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Sensory effects of foot orthoses

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Craig Payne, Feb 25, 2005.

  1. Craig Payne

    Craig Payne Moderator


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    Do foot orthoses exert there effects via altering sensory input signal?
    Sorry about the table, but I just can't seem to get it formated right.
  2. Craig Payne

    Craig Payne Moderator

    I should add a tribute to those brave students who trusted me when I said standing on a block of ice and immersed in ice water would not hurt ..... much ;)


    We only had 2 adverse reactions :rolleyes:
    Last edited by a moderator: Feb 28, 2005
  3. Bruce Williams

    Bruce Williams Well-Known Member

    Sensory effects of Foot orthotics

    Nice job as always. I would like to ask a question re: sensory vs. proprioceptive effects. I would assume that they are related, and not mutually exclusive. Though the sensory patterns may be decreased, as in you study, what effect, if any, do you think this had directly on the proprioceptive / positional sense of the patients feet/ limbs?
    I would imagine that this would be the next query for you to tackle, if past studies are any indication. Always best to do what you can to seperate out the fact from fiction! ;-)
    Keep up the good work!
    Bruce Williams
  4. Hylton Menz

    Hylton Menz Guest

    Do foot orthoses exert their effects via altering sensory input signal?


    Having used the ice immersion technique previously (see paper in Gait & Posture), I'd be interested to see how different the first few steps were to subsequent steps, as we found 'thawing out' to be a major issue. In our study, we were only able to collect three two-step gait initiation trials before the effect appeared to be wearing off. In addition, we also observed (but did not measure) an increase in base and angle of gait when the feet were numb, which might have created some difficulties visualising the frontal plane measurements.

    My guess on this one is that tactile sensory input probably is important in relation to balance, gait and postural control (as well as response to foot orthoses), but only in those with some degree of sensory deficit. There's some good emerging evidence that you can augment plantar tactile input to produce beneficial changes in postural control, particularly in older people (see paper by Brian Maki).


  5. Craig Payne

    Craig Payne Moderator

    We were aware that this could be an issue. We measured VPT, then immersed foot in ice --- as soon as 10 mins was up, they then were "rushed" into footwear and on to the treadmill for testing (to allow a minimal amount of time for acclimation before data collection) - then immediatly after data collection, off came the footwear and VPT was checked then -- mean VPT before ice was 3.3 and after testing, in which some thawing would have happened, it was 6.7 (p<0.001). As thawing would have taken place, the difference would have been greater when testing was taking place. We decided not to test VPT at end of ice (before testing) as the time taken to do this would have allowed an even greater thaw to occur.
    I do not recall noticing this happening at the time. We did not measure it, BUT, it will be easy to measure from the data we got.... Gerard got a spare hour next week?

    <added> I notice in your paper that you iced both feet for 30mins - we only did the one foot for 10mins (we weren't as mean as you :p) - your subjects probably had a much higher level of 'anaethesia' - we just wanted a reduced level of sensory input... - this may account for the wider base of gait differences </added>
    Last edited by a moderator: Feb 28, 2005
  6. Craig Payne

    Craig Payne Moderator

    Bruce asked:
    Hylton mentioned:
    ...on same track here.

    There is no doubt about the need for and contribution of plantar sensory input to balance - we were just testing if orthoses still had the same mechanical effect if you altered sensory input levels (they didn't) -- foot orthoses do improve balance, but not sure what that has to do with reducing patient's symptoms.

    I like to consider plantar sensory input to be a very different beast to proprioception (which is all about joint position sense) ... I know many make claims that foot orthoses may work via proprioception (I wonder if they know what the word means :rolleyes: ), but I need to be convinced how they would do that :confused: How does changing a joint's position with foot orthoses, improve or change the proprioceptive signal from that joint :confused: - to me the signal will be the same, except the joint will be in a different position - how will that lead to an improvement in symptoms :confused: Foot orthoses may provide more signals that the CNS can combine with proprioceptive signals and other inputs ---- this may be how foot orthoses improve balance ---- but as we showed above there are no differences in the mechanical function of the device, that affect the patients symptoms. How would an improvement in proprioception improve patient symptoms (unless they are balance related :confused: )

    I was a huge fan of the potential of these possible sensory or neuromechanical functions of foot orthoses. The above is the 3rd study we have done and no effects have been found (the first used Pedar and subjects function measured with and without foot orthoses before and after post tib nerve blocks --> no differences; the second was an RCT using rigid insoles vs soft insoles in soft shoes (aka Robbins & Gouw et al stuff) -- no differences in function at 4 weeks).
  7. Bruce Williams

    Bruce Williams Well-Known Member


    Thanks for the response. Re: your "patients" for these trials/studies. I think yoiu said they were students. Perhaps they are so young and good at compensation, and have few if any mechanical problems in the feet etc., that they don't or won't show too many changes. I don't really know.
    I'm not challenging your studies or results by any means! Just thinking out loud.
    Re: improvements in balance related to mechanical function. I do have experience in that realm, though not in a study related format as do you. Most of my patients have sever assymetries before hand in their foot function and need for compensations to correct/per se for these balance issues. I've never thought to ask any of them to come back for a PT block to see if they continue to function so well w/ their devices after they've aclimated. Maybe some day.
    Re: proprioception, as you say, " Foot orthoses may provide more signals that the CNS can combine with proprioceptive signals and other inputs ---- this may be how foot orthoses improve balance ". I think Howard Dananberg has commented that the CNS or a certain pathway can only carry one type of signal at a time, i.e proprioceptive, or pain. Not fully crediting Eric Fuller here, but Eric's contention is that if there is positional pain, I like to refer to it as interference of sagittal plane motion, that the foot will react to this. IN other words, if there is no restriction in forward motion or mechanical delay in the process, then the proprioceptive signal is not interrupted by a painful signal that something mechanical is wrong. This, I assume would directly aid in balance. My opinion only.
    Thanks Craig. Keep up the good work and say hello to your lovely wife for me!
    Bruce Williams
  8. Craig Payne

    Craig Payne Moderator

    We used the Foot Posture Index (FPI) as a screening tool - all had an FPI >5, meaning that all at least had a mildly pronated foot, meaning that if they had mechanical symptoms they would have had orthoses. Yes, they were young (mean age 21 ish), so they would have been better at adapting.

    At the end of the day, the question was "Do you have to feel a foot orthoses to respond mechanically to it?" and the answer was no.
    Last edited: Mar 1, 2005
  9. I believe that improving balance and improving patient's symptoms may be two unrelated mechanical effects of foot orthoses. In other words, certain orthosis designs may greatly improve balance but may also cause sufficient stress in a structural component of the foot and/or lower extremity to cause injury over time. In addition, orthosis designs that improve symptoms the best, may cause a tendency to cause patients to lose their balance more frequently. There are probably different design characteristics of orthoses that affect each of these treatment goals. In other words, the orthosis that is the best at both improving balance and improving symptoms may not exist.

    I agree, Craig. Joint proprioception is one sensory input and skin sensation is another sensory input into our central processing unit we call the central nervous system. I believe that foot orthoses affect both of these but that the mechanical factor is the strongest effect. As I said earlier, optimum balance and optimum symptom improvement may involve two very different orthosis design strategies.

    A change in kinetic function of the foot and lower extremity, I believe, will be shown to be the primary factor for the symptom reduction effect of foot orthoses.
  10. Arztin

    Arztin Guest

    Sensory/proprioceptive stimulation implemented in..

    I have attended the World Congress and Trade Show in Leipzig, Germany
    twice. The first time I attended, I learned by meeting with the inventor,
    Lothar Jahrling about his propriozeption Einlagen whilst it was still in its
    infancy. This was at the 2002 congress. At the 2004, he has come up
    with many different case reports based on the use of this innovative
    orthotic in such case as Cerebral palsy and habitual toe walking. After
    his discussion, I approached him & of course he remembered me from the
    1st encounter. At that time, his work shops were only done in Germany.
    When I asked him if he plans to expand this to America since our first meet-
    ing, he said that in 2 years time he has developed a heart condition and
    that he could not afford the stress associated with too much traveling.
    Perhaps someone out there especially those associated with orthotic
    labs can find out more about this particular fabrication process based
    on the CAD/CAM system and sign up for and participate in the work-
    shops. Labs that have international relationships abroad would probably
    be in the best position to learn more about this technique and bring it
    back to Canada and/or America. It is time to give the orthotic concept
    a complete overhaul espcially since more and more insurance companies
    seem to be paying less and less for them (in some cases not at all).
    Proprioceptive stimulation has been a big deal in Germany and this is
    implemented not only in their orthotics but also in bracing devices. It
    should be a big deal to us podiatrists in North America as well.
  11. Craig Payne

    Craig Payne Moderator

    I think they need to look up a dictionary as to what propioception is before they make the claims that they do. What they are doing is NOT proprioceptive - its is something else (probably stimulus of some primitive reflexes).
    Why? We just showed that the mechanical effect of foot orthoses (ie those related to symptoms) are NOT mediated by sensory input.
    What they are doing in CP and similar conditions has been well documented in the literature and is widely used in clinical practice and is NOT related to the mechanical effects we see with the functional foot orthoses used for biomechanical symptoms.
  12. Hylton Menz

    Hylton Menz Guest

    Craig said:

    I don't think you can write off the whole concept just yet, Craig, as the study was fairly small (n=13), and, in the words of Altman and Bland, "absence of evidence is not evidence of absence" (see BMJ paper). That is, it is still possible that there is an effect but you didn't find it as the study may have been underpowered.

    Having said that, I agree with your concerns that we may be jumping on the neurophysiological bandwagon in relation to foot orthoses a little too quickly. There's still a long, long way to go before we understand how tactile mechanoreceptors contribute to gait patterns, let alone how their function can be modified in a targeted manner with foot orthoses.


  13. Arztin

    Arztin Guest

    The senosory study

    I seem to have (as one former fellow student at NYCPM once said)
    touched a dendrite regarding my invitation to studying propriocep-
    tion in greater detail. Silly me. I was only trying to get us ALL
    to be better podiatrists for our patients with emphasis on ALL
    aspects of biomechanics not just the mechanics of the device.
    Many moons ago, I intended the American Association of Pod-
    itric Sports Medicine in Scottsdale, AZ. There was this one
    speaker who said that everytime he had a patient with shin splints
    who was treated with an orthotic with a forefoot extension and
    a crest pad-like elevation in this extension, the patient's shin
    splints would disappear. He never understood why. But that
    it just seemed to work. It would be years later and thousands
    of miles beyond the Atlantic before I would understand. He was
    simply stimulating the receptors of the flexor tendons in the
    plantar sulci of the toes to relax so that the extensor tendons
    do not have to work as hard. That's proprioception. It's
    basic neurological physiology with regards to the reflex arc.
    Anyone remembers that. Sorry for creating any misunder-
  14. Arztin:

    Since shin splints can include many different diagnoses, I would think it would be difficult to understand how a crest pad worked for "shin splints" since we don't know if "shin splints" means anterior compartment or posterior-medial compartment muscle strain, chronic exertional compartment syndrome, medial tibial stress syndrome, peroneal muscle strain or tibial or fibular stress fracture. In addition, just because a crest pad worked, there may be many reasons why it worked. I don't understand how a crest pad could "stimulate the receptors of the flexor tendons in the plantar sulci of the toes to relax so that the extensor tendons do not have to work as hard"?? Do we really know that the flexor tendons in the digits have sensory organs within them? Do we also know that these supposed sensory organs within the flexor tendon with the plantar sulcus area of the digits connect via afferent pathways to a reflex arc that sends efferent neural signals to the anterior muscle group, or is this just speculation??
  15. Craig Payne

    Craig Payne Moderator

    Thats NOT proprioception!! - all the texts I have on my desk define proprioception as something like "the ability to sense ones own body position" - what you are talking about a possible different neurophysiological response.

    BTW - the mechanism you are talking about is flawed. How does stimulatng the "receptors of the flexor tendons in the plantar sulci of the toes to relax so that the extensor tendons do not have to work as hard" actually work? - the muscles are not even working at the same time during the gait cycle!
  16. Arztin

    Arztin Guest

    ...as SOMETHING like? Let's just agree that more attention needs to be
    paid to this phenomenon and leave it at that. By the way, according
    the Stedman's Medical Dictionary 24th edition, "proprioceptive-capable
    of receiving stimuli ORIGINATING in muscles, tendons, and other inter-
    nal tissues."
    Incidentally, two great speakers at this past No-Nonsense Seminar
    held annually in Ohio discussed this topic and its relative importance:
    Dr. Allan Jacobs and Dr. John Beck (a very podiatrist friendly orthope-
    dic surgeon). Wake up guys. Schnell, schnell.

  17. achilles

    achilles Active Member

    "He was simply stimulating the receptors of the flexor tendons in the
    plantar sulci of the toes to relax so that the extensor tendons
    do not have to work as hard. That's proprioception."

    I am sorry but this is not propriception, but in the case of someone who has an Upper motor lesion, there is the presence of a gross motor reflex responses, particularly in this case, Duncan's reflexes.
    The use of tone inhibition by application of pressure, or its removal has been in use fro some time.
    In the individual with no neurological impairment, this would certainly not be the case, as tone inhibition is neither required or could be initiated.
    This has nothing to do with proprioception.
  18. Charlie Baycroft

    Charlie Baycroft Active Member


    Proprioception is a term used to descripe kineasthetic or position sense. It is an unconscious, reflex process by which movement is controlled or co-ordinated. Proprioception is medicated by changes in the patterns of stimulation of sensory neural end organs called Mechanoreceptors. Mechanoreceptors are widely distributed throughout soft tissues. The best known effect of proprioceptive activity is balance but it also effects function in many other ways by altering the firing patterns of muscles.
    We should not forget that all movement of parts of the body is under the control of muscles, including any kinematic effects that we attribute to FO's are probably also the result of changed motor patterns, which are likely the result of alteration of proprioceptive reflexes. Of course, this does not pertain to the results found by studying cadaveric specimens (who has seen a dead man walking?)
    Cooling the surface of the feet by immersion or icing does not necessarily anaesthetize the mechanoreceptors, especially not those in the deeper tissues, so the experiments referred to do not rule out alterations of neurosensory input as the mechanism of effect of the devices.
    The deeper we go, the deeper we get, and we might eventually discover the precise underlying "effector" of FO therapy. On the other hand, we might just discover that "we don't know" or even that "all people are different".
    Thanks are due people like Craig who ask the questions and look for the answers and in so doing stimulate the rest of us to wonder if we really know what's going on.
    Pain is mediated by nociceptor nerve endings. Relief of pain means that a force acting on a sprecific area of tissue is either reduced or moved to fall on another bit of tissue. Pain relief is not synonymous with improved foot and leg function!
    We need to think of indicators of function in assessing the total effects of FO's biomechanical, sensorimotor, and force related. Function of the body is the sum of all it's resources and parts and proprioceptive function is a pervasive factor worthy of more consideration.
    Charlie Baycroft
  19. chazcheh

    chazcheh Member

    Response to Charlie Baycroft

    Well said Charlie

    I am extremely interested in this area not only because I am looking for answers but I am actually trying to validate my way of practice which seems to work.

    I understand there is a company - Foot Levelers that focuses on this whole notion of proprioception, motor response and the whole CNS. The studies I found were all conducted internally.
    I had an allied professional ask me about this issue as he was focusing his PHD on the neurological effects on muscles and joints and was really interested and convinced that proprioceptive orthotics could be the key.

  20. admin

    admin Administrator Staff Member

    They don't work:
    Proprioceptive insoles and posture
  21. At the risk of getting more heat and warnings of "bad Karma" from DaFlip :mad: , I would have to agree with you, Craig, that proprioceptive insoles seem to be just another way for the uneducated, unsophisticated and/or unethical clinician to sell a useless product to the unsuspecting public.
  22. chazcheh

    chazcheh Member


    I don't know if I have missed anything but is there any significant research for or against this issue??

    If so please sned me links.
  23. Craig Payne

    Craig Payne Moderator

    Did you read the first message of this thread?
    Also the research linked to above:
    Proprioceptive insoles and posture

    I can not understand how foot orthoses affect proprioception, when all they do is alter pressure on the plantar mechanoreceptors - that exteroception and NOT proprioception.
  24. Proprioceptice / sensory feedback insoles

    Several questions occur
    The studies done by Craig (keep at it BTW some really interesting data there) were carried out on students (poor frostbitten sods!) who were presumably non pathological.

    I wonder if the results would have varied if the study had been carried out on people with musculoskeletal complaints secondary to antalgic / altered gait secondary to superficial planter pressure increases / abberrations? How many of the abnormal gait patterns we see in, for example, patients over 50 are due to muscle sequence / tension alterations, concious or otherwise, secondary to altered planter sensation?
    What i am trying, very inarticulatly, to ask is does proving that a "healthy" gait is not altered by changing sensation prove that a pathological gait would behave the same way?

    What would be the changes in gait, if any, caused by the covering materials we all use every day? Will a cover like Maxacaine or to a lesser extent neophrene, which drastically reduces skin torsion and friction against the ground alter the function of the orthotic?

    If there is an mechanism of superficial feedback, or exteroception, would it be based on direct pressure, friction, torsion, shearing or a combination?


    "searching in the dark for a truth one feels but cannot express"
  25. Craig Payne

    Craig Payne Moderator

    Think about it intuitivly ... if a foot orthoses worked via sensory, proprioceptive, or exteroceptive mechanisms then it must induce a change in foot posture by stimulating a muscular response to change foot function or posture ... surely increasing muscular effort and increasing energy expenditure is a bad thing?

    What if the pronated foot is corrected by a "stimulus" resulting in an eariler and more powerful contraction of the post tib muscle and what if the patient actually already has post tib dysfunction .... its nonsensical :rolleyes:
  26. Lawrence Bevan

    Lawrence Bevan Active Member

    Finally given in to temptation to post a message again. This I have found usually kills a discussion in its tracks! :D

    Doug Richie recently published a nice paper in Podiatry Today on Orthoses and Ankle Instability that touched on these issues. Well worth a read - its free!

    Orthoses have to have some neurologically mediated effect, the sole of the foot is so sensitive and plantar pressure feedback to the CNS is important to overall postural "control". No?

    Am I right in thinking the discussion is 3 fold.

    1 Do orthotics "work" - i.e. relieve symptoms and change gait - via a mechanical, neurological effect or both?

    2 What is the mechanism of any neurological effect and what label would it come under?

    3 What is the extent of any neurological effect and is something that we need to concern ourselfs about ?

    BTW I thought "proprioception" was the ability for the CNS to detect joint position not "body" position. Control of body position is a combination of a number of factors e.g. detecting joint positions, muscle reaction time, muscle strength etc
  27. David Smith

    David Smith Well-Known Member


    Oh dear! I'm probably gonna get roasted but---

    Your results show that by the method you used that there were no changes in the parameters you measured.

    Were there any observed changes in overall gait style? I find it difficult to believe the a person with numb frozen feet walks in the same manner as the same person without frozen feet. (I know from personal experience after many a long dive in the North sea in winter I walked like a duck until my feet thawed) If their gait style changes I would expect the kinematics of the rearfoot to change.

    With the greatest of respect, is the method reliable? Quantitative kinematic data obtained from recording by a single view 2D video should, in my view, be considered with caution.

    Respectfully Dave Smith
  28. I agree with many of the recent comments in this thread.

    Research has demonstrated that stimulation of H reflexes through both mechanical and electric stimulii has a phase of gait dependent effect on muscle activity patterns. Thus it is theoretically plausible that foot orthoses could have a sensory (prefer this term to proprioception) effect, providing they give sufficient stimulii. The problem is that we may not as yet, exploited the designs of orthoses which are capable of producing these effects. Time to start thinking outside of the box! For example, why not use an "active" (patent pending SOS biomechanics- no B.S. BTW) foot orthoses which provides electronic stimulus that target the sural nerve H reflex? Perhaps time to review our definition of foot orthoses?

    Craigs research demonstrates that in these individuals the methodology employed did not produce, or was not capable of detecting, any changes in variables measured.

    Craigs point re: increased muscle activity and energy expenditure is interesting, in a paper I read a long time ago the authors demonstrated an increase in efficiency in patients with flat foot when fitted with orthoses . They hypothesised that the orthoses reduced the need for supinator muscle activity. What if the orthoses increased soleus activity but decreased tib post activity?

    Lots of questions surround this interesting topic.
    Last edited: Dec 13, 2006
  29. Craig Payne

    Craig Payne Moderator

    I think I said that above (this is an old thread). There is no doubt about the importance of the plantar surface of the foot as a 'sensory organ' for gait and balance.
    There is only one way for orthotics to work at reliving symptoms - its has to be mechanical and it has to be a kinetic response --- otherwise how do the stress in the damaged tissues get reduced to a level low enough? Perhaps fans of the "proprioceptive" approach could explain how "changing proprioception" actually reduces stress in the tissues?
    If foot orthoses were to have any sort of neurological effect, it would be by altering pressure on the plantar mechanoreceptors, that the CNS then uses as an additional input before deciding on a particular output of changed (probably increased) muscle actvity (assuming foot orthoses actually do this)
    What we showed in the above study was that there was no change in frontal plane motion of the rearfoot when sensory input levels were altered --- ie no "neurological" effect.
    Thats my point - those that jump on the "orthoses work by proprioception" bandwagon because its the current hot sexy topic, need to go back to square one and look up the dictionary.
    The feet weren't numb - they where cooled (in version to be published we measured vibration perception to show level of altered sensory perception. Numb frozen feet would be ssssoooooo artificial.
    The reason we have not published this yet is that we have a paper coming up next issue of JAPMA on the technique used (it was incredibly reliable), so the bumping of this thread reminded me we need to get on with this. As it was repeated measures (even though only 2D), less caution is needed.
    Agree totally - I said in abstract "This study has shown that the alteration of sensory input by the methods used here (sandpaper covered foot orthoses and ice conditions) did not result in differences in foot function based on the parameters measured here (frontal plane changes in malleolus position). " - that does not rule out other effects.

    I have seen the work on the H-reflex, but as you said:
    We genuinely set out to expecting to show the opposite of what we found. I really thought we would find a difference. I am no longer a big a fan of sensory/neurological approaches that I used to be.
  30. DaVinci

    DaVinci Well-Known Member

    That a very important point that I had to read a couple of times to grasp. It does make sense.
  31. Agreed. As Kevin stated in a previous thread these kinetic responses can be attributed to direct mechanical effects of the orthoses, or through CNS mediated effects. This is the bone here, what is direct and what is indirect? Maybe one day we will understand, differentiate and control these, but ultimately patient outcome is all that counts.
  32. I believe that there two distinct types of mechanisms that may cause foot orthoses to change the kinematics and kinetics of gait.

    Here are some definitions of those two mechanisms:

    1. Direct mechanical effect: The kinetic and/or kinematic effect from a foot orthosis that can be explained by the alterations in the temporal patterns, locations and magnitudes of orthosis reaction forces acting across the joint axes of the foot and lower extremity.

    2. Central nervous system mediated effect: The kinetic and/or kinematic effect from a foot orthosis that can not be explained by a direct mechanical effect and must therefore be occurring due to alterations in central nervous system control of the temporal patterns, magnitude, and recruitment pattern of contractile activitiy of the foot and lower extremity muscles.

    Here is a good example of the very different effects that even a simple pad can have in causing both a direct mechanical effect and a CNS mediated effect. Take a subject and have them walk with increasingly larger thicknesses of adhesive felt pads plantar to the first metatarsal head. Initially, when the pad is thin, the patient may be more supinated during gait due to the direct mechanical effect of the increased STJ supination moment from the sub 1st MPJ pad. However, it may be noticed that as the pad is increased in thickness, instead of the patient's foot being increasingly more supinated, the patient may undergo greater amounts of late midstance pronation. A direct mechanical effect would predict that the increased STJ supination moment from the increasing thickness of 1st MPJ pad would cause increased STJ supination during gait. However, since increased STJ pronation was noticed to instead occur in late midstance, then the question that should be asked is why did the late midstance pronation occur? I believe this effect (that I have been noticing over the past 20+ years) is due to a CNS mediated effect where the CNS detects lateral instability (i.e. increased magnitudes of STJ supination moments) during late midstance and propulsion due to the increasing 1st MPJ pad thickness and, as a result, the CNS will increase peroneal contractile activity during these phases and thereby will cause late midstance pronation. [The decrease in stride length and ankle joint plantarflexion during propulsion that is also noticed during gait when this 1st MPJ padding maneuver is performed are also likely CNS mediated effects.]

    It is very important that both clinicians and researchers alike understand the differences between these very real and important orthosis mechanisms if we are to further our knowledge of the biomechanical effects of foot orthoses on the human locomotor apparatus.
    Last edited: Dec 14, 2006
  33. Charlie Baycroft

    Charlie Baycroft Active Member

    Craig, maybe you are missing the connection between kinetic effects, changes in the tension in various tissues as a result of altered moments of force, changes in mechanoreceptor stimulation (Golgi apparatus and muscle spindle), altered input into the CNS and consequntly altered efferent stimuli to muscles. So if by this mechanism movement is seen to be changed is the mechanism mechanical, neuromotor or a bit of both?
    One of the problems with discussions about orthotics is that they forget that the feet are a part of the lower extremity (T4 to the floor) and that a living human body (as opposed to cadaver specimens) is not a passive mechanical system.
    Orthoses alter the surface under the foot and this stimulates an adaptive response in the wearer's body. This adaptive response is likely to be neuromotor even if the result appears to be a "mechanical" change.
    Reliance on a mechanical model to explain how the body adapts and regulates itself to environmental changes has been abandoned in most fields of medical science years ago but for some curious reason it persists in relation to Podiatry and foot orthoses.
    There is ample evidence that foot orthoses create adaptive changes in Muscle function (EMG) and postural stability but people persist in trying to explain these findings biomechanically instead of admitting that they are complex neuromotor adaptions that are largely beyond our understanding and technical ability to fully appreciate.
    I think that the late Merton Root would probably be one of the first people to say "c'mon guys let's stop trying to unlock the mystery of how foot orthoses effect the function of the lower extremity with a "biomechanical key" that does not fit the lock".
    Functional adaptation of the musculoskeletal system is a complex and possibly very individual process, which we do not fully understand. Foot orthoses have a definite and potentially very important role in this because they alter the primary physical interface between the body and its environment. Let's get on with trying to better understand what is really going on instead of trying to beat all observations into the same mold with the invalid hammer of biomechanical theory.
    Comfort is something that people experience as a consequence of efficient function but it is very hard to quantify and study. Benno Nigg has demonstrated an assosciation between comfort and orthotic efficacy. Should we not have some more studies on orthoses and comfort? At least if they are comfortable people will wear them.
    Postural stability is a primary function of the lower extremity as are support and locomotion. Foot orthoses can be fitted and adjusted to improve postural stability but no studies have been done on this. Rather we have studies using devices that are prescribed to alter kinematics (even though we know they do not alter kinematcs) and assess their effects on postural stability. To me that is kind of like doing a study using hearing aids to assess their effects on vision.
    I am always meeting people who have sore feet and legs but are not getting orthoses because the mechanical model says their feet are not bad enough. When you fit them with simple comfortable and relatively inexpensive customized devices, their pains disappear, their postural stability improves and they feel better. Custom fitted foot orthoses (as opposed to hard compression formed insoles) are the easiest and most effective way to improve lower extremity function, comfort and mobility but they are tragiacally underutilized because of the confusing jargon of the prevailing biomechanical hypothesis and model that people feel has to be used to prescribe them.
    It's about to be a new year. How about opening our minds to some new thinking and possibilities for better understanding the functional effects of foot orthoses. People could start by reading Panjabi's papers on spinal stability and the neutral zone hypothesis and considering how to relate this to the foot and lower extremity.
    Merry Christmas and a wonderful New Year to all.
    Charlie Baycroft
    Last edited: Dec 21, 2008

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