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Ankle and midfoot function: interpreting clinical gait data

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Mart, Sep 18, 2008.

  1. Mart

    Mart Well-Known Member


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    thread split from


    Ankle Joint Equinus vs Talar Equinus

    more later

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  2. Mart

    Mart Well-Known Member

    For those who already visited this thread and found it bare, sorry about my tardy start . . . . . a busy week turned into a busy weekend. Also my intent was to start the post with a bunch of gait data for perusal and then I changed tack.

    Previously Bruce (Williams) had talked about qualified use of the term “equinus”, I think it was agreed that we should be thinking in terms of ankle and mid tarsal joint (MTJ) dorsiflexion stiffness when talking about related aspects of foot function.

    Some off forum discussion concurrently developed with me regarding the use of in-shoe and Mat plantar pressure measurement and augmented 2D computerized video analysis (using 2 synchronized 2D views); essentially what the merits and limitations might be given the paucity of definitive interpretative instruction on this subject and lack of validation of the underlying technology and data we might use for the purpose of understanding a patient lower limb function and improving outcomes by making better treatment decisions.

    My thought was to see how those of us using this technology might interpret the function attributed to ankle and MF stiffness and we embarked at the end of Bruce’s thread a token exploration of this, this thread now picks up on the start of this idea.

    Perhaps it would be a better initially to consider how those of us with the technology might employ it in a clinically useful way to explore the issue of rear foot stiffness.

    I have several ideas – this is the first and I guess, before spending too much time testing it, I am soliciting a reality check.

    In terms of clinical evaluation Kevin (Kirby) said “we are not simply measuring the ankle joint dorsiflexion when we measure the plantar foot to the tibia, we are also measuring subtalar, midtarsal and mid foot motion also.”

    Because of the limitations (outlined below) in measuring the angle formed between the lateral 5th Ray and fibular in the non weight-bearing foot “in neutral position” I started using the “lunge” test in selected patients to attempt to evaluate and predict ankle function. Again this has been discussed at some length and I cut and paste edited highlights at the end to make this post more complete.

    After a bit of testing I found the variance of values I obtained using an inclinometer against the anterior tibia larger than using carefully aligned video camera and measuring angles with software. My opinion was that it is often difficult to decide where the inclinometer rests because of the concave shape of the tibia.

    Also I decided to design and fabricate a plinth with an adjustable micro switch wired in series with a visible LED and positioned below the heel to detect the instant of heel rise which again I found reduced the variance in values for a series of trials.

    Whilst I feel this allowed me to quantify this tibial excursion over the foot with a good degree of confidence the issue of the flexibility threshold being detected by the heel rising because of MF dorsiflexion rather than ankle dorsiflexion remained unresolved.

    I tried adding a synchronized view of the medial segment of the foot to give some qualitative data but this often appeared ambiguous and I wanted to start this thread considering how to improve and interpret lunge test values.

    The lunge test is normally performed with the body COM behind the foot and the knee bent. I presume this is done to make balance easier, reduce the likelihood of “lifting the heel” and allow subject to concentrate on slowly advancing the measured knee rather than what is involved otherwise in maximally dorsiflexing ankle to heel raise which can be tricky.

    Whilst this works, the limb is not positioned as it would be during the “2nd rocker” with knee straight or slightly flexed and body COM roughly advancing above talo-crural joint.

    Although the lunge value makes no claim to represent a true functional gait parameter, the value of what it measures may be compromised if it doesn’t reflect normal gait position. Also, is it an index of things other than ankle stiffness, eg is low lunge value correlation with football injury more a reflection of identifying lateral ankle instability in those with laterally deviated sub-talar joint axis than those with posterior group contractures? (increased plantarflexion moment at mid tarsal joint in those with elevated sub-talar joint supination moment with increasing tendo-achilles force).

    I feel that a modified version of the lunge test may fill a gap in our measurement tool box.

    What I propose is;

    Modify lunge position to mimic gait posture.

    Kevin has nicely criticized our pre-existing clinical measurement of ankle flexibility citing lack of discrimination between ankle and mid foot motion. Likewise he criticized the lunge value for similar reasons. Although timing of heel rise is a function of the combination of ankle and MF stiffness, when viewed a kinematic clue it is also a function step length. Everyone with a normally functioning foot has an appropusive gait if they reduce step length which happens if you simply slow down without proportionally reducing cadence.

    If we have access to a pressure mat I believe we can exam, possibly quantify ankle and MF stiffness by doing the following:

    Stand on mat and record pressure data of stance foot whilst mimicking a step. Incrementally increase step length until heel rise occurs.

    View synchronized FMat data with saggital aligned 2D video. Measure tibial excursion against unloading of heel and when present, the increased plantar loading of MF.

    I believe this may allow us to separate the 2 motions using pre-existing equipment which many of us already use for other purposes.

    Reality check invited

    Cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com


    extra stuff for those unfamiliar with MF function and lunge test.

    My ideas on mid foot (MF) function evolved considerably as a result of this forum. I have cut and paste some edited text mostly from Kevin from previous thread on midfoot postion/function to illustrate this.

    Firstly finding a good alternative to my college day “Rootian” concepts of mid tarsal joint (MTJ) locking mechanisms from 20 years ago, Kevin Kirby truncated nicely Nestor et Al’s recent and well regarded work with;

    “The MTJ may have only one true instantaneous axis of rotation at any one time during its motion. This instantaneous axis of motion has multiple possible spatial locations depending not only on the internal morphology of the foot but also the internal forces and external forces generated across the MTJ. In other words, the MTJ is not a highly constrained joint, as is the subtalar joint, and may be moved in nearly any direction depending on how forces are acting across it. The subtalar joint, on the other hand, is a highly constrained joint, that will move along nearly the same joint axis regardless of how direction and point of application of the external forces acting across it”.

    He then gave us his excellent lecture notes on MF function and included these examples:

    Foot A: Foot with low forefoot dorsiflexion stiffness will allow increased forefoot dorsiflexion motion for a given increase in magnitude of GRF on plantar forefoot.
    Heel-off will be delayed since insufficient internal forefoot plantarflexion moments are developed during late midstance to resist forefoot dorsiflexion


    Foot B: Foot with medium forefoot dorsiflexion stiffness will allow average forefoot dorsiflexion motion for a given increase in magnitude of GRF
    Heel-off will be normal since sufficient internal forefoot plantarflexion moments are developed during late midstance to prevent excessive arch flattening


    Foot C: Foot with high forefoot dorsiflexion stiffness will allow decreased forefoot dorsiflexion motion for a given increase in magnitude of GRF on plantar forefoot
    Heel-off will be early since sufficient internal forefoot plantarflexion moments are developed early in stance phase so that the early restriction of forefoot dorsiflexion causes an early heel-off

    During clinical exam for “ankle joint dorsiflexion” in feet with different forefoot dorsiflexion stiffness…..

    Increase in forefoot dorsiflexion stiffness results in decrease in “ankle joint dorsiflexion” since forefoot dorsiflexes less on rearfoot for a given force exerted on the forefoot by examiner

    This of course raises the question

    Is standard measurement technique for ankle joint dorsiflexion measuring dorsiflexion of talus to tibia or is it actually measuring forefoot dorsiflexion relative to rearfoot?

    Kevin goes on to say;

    Effects of increase in forefoot dorsiflexion stiffness during weightbearing activities:
    – Arch of foot becomes higher during walking/standing
    – Heel off occurs earlier during stance phase of walking
    – Achilles tendon tensile force is increased for a given apparent ankle joint dorsiflexion angle
    – GRF forefoot will be greater at middle of midstance


    Adding bony issues to the equation: The dorsal-plantar thickness of the midtarsal-midfoot articulations would be one factor that would affect forefoot dorsiflexion stiffness for the medial-lateral MTJ axis. Increased dorsal-plantar thickness of the midtarsal-midfoot joints would tend to increase forefoot dorsiflexion stiffness.

    Also of relevance: The center of pressure (CoP) will tend to more anteriorly located in the foot with increased forefoot dorsiflexion stiffness due to its increased internal resistance to forefoot dorsiflexion, all other factors being equal. Kevin

    From Craig (Payne):

    LUNGE TEST
    1. Patient stands against wall with about 10cm between foot and wall.
    2. Have them move one foot back a foot's distance behind the other
    3. Bend knee of front limb until knee touchs wall - keep heel on ground.
    4a. If knee cannot touch wall without heel coming off ground, move foot closer to wall --> repeat
    4b. If knee can touch wall without heel coming off ground, move foot further away from wall --> repeat
    5. Keep repeating 4 until can just touch knee to wall and heel stays on ground.
    6. Measure either:
    a) Distance between wall and great toe (<9-10cm is considered restricted)
    b) The angle made by anterior tibia to vertical (<35-38 degrees is restricted)
    (see discussion in other thread on reasoning behind actual values)

    I do test when issuing/dispensing foot orthoses with them standing on foot orthoses and always add a heel raise (usually only ~3mm is enough) if they can not get to 35-38 degrees.

    I first learnt of the lunge test when Kim Bennell published their reliability study:

    Bennell K et al: Intra-rater and Inter-tester reliability of a weightbearing lunge measure of anbkle dorsiflexion. Australian Physiotherapy 24(2)211-217 1998

    I promptly ignored it becasue of my (and the professions) mindset of the time .... ie the test was not done with the STJ in neutral, allegedly increasing the range.

    After that a number of things influenced my thinking:
    1. We started to wake up re the "mindset"
    2. Numerous podiatrists and, especially, physiotherapists anecdotally started to comment on how useful the lunge test was (even though it was not done STJ neutral)
    3. I started to understand more about the concepts of "range of motion" vs "stiffness"
    4. We did our research on the 10 degrees of ankle dorsiflexion being considered normal (...it not)
    5. A number of clinicians were beginning to make throw away lines like - "if your orthoses does not work, then add a heel raise' - this was based on their good clinical experience, but where I come from, we have to do better.
    6. Pope et al (1998) showed the lunge test was prospectively predictive of injury in army recruits and Gabbe et al (2004) showed an association with lunge and football injuries.

    At the end of the day, a clinical decision had to be made when adding a heel raise to a foot orthoses if the calf muscles are tight. We can not use the standard measurement and 10 degrees. Taking the work of Pape et al (1998) and Gabbe et al (2004) we now testing a protocol that involves doing the lunge test while standing on foot orthoses - if the tibia can not get to 35-38 degrees, a heel raise (usually only 3mm) is added. Some of the work suggests that 9-10cm distance between the wall and foot as a cut off point - the problematic nature is that all shorter people will have less than that, so I prefer the tibial angle part of the measurement.

    It may well be that 35-38 degrees as the cut of point is not correct, but we had to make a 'judgement call' and start somewhere - I suspect that its in the "ballpark"

    Gabbe BJ, Finch CF, Wajswelner H, Bennell KL. Predictors of lower extremity injuries at the community level of Australian football.Clin J Sport Med. 2004 Mar;14(2):56-63.

    Rodney Pope, Rob Herbert and John Kirwan: Effect of ankle dorsiflexion range and pre-exercise calf muscle stretching on injury risk in Army recruits. Australian Physiotherapy 44(3)165-172

    We have found no correlation between the value obtained for traditional non-weightbearing ankle joint ROM and the weightbearing lunge test ROM.

    A 3mm heel raise moves most people past the 35-38 degrees. Shannon Munteanu has done a whole lot of trig calculations on this - I will see if he can reply.

    Why is this test used, and what are its benefits against other measures of equinus?

    1. It has been shown to prospectively predict injury (how many other clinical tests do that?)
    2. It is related to dynamic function (how many other clinical tests do that?)
    3. It may be predictive of orthotic outcomes (how many other clinical tests do that?)

    How many of the clinical tests do you use that meet those 3 criteria ... or even just one of them? None?

    Craig, please explain the mechanical reasons behind always adding a 3 mm heel lift to these patients when they have, for example, 33 degrees on the lunge test but their ankle joint is never dorsiflexed more than about 10 degrees during walking gait and they are not involved in running activities.


    Kevin, these same people who don't run, can't avoid inclines (escalators/slopes) and can't avoid descending steps or gutters.
    This undoubtedly quashes the magic '10 degree figure' that many believe and are side-tracked about. The other thing is that why do we assume that the sedentary don't hurry for a few steps during an intermittent but urgent activity (late for a pedestrian crossing; catching bus etc.)

    The whole point of the lunge is not a magic minimum figure/angle. It provides information about (a) symmetry (My advice is not to be too concerned about 10, 12, 33 or 35 degrees. The most important benchmark (in unilateral conditions) is the contra-lateral lunge reading.) and (b) ankle joint health and whether stretching is appropriate or inappropriate.

    I cannot fathom how one can fully understand the ankle joint in terms of complete diagnoses, prognosis and when to refer on, without first understanding and utilizing the lunge test.

    Kevin, how do you test for anterior ankle impingement(AAI)? I guess the classic AAI involves bone on bone and can be viewed in a lateral xray film. But the more common, under-diagnosed, misunderstood variety of AAI involves non-osseous structures.

    There is a huge difference in how one should treat an ankle equinus on the basis of end-feel. Physiologically, end-range dorsi-flexion is limited by posterior ankle joint structures. Pathologically, this is limited by anterior structures. Although most musculo-skeletal practitioners prescribe stretching for every equinus, to do so with an anteriorly impinging ankle does not make sense.

    As for an internally deranged ankle, I am confident the lunge test will be restricted on the ipsilateral side, and that the end-feel restriction will not be posterior to the joint; hence I disagree that the lunge has no place in testing for such pathology.

    The other thing, is that if used properly, the lunge test can determine whether the inferior tib/fib joint and/or syndesmosis is relevant in ankle joint hypomobility. I have presented this in Craig's presence, and have yet to fill in the research blanks.

    But I will stick to my foolish conclusion that "I cannot fathom how one can fully understand the ankle joint in terms of complete diagnoses, prognosis and when to refer on, without first understanding and utilizing the lunge test". I did not suggest foot nor lower extremity; simply the ankle joint.

    I would be interested to see how you test and treat AAI without the functional weightbearing dorsi-flexion lunge test.


    To answer your question, I use a weightbearing stress dorsiflexion radiographic projections of the ankle to diagnose "anterior ankle impingement".
    If you can only rely on radiology to detect/diagnose anterior ankle impingement, you are only picking up the classic osseous bone-to-bone variety; and I agree that this is one solitary pathology.

    However, you are not picking up the more common variety that accompanies many ankle conditions from a sprain to post-ORIF-immobilisation. The soft-tissue underpinning of anterior-ankle-impingement is a detrimental adjunct that will slow recovery; invariably will not respond to dorsi-flexion stretching; and be aggravated by fast walking, and/or slow walking up-hill or down stairs.

    I stand by my comment that "I cannot fathom how one can fully understand the ankle joint in terms of complete diagnoses, prognosis and when to refer on, without first understanding and utilizing the lunge test." Because if the practitioner misses a soft-tissue anterior ankle impingement, the diagnosis is not complete; the prescribed exercise(s) (eg. dorsi-flexion stretching) can be counter-productive; the prognosis is overestimated and referring back to a specialist is often delayed.

    In relation to "changed statements", how did you infer that I meant that if a "clinician does not use the lunge test that he or she can not properly diagnose and treat mechanically-based conditions of the foot and lower extremity."
     
  3. Martin:

    Must be starting to get cold again up there in Winnipeg....you seem to be having more time on your hands lately....with the length of your postings getting longer as the days grow shorter.;)

    I think your posting nicely summarizes my views on this important subject of what we call "ankle joint dorsiflexion". Current research certainly indicates that there is considerable sagittal plane movements of the midtarsal and midfoot joints within the sagittal plane. The mean sagittal plane motion (in degrees) for six live subjects with pins drilled into their foot and ankle bones during walking was as follows in a recent landmark research study by Lundgren et al: talo-navicular - 8.4, calcaneo-cuboid – 9.70, naviculo-cuneiform – 11.50, cuneiform-metatarsal – 5.30, cuboid-metatarsal – 13.30 (Lundgren P, Nester C, Liu A, Arndt A, Jones R, Stacoff A, Wolf P, Lundberg A: Invasive in vivo measurement of rear-, mid- and forefoot motion during walking. Gait and Posture, 28:93-100, 2008). This research clearly shows that not even half of the movement of the distal forefoot relative to the rearfoot is coming from the joints of the MTJ, as is commonly thought. This was the subject of my June and July 2008 Precision Intricast Newsletters Midtarsal Joint Locking-Real or Imaginary, Parts I & II which hopefully I will be publishing as part of my third book within the next six months.

    There is no perfect way to clinically assess "ankle joint dorsiflexion", since all examination methods have their problems. Assessing "ankle joint dorsiflexion" on an examination table with the examiner pushing on the plantar foot with their hand probably grossly underestimates the ability of the plantar foot to dorsiflex relative to the tibia. Using the lunge test with the knee flexed is not a realistic representation of the heel-off stage of walking gait, since the knee is extended at heel-off during walking gait. Using the lunge test with the knee extended does not take into account the internal ankle joint plantarflexion moment that comes from contractile activity of the gastrocnemius, soleus, flexor hallucis longus, posterior tibial, flexor digitorum longus and peroneals at the end of the midstance phase of gait. I don't know of a perfect test so maybe a combination of these tests is best to see which one more accurately represents the internal and external forces and moments which occur within the sagittal plane in the foot and ankle joints during weightbearing activities.

    I am excited to see many of us starting to use the new terminology I proposed for the load-deformation characteristics of the first ray, first ray dorsiflexion stiffness, to now being used for discussion of the load-deformation characteristics of the midtarsal, midfoot and ankle joints. Using "stiffness" as a precisely defined measure of the load-deformation characteristics of a joint or material is the standard within the international biomechanics community and makes much more sense to me than the terms "hypermobility" or "laxity". Understanding the load-deformation characteristics of the human foot and lower extremity with terms such as "stiffness" and "compliance" certainly is the way forward for the podiatric profession so that we can remain as leaders in the clinical treatment of the foot and lower extremity throughout the world.
     
  4. Mart

    Mart Well-Known Member

    Kevin

    Glad to hear that I did not misinterpret your prior posts. I actualy have to ration my participation on the forum, I find it stimulating and since I am probably mildly obsessive/compulsive I have to be careful or I start neglecting the rest of my life :).

    Since my initial post was so long you may have missed the final paragraph which was really the whole point, I have paste it below to clarify this


    If we have access to a pressure mat I believe we can examine, possibly quantify ankle and MF stiffness by doing the following:

    Stand on mat and record pressure data of stance foot whilst mimicking a step. Incrementally increase step length until heel rise occurs.

    View synchronized FMat data with saggital aligned 2D video. Measure tibial excursion against unloading of heel and when present, the increased plantar loading of MF.

    I believe this may allow us to separate the 2 motions using pre-existing equipment which many of us already use for other purposes. This may be done by comapring the loading/unloading curves under heel and MF and looking at correlation with tibial excursion.

    With those with high MF dorsiflexion stiffness this may need to be augmented by placing a non compliant segement under the cuboid during measurement to detect force caused by moments changing during excursion of calcaneal/cuboid joint with anterior tibial excursion.

    Any comments on this before I embark on testing these ideas?



    Cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  5. David Smith

    David Smith Well-Known Member

    Mart

    Nice post!:good:

    Recently, since setting up my gait lab with pressure mat and 2D video and treadmill with calibration sheets, I have been lucky enough to have had several patients with forefoot problems that I diagnosed as due to ankle equinus. The pressure mat readings showed early and prolonged forefoot loading with the CoP progression pausing or even reversing slightly during the mid stance phase to early propulsive phase. The one who has reverse velocity of the CoP progression had early, prolonged and extremely high sub hallux forces, which I interpreted as functional hallux limitus impeding saggital plane progression.

    A 2D video analysis of synchronised saggital and posterior veiws showed that there was a considerable equinus during stance phase and the tibia never progressed to more than 266dgs ie 4dgs from perpendicular to the plantar lateral aspect of the foot. Interestingly the right foot, which did not indicate high sub hallux pressures, became more cavus during stance phase than during RCSP.

    While it may be useful to have a demarkation of 33dgs lunge dorsiflexion as a predictor of pathology, I personally do not find the lunge test that useful. Clinically, I find the in chair, extended knee, STN position 10dgs active dorsiflexion test more useful and predictive of a type of gait that would be pathological.
    Mobilising ankles to achieve more dorsiflexion in this test also apprears to reduce pathology and increase customer comfort, pain relief and satisfaction.

    If this person had a more flexible midfoot, ie lower arched, then possibly she may have attained greater overall dorsiflexion / tibial progression. At the next appointment I intend to mobilise her ankles and feet and revideo. It will be interesting to see if there is significant increase in relative tibial progression and where that comes from, IE mid foot or TC joint.

    The major technical limitation here is that foot placement angles vary considerably from step to step and so trigonometrical errors will occur where the foot and leg are rotated out of the saggital plane.
    A major human error is deciding where to allocate the relevant anatomical landmarks and then placing a line on that mark and deciding where the centre is relative to the line dimensions.

    Have I gone off the point a bit?:bash:

    Bruce
    you wrote in the other related thread
    I nearly but still, havn't quite got my head around how flat force curves = delay of heel lift or stopping/retarding of motion, for example. Couldn't a flat curve indicate transition of force eg the total force is still increasing but it is increasing more or entirely on the forefoot as the heel force remains constant - for the above example for instance? Can you explain more please?

    Cheers Dave
     
  6. Dave:

    Good points. Any attempts at using dynamic gait as a way to determine sagittal plane stiffness of the ankle and foot joints will have technical problems. As you mentioned, angle of gait will affect parallax and interpretation of forces and angles. In addition, modelling of the ankle and foot joints will show that the internal forces which resist dorsiflexion of the plantar foot relative to the tibia may come from numerous sources, as follows:

    1. Internal tibio-talar plantarflexion moment from passive and active tensile forces within ankle joint plantarflexor muscles, posterior ankle joint capsular structures and interosseous compression forces (when anterior ankle impingement occurs).

    2. Internal talo-calcaneal plantarflexion moment from passive and active tensile forces within the gastrocnemius and soleus muscles and interosseous compression forces within the sinus tarsi.

    3. Internal midtarsal and midfoot flattening moment (i.e. forefoot plantarflexion moment) from passive and active tensile forces within the flexor hallucis longus, flexor digitorum longus, posterior tibial muscle, peroneus longus, plantar intrinsics and passive tensile forces within the plantar aponeurosis and plantar ligaments.

    If rotational equilbrium conditions exist, then the external moments at these joints will equal the internal moments so that the foot will remain in a static position or in a state of constant angular velocity. These external moments will largely be caused by ground reaction force.

    The problem in interpreting the experimental data will be in trying to determine which anatomical structure is contributing to the internal plantarflexion moments of the ankle, STJ, MTJ and midfoot joints, which cause the ankle joint/MTJ/midfoot dorsiflexion stiffness and that helps resist further dorsiflexion of the plantar foot relative to the tibia during weightbearing activities. I think we can only guess, at this stage of our knowledge, and, at best, propose different possible mechanical scenarios that may explain our experimental observations on our subjects/patients.

    However, these types of projects and ideas are what I live for and what keeps me very excited about podiatric biomechanics, even as I enter my 25th year of teaching the subject. Do you all realize what a change this all is for all of us compared to 25 years ago in podiatric biomechanics?
     
  7. Mart

    Mart Well-Known Member

    Dave and Kevin

    I agree about the parallax effect when trying to measure ankle range of motion from walking gait, however the set up I am using removes that issue by carefully lining the camera at 90 degs to the saggital axis of the foot and maintaining this position, this is not difficult. I believe my measurements have pretty low error in this respect.

    Variability of measured values is usually within 2 degrees.

    I think that if the variability over consecutive measurements is this low then it is unlikely that contractile structures are having any significant effects because of inter trial altered muscle contractility, or non contractile ones by having significant viscoelastic variability. I agree that if we were trying to detect within a few degrees this might be an issue but < 3 degrees or so of error for a lunge value perhaps not a problem.

    If I am really achieving this level of accuracy is my assumption plausible?

    Cheers

    Martin
     
  8. Bruce Williams

    Bruce Williams Well-Known Member

    Dave;

    see if this F/T curve can help:


    F vs T curve flat heel curve.jpg

    The dark blue and yellow curves represent the boxed out or masked regions of the heel curves.

    The constant force over time represents a stoppage of motion w/ constant force in that area of the foot. As you can see by observing the red adn green "gait curves", the delay in the heel curves is occuring during midstance.
    Midstance is where the AJ should be pivoting, but in this case is not, at least not effectively.
    This patient was having early knee flexion to compensate for loss of available ROM at both the AJ and MTJ's. The knee in these instances is the next joint available for sagittal plane motion.
    We manipulated her and got return of her normal motion as seen below.

    F vs T curve flat heel after manipulation.jpg

    Return of motion equals smoothing of the heel curve.

    I hope this explains things better. I appreciate the difficulty of our all understanding our unique terminologies.
    Cheers
    Bruce
     
  9. Bruce Williams

    Bruce Williams Well-Known Member

    Martin;
    while your idea may be plausible, the problem w/ 2D still remains.

    I appreciate your ideas and I think from a clinical perspective that you are aok. From a kinematic perspective you still will probably have parallax issues due to the fact that 1) the foot must not be adducted or abducted at all during the picture or video, 2) the foot mush not excessively pronate or supinate during the video or picture either.

    If either of these occurs then is can adn will have a definite effect on the ROM you calculate at the AJ. What occurs instead is a combination of teh available DFion ROM of both the midfoot and the AJ.

    This is a common problem in most papers utilizing kinematics where we see obvious problems that clinicians will correlate w/ limited AJ DFion ROM adn instead the investigators document an increase in the DFion of the AJ ROM.

    I think this will be the primary problems with what you are attempting to do, again not from a clinical standpoint, but from a true kinematic standpoint.

    Cheers;
    Bruce
     
  10. David Smith

    David Smith Well-Known Member

    Bruce

    Ah yes I see your perspective now. I take it that this is a view of left and right stance phases using either pressure insoles or a long pressure mat, the light blue and purple are the fore foot force integrals, yes?

    So the forefoot is loading early ie before the heel has significantly unloaded so it may be assumed that the CoM has not advanced beyond somewhere around the perpendicular position. Therefore pressure or force under the forefoot, in this circumstance, will decelerate the CoM while it is not in a position to rise under the influence of achilles tension / force. As something compensates, you suggest knee flexion, to re-establish the continued forward progression of the CoM the heel will start to rise again and the plantar pressure will drop and subsequently the forefoot plantar force will rise as the CoM goes into propulsive phase.

    It can be seen in force time curve figure 2 that the heel and forefoot curves are smooth and that forefoot loading does not start until the rearfoot force is significantly lowered and they both correlate with low peak midstance total force.

    Bruce, Is this the pattern (figure 2) you like to see to indicate a 'normal' or potentially non pathological gait.

    Cheers Dave :good:
     
  11. Bruce Williams

    Bruce Williams Well-Known Member

    Yes David you are corect re: the forefoot force integrals.


    Yes, this would be close to perfect for non-pathological gait. It happens, not as often as I'd like, but we do get there frequently!

    The rest of your assesment was dead on. We are getting closer to an understanding I think. Btw, these were from an in-shoe pressure evaluation, not a mat or long mat.

    Cheers;
    Bruce
     
  12. Mart

    Mart Well-Known Member


    Bruce

    this is a nice example, however I see shortcomings with your analysis.

    If you look at the total force/time curves they do not add up to the sum of the forefoot and rearfoot force during 2nd and 3rd rocker, clearly since you masked the secondary curves and there are some areas not being measured on your graphs.

    To evaluate this comprehensively we will need to know were the "missing" force is ( I am unaware of any suspicion of dark mattter being present in the foot).

    So it is either midfoot or digits. since forefoot loading appears delayed on your graph I suspect the former. If this is true then we are, I suggest, dealing with loss of MTJ stiffness which may be related to increased ankle stiffness but the data cannot tell us that. What would tell us that is synchronised sagital kinematics so that we can confirm what motion was occuring. If what you say is true then both feet will have exhibited knee flexion during second rocker, whilst this is possible I would love to see a snapshot of this if you got a chance to post it since I have never seen this as compensation for elevated ankle stiffness.


    Another issue is the change in excusion of COM, if you look at the 'post manipulation"graph, the subject may have have walked with a significant increase in step length, this may be due to increase ankle ROM or simply they walk faster. It could also be that knee flexion during 2nd rocker decreased upward acceleration of COM in the pre manipulation graph and flattened this part of the curve which would be consistent with your analysis. Since there is no time scale on your data or concurrent kinematics it is impossible to be sure about this.

    Will consider also your post on the parallel thread later when I get a bit more time. Good to start examining this stuff in some depth finally.

    cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Sep 25, 2008
  13. Mart

    Mart Well-Known Member

    Bruce and Dave

    Talking about the elevated ankle stiffness in subjects he has examined Dave said ”The pressure mat readings showed early and prolonged forefoot loading with the CoP progression pausing or even reversing slightly during the mid stance phase to early propulsive phase. The one who has reverse velocity of the CoP progression had early, prolonged and extremely high sub hallux forces, which I interpreted as functional hallux limitus impeding saggital plane progression”

    Curve shape wise, this is what I would expect to see theoretically, do see frequently and tend to interpret this way with Mat data in my practice too.

    Dave how to you define “high sub hallux forces”?

    Now in Bruce’s example this is not the case, forefoot loading is actually delayed. This would make no sense to me at least using a Mat. Most people I see with elevated ankle stiffness exibit a loss of dorsiflexion during swing phase (often slight plantarflexion, granted this could be parallax artifact) and almost instantaneous forefoot contact. My interperetation is that anterior group probably is not able to provide sufficient force to overcome posterior group contractures or other causes of elevated stiffness.

    I wonder what effect foot-wear and liner in Bruce’s example (using in shoe sensors) is having on the loading curves. I would anticipate that the effects of foot-wear might be to increase duration of 1st rocker (which would delay onset of forefoot loading) and if the sole of the shoe were flexible and complaint with some kind of contact modifying liner, might smooth out the transition from rear foot to forefoot loading particularly of there was some kind of forefoot rocker incorporated into it’s external contour. It would be interesting to look at some other representations of the data to see how and where the foot loaded. Any thoughts on this?

    Cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  14. David Smith

    David Smith Well-Known Member

    Mart

    You wrote
    I'll second that:cool:

    You also wrote
    I define high sub hallux force in relative terms and this is relative to the 1st MPJ forces IE where the sub hallux forces are increasing faster than the sub 1st MPJ forces in the propulsive stage.

    The theory is that;

    1) In the non FncHL foot the sub hallux forces should be reducing as the hallux dorsiflexes. The plantar fasia (PF) windlass action is drawing the rearfoot toward the forfoot in a supination action. Where there was not a relatively large magnitude of lowering of the MLA (perhaps due to pronation) the force required to supinate the rearfoot is low and the moments about the 1st MPJ as the hallux dorsiflexes is low. Therefore the equal and opposite force, ie the dorsiflexing sub hallux force, is also low and reducing a the heel raises and supinates.

    2) In the FncHL foot the MLA is relatively low (relatively low means - where the MLA continues to lower after ground contact by the hallux as it plantarflexes during the early to mid stance phase) and the plantar fascia is stretched, this equals high internal tensional force that is translated thru the windlass system and therefore must result in a force, sub hallux, that will balance the high magnitude of moments produced by the high tensional force in the PF.
    Where this happens the finite force available as GRF must be balance by a reducion of force elsewhere, this appears, and if one examines a freebody diagram of forces seems a reasonable assumption, to be sub 1st MPJ . Therefore in this case during propulsive phase the force sub hallux is increasing while the force sub 1st MPJ is decreasing.

    When this 2nd example is the case there are two limiting factors to the forward progression of the foot, tibia and CoM.

    1st it is difficut toi facillitate the third since the hallux does not dorsiflex easily there is no ball of the foot available to roll over.

    2nd the moments dorsiflexing the ankle, during late stance, and therefore tending to reverse the velocity of the CoM, or in otherwords accelerate the CoM posteriorly, are greater since the hallux centre for force has a longer moment arm and the forces here tend to be higher.

    This situation, when observing the characterisation of CoP progression on the pressure animation display, would result in a slowing of CoP velocity. If there is a delay in compenstaion that would allow continued CoM forward progression, then at this point it is possible for the CoM animation to show a small reversal of direction, possibly, for example, as the foot drops back onto the heel momentarily before late pronation start or as the progression is shifted to the lateral foot in order to utilise the lesser met heads as a more compliant rocker .

    This observation and theory is supported by research I have done examining the mechanical properties of the plantar fascia and its effect on the MLA in vivo .
    And also by Dr Danenburgh's work in his saggital plane theory and and the effects of functional hallux limitus.


    Does this make sense to you all??

    Hey excellent discussion!!

    Cheers Dave
     
  15. David Smith

    David Smith Well-Known Member

    Mart

    You wrote
    Bit confused here Martin, I see in the 1st example an early forefoot contact and in the second example, after mobilisation, a relatively later forefoot contact. Isn't this as expected by your own observational explaination above, which I would agree with in the main. However I do see people with equinus ankle who choose to walk on their heels and have very late forefoot contact, These are usually the people who others refer to when walking as sounding like an elephant coming down the corridor ie heavy thumping heel contact. A bit of ankle mobs and suddenly they walk as quiet and soft as Lianng Shang Po (grasshopper) on rice paper.

    All the best Dave
     
  16. David Smith

    David Smith Well-Known Member

    Mart

    You wrote
    Don't know at the moment but in this case I would say that the difference in comparison is what is notable and not the absolutes. It probably wouldn't be a good idea to check a gait barefoot on a mat then recheck after intervention shod with inshoe pressure apparatus.
    I think the power of the pressure recording systems is in comparative data and not absolute data unless the conditions of methodology are strictly controlled. IE clinical versus research use.

    Dave
     
  17. David Smith

    David Smith Well-Known Member

    Mart

    You wrote
    This is normal, no?

    and
    True

    also
    You are correct in that if you subdivide the foot into dicreet areas then all the masked discreet area forces should equal the total area force. This would give a better overall picture of the progression of plantar forces.

    Do you suspect that if the midfoot where masked then this would show high loading here if it were more compliant to moments about that joint / joints?

    What if those joints were compliant but elevated above the mat? how could we say anything about the forces or magnitude of moments about the midfoot then, - by analysing the forces acting distally to it? This should be done with caution since we only know somthing about the vertical forces and horizontal forces may have a significant effect on magnitude and direction of moments acting about the joint of interest.

    Low resolution low frequency 2D video is in my opinion not capable of accuratel and precicely distinguishing joint motion within the foot unless these motions are gross and slow and do not rotate out of the plane of interest and are not subject to the effects of parrallax, lens distortion and perspective and the subject has vey skinny boney feet.

    This goes back to you query on your proposed experiment. I think you would find it difficult for the above reasons. But I would go ahead anyway and see waht comes out. Again this may be more of interest compartively speaking.

    Regarding flexed knees isn't this the way many elderly people walk, flat footed, apropulsive with flexed knees that allow them to move forward more easily and give some eatra propulsion that doen't come from the Gastroc -Soleous / ankle complex?

    Cheers Dave
     
  18. Dave, Martin, Bruce and Colleagues:

    I am having a bit of a problem with this discussion of the center of mass (CoM) of the body and how we are attempting to discuss its movement and acceleration and deceleration by simply analyzing only the ground reaction force (GRF) from a pressure insole/mat system. First of all, the CoM never has its "velocity reversed" during walking. This would imply that the body actually stopped moving forward and started going backward which does not occur during normal walking. Secondly, just because there is a flat slope of the GRF curve this may or may not have anything to do with whether the CoM is accelerating or decelerating forward during that stage of the gait cycle.

    All that a pressure mat, pressure insole and force plate can measure, by itself, is the forces acting on the plantar foot. These gait analysis methods can not directly measure the velocity, acceleration or deceleration of the CoM of the body and suggesting that these gait analysis methods can measure CoM movement is not only innaccurate but also misleading to the clinician that is attempting to grasp the possibilities and limitations of such gait analysis methods.

    If one said that, in general, that the pressure mat/insole or force plate will tend to reflect the movements of the CoM, then I have no problems with that. However, to look at an aberrant force vs time curve from a F-scan system and then say that the CoM did this or that, when no attempt has been made by the clinician or researcher to perform a kinematic analysis of the progression of the CoM over the foot, is highly questionable.

    I therefore suggest that in future discussions, to maintain more accurate and valuable scientific value to the discussions, that it is made clear that the CoM movement has not been measured and that any suggestion of CoM change of movement in the interpertation of a pressure mat/insole force vs time curve is declared by the author as being only one of the many possible mechanical events that could have occured within the body of the individual to produce that characteristic pressure mat/insole force vs time curve.

    Other than that, I am enjoying the discussion greatly.:drinks
     
  19. Mart

    Mart Well-Known Member

    Dave

    you have made lots of interesting comments in this post and I would like to take some time over the weekend to try and systematicaly look at the papers I have in my library citing plantar force measurement and go see how exisiting published evidence stacks up against your points before jumping off the deep end :).

    cheers

    Martin
     
  20. Mart

    Mart Well-Known Member

    Agreed.

    My hope is that one consequence of these discussions will be to hone our understanding the limitations of our interpretation and optimistically to improve it, at least by recognising important pitfalls.

    It would be great to get other plantar sensor and camera users contributing because the more individual user's interpretation is revealed, the better chance we have collectively to decide if, as I suspect, we need professional guidelines and training on this issue of interpretation.

    cheers

    Martin
     
  21. David Smith

    David Smith Well-Known Member

    Kevin

    I fully understand where you are coming from and appreciate your important attention to precision in descriptions of mechanical and anatomical actions. Often when talking about progression we (me at least) are refering to the characterisation of the CoF or CoP progression on the plantar foot, which can reverse direction. I note I did write CoM at one point where I intended to write CoP progression (25th sep 1300hrs 7th paragraph) We must be careful in our interpretation of data so as not to extrapolate outside the parameters of that data. This is the problem with a single force characterisation of GRF, without the other two forces we have no idea of the force vector and its relatioship to the centre of mass during gait.

    I think Mart, and I are exploring the interpretation of pressure mat data with a view to clarifying and standardising terminology and hoprfully increasing our ability to use thius technology in our practice more efficiently. This type of interjection will keep our feet on the ground (no pun intended)

    Having said that I think we have been refering to specific cases where we know the general kinematic pattern and make general assumptions for the sake of discussion.

    I understand your point that the CoM never reverses velocity during gait, although I have observed a few drunks where this is the case and perhaps some people with neurological problems may experience reversal of CoM velocity. However it is posible and normal for the CoM to experience magnitude and direction changes in acceleration and this I believe can more saftely be assumed from vertical force evaluation. Even so kinematic data will make this more reliable.
    This is why I have 2D video software that can simultaneously synchronize gait to pressure mat data. In this way I can see the leg fot and body position relative to the vertical GRF/pressure.

    Cheers Dave
     

  22. Dave and Martin:

    Probably the best place to start in understanding how center of pressure (CoP) and center of mass (CoM) affect each other is in David Winter's analysis of these during standing and walking in his book (Winter, David A.: A.B.C. (Anatomy, Biomechanics and Control) of Balance During Standing and Walking. Waterloo Biomechanics, Waterloo, Ontario, Canada, 1995). It is one of the best "short book" I have ever read.
     

  23. Dave and Martin:

    Probably the best place to start in understanding how center of pressure (CoP) and center of mass (CoM) affect each other is in David Winter's analysis of these during standing and walking in his book (Winter, David A.: A.B.C. (Anatomy, Biomechanics and Control) of Balance During Standing and Walking. Waterloo Biomechanics, Waterloo, Ontario, Canada, 1995). It is one of the best "short books" I have ever read.
     
  24. Mart

    Mart Well-Known Member

     
  25. Bruce Williams

    Bruce Williams Well-Known Member

    Guys;
    it is going to take me most of the weekend to digest all the new posts.
    I'll get to them as I can and combine replies as much as I can as well.
    I have a few other slides of the patient I posted, video still(s) that I will post as well.
    much of this discussion, at least on the patient I posted, will overlap w/ the Talar Equinus thread for David and Ron and I may ask that they both look here for a reply.
    Have a great weekend, and slow the hell down!!!
    Cheers
    Bruce
     
  26. Mart

    Mart Well-Known Member

    yes it does make sence but of course this doesnt mean that it is true..

    take a look at these papers . . . . it suggests that it may not be or may be . . . . . sometimes


    cheers


    Martin


    View attachment Pressure and force distribution characteristics normal foot during pushoff phase of gait.pdf

    View attachment Effects of Hallux Limitus on Plantar Foot Pressure and Foot Kinematics During Walking.pdf
     
    Last edited: Sep 25, 2008
  27.  
  28. David Smith

    David Smith Well-Known Member

    Mart

    You wrote

    No, increased propulsion from the knee extension.

    Dave
     
  29. Mart

    Mart Well-Known Member

    Bruce

    agreed . . . . . I am struggling to keep up now, look forward to slowly making some progress though

    cheers

    Martin
     
  30. Mart

    Mart Well-Known Member

     
  31. Martin:

    I would like to see this experiment show the following:

    1) How much angular change in the tibia is required from knee extend to knee flexed lunge tests to reach the same level of plantar heel minimal GRF in different subjects.

    2) Whether this change in lunge test type (i.e. knee extended vs knee flexed) also changes the plantar forefoot GRF.

    3) How much change in plantar forefoot and plantar rearfoot pressure occurs with the same tibial angle in the knee flexed and knee extended position which will give us an idea of changes in internal plantarflexion moment changes from the knee flexed to knee extended positions.

    As for your suggetions: Issue of anterior inpingement (bony vs fibrous) (by rate of change of forefoot loading in both test conditions)

    Position of body COM (on measured angle; to allow comparison with prior research )

    Effect of mid tarsal joint stiffness ( rate of forefoot loading)


    I don't know how my proposed experiment will detemine these factors.
     
  32. Bruce Williams

    Bruce Williams Well-Known Member


    Martin;
    any missing forces in the graphs are usually due to the toes not being masked, and neither is the midfoot. I only mask or box out the heel section of teh foot, the MPJ's and the entire foot.

    Regarding your interpretation of my interpretation I am a little confused on your suggestion that CoM information is available on these curves. Please explain how you would infer CoM position from these basic F/T curves. If you used the CoM'Nalysis program ok, but otherwise, diffictult to say for exactly.

    Thanks
    Bruce
     
  33. Mart

    Mart Well-Known Member

    Kevin

    I understand what would actually be measured, I guess what I was meaning is why these values would be of interest, and what might be infered from this information. More correctly I have talked about possible inferences not variables.
    I am still curious about were this might lead in our understanding of foot function.

    cheers


    Martin
     
  34. Martin:

    Mostly wanting to find out how the internal ankle joint plantarflexion moments will change from a knee flexed to a knee extended position and get a better idea of how much reducing effect of the gastrocnemius muscle changes the angle at which heel off occurs and the tibial angle to forefoot GRF changes with varying knee angle positions. Something similar to this could be an excellent paper for publication in JAPMA if done correctly and on enough subjects.
     
  35. Mart

    Mart Well-Known Member

    Bruce

    Typing this whilst trying to listen to US presidential debate so hope it is coherent!

    I find some people with large mid foot forces and these correlate often with what I regard as "abnormal" rear foot and forefoot loading curves which was my concern with your example.

    Kevin also has taken issue with my suggestion of there being information regarding COM.

    My reasoning is:

    Using the conventions of F1 representing the 1st peak, F2 the valley and F3 the second peak of the single foot vertical GRF walking force/time curve.

    The slope leading to F1 represents the body COM decelerating against the ground moving to it’s lowest point at end of 1st rocker. Leading to F2 represents the acceleration of COM to highest point with this directly above the ankle, added to this is the effect of the momentum of the swinging limb which adds to this upward acceleration. F3 represents the return to low point as COM progresses forward and downward until contra lateral foot contact at which time the curve reflects shift of mass to weight-bearing foot.

    As gait speed slows and becomes appropulsive the curve will gradually flatten as COM excursion decreases with reduced step length, as speed increases the F1 amplitude increases because of increased momentum, and F2decreases as step length increases. The excursion of COM as seen with the inverted pendulum will trace a similar curve to the vertical GRF. This explains why once we switch to running, the GRF curve becomes monophasic.

    I am not saying that the GRF is a measure of COM and I understand there is some concern regarding using the COM calculating software module which calculates this from the acceleration data. However in normal gait it does primarily reflect the effect of COM excursion on the measured GRF.

    back to Obama and McCain

    cheers


    Martin



     
  36. Mart

    Mart Well-Known Member


    Kevin

    thanks for clarification. If I find time I'll measure a couple subjects and post results for interest

    cheers

    Martin
     
  37. David Smith

    David Smith Well-Known Member

    Mart

    You wrote
    I've read both the papers you cited. I think that the Gelhuwe Dananberg paper pretty much confirms my explaination. They observe increased magnitude and increased loading rate sub hallux with corresponding redution in MPJ 1 loading in feet with hallux limitus, functional or structural, with the previso that some structural hallux limitus do not exhibit this load pattern, which to my mind is the exception that proves the rule as they were not actualy functionally limitus during ambulation. (sorry aboiut the long sentence, now breath---- and relax) The Hayafune Jacob paper only looked at defining normal but only filtered for structuraly abnormal feet. They did not filter variables for functionaly abnormal feet and so their normal will give statistical means that include all types of feet. Even so the hallux V's 1st MPJ loading appears to be similar to a little less loading on the hallux. This what might be expected in 'normal' feet and agian, IMO, supports my theory posted earlier.

    You say "Sometimes" - there will always be sometimes - its the nature of the relationship between experimental research and probability, there can be no scientific empirical experimentation without falsifiability or exceptions "sometimes".
    In fact the greater the possibility of falsifiability the more probable the outcome is true.
    (but that's another discussion.)

    All the best Dave:drinks
     
  38. Bruce Williams

    Bruce Williams Well-Known Member

    Martin and Dave;

    in my F/T example therre was not FF delay in the curves. The patient was compensated appropriately with her orthoses so that was not the problem. As well, her midfoot was stabel enough not to lend to an uncontrollable increase in DFion of the first ray.

    Keep in mind that in-shoe pressure data is very different from mat-scan data. I do not as a rule utilize F/T curve w/ my mat-scan data. I don't think it gives me enough info and the patients also have a tendencey to alter their gait to step onto the mat. Also it does not allow for testing of the orthotic. I"m not saying it is of no value, I just find much greater value utilizing in-shoe data.

    HIgh hallux pressures will be seen w/ lower 1st mpj pressures in most instances. In these patients you will not see a delay in the initial loading of the FF curve, but an early contact usually. As well, you will see a plateua or delay within the loading of the FF curve as it rises.

    Finally, you can see delays solely in the FF or soley in the RF curves. They are not mutually exclusive most of the time, but I have many examples of this.

    cheers
    Bruce
     
  39. Bruce Williams

    Bruce Williams Well-Known Member

    Kevin;

    unfortunately many of us utilize CoM interchangebly with CoP. The CoP is trackable w/in in-shoe and mat systems. The CoP does regularly reverse course during recordings adn must indicate a change in direction of foot motion. This is not sayng that the CoM is reversingy, you are correct in that.

    Bruce
     
  40. Bruce Williams

    Bruce Williams Well-Known Member

    Martin;

    No worries on coherence, I wrote my replay at the beginning of the debate as well. :D

    I like your explanation very much and it gives me a much greater insight to your thoughts and to things overall.

    :drinks
    Bruce
     
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