter a debate far beyond my capabilities (advanced kinematics and kinetics).

    Students and young graduates (and maybe a few oldies) have enough trouble with the biomechanics in day-to-day musculo-skeletal medicine. And in view of this, and my feeling that simple basic (albeit slightly flawed) concepts adequately describe what may be wrong and what we as clinicians must do to address it, teaching must remain simple. And teachers should be comfortable with this.


    Even if and when we discover the complex answers, I can't see how this can be re-formatted in a simple teaching version.

    In the ideal world though, yes, lets get the complex correct answers and transfer all of this across to the learners.
     
  31. The prevailing research seems to indicate that moments are affected much more than motion by foot orthoses. Benno Nigg has his "preferred movement pathway" theory that states that the individual will tend to move in a certain movement pattern during gait. Therefore, this is why he feels that motion is relatively unaffected by foot orthoses. However, when I lectured with Benno at the University of Calgary a few years back, he said his knee feels better with foot orthoses so he knows that foot orthoses do work, he just couldn't be certain how they work at the time.

    I believe that one of the reasons that much of the foot orthosis research to date has not shown much difference in motion of the foot is the foot orthoses used were not corrective enough or were not custom foot orthoses. Clinically, if one wants to see a change in kinematics, the foot orthosis must be quite corrective, often with medial heel skives, inverted balancing positions, rigid plate materials. Without these corrections (i.e. vertically balanced foot orthosis made with a semi-flexible material) the foot orthosis will not resist the motions of the foot enough to show a change in kinematics.

    Neil Humble was wise to use such corrective orthoses in the Mundermann et al study and I think that this was one of the main reasons why Mundermann's study showed the changes in kinetics that it did. In addition, in the study by Williams et al, Steve Baitch made Blake inverted orthoses that were used to demonstrate the kinetic changes. The moral of this story is that if you want your research study to show that orthoses change gait kinetics or kinematics, the more corrective the orthosis, the more likely that changes will be seen. In other words, don't use vertically balanced foot orthoses without medial heel skives or without inverted heel cups!

    Kinetics of the rearfoot can be changed without a change in kinematics during both walking and running. If the subtalar joint (STJ) is maximally pronated throughout the midstance phase of gait and the patient wears a foot orthosis that relieves their sinus tarsi pain by decreasing the interosseous compression force within the sinus tarsi, but the orthosis is not corrective enough to supinate the STJ out of the maximally pronated position in midstance, then the kinematics of the rearfoot during midstance will not likely change (Kirby, KA.: Rotational equilibrium across the subtalar joint axis. JAPMA, 79: 1-14, 1989). This is a fact that few biomechanics researchers mention in their papers on the kinetic effects of foot orthoses.

    I agree. However, quasi-static models may be used quite effectively to model the internal forces within the foot and lower extremity. In addition, finite element analysis can be quite effective at determining internal forces. Simon Bartold's research group at Asics currently is using such a model that has defined nearly all the ligaments, muscles and bones of the foot and lower extremity as a way to test mechanical effects on the foot with different sport shoe designs. Dynamics is nice, but statics can tell you a whole lot also.

    I am currently working with Steve Piazza and Greg Lewis from Penn State on STJ axis location in cadavers. They have been trying to determine STJ axis location mathematically by optimization techniques for calcaneal to tibial motion. I recommended some changes in technique that we applied to cadavers last fall when I went to Penn State to help them with their research. Greg is presenting our work on STJ axis location at the GCMAS meeting in Portland, Oregon in a few weeks which I will be attending. In addition, Neil Sharkey is still using his Dynamic Gait Simulator at Penn State to research kinematics and kinetics of gait in cadaver specimens that are "walked" using servomotors attached to the tendons of the foot. Neil and I will be presenting together this June at the WPC at Disneyland Hotel and I hope to collaborate with their group in the future.

    Quasi-static modelling is an acceptable method of taking "snap-shots" of each instance of gait to determine the approximate STJ moments that are occuring at any instant in gait. This can be used to give the clinician a better idea of how STJ moments are affected by pathologies such as PT dysfunction or metatarsus adductus and how treatments such as medial heel skive or Blake inverted orthoses affect STJ moments. That is not to say that gait dynamics is not important, but for the clinician, I have found that the static model is a much better starting point to allow them to progress intellectually toward the greater complexities of gait dynamics.

    The more segments, the greater the complexity. I think a better question is how much complexity do students and clinicians need to optimize their understanding of foot and lower extremity function. I think that this will depend greatly on their previous comfort and knowledge with mathematics and physics.

    Chris Nester and Andrew Findlow will be introducing a new model for the midtarsal joint in a new article to be published soon in JAPMA. I have read the article and discussed this model quite a bit with Chris and I really like the direction that Chris and coworkers are headed with the midtarsal joint. I think that having more segments is great for those clinicians who have the capacity to "soak it all in". Unfortunately, in my 20 years of teaching, I have found that most clinicians either don't want to spend the time learning biomechanics or don't have enough basic biomechanics knowledge to understand the complexities of foot and lower extremity biomechanics.

    By the way, Kerry, I enjoyed your article and please tell Gordon Robertson that I greatly enjoyed his book "Introduction to Biomechanics for Human Motion Analysis" and have recommended it to many of my students and clinician-students to increase their knowledge of biomechanics.
     
  32. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    The research that started this thread has been published:

    Relationship Between Positive Clinical Outcomes of Foot Orthotic Treatment and Changes in Rearfoot Kinematics
    Gerard V. Zammit and Craig B. Payne
    J Am Podiatr Med Assoc 97(3): 207–212, 2007
     
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