Stiffness of the human foot and evolution of the transverse arch
Venkadesan, M. et al.
Nature (2020) Vol. 579: 97-100.
The importance of midfoot stiffness for propulsion of human locomotion has been extensively studied. Much of the research however, has centered around the role of the medial longitudinal arch, with little investigation into the role of the transverse tarsal arch (TTA).
Considering a model similar in conceptualization to that of the increasing stiffness properties of a sheet of paper when curled longitudinally, the role of the TTA in contributing to midfoot stiffness via bony and soft tissue configuration can be similarly applied.
The purpose of this study was to examine the relationship between curvature and stiffness of the TTA.
The TTA was modelled during both computer simulations and physical experiments. Three-point bending tests were performed on arched continuum shells, mechanical mimics of the midfoot, and on human cadaveric feet.
Shells with greater transverse curvature were found to be stiffer in longitudinal bending.
Noted was that stiffness also depended the thickness, length, width, Young’s modulus, and Poisson’s ratio of the material.
The three-point bending tests on the foot models (3 metatarsals with springs mimicking intermetatarsal tissues plus hinges towards the midfoot), demonstrated results similar to the shells based on degree of transverse curvature.
The cadaveric feet demonstrated that intermetatarsal tissues significantly contributed to foot stiffness and greater than that of the longitudinal arch (LA) and plantar fascia.
The structural curvature of the TTA, as well as the stiffness and slack contributed by intermetatarsal tissues, were found important for the longitudinal stiffness of the foot. Thus, the authors demonstrated that biomechanical understanding of the feet should expand beyond that of the longitudinal arch and include that of the transverse arch and its related soft tissues.
Personal Interpretation and Significance:
Like demonstrated in previous studies, it is important for us to look beyond static architecture of the foot and more toward the role dynamic activity plays in arch stiffness. Through this study, it is apparent that we must look at multiple planes and not ignore the role that soft tissues play in contributing to human locomotion.