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Foot orthoses and the MTJ

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Aug 18, 2015.

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    Just got back from teaching in South Africa. One of the topics I taught on was the influence of foot orthoses at the midtarsal joints (MTJ): calcaneo-cuboid joint(CCJ) + talonavicular joint (TNJ)= CCJ + TNJ= MTJ. As we know, joints don't "lock", therefore it seems reasonable to assume that some of the influence in MTJ stiffness change observed with variable positioning of the subtalar joint should be due to changes in the 2nd moment of area (it's stiffer because it's thicker) due to the orientation in the articular surfaces of the CCJ and TNJ with varying subtalar joint (STJ) positions and the MTJ "stacking" as a result of this- see diagram attached. This leads to the conclusion that there is a position (unique to each individual) about which the 2nd moment of area is equal about both the medio-lateral, and vertical MTJ reference axes... Indeed, about all three reference axes? This should be the position of maximal midfoot stability to a force coming from any direction- right? Now, it might be that the foot needs more stiffness in one direction than another, however: there should be a STJ position in which the 2nd moment of area in all three directions- plantarflexion/ dorsiflexion; inversion/ eversion; abduction/ adduction are all equal- agreed, hmmm? Wouldn't that be when the centre of the articular facet at the TNJ is at 45 degrees to the centre of the articular facet at the CCJ? Let's call this position "Midtarsal Joint Neutral". It's probably no ideal, will certainly vary between individuals and since the greatest need for stiffness probably comes about the medio-lateral axis... I'm just thinking out loud.

    Attached Files:

  2. Thanks Simon

    I do wonder if things would be easier if we discussed the 2 joints ( calcaneo-cuboid joint(CCJ) + talonavicular joint (TNJ) and their individual axis, rather than the MTJ reference axes of Nester et al, I do keep on about it but, with most people understanding the STJ axis etc it easier to transfer similar thought patterns to the TNJ and CCJ

    Agree on the stiffness side of things, but you have me thinking, thought the post was interesting and worth discussing, rather than let it go with a thanks ......
  3. I used to think that modelling the TNJ and CCJ individually was the way forward too. These days, I find that teaching MTJ biomechanics via the reference axis system makes a lot of sense and that students are able to take this model on board quite well.

    It would seem to me that the dorso-plantar stiffness should be needed to be higher at midstance than in the other directions. But lets think for a minute about STJ position during the contact phase of gait and how this will dynamically influence the 2nd moment of area at the MTJ from forefoot loading through to heel off- time to look up the bone pin data on STJ motion... remember STJ pronation = reduction in 2nd moment of area in vertical plane and viz. dorso-plantar stiffness. Remember too, that evolution was at work here.... BTW anyone who doesn't believe in evolution should take a look at how bacterial evolution is impacting upon antibiotic therapy and shut the funk up.
  4. Simon:

    Still on vacation here in Gordon's Bay, South Africa. I took some great gait videos of the African penguins in Betty's Bay today, but won't be able to upload them until I get a better internet connection. Penguins have a very interesting bipedal walking gait pattern and two-foot jumping kinematics. Fascinating to watch!

    As you know, I have been giving lectures on midtarsal joint (MTJ) biomechanics for quite a few years and most recently gave one at Biomechanics Summer School in Manchester in June. In this lecture, I also talk about talo-navicular joint (TNJ) and calcaneo-cuboid joint "stacking" and the dorsal-plantar thickness of the MTJ (i.e. second moment of area).

    As you know, the thicker the beam, the stiffer the beam. In fact, stiffness varies at the cube of the beam's cross-sectional stiffness so that a doubling of a beam's cross-sectional thickness will mean an eight-fold increase in beam stiffness. Therefore, as MTJ dorsal-plantar cross-sectional thickness increases so too will its forefoot dorsiflexion stiffness (i.e. sagittal plane stiffness of the MTJ-midfoot).

    Another important factor when considering forefoot dorsiflexion stiffness is the vertical distance from the plantar aponeurosis to the TNJ. As the vertical distance from the plantar aponeurosis to the TNJ increases, the sagittal plane MTJ-midfoot stiffness will also increase. Tension within the plantar fascia will also increase as gait progresses from early midstance to late midstance which will also "automatically" increase MTJ-midfoot sagittal plane stiffness as midstance progresses. Plantar instrinsic muscle activation and deep posterior compartment and peroneus longus activation will also increase MTJ-midooft stiffness. In other words, any increase in plantar ligament-plantar aponeurosis tension force and deep posterior compartment and pereoneus longus tendon force will increase MTJ-midfoot dorsiflexion stiffness.

    In other words, there are a number of factors other than just MTJ dorsal-plantar cross-sectional stiffness that influence MTJ sagittal plane stiffness. However, certainly we have come a long way from Elftman's speculation that the increase in MTJ sagittal plane stiffness comes from a "crossing of the TNJ and calcaneo-cuboind joint axes of motion. Elftman's ideas are still widely taught but Elftman's ideas do not have a shred of research evidence to support them. We are making progress!:drinks
  5. Yep, I appreciate that, but I figured that if we look at beam theory and see where it doesn't fit with the in-vivo observations, we might start to explore the "why not's"... so STJ position during gait and midfoot stacking... how does it fit in with our expectations/ observations? Moreover, where doesn't it fit? After all, this is supposed to be the one thing "Root" got right, right?

    So, for example, if we see the STJ position at midstance to result in a midfoot "stacking" which might appear to result in a decreased dorso-plantar stiffness, this would seem to be less than ideal from an evolutionary point of view- so what other factors are increasing the dorso-plantar stiffness at this time of need to meet the evolutionary need for metabolic efficiency, for example? Muscle force costs energy... The plantar fascia does not.

    Needs to be explored for the benefit of others, Kevin....

    Anyway all that said, maximal STJ supination should be the way forward to oppose maximal dorso-plantar "bending moments" at the midfoot during gait... is this what we see?

    Question 1: when do maximal dorso-plantar midfoot "bending" moments occur during walking gait?

    Question 2: What is the STJ position at this point in time during the walking gait cycle?
  6. I believe that there is quite a range of sagittal plane midtarsal joint (MTJ) and midfoot joint sagittal plane stiffnesses that will allow efficient bipedal locomotion (i.e. walking and running). There may be some activities will be enhanced mechanically by lower MTJ/midfoot sagittal plane stiffness, while they be other activities that will be enhanced mechanically by higher MTJ/midfoot sagittal plane stiffness.

    Therefore, there may be many foot structural variances at the subtalar joint (STJ), MTJ and midfoot that allow efficient bipedal locomotion patterns, but with quite substantial differences in MTJ/midfoot sagittal plane stiffness. My belief is that the central nervous system (CNS) regulates the stiffnesses of the hip, knee, ankle and MTJ/midfoot joints all simultaneously to optimize gait function for an individual's given foot and lower extremity structure and muscle function. Thus, even though the range of MTJ/midfoot stiffnesses may vary largely from one individual to another, the CNS will adjust for these "foot flexibility" differences in order to allow:
    1) decreased metabolic energy cost of locomotion,
    2) avoidance of pain, and
    3) avoidance of injury.

    One major issue we must consider, Simon, when looking at the optimization of MTJ/midfoot function and STJ function for individuals is that the common denominator for stance phase function of the foot seems to be largely the plantigrade position of the forefoot on the ground. For the majority of the stance phase, the plantar forefoot is resting on the ground and, I believe, that the relatively flat and wide contour of the plantar forefoot is extremely important in determining the mechanics of the STJ, MTJ and midfoot joints.

    I have long believed the plantigrade forefoot position on the ground to be very important mechanically (ever since my Biomechanics Fellowship over 30 years ago) and was the primary reason I came up with the "Plantar Parallel Position" for determining the STJ axis location by palpation (and not the STJ neutral position that Daryl Phillips liked to use when determining STJ axis location), because the plantigrade forefoot position is probably the most reliable and consistent position, and most realistic position, that the foot has relative to the ground during the stance phase of gait (Kirby KA: Methods for determination of positional variations in the subtalar joint axis. JAPMA, 77: 228-234, 1987).

    Therefore, if we are to look at the "maximally supinated STJ" as the position of maximum MTJ/midfoot stiffness, we must also consider the fact that the maximally supinated STJ rotational position will, in nearly all individuals, leave the individuals trying to walk on a forefoot highly inverted to the ground, which will increase the risk of injury to the individual. Therefore, when considering the optimization of STJ and MTJ/midfoot biomechanics, I believe it is best first considering that we use the plantigrade forefoot position as our plane of reference since the plantigrade forefoot position seems to be the one constant that the bipedal human prefers to function in during the majority of stance phase during walking and running gait patterns.

    Good discussion.:drinks
  7. efuller

    efuller MVP

    The time between heel off of the foot we are talking about and the time of heel contact of the contralateral foot. (Assuming that value is not negative as it would be in those shufflers)

    That position is usually near the position of maximal pronation of the STJ. Which is interesting in light of the McConail/ Sarafian twisted plate concept. They discuss how you would increase tension in the plantar fascia by pronating the STJ and increasing load on the medial forefoot. Their idea is that in this position you get the most rigid foot by using the plantar fascia to make it rigid. This makes good mechanical sense up to the point where you get overuse of the plantar fascia.

    The problem with the stacking / "joist effect" improvement of rigidity from bony position of the STJ is that to get that effect you have to be near the supination end of range of motion of the STJ. When you look at the position over the course of gait of the STJ during gait it moves only a small percentage of the available range of motion. Even with the most aggressive increased supination moment orthtotic you don't see large changes in STJ position. Also, as Kevin pointed out, if you could get that much change in position only the fifth metatarsal would be on the ground. (Which might help medial band plantar fasciitis, but might cause other problems.) It doesn't look like stacking is going to be a big part of the explanation of orthotic effectiveness. It might be part of it a few people, but not a large number.

    Another area to look is the decrease in range of motion of the midtarsal joint with supination of the STJ. There can be a dramatic decrease in MTJ range of motion with an Evans calcaneal osteotomy or a subtalar arthroresis. It would be very interesting to look to see if this decrease in range of motion also increased rigidity at the end of range of motion. Many past writers have confused the concepts of total range of motion with rigidity at the end of range of motion. (By end of range of motion I mean the transition from essentially zero stiffness to some stiffness. Specifically, in a joint whose range of motion is limited by ligament tension, the point where the ligaments start to develop tension. Of course if you increased the load you could stretch the ligament and that would give you more motion.)

    I've written before about how the anterior facet of the CC joint is like a door stop that moves with STJ range of motion. I think this has something to do with why there is a change in range of motion of the MTJ with STJ motion.

  8. Yet, using a rigid body approximation between navicular and cuboid, Nesters data suggests that the MTJ is not undergoing what we would consider "pronation" at this phase of gait. How does Nesters work impact here with twisted plate theory? See image attached.

    So, are we discounting the change in the second moment of area as being significant in influencing MTJ stiffness during gait?

    Attached Files:

  9. efuller

    efuller MVP

    Here we run in to the kinematics versus kinetics problem. One could say that the plantar fascia is resisting STJ pronation and to some extent midtarsal dorsiflexion and the motion that is seen is in some other direction that is not resisted by plantar fascial tension.

    There is comparision within a foot with different STJ positions and then there is comparison across feet with different tarsal orientations that will have a different second moment of area. I think we can discount the change in the second moment of area within a foot, over gait, because the amount of motion in the STJ is small and this won't change the second moment of area significantly.

  10. I can't agree completely with this. The subtalar joint (STJ) rotational motions during gait, though not large in magnitude, do cause significant changes in spatial orientations of the talo-navicular joint (TNJ) relative to the calcaneo-cuboid joint (CCJ). I think that these alterations in spatial location of the TNJ to CCJ that do occur with STJ rotational motion during the stance phase of gait are large enough to change the dorsiflexion stiffness of the midtarsal-midfoot joints. However, I do agree that comparing one foot to another foot will show much larger changes in second moment of area of the feet than when compared to the second moment of area on one foot at different points during the stance phase of gait.

    With that in mind, I believe the most significant change in the midtarsal-midfoot dorsiflexion stiffness that occurs during gait is not the alteration in TNJ to CCJ spatial relationship but rather is more likely is due to the increase in passive tension forces within the plantar aponeurosis and plantar ligaments that occurs from early midstance to late midstance. This large increase in plantar ligament/plantar aponeurosis tension forces as midstance progresses is lone of the most significant factors that increases the dorsiflexion stiffness of the midtarsal-midfoot joints during the midstance phase of gait.
  11. Will not the above verse Joint stiffness at the TNJ and CCJ and altered Midtarsal joint stiffness be somewhat dictated but the inclination angle of the Calcaneous ? and the available ROM ?

    The higher the inclination angle the greater the TNJ and CCJ affect on midtarsal dorsiflexion stiffness

    The less the ROM available at the ROM ath TNJ and CCJ the greater effect it has on Dorsiflexion stiffness at the Midtarsal joint

    and the the opposite ?
  12. Mike:

    There are multiple factors affecting midtarsal joint (MTJ) dorsiflexion stiffness in the sagittal plane. Longitudinal arch height (which correlates fairly roughly with calcaneal inclination angle) will significantly affect MTJ dorsiflexion stiffness since the plantar fascia is a longer distance away from the MTJ (i.e. plantar to dorsal height) in a pes cavus deformity versus a pes planus deformity.

    Another factor affecting MTJ dorsiflexion stiffness is the spatial relationship of the talo-navicular joint (TNJ) to the calcaneo-cuboid joint (CCJ). When the TNJ is more "on top of" or dorsal to the CCJ, there will be greater MTJ dorsiflexion stiffness. The TNJ becomes more dorsally located relative to the CCJ in feet which are more supinated at the STJ and in feet which have a laterally deviated STJ axis.

    Even another factor which is not mentioned, but which I think is quite significant is the thickness and stiffness of the plantar aponeurosis and plantar ligaments in the individual. There is probably quite a bit of inter-individual difference in plantar ligament and plantar aponeurosis thickness and elastic modulus which will greatly affect the MTJ dorsiflexion stiffness, and may also affect whether an individual, over time, during their childhood and adolescent years, develops either a low-arched foot, a normal arched foot or a high-arched foot.

    I believe that, once the research is done in the future, we will find that much of adult foot longitudinal arch structure is predetermined by the load-deformation characteristics of the plantar aponeurosis and plantar ligaments of the individual, and not solely due to the predetermined pedal osseous structure of the individual. In other words, those individuals with more stiff plantar ligaments and more stiff plantar fascias develop more cavus foot structure and those individual with more compliant plantar ligaments and more compliant plantar fascias develop more planus foot structure during their growth and development years from the time they first start walking to the time their foot fully matures.

    I've considered writing a theoretical article over the past two decades on this topic but, unfortunately, I haven't had the time to get to it. Should be interesting to see what future research tells us about this very interesting subject. Something definitely that needs to considered!:drinks

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