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Volume of space between the plantar fascia and bony arch of the foot .

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Aug 11, 2019.

  1. scotfoot

    scotfoot Well-Known Member


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    During gait , does the volume of space between the plantar fascia and the bony arch of the foot change , and if yes , what does this mean for the tissues that occupy this space ?
     
  2. scotfoot

    scotfoot Well-Known Member

    With regard to the above , and speaking hypothetically , would the kinematics of the foot change directly as a result the tissue bulk between the PF and the bony arch no longer being present .

    Could this be modeled using the properties skeletal muscle under compression to represent the tissue bulk ?
     
  3. scotfoot

    scotfoot Well-Known Member

    Very recently a paper was produced by a group of searchers looking into the windlass mechanism . The paper was -

    Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation.
    Welte L, Kelly LA, Lichtwark GA, Rainbow MJ.
    J R Soc Interface. 2018 Aug;15(145). pii: 20180270. doi: 10.1098/rsif.2018.0270.
    Here is a quotation from the paper .
    "The purpose of this investigation was to understand the interaction between the windlass and arch-spring mechanisms, by engaging the windlass through MTPJ dorsiflexion, and investigating the effects on arch energetics during a dynamic compression. We hypothesized that MTPJ dorsiflexion would pre-tension the plantar fascia and stiffen the arch. However, in contrast to our hypothesis, the engagement of the windlass mechanism reduced the stiffness of the arch and increased energy absorption and dissipation. The effect of MTPJ dorsiflexion therefore has the potential to affect locomotion by altering the mechanical energy profile within the foot. "

    So the researchers did not find what they thought they would .

    They forward an explanation of their results as follows -

    " The windlass did, however, modulate the energetics of the arch during dynamic loading. When the windlass mechanism was engaged, the arch was shortened significantly, which probably placed other tissues crossing the arch closer to their resting length. The arch could therefore go through a greater excursion due to the nonlinear elastic properties of the arch-spanning tissues. This would functionally reduce the bulk stiffness of the arch and lead to greater elongation, and consequently facilitate greater energy absorption and dissipation during cyclic loading of the foot "

    However , an alternative explanation might be that when the toes are plantarflexed , and force is applied down through the foot as shown in the experimental set up , the tissues of the foot between fascia and bony arch resist compression . When the toes are dorsiflexed through the windlass mechanism , the volume of space between the bony arch and plantar fascia is increased allowing the foot to compress more easily (reduced stiffness ) .

    I feel this is a more likely explanation .
     
  4. efuller

    efuller MVP

    Gerry,
    Have you looked at wet foot prints at the swimming pool? The medial arch does not contact the ground for a vast majority of people. When the skin does not contact the ground, the muscles of the medial arch are not going to be compressed.

    The explanation in the paper, I believe, is closer to the truth. I do have a problem with their notion of resting length for the other structures that stiffen the arch. I believe a better explanation is that there are many structures that, when under tension, add plantar flexion moment to the forefoot relative to the rearfoot. When the toe is dorsiflexed the windlass shortens the arch and some of the other structures are under less tension in this arch position. This makes the plantar fascia the only structure resisting forefoot dorsiflexion from this high arched position. When loaded, with the toe dorsiflexed, and the arch height increased, the plantar fascia is the only structure resisting the exernal load and it will be less stiff.
     
  5. scotfoot

    scotfoot Well-Known Member

    Hi Eric .
    Quote
    "Gerry,
    Have you looked at wet foot prints at the swimming pool? The medial arch does not contact the ground for a vast majority of people. When the skin does not contact the ground, the muscles of the medial arch are not going to be compressed. "

    I am not saying that the structures in in medial arch area are compressed between the bony arch of the foot (BAF) and the ground but that they are compressed between the tensioned plantar fascia and the BAF .

    Is there any evidence that this types of compression exists ? I believe so , namely the pressures generated by the plantar venous plexus . As I have outlined previously , this mechanism can be viewed as an indwelling , pressure measuring system .

    Note that the plantar venous plexus functions equally as well with no ground /midfoot contact at all . ( Gardner and Fox )

    By way of further explanation here is something from a few years ago . I am quoting myself but it's all simple mechanics .

    Gerry

    November 16, 2014 at 11:22 am
    Hi Casey
    As outlined above I wondered if the plantar intrinsic foot muscles (PIFM) located between the bony arch of the foot (BA) and the plantar fascia might be subjected to passive transverse compression (PTC)when acted upon by these structures during early stance .
    I also wondered if ,during mid to late stance when the PIFM are active ,an increase in the stiffness of the “intrinsic core “might provide even greater support to the BA and its articulating joints .
    So the question for me is -Is there an increase in the intra and inter muscular pressure in early stance and can this be attributed to PTC ?
    An in vivo study to investigate this might involve indwelling intramuscular pressure sensors but why go down this road when such a sensor may already be in place in the form of plantar venous plexus (PVP).
    So can the PVP be looked at in this way? Is the pump emptied by inter-muscular pressure or by stretching and necking down ?
    NECKING DOWN-
    Since the veins of the plexus are elastic longitudinally and viscoelastic transversely the effective emptying of the PVP by stretching and necking down is ,in my inexpert view ,unlikely .
    So if necking down is not the mechanism of PVP emptying then the pump must be emptied by increased inter- muscular pressure .But what cases this ?
    If the pump empties in early stance when the plantar intrinsic muscles are not activated then the pressure must be created by stretching of the PIFM or by PTC.
    A study by BJ Broderick et al(1)showed that the PVP is emptied when a standing individual performs toe curls so it can be inferred that inter-muscular pressure is increased when the muscles become activated and contract. I believe that it is reasonable to think that inter-muscular pressure is therefore not increased when the same muscles become less active and return to their original more lengthened positions .
    So, in my opinion, it is most likely that in early stance the PVP is emptied by the passive transverse compression of the “intrinsic core” and indeed that the existence of a functioning PVP confirms the existence of a significant level of PTC . I also think it likely that the pressure generated in the pump reflects the inter and intra-muscular pressures generated within the “intrinsic core” and hence the pressures generated at the interfaces between the core and the plantar fascia and BA .
    I would welcome any comments on the above
    Kind regards
    Gerry
    Gerrard Farrell
    Glasgow
    Ref (1) Broderick et al -Venous emptying from the foot ; influences of weight bearing ,toe curls,electrical stimulation ,passive compression and posture 2010
    REPLY
     
  6. scotfoot

    scotfoot Well-Known Member

    Following on from the above , it seems quite possible to me that at toe off ,and as the 2nd phase of the windlass mechanism comes into play ("Hick's Phase ") , the space between the bony arch of the foot and the taut plantar fascia will increase . This will in turn lead to less transverse compression of the intrinsics in this space ,reduced work partitioning and increased power at the MTPJ .
     
  7. scotfoot

    scotfoot Well-Known Member

    Below is an abstract from a recent paper ( DJ Farris et al 2019 ) ,which looks at the effects of nerve blocks on the intrinsic foot muscles .

    Muscle is a viscoelastic material who's properties change depending on activation levels within the muscle .

    An alternative explanation of the research groups findings , is that at low speeds , the less than normally activate intrinsics show more strain (deformation ) than would normally be the case .

    Strain in a viscoelastic materials is time dependent , so rapidly applied forces are less likely to produce strain in the "foot core" even with reduced innervation , and so nerve blocks are less likely to affect foot function at higher (faster ) loading rates .

    I once suggested that to many academics seem to spend their time trying to shoehorn hippopotamus feet into size 3 class slippers , before claiming to have found Cinderella ,and perhaps I am falling into the same trap here . But I don't think so .

    This groups results seem to fit the idea of the intrinsics acting as movers of levers as well as being a collective "viscoelastic core" at the center of the foot . Acing in this way ,small levels of energy can make a dramatic difference to foot function and robustness .
    Abstract

    Human feet have evolved to facilitate bipedal locomotion, losing an opposable digit that grasped branches in favor of a longitudinal arch (LA) that stiffens the foot and aids bipedal gait. Passive elastic structures are credited with supporting the LA, but recent evidence suggests that plantar intrinsic muscles (PIMs) within the foot actively contribute to foot stiffness. To test the functional significance of the PIMs, we compared foot and lower limb mechanics with and without a tibial nerve block that prevented contraction of these muscles. Comparisons were made during controlled limb loading, walking, and running in healthy humans. An inability to activate the PIMs caused slightly greater compression of the LA when controlled loads were applied to the lower limb by a linear actuator. However, when greater loads were experienced during ground contact in walking and running, the stiffness of the LA was not altered by the block, indicating that the PIMs’ contribution to LA stiffness is minimal, probably because of their small size. With the PIMs blocked, the distal joints of the foot could not be stiffened sufficiently to provide normal push-off against the ground during late stance. This led to an increase in stride rate and compensatory power generated by the hip musculature, but no increase in the metabolic cost of transport. The results reveal that the PIMs have a minimal effect on the stiffness of the LA when absorbing high loads, but help stiffen the distal foot to aid push-off against the ground when walking or running bipedally.
     
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