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Foot Orthotic Prescriptions

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Trevor Prior, Oct 3, 2013.

  1. Trevor Prior

    Trevor Prior Active Member


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    I am sure you have had discussions along these lines before but I am intrigued to know people's current thoughts so I would like to pose a hypothetical question/s if you would indulge me.

    There are two patients who are identical in every way (I know highly unlikely but I did say indulge me) except for the degree of tibial varum - one has 5 degrees, the other 10. In relaxed standing, the heel is perpendicular to the supporting surface. The foot posture index (accepting it does not account for tibial position per se) , in this instance is 2 due to the talar head and fibula malleolus - just to give a broad outline as there are no other significant findings (i.e. forefoot to rearfoot fine, no inflexibility etc.).

    We will assume patient A has the 5 degree varum and patient B the 10 degree varum.

    So the questions:

    1. Which of these patients is more pronated (A or B)?
    2. What is the base line from which this decision is made?
    3. If the patients had plantar fasciitis, what orthotic would you prescribe?
    4. If they had MTSS what would you prescribe - would it be any different?

    I know this is simplistic and I have not given you any dynamic data. If you wish to apply some dynamic data and there would be observations that would affect your prescription, then detail these but apply the same criteria to both patients such that the only difference is the tibial varum.

    Thank you for your indulgence in advance.

    Trevor
     
  2. 1. it does not really matter

    2. see above

    3. look for the reason why they have too much load on the Plantar fascia and design a treatment program to reduce said loads and to aid healing of tissue

    4. see above

    I think it is a mistake to work from measurements 1st then Diagnosis

    Diagnosis 1st then look at the variables as a whole , it some an Tibial Varum will be important other not so much

    Not what you were looking for I guess
     
  3. Trevor Prior

    Trevor Prior Active Member

    The measures were simply to give an idea of the difference rather than an absolute. For all the criticisms of assessment criteria, I would hope that the picture painted at least gives the majority a feel for what this foot type would like in clinic.

    So, bearing in mind in this hypothetical case, there were no other significant factors, what would you be looking for to explain the increased load to the structures?

    Perhaps you could give 2-3 examples and then what you would do for each?

    Trevor
     
  4. Trev, I'll try to indulge you:

    1 and 2> Depends on our point of reference. If the reference is a bisection of the tibia then the patient with the higher tibial varum has a reafoot which is everted by a greater number of degrees to the tibia in static stance; if the reference is the ground then both heels are everted by the same amount. Does it matter?

    3> The literature suggests that plantar fasciitis is associated with increased tensile and compressive forces acting most commonly at the attachment of the plantar fascia at the medial tubercle of the calcaneus, thus the device should attempt to reduce compression at the heel through the use of compliant materials and to reduce the tensile loading of the plantar fascia. There are a number of ways to achieve this which may be clinically efficacious; in our article I termed these "positive orthoses solution sets" (Kirby KA, Spooner SK, Scherer PR, Schuberth JM: Foot Orthoses. Foot & Ankle Specialist 5: 334, 2012). These positive solutions may include some or all of the following design features: a heel lift which should help to lower the external forefoot dorsiflexion moment, some form of rearfoot varus posting which should increase the external supination moment about the subtalar joint axis, a soft spot in the heel cup, a shell modification to lower direct pressure on the medial band of the fascia such as a plantar fascial groove, a shell modification which reduces the external dorsiflexion moment acting on the first metatarsal such as increased medial addition on positive cast, first ray cut-out, increased shell compliance beneath the shaft of the metatarsal and some form of forefoot extension that shifts the centre of pressure laterally and reduces hallux dorsiflexion stiffness, for example a reverse Mortons extension, Kinetic wedge. I may have missed some modifications, but I got to get back to patients.

    4> MTSS stress syndrome is thought to occur in response to bending of the tibia under loading- I'll let Kevin chime in here as he has written extensively on it- suffice for now, to say the device will be different.

    Edit: I've attached a .pdf of the paper I referred to.
     

    Attached Files:

  5. Trevor Prior

    Trevor Prior Active Member

    Apologies if this comes through twice but I think I may have hit the wrong button first time.

    Simon

    Indulge you did, many thanks. Do you have a preference of reference point or do you consider both?

    Your answer regarding plantar fasciitis was extremely well written and presented and would be difficult to better – more importantly, something others can follow and build upon, particularly when newer to the profession. Something tangible.
    Perhaps not surprisingly it raises some further questions:

    a. Where you wish to alter the external moments or shift the centre of pressure line – how do you assess if this has been achieved / you are successful?
    b. Would you or do you with your experience feel an altered tibial position can affect the prescription variables chosen and / or the response?
    c. If the patient had a more supinated foot type, would you still be considering rearfoot varus posting i.e. are there any factors that would suggest to you this was not a component that required altering?

    I am sure Kevin will provide his insight but, in the meantime, let’s assume the device is different compared to the PF device, I am also interested if it is different between patients as per above i.e. is the tibial varum relevant?
    Perhaps more importantly, let us now take just one of those patients (a or b) and hypothesis that this one patient might develop PF or MTSS – would your prescription be different for the two conditions for the same patient?
    However, if this is the case, at what point / how can you determine that that either device has established more normal (or less abnormal function) and may not precipitate another problem – what is good for one structure may not be for another (laterally posted orthoses for OA of the knee might be an example).
    What assessment criteria would you use to help you make this decision?
    In the paper you reference you refer to ZOOS (Zone of optimal stress) within which the affected tissue will have a positive response. In my response to Griff's recent piece on orthoses, I referred to a range within which treatment will prove successful and that the range for any given individual will be variable. I believe we are talking about the same thing here – you are just more articulate despite the accent!!
    Effectively, you are acknowledging what we all see, there are a range of treatment options (you term this ‘positive orthoses solution sets’), all of which have the ability to alter function and reduce symptoms to a structure.

    I deliberately chose the conditions described to gauge an opinion amongst colleagues as to whether or not they feel structural alignment (I narrowed it to one specific) contributes to the kinematic and kinetic function of an individual.

    Graduates could be forgiven, if they read all of the information available that this is not the case. However, it would seem logical there would become a point at which a specific structural alignment must have an effect on kinetic function given the relative force vectors.

    So, to all, going back to the origin, at what point does the degree of tibial varum for instance influence part of the orthotic prescription process in the individuals described or does it never or only sometimes? If the latter how do you determine when?

    Trevor
     
  6. Trev,
    Thank you for your praise. I'm short on time catching up from being away lecturing now. But of course the structural alignment is significant. Kevin and Eric Fuller describe this beautifully in their chapter in Lower Extremity Biomechanics: Theory and practice vol. 1 Edited by Stephen Albert and Sarah Curran.

    Here are some slides from a powerpoint I use which is based on Eric and Kevin's chapter and using the elegant diagrams which are the trademark of Prof. Kirby with his permission, I have attempted to teach the significance of tibial position in terms of kinetic effects over a number of years. The analysis here uses the knee as the example, but the principles of free body analysis defined within could be applied to the tibia at the talus. What's interesting is Nesters bone pine studies of movement within the ankle mortice and analyses like this http://www.asbweb.org/conferences/2008/abstracts/25.pdf which show how foot orthoses are likely to shift the centre of pressure at the tibio-talar interface- thus altering the force couple acting upon the talus and also the tibia.

    Eric's paper: http://www.ncbi.nlm.nih.gov/pubmed/10659531 is a must read for all who wish to understand this kind of biomechanical modelling.

    BTW, I believe tibial varum is particularly significant in MTSS- over to you Kevin.
     

    Attached Files:

  7. Trevor:

    You have a lot of questions here, many of which I don't know exactly how to answer. However, let me try establish some biomechanical, physiological and historical facts to help explain what I now consider when confronted by questions you now ask.

    First of all, I do believe that structure affects function. For example, when a patient has a first metatarsal which is excessively surgically elevated, a metatarsus primus elevatus deformity is created which will tend to increase the load from ground reaction force (GRF) on the second metatarsal head. Also, when a patient has a large degree of congenital metatarsus deformity, that patient will have more tendency of having excessive lateral forefoot loading forces and will also tend to have a subtalar joint (STJ) axis which is laterally deviated which may, over time, cause peroneal tendinopathy and/or increased incidence of inversion ankle sprains. In addition, when a patient has a congenital high degree of rearfoot varus and forefoot varus deformity, that patient will tend to have excessive lateral forefoot GRF loads, especially if their STJ range of motion is limited in eversion. I could go on and on with examples of where changes in structure in the foot and lower extremity may not only produce a change in kinetics but also may create a change in kinematics.

    However, the problem with angular measurements of the tibia, rearfoot or forefoot which you are suggesting in your questions as being important is they are all highly variable, from one examiner to another. All of us who have taught biomechanics for years know how one clinician's 10 degrees of rearfoot varus may be another clinician's 5 degrees of rearfoot varus. This creates difficulty in being able to communicate a "foot or leg deformity" from one clinician to another and also in being able to perform a scientific study which measures structural deformities and ranges of motions of the joints of the foot and lower extremity. Here is a such a scientific study I was coauthor on from over a decade ago (Van Gheluwe B, Kirby KA, Roosen P, Phillips RD: Reliability and accuracy of biomechanical measurements of the lower extremities. JAPMA, 92:317-326, 2002).

    Another problem with using angular and structural measurements of the foot and lower extremity to decide on treatment protocols, whether they are surgical or non-surgical, is that by assessing only angles, structure and plain film radiographs, the clinician is totally ignoring the very significant effect that central nervous system (CNS) function and muscle function may have on the variability of weightbearing activities from one individual to another.

    This acknowledgement that structure does affect function but that CNS variability may also greatly affect function and that foot and lower extremity structure is very difficult to measure reliably and repeatedly in a clinical setting creates a special problem. This special problem is that we can not reliably predict human foot and lower extremity function during weightbearing activities on simple measurement of tibial varum/valgum, hip range of motion, ankle joint dorsiflexion, STJ neutral, STJ range of motion, forefoot to rearfoot relationship, relaxed calcaneal stance position, neutral calcaneal stance position, and first ray range of motion without also realizing that the CNS variability in afferent input and muscle output forces may also greatly affect foot and lower extremity function. This special problem is also caused by the fact that what we measure in foot and lower extremity structure and range of motions may have absolutely no relevance as to how the patient functions during gait or as to what specific pathologies our patients present to our clinics with.

    This special problem I speak of has resulted, over the past half century, in theorists that have tried to propose and establish treatment systems solely on structural and angular deformities, stating that structure will always change function and suggesting that certain structures should always be treated with certain types of foot orthoses. These theorists, unfortunately, did not take into account the important consideration that specific mechanically-based pathologies may require specific foot orthosis modifications to optimize the treatment results with foot orthoses.

    Merton Root's classification system of foot and lower extremity structural deformities and his foot orthosis treatment philosophy that depended only on foot and lower extremity structure and ranges of motion and not on the anatomic location of the injured structure comes to mind as being the most prominent theoretical system of classification and treatment philosophy that has failed to be supported or validated by any scientific research. It is interesting that even though Root's classification system and foot orthosis treatment system has not been supported by scientific research, it still continues to be taught around the world by podiatric medical institutions as the preferred method of foot and lower extremity evaluation and foot orthosis treatment. This seems potentially problematic for the podiatric profession of today, and in the future, in this era of evidence-based medicine.

    With these facts in mind, as you know, I have been involved in, along with many of my outstanding colleagues and friends who also contribute here on Podiatry Arena, in developing what we feel is a better approach to biomechanical therapy of foot and lower extremity mechanically-based pathologies: the Tissue Stress Approach (Fuller EA, Kirby KA: Subtalar joint equilibrium and tissue stress approach to biomechanical therapy of the foot and lower extremity. In Albert SF, Curran SA (eds): Biomechanics of the Lower Extremity: Theory and Practice, Volume 1. Bipedmed, LLC, Denver, 2013, pp. 205-264.)

    The reason that the Tissue Stress Approach works so much better for many of us who have busy podiatric biomechanical practices is that it decreases our dependence on unreliable structural and range of motion measurements that had been taught by the Root theorists as being all-important and critical to our abilities to heal our patients with "biomechanically correct foot orthoses". The Tissue Stress Approach allows us on focus our treatment efforts on reducing the pathological loading forces acting on and within the injured structural components of foot and lower extremity of our patients so that more effect conservative treatment and surgical treatment protocols may be designed and implemented to heal their painful feet and lower extremities without being hampered by attempting to consider the often unreliable and sometimes unimportant angular measurements of foot and lower extremity structure and ranges of motion.

    Even though I know I haven't answered your questions, Trevor, my dialogue above may help explain why it would be difficult, given my current level of knowledge on this subject, to be able to answer your questions with any confidence considering your own frame of reference which appears to be evident within your questions.:drinks
     
  8. was thinking about this on the way home

    say we for point of discussion have the 5 degree and 10 degree Tibial Varum that Trevor mentions.

    We consider a MTSS Patient in the 10 degree not the 5 degree with same stiffness of boney tissue , which I think is a key part of why some patients get injuried and other not , would the increase In Varum mean increased bending moments or make them more focused. ie occur at a more specific point. I guess it could be and/or

    does that make sense and of course there may be no way of knowing
     
  9. Yep, still waiting for Kevin to link to his writings on MTSS. Think ZOOS, trabecular patterns and how over-training may influence the risk of MTSS- the majority of MTSS I see is in the "too-much, too soon type" patient. Viz. increased tibial varus due to running kinematics= increased bending moment; too much, too soon = bone does not have time to adapt and modify trabecular pattern = ZOOS exceeded = microfracture of bone = pain; varus posted foot orthosis = reduction in tibial bending moment = bone healing + remodelling = reduction in pain. Something like that. See also Kirby K.A.: Foot and lower extremity biomechanics III P.143-150. Precision Intricast.
     
  10. OK, so...

    A) if the patients pain decreases and/ or their functional capacity increases. I do not have the time to explain how in using in-shoe pressure measurement, the magnitude and line of action of the net GRF vector cannot be determined (suffice to say it can't) nor how the position of the centre of pressure in isolation from such systems can be seen as being accurate and even if it could would only tell us the point of application of the net GRF vector- for example, a CoP wich is medial to the STJ axis may still be associaed with a force vector with a line of action passing laterally to the STJ axis and producing an external STJ pronation moment- right? When we observe coP pathways in-isolation it tells us little if anything regarding the kinematics of the body above. So in essence, I suck it and see, as we all do, including those who employ the quasi-scientific machines that go "ping" with their patients. See: http://www.ncbi.nlm.nih.gov/pubmed/21084541 The difference being, I'm honest with my patients and tell them we have to suck it and see, I don't pretend that the machines that go "ping" are producing anything more tangible to hold our hats on in terms of their treatment outcomes than sucking it an seeing.

    B) See previous posts

    C) I said that the orthoses may have some of the design features listed. Obviously, you need to look at STJ axial position and specifically supination resistance; if supination resistance were low, for example >100N, you may choose to go with a heel-lift without varus posting or just a compliant heel cup.
     
  11. Simon:

    I don't know if I have any more time today to discuss the specifics of medial tibial stress syndrome (MTSS) but this article I wrote over three years ago pretty much sums up the latest research on the subject.

    Current Concepts in Treating Medial Tibial Stress Syndrome

    Increased tibial varum may lead to MTSS but it also may have no effect since many runners with quite substantial tibial varum deformity will never get MTSS, including myself.

    As far as specific orthosis modifications, nearly all my runners with MTSS get varus forefoot extensions added to their orthoses which, in my experience, when combined with a rearfoot post, medial heel skive, excellent medial arch contour and good medial arch stiffness, is highly successful in healing MTSS and medial tibial stress fracture. I believe you already covered orthosis treatment of proximal plantar fasciitis quite nicely already in your previous post in this thread.

    Hope you enjoyed Spain, Simon. Looking forward to lecturing with you again in Valladolid in four months. I've already changed one of my lectures for that seminar so I can lecture exclusively for 45 minutes on Tissue Stress Theory.:drinks
     
  12. Trevor Prior

    Trevor Prior Active Member

    Kevin

    Many thanks for your detailed and well structured reply which does actually answer my questions - in the main (I will come back to this).

    Firstly, I agree with all you have written and, whilst I used degrees to describe the position it was more to give a visual picture of the difference and could have equally been a bit of tibial varum and a bit more tibial varum.

    What I believe Root et all gave us is a form of system by which to structure the foot alignment (i.e. forefoot varus, rearfoot varus etc.). However, as we have established, the subsequent model for function and thus orthotic solutions were flawed albeit our starting point all those years ago.
    For my part, I have always considered that, if I take a structure (in this case the foot, leg, hip etc.) and assess the basic direction of motion and alignment available, I could make a reasoned assumption of how that may load ASSUMING there are no other factors.

    Thus, when I observe actual function, the further it deviates from the path that would be governed by alignment alone, the more additional factors that need to be considered. In other words, if a structure should do something based on these alignments and it does not, why not, thus let’s look for those causes. In some instances it may be simple – tight calves, weak hip abductors etc. In others it may be less obvious and could be due to the unique constitution of an individual – i.e. the range and direction of motion of the rearfoot / midfoot simply directing motion in a different pattern to that expected.

    If we are happy to accept that there is a ‘range’ within which and individual can function with reduced symptoms for a given level of activity, directing them to that range is the goal.

    Now back to my first sentence whereby I said you had answered in the main. My hope with the simple question was to go down a direction that may be able to outline an approach many could take to evaluating, prescribing and re-evaluating orthoses. Your response has cut to the quick, which is great.

    Clearly you and many of those reading these posts are highly experienced, skilled and knowledgeable clinicians and are able to draw on that to assess and review your patients. However, if we assume all of the variables exist as described, that we need to consider both kinematic and kinetic variables, how do we reasonably assess the effect of our interventions?
    For instance, a less experienced clinician may choose to make an assessment of basic structure, see some gait variations and determine a basic orthotic design based on the structure although they are not sure how the patient will respond. When they implement the orthotic, what criteria can they use to determine that it has altered function and, more importantly, resulted in an improvement in function (other than it hurts less)?

    What do you experienced clinicians do REGULARY:
    1. Eyeball / use experience
    2. Video analysis
    3. 3D gait analysis
    4. Pressure analysis
    5. Other

    Trevor
     
  13. Trevor Prior

    Trevor Prior Active Member

    Mike / Simon,

    the MTSS example was deliberate as well and I agree with your comments although it does not all have to be down to bending, it could be due to muscular activity / fascial tension on the tibia.

    My observation is that many with MTSS that I see, have increased tibial varum. I would initially go with fairly standard orthoses (i.e. nothing fancy) to assess effect. If this is insufficient, I provide a whole shoe wedge (in the form of an insole) to bring the whole foot in line with the leg (rather like running on the camber of the road) and the orthotic sits on this wedge. I check this with inshoe analysis to see if I am throwing too far laterally or not but consider this ‘compromised control’. By that I mean it is far greater than I would generally provide and I cannot be certain that this degree, whilst providing tissue stress relief (or putting it further into its ZOOS), does not prevent motion in another direction / area and potential cause another problem in the longer term.

    I tend to find that, after a period of time and recovery, this degree of additional wedging can be reduced and removed. Absolutely no scientific evidence to support this approach and the degree of tibial varum is what leans me to this approach in certain cases.

    Trevor
     
  14. Trevor not really sure we have much more than in hurts less to go with

    ZOOS as Simon mentioned or Pysiological window we only really know if someone is out of these zones when they are is pain or discomfort .

    we may also consider that being around the ´upper ´ border of these zones as the area at which tissue breakdown and adaption is at the greatest which the correct amount of rest. The adaption will of course lead to stronger tissue able to undergo greater stresses -
     
  15. N.Knight

    N.Knight Active Member

    This is quite spooky, I thinking about the exact same thing that Trevor has mentioned 2 or 3 days ago and could not come up with the answer, great discussion guys.

    So is there any correlation between thickness of Tibia and amount of Tibia bending moments occurring and try to work out some ones risk of getting MTSS (I understand all the other factors contributing towards MTSS) just thinking out loud, as it is an area that interests me and would like to start doing some research into it.

    Nick
     
  16. Strangely enough, I varus wedge from rearfoot through to forefoot with an orthosis shell with minimal medial addition, made on an inverted positive cast etc etc. If traction is coming from anywhere, in most cases it's likely to be from FDL- so what are the internal moments created by FDL in running (MTSS is most prevelant in runner)? And how should we design our orthoses to provide an external source of these moments?

    There is a model which predicts MTSS in about 75% of runners which employs only two predictive variables: gender and navicular drop- since we can't change gender- my orthoses focus on minimising navicular drop- a kinematic variable. I can find the ref for the model if you want.

    ZOOS theory tells us that orthoses may not need to be permanent.
     
  17. this might be a start , http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=39126
     
  18. The bending moment is not going to be predicted by the tibial thickness so much as the angulation of the tibia and the force couple acting across it; the tibial response to this bending moment (i.e. how and where it bends) will be determined by the bone thickness/ density/ trabecular pattern etc.
     
  19. Trev, you are describing a qualitative approach to inverse dynamics, that is looking at the kinematics to determine the segmental kinetics.

    Ultimately, we can do all the things you list in 1-4 above but due to the limitations of kinematic analyses, and due to the limitations in pressure analyses systems, the best that any of us are doing is guessing- despite the quasi-scientific quantifications that some try to apply. Ultimately the only way we know if we are doing the right thing by our patients (and not the wrong thing) is if the patient gets better without developing other symptoms- end of. Until the techology allows us to measure 3D force vectors at the foot orthoses interface and we employ 3D kinematic analyse in concert with this technology, we can only guess and "suck it and see"- even then the introduction of the sensor between the foot and the orthoses and the skin displacement of the kinematic markers will both lead to errors, just as they do today.

    Funnily enough, a well respected colleague whom we all know sent me an e-mail today asking about kinematics and kinetics. Here's my opinion: kinematics without kinetics is a blunt instrument; kinetics without kinematics is a blunt instrument; accurate kinematics with inaccurate kinetics is blunt instrument; inaccurate kinematics with accurate kinematics is a blunt instrument. Viz. what most, if not all foot biomechanical clinicians do, is based on blunt instruments and guess work- end of story.

    Ultimately the type of pathology someone gets and their response to the interventions prescribed come down to a very simple equation:

    P = G + E + (G x E) +i

    where:
    P= the phenotype (the injury/ pathology if you like)
    G = the individuals genotype
    E = environment (all the non genetic factors)
    i = the error in measurements in G and E

    A simple equation that I employed within my PhD, which tells us that everyone is unique, including Mz twins. It also tells us that we need to treat each individual as an individual and not try to apply "criterias for normalcy" nor preconceived patterns of normal and abnormal kinematics nor kinetics; what's "normal" for one may be "abnormal" for another and vice versa. Moreover, if we assume that biomechanical function is the phenotype (some global measure if you like, or at an individual tissue level if you prefer) it is subject and environment dependent and determined by the interaction of G and E. We have to realise then, that even if we had all the tools to accurately measure the kinematics and kinetics of our patients within the lab and "know" that the kinematics and kinetic responses of our foot orthoses are placing the tissues within their ZOOS in this environment- we still have no idea what's happening in the "real world"- where the ground is not flat and level, where we have to climb stairs and descend them, where we walk forwards and side step and sit and stand and drive and run and walk and jump and ride bikes and kick balls and dance and hop and skip and jump... We have to guess when we prescribe foot orthoses and always will, et tu Brute. Me? I'm comfortable with this and don't pretend that I'm doing anything other than providing a foot orthosis which is based on anything more than educated guess work, just like everyone else; unlike some other people, I let the patient know this before I take their money.
     
  20. Nick:

    As Simon already stated, the tibial bending moment is due to the magnitude and distance at which the forces that are acting across the longitudinal axis of the tibia are located away from the longitudinal axis of the tibia, not the thickness or cross-sectional diameter of the tibia. Compression forces acting exactly in line and on the longitudinal axis of the tibia will produce a minimum of bending moments and a maximum of compression forces and are known as axial loading forces. Compression forces acting away from the longitudinal axis of the tibia will produce more bending moments and less compression force and are known as eccentric loading forces.

    The cross-sectional thickness of the tibia or area moment of inertia of the tibia will not determine the bending moment on the tibia but will, instead determine the magnitude of compression and tension stresses within the section of the tibia that is being subjected to the bending moments. A tibia with thinner cortical walls and thinner medial to lateral diameter will have decreased area moment of inertia and, as a result, will experience higher bone stresses than a tibia with thicker cortical walls and wider diameters.

    This is the most likely mechanical explanation why MTSS is most commonly seen at the junction of the proximal two-thirds and distal third of the tibia: this area of the tibia is the narrowest part of the tibia and will be subjected to the highest bone stresses and bone strains during eccentric loading of the tibia. This is also the most likely mechanical explanation why MTSS is most commonly seen in female vs male runners: females tend to have more narrow tibial cortices and have lower bone density that their male counterparts.

    Hope this helps.
     
  21. N.Knight

    N.Knight Active Member

    Yes Kevin it does, many thanks, picture paints a 1000 words.
     
  22. They also have a wider pelvis than a male (height for height) which increases the tibia's varus angulation to the ground to maintain the area of support beneath the COM when running...
     
  23. However, most female runners seem to have less tibial varum than their male counterparts, probably due to increased genu valgum angle at the knee compared to their male counterparts.
     
  24. Trevor Prior

    Trevor Prior Active Member

    Simon

    I freely admit I have not read all of the many posts on the forum but, over the years, have read many and think that is the first time I have seen anyone actually state the degree of guess work that occurs. Very refreshing Simon. Clearly, as we get more experience and read new developments, our guesses get better which is why you cannot teach experience eh?

    The primary driver for me posting was around prescriptions as what concerns me most is how we educate and develop students and those with less experience. Our message to these is essentially, we have some idea as to what will influence foot function and we have some idea as to what types of prescription variables (orthoses solutions sets – could be positive or negative) can influence function. However, it is very difficult to accurately assess to either guide the prescription or evaluate the outcome, other than it hurts less. It hurts less, probably because we have either placed a structure in a range / position / dynamic situation which stresses it less or allows it to function more efficiently.

    Thus, in reality, anyone assessing patients and prescribing orthoses can apply whichever criteria they wish as long as they appreciate the limitations, consider the functional anatomy and re-evaluate their patients.

    As a start point, an understanding of how the basic structural alignment can affect function would be a perfectly reasonable position on which to start your journey, just be realistic that your interventions will not provide magical re-alignment and there are many variables.

    Mind you, this reality should urge caution to anyone wishing to criticise a prescription provided by another practitioner.

    I take your point regarding assessment tools and the limitations, although feel they have a role in the process. Regarding pressure analysis, I would agree that the CoP has limited use as there are a range of variables which affect the direction. I use pressure analysis fairly frequently but I advise my patients it is my subjective interpretation of the data that I use to guide my assessment. I have certain criteria I look for and use these to help me formulate my management strategy and give some structure / consistency to the process.

    I do believe that there are patterns of structure / function and that there is a more ‘normal’ or rather less ‘abnormal’ range of overall function for everyone, we just do not have enough evidence or accurate enough tools to identify this as yet – should not stop us striving. That’s the fun.

    I am not sure how much more mileage there is in this debate but I thank all those who have contributed. My day of admin is drawing to an end and, you will not be surprised to hear, I did not achieve as much with my other work as I had hoped but I enjoyed the debate. Two days of theatre followed by a Sunday tournament with Woodford RFC U16s covers my next 3 days.

    All the best

    Trevor
     
  25. efuller

    efuller MVP

    1 and 2. depends how you define pronated. Why does one being more pronated matter?

    Plantar fasciitis is usually caused by high loads on the medial forefoot with a high STJ pronation moment. (Or that it is what modeling would predict. ) If all things are identical and one foot had more tibial varum than the other you would need more information to predict which one would be more likely to have plantar fasciitis. As you increase tibial varum, you may run out of range of motion available to evert the foot further. When you run out of range of motion to evert, increasing the tibial varum will tend to increase the lateral forefoot load. With increased lateral load there will be a tendency toward lower medial column load and hence a decreased chance of getting plantar faciitis. So, one would want to know the maximum eversion height before making predictions. The maximum eversion height would also change the amount of forefoot valgus correction in the prescription.

    There are two kinds of pronators and they are based on the position of the STJ axis. People with a medially positioned STJ axis are what I call ground caused pronators. People with a laterally deviated STJ axis will have lateral instability that they need to constantly counter with peroneal activation. These people I call muscle caused pronators. Where the STJ axis is is a big determinent of how I make my orthoses. Tibial varum is independent of STJ axis position.
    So, tibial varum has an effect on maximum eversion height, so that would effect my prescription. However, I wouldn't be changing my prescription based on tibial varum, but maximum eversion height.

    On theory on MTSS is that is is caused by a valgus moment on the tibia. That is the line of action of ground reaction force runs lateral to femoral reaction force on the top of the tibia. This may not be the only mechanism of tibial pain. So to treat MTSS that is caused by the valgus moment applied to the tiba, you would shift the center of pressure more medial under the tiba with a varus wedge type device. But, if this foot had a laterally deviated STJ axis then this would increase the chance of peroneal overload. So you need to STJ axis position to write a good prescription. Or to be able to warn the patient what to look for (in terms of unintended consequences)

    Nice thread
    Eric
     
  26. Simon and Colleagues:

    I don't think that all our knowledge and techniques as practitioners of podiatric biomechanics are "blunt instruments". Knowledge of the kinematics and kinetics of the human gait cycle in walking and running, being able to do a complete biomechanical examination and muscle testing of a patient, knowledge of the presenting signs and symptoms of various pathologies, detailed knowledge of the anatomy of the foot and lower extremity, knowledge of various stretching, strengthening and strapping techniques and knowing how to design and adjust foot orthoses to alter pathological external and internal forces are not, in my opinion, "blunt instruments".

    These skills and techniques all require years of education and practice, which, by the way, very few other medical professionals possess. If these skills were indeed "blunt instruments" as you suggest, then other medical professionals should be able to use their "sharper instruments" to better treat the patients that we often see in our practices who have failed their own treatment methods. In my opinion, our methods are much more "sharp instruments" than most of the "instruments" our other medical colleagues possess.

    Indeed, that is part of the beauty of the Tissue Stress Approach. One does not need to know what the exact kinematics or what the exact kinetics of every joint of the foot and lower extremity of a patient in order to make a profound difference within their lives. All one needs to do is determine which anatomical structure is injured and determine at least one method to decrease the pathological loading forces which has caused the anatomical structure to become injured without causing other pathologies.

    I don't consider this "guess work". I consider this way that myself, and many other talented practitioners, including yourself, Simon, practice in a clinical setting as a time-tested method of using applied physiology and engineering principles to reliably and predictably produce a reduction of pain and an increase in weightbearing function in the vast majority of patients who have this treatment approach applied. While I would agree that we may not know everything that is going on within a patient's foot and lower extremity mechanically, if our treatment techniques truly involved only "guess work", we would not be able to so reliably reduce and cure patient's pain when properly applied.

    I hope that I didn't spend the last three decades fo my practice career using only"guess work" to heal the thousands of patients I have seen over this time. I hope that what has healed these patients is my education, my knowledge, my technical skill and my ability to pay close attention to detail in order to obtain the goal of improving the lives of my patients....not "guess work".

    Over to you, Dr. Spooner.:drinks
     
  27. Trevor Prior

    Trevor Prior Active Member

    Eric / Kevin

    Thanks for adding further to this debate. Eric, I would agree with your comments regarding the relative amounts of motion entirely and is a good example of how the structural alignment can influence function but overall function is determined by other factors (i.e. range of motion for instance). Interestingly, this is one aspect pressure analysis can help guide. As the range of motion (or level of alignment) change it can nicely pick up whether or not someone is transferring load or maintining lateral load for instance. Whilst there are some complex analysis techniques that allow pure data, simply watching the loading pattern dynamically wil show that nicely. So, in this instance, I think you have a realtively high tibial varum, your range of motion is on the lower side and I would expect you to maintain load more laterally. I now look at the analysis and see this to be the case so I will implement the treatment strategy I feel appropriate for this type of function.

    I think kevin made one very salient point which I guess is why he put it in bold:

    "determine at least one method to decrease the pathological loading forces"

    My interpretation of this comment is that there are a range of ways in which one can achieve an effect and returns to our 'treatment range' or Simon's ZOOS.

    In my opinion, it is experience that allows one to provide treatment that places the individual in a better range / position or whatever term you would like to use, with less risk of that particular design feature potentially causing issues elsewhere. My concern with a pure tissue stress approach is that one could take the view that as long as it reduces the stress and the symptoms, it is fine - we simply do not know that and, if we block motion in one direction (or increase force / vectors etc.), it must have mutlidirectional effects at some stage. These could be negative.

    If I go back to the case above, if there is increased lateral laod and I place a varus wedge beneath the rearfoot of incremental amounts (Jim Woodburn has recently published on this), the lower values will essentially support the position and, at some point, the forces beneath the rearfoot will be more uniform. There will then be a range wherin, the loading does not significantly alter medial to lateral but be sufficient to alter the compression across the joints (Kevin described this years ago for sinus tarsi syndrome - alter the joint forces not necessarily the position). Past this point, my wedge will simply push further laterally and increase lateral load. Eric, this would then place increased activity through the peroneals as per your example but be iatrogenic. This increased lateral load can be seen on dynamic pressure (or rather force) analysis.

    Accepting the limitations Simon has highlighted, that is something tangible for that individual and can help to guide me with my treatment. If the increased lateral load is what is required for symptom relief then so be it but I might want to consider reducing that as and when the patient has recovered as I may risk injury to the peroneals or elsewhere.

    So, in essence, I agree with you all - there are limitations, we do not know everything, we all have our approaches and orthotic solution sets and there is a role for adjunctive assessment methods to help guide what we do. This, combined with our experience, allows us to be extremely effective but we need to be realistic about how we achieve our aims and what we claim.

    Trevor
     
  28. Kevin,

    Here is good defnition of a foot orthosis that you may recognise: “An in-shoe medical device which is designed to alter the magnitude and temporal patterns of the reaction forces acting on the plantar aspect of the foot”, in other words a foot orthosis works by altering kinetics.

    Here is what I think:
    kinematics without kinetics is a blunt instrument; looking at kinematics in isolation tells us little about how the kinetics have been altered by our foot orthoses, which by your definition above work by altering kinetics. The problem being that while kinetics drive the motion and a change in kinematics may be ascribed to alteration in the kinetics, we may also see no change in the kinematics even though the kinetics have been changed. Thus, looking at kinematics in isolation may be erroneous. Hence in isolation kinematics are a blunt intstrument when we wish to understand how a kinetic device is functioning since it tells us little regarding the "magnitude and temporal patterns of the reaction forces acting on the plantar aspect of the foot".

    kinetics without kinematics is a blunt instrument; If we see a change in force distribution under the foot when we use an in-shoe pressure measurement system, lets say we see the centre of pressure shift medially, unless we observe the kinematic change of the body above we have no idea whether this shift resulted in an increased external supination moment acting about the STJ axis, or whether the STJ as simply pronating more in response to our foot orthosis; both may be associated with a medial shift in the centre of pressure. Hence without measuring the kinematics in concert with the kinetics we really don't know the sense of the moments our foot orthoses are generating about the joint axes. In reality the present technology is too limited to tell us the exact magnitude of reaction forces acting on the plantar foot and even the use of such technology to ascertain the temporal patterns as they relate to the plantar foot are questionable.

    accurate kinematics with inaccurate kinetics is blunt instrument;
    inaccurate kinematics with accurate kinematics is a blunt instrument.

    Foot orthoses alter kinetics yet we do not have an accurate way of measuring 3D kinetics at the foot-orthosis interface; clinicallly most clinicians perform 2D kinematic analysis, even those who do perform 3D analysis are likely to use skin mounted markers to make inferences regarding bone position and movement, we've learnt that many of assumption from surface mounted markers are erroneous from the bone pin studies.

    Thus, I believe that clinically we are currently using blunt instruments and a great deal of educated guess work. Moreover, foot orthoses work by altering kinetics yet are still prescribed using kinematic variables- we have little idea of how the kinematic variables such as rearfoot posting angle relate to absolute values of change in the kinetics at the foot-orthoses interface, we do know that this is liikely to vary within and between individuals- hence we use educated guesses.

    We may have to agree to disagree on this one, but because we simply cannot measure the magnitude and temporal patterns of the reaction forces acting on the plantar aspect of the foot with our orthoses in situ and because that's how foot orthoses work, we all have to make educated guesses, including you my friend.

    CNS mediated effects are a great example of our guess work falling short. We have a patient with a pathology which we believe (using our understanding of engineering principles and physiology and diagnostic skills etc) is being caused by excessive external pronation moments acting upon that tissue, so we proceed to design a foot orthosis which we believe should increase the external supination moments, but because we don't have any way of exactly knowing how to control the kinetics at the foot-orthoses interface, the magnitude and temporal patterns of the reaction forces acting on the plantar aspect of the foot, we have to guess the degree of angulation we should make the rearfoot post (for example). Some use pseudoscience and measure angles from the leg and foot and erroneously think this imparts some level of accuracy and validation of their choice, but in reality we have no idea how posting angles relate to kinetic change, so it's at best a guess. We prescribe the device and the patient displays a kinematic change by pronating more due to a CNS mediated effect and increased peroneal muscle activity, we have no way of predicting how much posting would have been suffice to prevent that happening since it will vary from individual to individual, thus in this case we made a bad guess. Now we have to guess how much posting to remove that will prevent the CNS mediated effect from kicking in, but still try to provide enough external supination moment to help the initial pathology. It's all guess work, albeit educated.
     
  29. Simon:

    Are we, as podiatrists who specialize in biomechanical treatment of foot and lower extremity injuries, any different then from any other medical specialty on this planet of ours? Don't all medical specialties also use "blunt instruments" and a "great deal of educated guess work" to help the people who come to them for medical advise and treatment?

    I agree with you, Simon, that we certainly don't know everything about what is going on mechanically inside patient's bodies. However, do you feel we need to know everything mechanically about an individual to, for example, make their plantar heel pain better? Maybe the "blunt instruments" that you describe that we use to make people better are really much "sharper instruments" than what many of our other medical colleagues use?
     
  30. Kevin, I think much of medicine is based on educated guesses and tell patients so on a daily basis. I have no problem in using the blunt instruments, but I try to make my instruments as bright as they can be by reading and exploring biomechanics of the foot and lower limb on a daily basis. :drinks

    Now, you should be off visiting National Parks in your motorhome- go, enjoy.
     
  31. We don't leave until a week from now in our motorhome but unless the Congress gets it's act together before then, Grand Canyon and Zion National Parks will probably still be closed.


    The US Congress?.....now there's a blunt instrument!!
     
  32. What's occuring out there? Why are the National Parks closed? I've not seen much news during the last week due to being in Spain. How do they close the Grand Canyon?

    I'm guessing, but I think you are going to struggle to pass as an under 16 playing in a rugby match, Trevor.:drinks:pigs:;)
     
  33. Trevor Prior

    Trevor Prior Active Member

    I only just pass as their coach!! Mind you, were I to play, I think I might just break given the size of some of the lads.
     
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