Abstract
Multi-line segment foot models propose a triple-line segmentation into hindfoot, midfoot and forefoot; oftentimes, the midfoot is regarded as a rigid line segment. We here begin our presentation of a new model of the hind-midfoot bone complex, regarded as a system of rigid blocks, the bones, with perfect mutual constraints, the bone joints. Firstly, we give a qualitative description of the deformations of the foot per se, as if it were severed from the body or made to move passively in vivo, the talocrural joint being kept locked; the descriptive capabilities of our model are illustrated by progressively locking more and more bone joints. Secondly, we derive two interdependent systems of nonlinear algebraic equations which render the geometrical and kinematic complexity of the hind-midfoot complex: one system locates individual bones in space, the other selects all location sets classifiable as unbroken kinematic chains, that is to say, all admissible hind-midfoot configurations. We define the relative multi-parameter configuration manifold, indicate how to inspect it hierarchically, and furnish a representative example amenable to geometrical description. The accompanying dataset document features graphical information and configurational data helping to motivate our modelling choices, as well as analytical information concerning certain mathematical developments we here omit.
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Notes
It is important to realise that in our study of HMF kinematics the values of certain anatomical parameters are kept fixed while others do change when the HMF chain changes its shape.The chain parameters keeping their reference values are the radii of hinges 01 and 02 and of cylinder 26; the parameters in the need of adjournment according to shape changes are the axes of those three joints, the normal to plane 56 and the centres of spheres 13, 34, 35, and 56.
Surface corrugation is meant to suggest that translations along the axes of these tubes are forbidden.
Here is a relevant quotations from [5]: “The talo-navicular articulation being of ball-and-socket shape ...”.
Alternatively, we might have chosen to make use here of \(R^{(13)}\), the rotation of the navicular with respect to the talus, which satisfies the composition condition \(\,R^{(13)}_{\circ } = R^{(01)} R^{(13)}\).
Here \(m^{(36)}_{*}\) is an arbitrarily chosen unit vector orthogonal to \(n^{(36)}_{*}\).
Cf. the proposition proved in DSS4.
Here \(m^{(56)}_{*}\) is an arbitrarily chosen unit vector orthogonal to \(n^{(56)}_{*}\).
A linearization of problem (25–52) about a chosen admissible configuration is available in DSS5. A kinematically admissible motion of the HMF chain is a one-parameter path over \({\mathcal {S}}\); granted differentiability, and on interpreting the evolution parameter as time, the motion-velocity multivector is a solution of the linear problem just mentioned.
Since \(\vartheta _3\in [0,\pi /2)\) and \(|N^{(13)}_{\circ }|^2=2\), (31) implies that
$$\begin{aligned} \sin \vartheta _3=\frac{1}{\sqrt{2}}\,|\mathrm {skw}(R^{(02)}R^{(26)}R^{(36)T})| \end{aligned}$$and
$$N_{^\circ }^{{(13)}} = \sqrt 2 {\mkern 1mu} \frac{{skw(R^{{(02)}} R^{{(26)}} R^{{(36)T}} )}}{{|skw(R^{{(02)}} R^{{(26)}} R^{{(36)T}} )|}}{\text{ }} $$(composition of the rotations on the right side can be performed with perusal of the Gibbs relations to be found in DSS4).
We reiterate that this sublist locates body 5 in space with respect to body 3 (the location of the latter being determined as a part of CLC1), while the sublist \(\ell _3^{(\beta )}=(\vartheta _{8},\xi _{4},\xi _{5})\) locates body 5 with respect to body 6, the proximal cuneiform, another part of CLC1.
See e.g. https://www.youmath.it/lezioni/algebra-elementare/equazioni/569-equazioni-goniometriche-lineari-in-seno-coseno.html. Visited on 15/05/2021.
Relation (40) yields
$$\begin{aligned}&\vartheta _5=2\arctan \sqrt{\frac{r_2\circ r_1+r_3+r_3\times (r_2\circ r_1)}{1-(r_2\circ r_1)\cdot r_3}},\\&n^{(35)}_{\circ }=\big (\tan \frac{\vartheta _5}{2}\big )^{-1}\frac{r_2\circ r_1+r_3+r_3\times (r_2\circ r_1)}{1-(r_2\circ r_1)\cdot r_3}\,. \end{aligned}$$Either sublist of \(\ell _2\) is equivalent to 3 scalar variables providing enough information to locate in space body 4, the proximal cuneiform; these triplets are not assignable freely, though: in fact, as we have just shown, compatibility with CLC1 and CLC3 reduces to 1 the number of DFs of CLC2. The geometrical reason for this is that the referential and current centres of the spheres associated with ball joints 34 and 35 coincide. Consequently, when body 5 entrains the centre of ball joint 45 in any motion allowed by joint 35, the new position of joint 45 is always compatible with that of joint 34: the only possible motions of body 4 are rotations about the axis passing through the current centres of the spheres associated with joints 34 and 45.
Abbreviations
- CLC:
-
Closed-loop chain
- DF:
-
Degree of freedom
- DSS:
-
DataSet section
- HMF:
-
Hind-MidFoot
- MFM:
-
Multi-line segment foot model
- OLC:
-
Open-loop chain
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Acknowledgements
The early stages of this work took place at the Okinawa Institute of Science and Technology (OIST) Graduate University, Japan, whose hospitality we both gratefully acknowledge, where we profited from many discussions with Prof. Eliot Fried, head of the Mathematics, Mechanics, and Materials Unit, and with Mr. Michael Grunwald, a member of the same Unit. PPG also benefited from a couple of short stays at and supported by the GSA Laboratory – ENSA Paris-Malaquais, Paris, France. We are indebted to Alberto Leardini, DPhil, head of Movement Analysis Laboratory, IRCCS Istituto Ortopedico Rizzoli, Bologna, Italy, for many illuminating conversations about current status and future trends of foot-mechanics related research; in particular, Dr. Leardini suggested the all-important connection between our approach to foot modelling and Huson’s [6,7,8,9]. Finally, it is a pleasure to thank Prof. Vincenzo Parenti Castelli, Prof. Nicola Sancisi and Dr. Michele Conconi, Department of Industrial Engineering, University of Bologna, Italy, for their many competent comments about our work.
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Brocato, M., Podio-Guidugli, P. A bone-wise approach for modeling the human hind-midfoot. Part I: kinematics. Meccanica 57, 977–998 (2022). https://doi.org/10.1007/s11012-021-01460-x
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DOI: https://doi.org/10.1007/s11012-021-01460-x