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Plantar fascosis and dorsiflexion stiffness

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Nov 19, 2012.

  1. Members do not see these Ads. Sign Up.
    was thinking about this the other day.

    With the elastic changes in the fascia that occur with plantar fascosis, would that lead to an increase in dorsiflexion stiffness at the MTP joints ?

    If so, which I think it does , are we treating the chicken or the egg ? ( I also think it does not really matter tbh )

    Then if the change in elastic properties causes an increase in dorsiflexion stiffness at the MTP joints, how does the tissue problem resolve without treatment in general as noted in studies after 12 months.

    ie if an increase in dorsiflexion stiffness is a cause of the plantar fascia issue, and a by product of the healing from the excessive strain in the fascia is a thickened, less elastic tissue, which leads to increased dorsiflexion .....

    well you get the idea

    but thought it might lead to a interesting biomechanics discussion.
  2. Phil Wells

    Phil Wells Active Member


    If dorsiflexion stiffness increases, does this equate to decreased elongation of the plantarfascia at loading? If so, does the change in rate of loading/elongation result in a more beneficial Young's Modulus of the tissues?
    This may be the bodies answer to PF - and is often all that is needed. However if a vicious circle of excessive loading/lengthening is occurring then we may get chronic symptoms.

    Alternatively this increased stiffness may change rearfoot-forefoot coupling moments.


    Just having a stab at it.


  3. That is sort of what I was thinking, the fascia gets injured, heals changes elastic properties, which increases the dorsiflexion stiffness at the MTP joints etc until finally we get a point at which the patient functions pain free. But agreed the less elastic the greater the effectiveness of the fascia is preventing elongation.

    also I maybe was not clear in my 1st post the higher the dorsiflexion stiffness the greater the load on the fascia, due to changes in the effectiveness of windlass not the old argument of what comes 1st re dorsiflexion stiffness.

    re coupling maybe Phil, but the coupling pattern may stay the same but take greater force to achieve it, ie tension in the Achilles tendon.

    although I am feeling this is beer napkin discussion with pictures, see how we go ?
  4. Craig Payne

    Craig Payne Moderator

    Mike, here is some data (see attachment)

    The force to dorsiflex hallux almost double on painful side in those with unilateral plantar fasciitis.

    chicken or egg?

    Do Jacks test both sides in those with unilateral plantar fasciitis - almost always it harder on the painful side.

    Attached Files:

  5. Do we know that plantar fasciosis causes an increase in tensile stiffness of the plantar fascia, or is that speculation?
  6. speculation and assumption

    but I assume the breakdown in tissue and then repair material must be added, which I again assume will change the tensile stiffness of the fascia.

  7. I don't think this has been studied before so, as far as we know, the tensile stiffness of the plantar fascia may decrease with plantar fasciosis.
  8. I was thinking during the cellular breakdown it might decrease, but then once the tissue repair process began it would increase.

    Would you or others agree ?
  9. I don't have a clue.
  10. efuller

    efuller MVP

    There are two big ideas here. Wound healing and its effect on the tensile properties of the tissue and mechanics of the plantar fascia.

    Wound healing. Fasciosis? Well, if it is a high tensile load injury then there will be tissue damage and then tissue repair will happen. Inflammatory response etc. Eventually the scar tissue will remodel to become collagen. The fascia was collagen to begin with and if the wound eventually differentiates into the same type of collagen then it should have the same mechanical properties as the original fascia. It's been a long time since I reviewed wound healing so I'd defer to someone else on that.

    Mechanics of the Windlass and MPJ stiffness. The MPJ is variably stiff because of the windlass mechanism. When the foot, or more specifically the ray, is unloaded there will be very little tension in the fascia and the MPJ will not be stiff. Upon weight bearing, the ray is dorsiflexed and the distance from the proximal attachment of the fascia and the distal attachment is increased and this will generally increase the tension in the fascia and this will increase the dorsiflexion stiffness of the MPJ.

    Sitting here on my couch, I would wager that the change in stiffness from mechanics will be much greater than any stiffness changes from inflammation of the fascia.

  11. efuller

    efuller MVP

    It probably depends on where, or when, it is in the healing process. The analagous process that I remember from back in school was healing of a skin laceration. I remember some studies assessing tensile strength vs time. Which is quite relevant on the timing of removing sutures. The strength of the skin changes over time and at some point the skin is stronger than the sutures.

    I think we are still debating what exactly is the injury in plantar fasciitis/ fasciosis is. Does the injury involve partial tear of the tissue? Does it change the tensile properties of the fascia?

  12. In addition to the factors mentioned already by Eric, we must be careful when we talk about the stiffness of biological structures. It is important that we understand that the structural components of the foot and lower extremity will not exhibit the same stiffness throughout their functional range of loading and deformation and that stiffness is not the only mechanical factor that affects these structures.

    For example, lets say that the foot is non-weightbearing, with the individual laying on an examination table, so that the plantar fascia has neglibible tensile force acting on it. Then an examiner loads the forefoot so that he/she manually exerts 5 pounds of force on the plantar forefoot. Would you assume that the stiffness of the plantar fascia with this 5 pounds of force is the same stiffness that the plantar fascia would possess when that same individual is running and exerting 250 pounds of force on the plantar forefoot? I hope not.

    In load vs deformation testing of the plantar fascia (see illustration), the stiffness will generally increase as the load is increased past a certain force, at which point it will tend to form a straight line called the "Hookean region" or "elastic region" of the load vs deformation curve (see illustration). This Hookean region (named after the great 17th century British scientist, Robert Hooke) of the plantar fascia is where the plantar fascia will act as a relatively elastic material when loaded and unloaded with increasing and decreasing tension force. However, if the plantar fascia is loaded with too much tension force, then it will become less stiff as it begins to undergo plastic deformation and permanently elongate or tear (see illustration).

    Therefore, when we speak of the stiffness of an isolated structural component of the foot or lower extremity, whether it is the plantar fascia, the Achilles tendon or the second metatarsal, we must be careful to also understand that during physiologic and pathologic loading conditions, the stiffness of a material is not a constant. The stiffness will vary not only with the magnitude of load being applied but will also vary depending of the direction and point of application of load vector on that specific structural component.

    As far as plantar fasciosis is concerned, if the thickening of the plantar fascia that occurs with plantar fasciosis consists of a material which is the same as the molecular structure of the original plantar fascia (i.e. the plantar fascia is homogeneous), then, yes, this additional thickening of the plantar fascia would tend to increase the tensile stiffness of the plantar fascia as a whole. However, in this case, the Young's modulus of the plantar fascia would not change, even though the plantar fascia is thicker, since Young's modulus is calculated by the stress/strain of a material [stress being determined by force/cross sectional area and strain being a dimensionless number representing the change in length of the material being loaded].

    Therefore, stress/strain = Young's modulus, may not necessarily be predictive of putting the plantar fascia into a materials testing device (see illustration) and measuring the tensile force (in Newtons) required to elongate the plantar fascia a certain number of millimeters since the thickness of the plantar fascia will increase the stiffness of the plantar fascia measured by the materials testing device (if we define stiffness as Newtons/mm). In other words, adding thickness to the plantar fascia (i.e. increasing the cross-sectional area of the plantar fascia) will not increase the Young's modulus of the plantar fascia if the fascia is homogeneous since cross-sectional area of the plantar fascia is used to calculate Young's modulus but Young's modulus is not necessary to determine the stiffness of the anatomical structure, since stiffness may be defined differently than Young's modulus.

    Therefore, trying to answer the original question of trying to determine how "plantar fasciosis" affects the tensile force within the plantar fascia is relatively complicated, especially since we don't have any experimental data, to my knowledge, of how plantar fasciosis actually affects the load vs deformation characteristics of the plantar fascia as a whole.

    Hope this helps.
  13. translation

    there is 10 research papers - :D

    seriously thanks Eric and Kevin much to consider.

    Happy thanksgiving to you both and your families and of course all others reading from the US :drinks
  14. One of the other factors that makes it difficult to determine how much tensile load the plantar fascia is subjected to during weightbearing activities is that there are other tensile load-bearing structures in the plantar arch of the foot that can share the load that help prevent arch flattening. In combination, these structures form a Load-Sharing System of the Longitudinal Arch:

    From superficial to deep, the structures comprising the Load-Sharing System of the Longitudinal Arch are:

    1. Central component of plantar aponeurosis (i.e. plantar fascia)
    2. Plantar intrinsic mucles
    3. Deep flexor muscles (i.e. PT, FDL & FHL) and peroneus longus muscle
    4. Plantar ligaments

    When ground reaction force (GRF) acts on the plantar forefoot during weightbearing activities, a forefoot dorsiflexion moment is produced. This forefoot dorsiflexion moment will tend to cause a flattening of the longitudinal arch of the foot unless it is resisted by a forefoot plantarflexion moment from some other source. In the human foot, the sources for these forefoot plantarflexion moments are #1-4 above or, in other words, is the Load-Sharing System of the Longitudinal Arch (LSSLA).

    Each of the components of the LSSLA share the common function of causing a forefoot plantarflexion momen. As a result, all of these components of the LSSLA will all work together to help resist longitudinal arch flattening and, thus, will also all work together to help maintain the arch height of the foot during weightbearing activities. In other words, when you see a foot standing on the ground with a normal longitidinal arch height, and you know that GRF acting on the plantar forefoot will tend to cause a flattening of the longitudinal arch of the foot, you may also then be able to very confidently state that there must be other internal forces at work within the foot which resist forefoot dorsiflexion and longitudinal arch flattening. Those internal forces which are at work during weightbearing activities are each of the components of the LSSLA.

    As a result of the LSSLA, where multiple structures perform the same function, it would be nearly impossible to predict the actual tensile force within the plantar fascia unless one also knew the tensile forces in the other tensile load-bearing structures of the LSSLA, since they all share the tensile loading forces which help maintain the human foot's longitudinal arch. However, the practical mechanial advantage of the LSSLA is that if one structure fails (i.e. partial or complete tear), then there are other tensile load-bearing structures within the plantar arch that can still act to help maintain longitudinal arch height (by exerting a forefoot plantarflexion moment). Eric Fuller likes to call this system "redundancy", which also nicely describes this important concept.

    My March 2012 and April 2012 Precision Intricast Newsletters cover these concepts in greater detail. These newsletters which will be included in my fourth book to be tentatively published in early 2014. ,

    Here is an illustration from my March 2012 Precision Intricast Newsletter which uses a simplied model of the longitudinal arch of the foot to demonstrate one of the concepts of the LSSLA. A surgically cut (or ruptured) plantar fascia will tend to increase the tensile load on the plantar ligaments and plantar intrinsic muscles during weightbearing activities since, without the forefoot plantarflexion moments that are normally generated by passive stretching of the plantar fascia, the other components of the LSSLA will be subjected to increased tensile forces to maintain longitudinal arch height.
  15. drsha

    drsha Banned

    The Egg, most of the time.


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