Elsevier

Journal of Biomechanics

Volume 38, Issue 12, December 2005, Pages 2423-2430
Journal of Biomechanics

The damping properties of the venous plexus of the heel region of the foot during simulated heelstrike

https://doi.org/10.1016/j.jbiomech.2004.10.006Get rights and content

Abstract

The damping mechanisms that are operational in the heel pad during the impact phase of locomotion have the important function to protect the musculo-skeletal system from injuries. How this is achieved is still not fully understood, as is for instance illustrated by the ‘heel pad paradox’, the observation that in vivo and in vitro experiments yielded widely different results. This paradox could so far only partially be explained. In the light of this paradox, and a previous study by our group, we conjectured that the venous plexus might contribute as a hydraulic shock absorber to the damping properties of the heel pad. To investigate this hypothesis in vivo, heel pads of 11 volunteers were subjected to pendulum impact tests, using velocities of 0.2, 0.4, and 0.6 m/s, and three physiologically different, consecutive conditions: (i) a relatively empty venous plexus, (ii) a congested venous plexus, and (iii) a decongested venous plexus. At congestion, the maximum impact force decreased slightly but significantly by 2.6% at 0.2 m/s and 1.8% at 0.4 m/s. This effect was no longer found at 0.6 m/s. Although these effects are rather small, they confirm the fundamental hypothesis that the venous plexus contributes to the damping properties of the heel pad during walking. It is likely that some underestimation of the effect has occurred.

Introduction

Neutralisation of the effects of the impact forces that arise during heelstrike in locomotion is essential in preventing damage to the musculo-skeletal system (Collins and Whittle, 1989). Notwithstanding several studies, the mechanisms that damp the impact are still not fully understood. Based on the results of a previous study (Weijers et al., 2003), we hypothesised that the venous structures in the soft tissue of the heel pad might contribute to the damping by functioning as a hydro-mechanical shock absorber. In a search in the available literature on the mechanical properties of the heel pad, no systematic study on this matter was found. We did find controversial results in the reported mechanical properties of the heel pad, however. Most striking were the differences between studies conducted on healthy volunteers and studies conducted on isolated cadaver heel pads, ‘the heel pad paradox’ (Aerts et al., 1995). Although methodological factors explained most of these differences, a functional venous plexus in the in vivo test might also explain part of the ‘paradox’. The reported haemolysis in long-distance runners corroborates a relation between mechanical loading and the presence of blood in the sole of the foot (Dang, 2001; Telford et al., 2003). With this in mind, we conducted this study to quantitatively answer the question whether the venous plexus influenced the mechanical properties of the heel pad. The results would be of fundamental interest in basic science, and might also improve the insight in the patho-physiology linked to impact forces during locomotion.

Section snippets

Subjects

The subjects were healthy males, without physical complaints of their feet. No plantar callus formation was present. Eleven subjects were included (mean age: 38.1 years, range: 29–54; mean weight: 79.1 kg, range: 70–89; mean length: 1.82 m; range: 1.74–1.93). The study was approved by our Medical Ethic Committee. All volunteers gave informed consent.

Principle of the experiments

The effect of the venous plexus was investigated by comparing pendulum impact experiments on heel pads with empty veins and heel pads with

Results

The statistical descriptions of the parameters at the three impact velocities were summarised in Table 1. To test the effect of venous (de)congestion on the parameters at the three impact velocities separately, the two-tailed student t-test was used. The results were summarised in Table 2. At congestion, the Fmax decreased significantly from 2.6% at 0.2 m/s to 0% at 0.6 m/s. Decongestion gave a (smaller) opposite effect, although not significant at all velocities.

The stiffness decreased on

Discussion

The results of this study support the fundamental hypothesis that part of the damping properties of the heel pad comes from a distended venous plexus. Nevertheless, its contribution appears to be limited, even if some underestimation is taken into account.

At the end of the swing phase of gait, the foot contacts the ground and generates a reactive force. This force starts with a short spike with a duration of 10–20 ms that is superimposed on the slower upslope of the ground reactive force. This

Acknowledgements

We thank Martin van der Wolf and Emile Arnoldussen of the IDEE of the University Maastricht for their technical support.

References (18)

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