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Plantar ligaments and toe off

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Mar 21, 2019.

  1. scotfoot

    scotfoot Well-Known Member


    Members do not see these Ads. Sign Up.
    In part , this is a continuation of a previous thread .
    My question is , during push off , is the long plantar ligament under any tension ?
    I suspect it may not be .

    This can be understood clearly by looking at this video from Dr Kevin Kirby .

    In the video pink cords represent the plantar ligaments of the foot and blue cords the plantar fascia .

    During the later part of stance , as push off is approached ,the fascia is wound around the MTFJ causing a shortening of the distance between the MTFJ and the attachment of the PF on the calcaneus . If this distance shortens then does the distance between the points of attachment of the long plantar ligament also shorten to a point were the ligament is no longer under significant tension ?

    If so then clearly the long plantar ligament does not support the arch during push off .

    Any thoughts
    Longitudinal Arch Load-Sharing System Demonstration with Wooden ...



    upload_2019-3-21_12-50-3.jpeg ▶ 4:33
    21 Sep 2018 - Uploaded by Kevin KirbyThis wooden model of the foot shows how the plantar ligaments and plantar fascia work together to help ...
     
  2. scotfoot

    scotfoot Well-Known Member

    Related to the above , does the spring ligament have any role to play in supporting the medial arch of the foot during push off ? If it is not under tension then it won't have .
     
  3. efuller

    efuller MVP

    In some feet, the windlass may raise medial longitudinal arch decreasing tension in the spring ligament. In other feet, the windlass won't and the spring ligament will remain important for maintaining the arch. Sometimes, in posterior tibial tendon dysfunction the spring ligament becomes damaged. The absence of the supination moment from the PT tendon will make it harder for the windlass to raise the arch. Feet are different.
     
  4. scotfoot

    scotfoot Well-Known Member

    So would you agree that during push off the dorsally placed ligaments of the foot ,for example the tarsometatarsal ligaments , are being put under greater stress than the plantar ligaments ?
     
  5. efuller

    efuller MVP

    No. In gait, at push off, the external load is high dorsiflexion moment on the forefoot. A plantar structure, or many plantar structures, have to resist that forefoot dorsiflexion load. There is some range of motion of the joints that occurs before they become loaded. To get load in the dorsal ligaments in the face of a large dorsiflexion moment applied to the forefoot, the plantar fascia, and the plantar muscles would have enough tension in them to fully plantar flex the joint in question. Once the joint was fully plantar flexed, additional increase in tension in the plantar structures, would start to cause an increase in tension in the dorsal ligaments. I don't think that the plantar fascia can induce enough motion to fully tighten the dorsal ligaments.
     
  6. scotfoot

    scotfoot Well-Known Member

    Going back to Kevin's model in post 1 , if you shorten the blue cords to represent the winding of the PF around the MTFJ ,then the pink cords representing the plantar ligaments , become loose .
    On the other hand the hinged gap widens on the top surface of the model indicating increased stress /strain in dorsal ligaments .
    No ?
     
  7. efuller

    efuller MVP

    This illustrates the problem of talking about stiffness without talking about position of the joint. The joint motion in both dorsiflexion and plantar flexion is limited by tension in the ligaments. When the joint is in a position between the two extremes both dorsal and plantar ligaments can be loose. For an extreme case, look at the metatarsal phalangeal joints. The dorsal joint capsule (ligament) has folds that unfold when the joint is maximally plantar flexed. The same is true, but with not as much fold, for the dorsal ligaments of the first ray.

    To measure stiffness, you apply a force and see how much motion occurs. Starting at the middle of the range of motion of a joint when the ligaments have not tension, it takes very little force to move the joint. After some distance of movement, the ligaments will develop tension. When this happens, it will take more force to move the distal part relative to the proximal part and this will result in an increase in stiffness. For some positions of a joint there will be a very low stiffness. For a small range of other positions the stiffness will be much higher. For this reason you still need to consider joint position when examining joint stiffness.

    When you see separation of the parts of the model, you don't know if the ligaments are tight yet. When I have looked at cadaver range of motion, I don't think I saw the dorsal ligaments become tight when winding the windlass as far as it could go.
     
  8. scotfoot

    scotfoot Well-Known Member

    Quote "When I have looked at cadaver range of motion, I don't think I saw the dorsal ligaments become tight when winding the windlass as far as it could go. "

    So when do the dorsal ligaments become tight ? During which phase of gait are they most likely to become over stressed ?
     
  9. efuller

    efuller MVP

    To answer this question you need to look at the load. The dorsal ligaments become tight when the forefoot is maximally plantar flexed on the rearfoot. In the stance phase of gait, the external load on the foot tends to dorsiflex the forefoot on the rearfoot, so you would not expect the dorsal ligaments to become tight then. In swing phase, the loads are much lower and come the anterior tibial and extensor tendons. Here, the load also tends to dorsiflex the forefoot on the rearfoot. The dorsal ligaments are very unlikely to be overstressed, or even stressed, in normal gait.

    Kicking a ball? Maybe? Extensors are active in that activity and may counteract the external platnar flexion loads on the forefoot.
     
  10. scotfoot

    scotfoot Well-Known Member

    If it were not for the windlass mechanism I would agree . However with this in play , and especially at push off , although the force on the forefoot would be a dorsiflexing force , the plantar fascia tightens as the toes dorsiflex causing the bony arch of the foot to become more pronounced . That is to say it is plantarflexed distally and dorsiflexed proximally .

    Overall, the effect is not unlike a bow with the bow string represented by the PF . As the bow string is drawn, the back (dorsal aspect of foot ) of the bow is subject to tension and the belly ( plantar ) compression .

    At push off then , the plantar ligaments are not under stress but the dorsal ligaments are . The situation is quite different to midstance when the plantar ligaments are under stress and provide most of the rigidity to the foot .
     
  11. efuller

    efuller MVP

    The erroneous assumption that you are making is that the toes dorsiflex enough to make the dorsal ligaments tight. In some feet the toes don't dorsiflex at all. Have you ever tried these motions on a foot?


    The foot is not like a bow. The external forces are quite different.
     
  12. scotfoot

    scotfoot Well-Known Member

    It would be true to say that I am feeling my way along on this subject . My interest lies in midfoot mobility , or lack thereof ,and its effects on the functioning of the foot during push off .

    Are you aware of any papers which cover the topic of dorsal ligament tensions during gait ?
     
  13. scotfoot

    scotfoot Well-Known Member

    Can reduced midfoot mobility impact on the windlass mechanism and so compromise toe off by reducing the extent to which the toes can dorsiflex on the metatarsal heads ?
    I can't find anything specific on this so would greatly appreciate any references .

    Of course toe off is not just about propulsion .I wrote the following some time ago under the pseudonym "Blue " -

    Blue says
    June 28, 2012 at 10:38 pm
    Reading the comments of Mr Peter Bird above I wonder if he has considered the role that the contralateral foot plays in the placement of ,and subsequent weight transference onto, the reference foot and of the role that the contralateral intrisics play in this .

    So basically what I was saying is that if push off is compromised in the standing foot then so is the loading of the other foot during weight acceptance . Weight transference might never be fully completed .

    We now have a good idea that the intrinsics are important in toe off , assisting the plantar fascia to give the foot stiffness , but how does lack of midfoot mobility play affect the windlass and toe off ?
     
  14. efuller

    efuller MVP

    I don't understand why you think dorsal ligament tension is important during foot push off.

    There can be push off with or without midfoot mobility. Plantar flexion of the forefoot on the rearfoot can contribute to push off. My sense is that this contribution, if present, is small compared to push off from the ankle. There have been some papers on joint power at various foot joints. I don't recall if any of them looked at midfoot joint power.

    Winter looked at joint power and found an inverse correlation between ankle push and hip pull. It is possible to have 100% hip pull in gait with no ankle (foot) push. My recollection of the Winter paper is that the way they measured ankle push is it would include the contribution of push from within the foot.
     
  15. scotfoot

    scotfoot Well-Known Member

    During push off the windlass mechanism is engaged and the calcaneus and met heads are pulled closer to each other . This is thought to reduce the tension in the plantar ligaments as they get nearer to their resting lengths .

    Foot stiffness is thought to be provided by the plantar fascia and the intrinsic foot muscles acting to plantar flex the bony arch of the foot distally and dorsiflex it proximally . So at toe off the articulating bones of the arch are being pressed together at the more plantar aspect of their articulating surfaces .
    If there were no tension in the dorsal ligaments connecting the tarsals/metatarsals the whole system would fail and no stiffness would exist in the foot .

    You might imagine the following . Using your imagination take a few blocks of something like lego and tape the blocks together on their top and bottom surfaces to represent dorsal and plantar ligaments .

    This will give you a lego rod made of say five pieces of lego taped together . Now bend the rod a little and attach an elastic band (PF) ,under tension to either end .

    Ok , so now you have a rod under tension . Now imagine snipping through a bit of tape on the top surface of your arch between the blocks . The whole thing collapses .
     
  16. efuller

    efuller MVP

    No.

    Go buy the lego, make a stack and put tape on one side. Place the stack horizontally on the support and load the stack. When the tape is down it will require much more force to make the stack fail when compared to when the tape is on top. When a structure is supported at its ends and loaded in its middle, the load will increase tension on the bottom and increase tension on the top. In the case of the foot there is redundancy. That is, when the foot is loaded, the tension can be either in the plantar ligaments or the plantar fascia, or both.
     
  17. scotfoot

    scotfoot Well-Known Member

    Yes .
    I understand exactly what you are saying and don't disagree with the mechanics of your model . However you are talking about a line of blocks not and arch . And you have left out the plantar fascia . And the angle at push off is far from horizontal . Your model would work just the way you say it would , bit it's not representative of push off.

    The question is to what extent the PF unloads the plantar ligaments as it is wound around the MTFJ .
    It all about the windlass mechanism .


    I used to love Lego but my parents donated all mine to a local school about 40 years ago .
     
  18. scotfoot

    scotfoot Well-Known Member

    Below is a link to a scan of a foot , where the foot is being held in the sort of push off position that a sprinters foot would go through . In this type of position I would expect the dorsal ligaments of the arch of the foot to be under stress .

    Two other points about this scan .
    1 The energy stored in the foot can only propel the foot vertically . This will assist with cadence
    2 Look at the metatarsals . The metatarsal parabola of the foot in a horizontal position has given rise to a transverse arch all the way to the ground .

    https://twitter.com/DAllanBiomech/status/1114500089853218816
     
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