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PTTD, RF Varus

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Viv Grey, Nov 5, 2012.

  1. Viv Grey

    Viv Grey Member

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    I am one of a group of students undertaking a case study/treatment of a patient with unilateral Stage I PTTD (previously diagnosed and supported by symptoms/history). Valgus heel in RCSP and perpendicular in neutral and the 1st met head and hallux do not make contact with the ground in STJ neutral. Dynamic analysis demonstrates bilateral RF varus. On POP casting (in STJ neutral), a significant FF Varus/Supinatus is evident which we suspect is demonstrative of the RF Varus (due to the neutral position) but are uncertain as to the relevance of this.

    The patient already has casted orthoses which manage their symptoms, but requires new ones and we intend to support the MLA but are uncertain as to what degree of (if any) medial posting we should use?

    Also, can PTTD occur as a result of varus compensation? The patient reports their MLA has decreased throughout life but currently maintains a low arch.

    We would appreciate any guidance or pointers you can offer as we are struggling to find an evidence base which works with our findings! :sinking:
  2. efuller

    efuller MVP

    First off I would move away from the RCSP, NCSP paradigm in explaining why PT dysfunction occurs. Are you familiar with Kevin Kirby's paper on rotational equilibrium? You need to understand the difference between pronation the motion and pronation moment the forces that cause the motion.

    The function of the PT muscle is to shift weight to the lateral foot. When the PT muscle is weak and or ineffective, if there is available range of motion, the foot will pronate and load the medial column. High medial column loads is what causes the progressive flatening of the medial longitudenal arch that is commonly seen with PT dysfunction.

    Read Kevin's paper and think about the medial heel skive modifcation of an orthosis and come back with any other questions.

  3. Viv as a by the way where are you at Pod school ?

    Also agree with Eric, Kevin Kirby's Subtalar joint axis papers plus also look in here under PTTD, some good stuff.
  4. David Smith

    David Smith Well-Known Member


    Posterior tibial tendon dysfunction is due to trauma caused by excessive stress to the PTT/muscle unit. Stress is the internal force applied across the cross sectional area of the muscle tendon unit. How does this excessive stress occur? The PT exerts a force that inverts the STJ and raises the Medial Longitudinal Arch so those forces that lower the MLA and evert the STJ will load the PT. So those interventions that assist in inverting the foot and raising the MLA or reducing the aforementioned forces. will reduce stress in the PTT/muscle unit. Also you might imagine that the tendon having a much smaller cross sectional area than the muscle body will therefore have a much higher internal stress.
    Reading the paper cited by Eric will reveal more about this.

    Regards Dave Smith
    Last edited: Nov 6, 2012
  5. Lorcan

    Lorcan Active Member

    How much you invert the foot really depends on how much the patient needs to be controlled/inverted. This is subjective and depends on the patients respone. I commonly would provide a 20+ degree medial heel skive and a 5+degree rearfoot varus external post and a poron arch pad usually from 6-9mm depending on the patients response.
    Simply taking a measurement and then saying this tells me I need X invertion is not a ideal way to approach the problem as it may be too much for some and too little for others. Follow the tissue stress approach.
  6. Indeed.

    In simply terms, the Ptt is knackered from having to pull the foot too hard. Your insole needs to push the foot in the same direction hard enough that the ptt no longer has to pull so hard. Then it can heal. Simples.

    Free your mind of degrees, positions and angles. Remember what an insole does is push. Not hold, not place the foot in a certain position, just push. Push the foot the same way as a tendon pulls it, you reduce the demand on that tendon.
  7. Lab Guy

    Lab Guy Well-Known Member

  8. Viv Grey

    Viv Grey Member

    Many thanks to you all for your most helpful responses. I have previously used Kevin Kirby's paper earlier in gait studies and with Bio not being my strongest subject, I was a bit overwhelmed by it! :confused: However, with a bit more knowledge and experience under my belt, I was much more able to digest and comprehend it and it does answer all the questions that go against the lecture material which is predominantly Root. I haven't heard back from my group as yet, but I feel much more confident in tackling this. :D

    Mike, we are studying at Salford Uni.
  9. Viv Grey

    Viv Grey Member

    I like this a lot. :D
  10. Griff

    Griff Moderator

    I'm not sure that I agree that insoles/orthoses push...
  11. Viv:

    Here is another paper I wrote on your subject of interest which may help.:drinks
  12. Do they instead pull??
  13. efuller

    efuller MVP

    Yea, when you plantar flex the 1st met when you cast the orthotic reaches up and pulls the metatarsal down to plantar flex it. ;)

  14. Griff

    Griff Moderator

    No. They are inert. They do neither.
  15. So when your foot pushes down on the ground, the ground doesn't push upward on the foot, because the ground is inert?? Semantics is fun, isn't it Griff? By the way, you are up way too late! I think you will find that both an orthosis and ground pushes on the foot.......in the morning...after you get some rest.;)
  16. Griff

    Griff Moderator

    The ground provides a reaction force (as do orthoses). Surely a piece of plastic is not physically capable of 'pushing' anything right? ..... Jeez it was you who taught me this stuff ;)

    I'm on way way home from the Tennis ATP world tour finals and my train is delayed!
  17. That explains things....you're bored and don't have anything better to do.

    I do believe that the word "push" has multiple definitions.

    You are correct, however, Ian, in that Robert should have been more precise in his language. I prefer not to use the word "push" when describing orthosis function since the term "push" is ambiguous and imprecise. It would have been better for Robert to say that the foot orthosis exerts a compression force on the foot and the posterior tibial tendon exerts a tension force on the foot.

    Hope you get home safely.:drinks
  18. Here is how I described it:

    "The fundamental purpose of a foot orthosis is to transmit loads from the point of application to the point of support and, ultimately, through the shoe to the ground. During activities of daily living the orthosis may be subjected to a wide variety of loading patterns. In order to produce equilibrium, it must provide an equal and opposite reaction. When loads are applied to an orthosis, the orthosis tries to absorb its effects by developing internal forces that, in general, vary from one point to another. The intensity of these internal forces is called stress. When subjected to external loads, orthoses change their shape; though sometimes imperceptibly. This change in shape is termed deformation and is measured by the mechanical strain. Thus, the necessary orthosis reaction is generated by the stress caused by the action of the loads within the orthosis material, and by the ensuing strain in the elements of the orthosis structure. Stress and strain within the orthosis are the direct outcome of the action of forces and the deformations they produce."
  19. What determines the direction of the orthotic reaction force?
  20. Also I would have thought that an orthotic does push the foot if the devices elastic nature is able return to it to it´s original shape and the foot is still in contact with the device .
  21. David Smith

    David Smith Well-Known Member

    Push and Pull have an intuitive quality that can be useful in everyday conversation but in physics and mechanics push and pull as definitive terminology have no useful place. Applied force and reaction force are far more useful in this case.

    You can't apply a force without having a reaction force and both are equal in magnitude and opposite in direction ( You will recognise Newtons Law here). Which one is the applied and which one is the reaction force is a matter of perspective. But using the term push I don't think that anyone would deny that the foot pushes on the ground so intuitively and for our purpose this is the applied force and therefore the opposite reaction force is the ground or any interface between the ground and the foot and therefore is pushing back.

    So if you have a car with a tow bar attached to a caravan then the applied force is the force from the car which is pulling the caravan and the reaction force is from the caravan which is pulling the car.

    Push and pull often have connotations of movement but if you push on a house it doesn't move, would you say the house is inert and cannot push back?

    But if you were trying to push your best mate over a cliff and he was pushing back (like they do) then even though your both not moving you wouldn't deny that your mate is pushing back against you.

    Regards Dave
    Last edited: Nov 7, 2012
  22. Yes, I was being less than precise ;). Since viv is a student, I thought it best to get her to grasp the basic concept first before unwrapping it. But you are, of course correct.
  23. I would say it was a derivation of the angle of incident force, the angle of the supporting surface, and the friction co-efficient of the interface.
  24. David Smith

    David Smith Well-Known Member

    Sorry Robert I wasn't correcting you're terminology per se as I thought your explanation was very useful, however others had a problem with imagining how the ground can push.

    Regards Dave
  25. Ultimately it's the angle of the loading force. But this is itself partially determined by the surface geometry and friction and probably the load/deformation characteristics of the orthosis too.

    So, taking our example of the tibialis posterior tendon, how might we best design the surface geometry of the orthosis to help provide an orthotic reaction force which "pushes" in the same direction as the "pulling" force from the tibialis posterior tendon? My guess is that we need an orthosis with a surface angulation which is the mirror image of the line of pull of the tibialis posterior tendon at it's insertion sites.

    A foot orthoses with vectored surfaces...hmmm vector to the foot motion about the interface axis at a given time?
  26. Viv Grey

    Viv Grey Member

    Many thanks Kevin. We are using this paper but needed to understand the relationship between the varus foot and PTTD as all the literature points to a valgus foot. However, your paper on STJ axis and rotational equilibrium covers this very nicely. :D
  27. Viv Grey

    Viv Grey Member

    And only a 2nd year student at that! Simple terms are always appreciated. ;)
  28. RobinP

    RobinP Well-Known Member

    I suspect I am not alone in wondering why a well established podiatry school like Salford is teaching you to think in this way. It is hardly current and in my opinion, makes, what is essentially quite a simple concept, into one that is far more difficult for a student to grasp.

    Think of it this way Viv.

    In your original post, eliminate sub talar joint neutral from the equation(as it doesn't exist) and what are you left with?

    So to answer the questions

    The bit in between which has been replaced by the dots above is not relevant

    You need as much force as is required to reduce the load going through the tibialis posterior tendon to a point where it can heal. None of us know what that point is but if he is currently wearing orthoses that resolve the problem then it is probably about that amount(although, it could be significantly less)

  29. Nice. As Robin has said, you know the patients current foot orthoses are placing the tibialis posterior tendon somewhere within it's zone of optimal stress (ZOOS), but you don't know exactly where within the ZOOS the present prescription is placing the loading on the tendon. It could be right in the middle or right on the cusp between success and failure. In the middle, you can probably change the prescription to an extent and still achieve success; if it is towards the upper or lower boundaries of the ZOOS then a small change in the prescription could result in clinical failure, or improvement in the patients symptoms/ functional capacity.

    I wrote about this in the attached paper.

    Attached Files:

  30. Especially when some now consider the STJ axis location/rotational equilibrium theory as being "traditional".....;)
  31. Viv Grey

    Viv Grey Member

    Hi Robin,

    Thanks for your response. Salford do teach us Root...but they do acknowledge, guide and encourage us to seek and apply other more relevant theories. Hopefully this embraces the science elements and will enable us to analyse and evaluate the numerous theories we will come across as practitioners. I personally found it all rather confusing to start with but feel that I am finding my own way...with some guidance on here to point me in the right direction!

    If the current orthotic has failed to heal the tendon, which is significantly thickened and bearing in mind the varus angle resulting in an increased pronation moment and avascularity of the tendon around the medial malleolus, can we aim to heal the tendon or it is more a case of managing the symptoms and preventing/reducing progression of the condition?

  32. RobinP

    RobinP Well-Known Member

    SALRE is like a good pair of brogues - fashionable and traditional ;)
  33. RobinP

    RobinP Well-Known Member

    I'm glad to hear that they do encourage other theories that are more relevant. I would hope that in doing so, they would have steered you away from the tautological terminology that is sub talar joint neutral. Yet, it seems to be the thing that most students posting on this forum use as a reference point.

    Regarding your questions as above, I'm sorry, I misunderstood your original post. I thought you meant by managing the symptoms, you meant that they maintained resolution with use of the orthosis.

    If the tendon is still problematic, then that is perhaps a different case. It is worth bearing in mind that an orthosis cannot heal a tendon but I get what you are talking about.

    The damaged tendon is thickened and in many cases will stay thickened. It will not necessarily return to normal despite not being problematic

    I'm not sure what varus angle you refer to?

    Is the tendon avascular? How do you know?

    With regards to healing the tendon, you should probably re read what Simon has written a couple of posts ago. If a given tissue operates within its zone of optimal stress(ZOOS) it will not become injured. If it exceeds the threshold, it will become injured.

    So, if you want the tendon to function as normally as possible, its ZOOS needs to be increased(This is a little simplistic and inaccurate but this is how I like to think about it - thickened tendon is one that is probably more fibrous and less elastic. Smaller elastic zone on a stress strain curve = smaller ZOOS)

    So how can the posterior tibial tendon be made "stronger" and capable of absorbing more load without being damaged? (ie bigger ZOOS)

    1. Weight loss - the tendon is actually no "stronger" but if the load it is having to absorb is less, then it should have a bigger ZOOS
    2. Mechanical advantage - again, the tendon doesn't become any stronger but increasing the lever arm over which it is acting will increase it's ability to create an internal supination moment
    3. Make the muscle stronger - work out like Arnie(Schwarzenneger)

    It is also worth adding that although making the plantar intrinsic muscles of the feet stronger doesn't directly affect the tib post tendon, it will absorb a proportion of the total external pronation moment, meaning that the tib post will not have to do so.

    So, what can you do to heal the tendon - not much

    What can you do to prevent the tib post tendon from further damage and even improve in function?

    1. If patient has some timber to lose, let them know
    2. Use an orthosis to improve the ability of the tib post tendon to generate an internal supination moment. As an aside, I hope that they have taught you the supinaton resistance test and the maximum eversion test as that will give you some ideas about the amount of posting/skiving etc required. Does the current Rx have a FF varus post?
    3. Give the patient a strengthening programme for tib post
    4. Give a strehgthening programme for other structures that create an internal supintion moment.
    5 Utilise mechanisms that will resist the external pronation moment - Windlass(hence the reason I asked about the FF varus post)

    Sorry this was meant to be a one line answer and i have rambled for ages now
  34. Is the spring ligament intact? Too many toes sign? Navicular displacement on sit to stand? These will influence the geometry of the orthoses required.
  35. Lorcan

    Lorcan Active Member

    Perhaps also consider the Peroneals. If they are hypertonic they will by Recipricol Inhibition "weaken" the Tib Post. Reducing the Hypertonicity in the Peroneals will encourage the Tib Post muscle to "switch on".
  36. phil

    phil Active Member

    Could you elaborate on how these factors influence required orthotic geometry?
  37. Sure. Generally if there is a high proportion of horizontal displacement of the navicular (drift) you'll tend to increase the height of the medial arch flange of the shell; if there isn't much drift but a predominance of vertical displacement of the navicular (drop) you don't need such a high medial flange since the foot is tending to deform vertically downwards more than it is attempting to deform horizontally. When the spring ligament is torn and you have "too many toes sign" a good approach is to emulate a 3 point fixation with a high lateral heel cup, a high medial flange and a clip at the lateral forefoot.

    Think about the direction of deformation of the foot and design a device which will provide resistive force to that deformation. For example, if you wanted to be clever you could measure the navicular drop and drift, work out the displacement vector and have your orthotic shell angled perpendicular to that vector in the area of the navicular. We talked about this elsewhere, I'll see if I can find it later.
  38. drsha

    drsha Banned

    I am one of a group of biomechanists that focuses more on sagittal and transeverse plane biomechanics than on RF Frontal plane biomechanics.

    STJ Equilibrium and where and how much to skive the RF does little to explain the impact that your patient's forefoot disease plays in this case and on its influence to deviate the STJ Axis as a compensation to its pathology.

    The FHL that the patient has compensates proximally by deviating the STJ Axis medically even if there is little frontal plane motion available in the direction of pronation on the frontal plane.

    If you continue to value the RCSP as part of your exam, you will realize that it is the sagittal plane biomechanics of this case (and transverse to a lesser degree() that you are being asked to abandon by relying so heavily on Kevin's papers and the STJ Axis as is so strongly being suggested here (not that they are not important, they are just not necessarily leading).
  39. RobinP

    RobinP Well-Known Member

    Two words....Forefoot Disease :bang:
  40. efuller

    efuller MVP

    This is a classic straw man argument where you set up a false argument, straw man (Rotational equilibrium is purely frontal plane) and then beat up the straw man. The STJ motion and its axis are three dimensional and moments can be calculated about the axis in three dimensions.

    If you have read Kevin's paper you can decide for your self if rotational equilbrium explains the pathology and treatment of PTTD. Don't take his Dennis' word for it.

    I'm sure you meant medially, not medically. Maybe you can deviate it medically with hallucinogens.

    Compensation is a word to be warry of. Neutral position biomechanics uses it a lot. When you want to know why a motion occurs you have to identify the forces and moments.

    Viv, and other students, Dennis has an incomplete theory on typing of the foot. We've asked him many times to explain how foot types are connected to pathology and he can't. For example, the tissue stress explanation of PTTD is that a medially deviated STJ axis will tend to have higher pronation moments from the ground and that a posterior tibial tendon, in this foot, will have to work harder than a foot with an average STJ axis to produce the same motion. This harder work will create more stress on the tendon and make it more likely to become injured. An orthosis that decreases the pronation moment from the ground will decrease the stress on the tendon and allow it to heal.

    So Dennis, the challange is to explain why one foot type would get PTTD more than another and what treatment variables do you change based on foot types. Viv, Dennis has seen this question many times and he will probably throw a rant about how this is off topic rather than answer the question. But, he still has not answered the question. He may even think that we are asking for evidence. I'm not even asking for evidence, I'm jjust asking for a logical reason why foot typing, as he has described it, should be predictive of anything.



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