There is nothing more incomprehensible

By Theresa Hicks,2014-01-20 04:22
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There is nothing more incomprehensible

    This is a kinematic and kinetic model and therfore requires BodyBuilder version 3.5. if you are still running an earlier releae please contact your local distributor. The download has a detailed

    introduction which should not be included in the .mod file when run.

“There is nothing more incomprehensible “Nulla di più incomprensibile

    than language which is useful only for del linguaggio che non serve

    understanding” ad altro che a farsi capire”

Karl Krauss Karl Krauss


    ? Why should anyone write a foot model? Advantages and drawbacks The human foot and ankle complex is a multi-joint system which determines the critical interaction between the lower limbs and the ground during locomotion. The foot consists of a lot of small bones, which have often more than one joint in themselves. Nowadays, in the gait analysis practice, the foot is always considered as an only segment system. The reality is quite different: for example, when you model just the foot, the tibia and the femur for the lower limbs, you do not take into account that the ankle joint complex is not a simple hinge; a lot of papers in the literature have already shown that that joint complex may be quite well described using a two-hinge model: one for the subtalar axis (between the talus and the calcaneus), the other one for the proper ankle joint (the joint between the tibia and the talus). So, if you wanted an assessment of the kinematics of the foot, which curiously is the only part of the body that touches the ground and which the force and the moment go through, you could not do anything with the usual models.

    A great problem in this kind of approach is, first, that you can not stick any reflective markers on the talus. Then obviously you have some technical problems: you have quite a small area to investigate, so you have many markers which are very close to each other; the area of the foot, moreover, has got a lot of tendons and ligaments, which move a lot during the phases of walking. Besides, on the human foot you have a lot of lumpy bones and areas of soft tissue. With these shortcomings you expect that all the flaws in the capture data mean that the game is not worth the candle.

    But the point is: is it important to know anything about the behaviour of the foot, even if the data are not that clean? Is it worth making a lot of x-ray trials to investigate the foot? And then, how can I find the trajectories without using an high frequency x-ray system? (By the way, a new paper by Cavanagh, which focuses on the differences between stereophotogrammetry technique and x-ray technique, has just come out for gait analysis; Cavanagh, P.R. et al. The relationship of static foot structure to dynamic foot function, J. Biomech 1997, 30(3): 243-250).

    What would the harm be? And again, what about the kinetics?

    Do we need a more specific model in order to track the trajectories of the major segments of the foot?

    These are the reasons I have found to write this model.

? The model

    I have defined five segments for each foot: the tibia, the talus, the calcaneus, the midfoot

    tibia is assumed to be a single rigid body with the fibula. It is defined and the toe. The

    using four technical markers. It is not important, with respect of the tibia, the shape and the size of the markers stuck on it, because the it is defined using only four calibrated anatomical landmarks, according to Cappozzo`s methodology (Cappozzo, A et al. Position and orientation space of bones during movement: anatomical frame definition and determination. Clinical Biomechanics, 10(4): 171-178, 1995): the CAST (Calibrated Anatomical System Technique) has been used to reconstruct the trajectories of the anatomical landmark of the shank and of the foot in the lab frame, during some walking trials. This entails the location of the anatomical landmarks in the technical reference frame defined by the technical markers through some dedicated acquisitions (that can be termed “anatomical landmark calibrations”) and their reconstruction in the lab reference system using the trajectories of the same markers collected during the walking trials. To calibrate (which means to find the positions of the selected anatomical landmarks) the four points (anatomical landmark) I used simply a rod with three markers along its axis. For, it is not important, for the tibia, where to stick the markers, because of the calibration: actually, I defined a dummy segment “tibia”, with respect to which I have found the coordinates of the calibrated points. Then I have defined the proper tibia segment using only the calibrated points. This means that you can stick the marker whenever you prefer, though not co-linear, to avoid some artefacts concerned with the movement of the skin, the lumpy prominences etc ...The calibration has got the most important role in the description of the tibia. Then you can precisely define the position of the apices of the malleoli in order to find a kind of ankle axis.

    The location of anatomical landmarks using the tip of a pointer is usually more practical and accurate than the direct marker placement, especially when the anatomical landmarks are located in awkward, sharpen positions or are close to an area of soft tissue The tibia is known with all its six degrees of freedom.

    The calcaneus is defined using four markers. The calcaneus is known with all its six

    degrees of freedom. The talus is assumed to be constrained between the tibia and the

    calcaneus using a sort of two-hinge model. I have preferred to keep the six degrees of freedom for the tibia and the calcaneus, rather than using a proper two-hinge model. Actually I would have defined two segments for the talus which are fixed one another. In my model the talus is not really constrained between two fixed hinges, but it is constrained between a fixed hinge (the one with the tibia) and another one with a slightly moving axis (subtalar axis).

    The graphics of the angles between the two segments on the talus reveal that the movement is often less than the expected error (10%). The midfoot is composed of the

    metatarsals, the cuneiforms, the navicular and the cuboid and has got four markers stuck on it. The relative movement of the bones belonging to the midfoot is negligible. With this assumption the midfoot, in its complex, has got six degrees of freedom.

    The toe is captured using a cluster with three markers. I have paid attention not to make

    the cluster awkward for the patient in a normal gait.

    The shape of the cluster is a tiny coordinate system.

    With this device the toe has six degrees of freedom. This can be useful if you have to capture a person with the hallux valgus, i.e.

The inertia properties have been merely guessed, because I didn’t have that kind of

    information at my disposal.

    ? The marker placement

These following landmarks were arranged by Alberto Leardini and Stefano Taioli in a first group of trials

    at OML on Wed 24 Sept.

    To have the extension to the left/right foot put a L/R as a prefix

    TOE CLUSTER: it is a 3-little-markers system which is more or less

     Orthogonal (according to the rule of the right hand)

     TOE 2TOE 3TOE1 (TOE CLUSTER) Marker aligned with the length of the Toe

    TOE2 (TOE CLUSTER) Marker towards the medial side

    TOE 1

    TOE3 (TOE CLUSTER) Marker towards the lateral side

C/D = Calibrated/Direct T = Technical marker


    Apex of the Head FibulaHFIBDsegm. definitionTibia+Fibula

    Prominence of the Tibial TuberosityTTUBDto avoid dropoutsTibia+FibulaSHIN1D TMedial upper flat part of the tibiasegm. definitionTibia+Fibula

    SHIN2D TMedial lower flat part of the tibiasegm. definitionTibia+Fibula

    Medial EpicondyleMEPCCsegm. definitionTibia+Fibula

    Lateral EpicondyleLEPCCsegm. definitionTibia+Fibula

    rot. axis definition Tibia+Fibula CMMALDistal apex of the Medial Malleoulusand segm.definitionand Talus

    rot. axis definition Tibia+Fibula CLMALDistal apex of the Lateral Malleoulusand segm.definitionand Talus

    Most Medial Projection of the Sustentaculum TaliSTALDsegm. definitionCalcaneus

    On the Medial part of the top of the Calcaneus in the to avoid dropouts and Calcaneus and D Tdepression between the Achilles tendon termination and MCALsegm.definitionTalusthe Medial Malleoulus

    On the Lateral part of the top of the Calcaneus in the Calcaneus and D Tdepression between the Achilles tendon termination and segm. definitionLCALTalusthe Lateral Malleoulus Lateral prominence of the Peroneal TuberclePTUBDCalcaneussegm. definition

    Medial part of the base of the 1st MetatarsalME1BDMidfootsegm. definition

    Medial part of the head of the 1st MetatarsalME1HDMidfootsegm. definition

    Dto avoid dropoutsMidfootOn the tuberosity of the base of the 5th Metatarsal, ME5Blaterally

    Lateral head of the head of the 5th MetatarsalME5HDMidfootsegm. definitionNAVICOn the top of the talo-navicular joint, upwardrot. axis definitionMidfoot

    TOE1D TMarker aligned with the axis of the ToeToesegm. definitionTOE2D TIn a "V" configuration medially directed (right foot)Toesegm. definitionTOE3D TIn a "V" configuration laterally directed (right foot)Toesegm. definition

The sequence of the landmarks you have to calibrate can be decided before, so that you can have just one

    static trial with all the calibrations. Otherwise you need one “static” trial for each calibration.


The complete foot model consists of two model scripts: the proper model and the scrip for

    the calibration.

    If you want to use the kinetic extensions, run the files BothFeet2Kin.mkr, BothFeetKin.mod and

    The foot model without kinetics is BothFeet.mod (or Foot.mod). The parameters file is (or

    The marker set file is BothFeet.mkr or BothFeet2.mkr for the autolabelling (or Foot.mkr).

    First, the proper foot model assumes that 5 points for each foot are calibrated. This means

    that you need 5 “static” trials for each foot to point at those points. Then, after setting the

    right name and the right segment in the call of the macro Rod and after labelling just the

    markers related to the segment to which the calibrated point belongs, you have to run the

    first model (i.e. BothFeetCalibration.mod or FootCalibration.mod with the

and Calibration and BothDrawFeetSegments.mkr or with and Foot.mkr) one

    trial at the time. When you have in the parameters file the 10 (5) points referred to their

    segment, you can run the proper model. Pay attention during the labelling of the

    ToeCluster. The marker along the toe is ToeCluster1, the ToeCluster2 is always on the

    left of the subject.

    Besides, you can find another model called BothDrawFeetSegments.mod (to use with and Calibration and BothDrawFeetSegments.mkr or

    something similar for the one foot model) to draw the segments (the coordinate systems)

    in the workspace.

    Then, you can find the explanations you need for each macro in a file called

    NameOfTheMacro.mod in the Macros folder.

? The macros: a brief explanation

    Replace4: replaces and outputs any point missing from a set of four fixed markers in a 1.


    2. ClusterOrigin: finds the origin of the cluster. You have to pass the name of the

    segment and the three points. Please have a look in the Macro folder and in the

    Drawing folder if you want to understand how it works.

    3. DrawGlobal: draws the global axis system

    4. Moment: it is for a kind of a representation of each component of the moment for each


    5. ConversionReaction: it is in order to change the coordinate system and to draw the

    forces properly

    6. Rod: this is used only in the calibration part. It finds the coordinates of the point of the


    Please, check in the folder Macros for more comments.

19/12/97 Stefano Taioli

    Error! Bookmark not defined.

    Error! Bookmark not defined.

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