A novel experimental design for the measurement of metacarpal bone loading and deformation and fingertip force.

Szu-Ching Lu,Evie E Vereecke,Dieter H Pahr,Alexander Synek,Tracy L Kivell

doi:10.7717/peerj.5480

Szu-Ching Lu, Evie E Vereecke + Show 3 more

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https://doi.org/10.7717/peerj.5480

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Abstract

BackgroundMusculoskeletal and finite element modelling are often used to predict joint loading and bone strength within the human hand, but there is a lack of in vitro evidence of the force and strain experienced by hand bones.MethodsThis study presents a novel experimental setup that allows the positioning of a cadaveric digit in a variety of postures with the measurement of force and strain experienced by the third metacarpal. The setup allows for the measurement of fingertip force as well. We tested this experimental setup using three cadaveric human third digits in which the flexor tendons were loaded in two tendon pathways: (1) parallel to the metacarpal bone shaft, with bowstringing; (2) a semi-physiological condition in which the tendons were positioned closer to the bone shaft.ResultsThere is substantial variation in metacarpal net force, metacarpal strain and fingertip force between the two tendon pathways. The net force acting on the metacarpal bone is oriented palmarly in the parallel tendon condition, causing tension along the dorsum of the metacarpal shaft, while the force increases and is oriented dorsally in the semi-physiological condition, causing compression of the dorsal metacarpal shaft. Fingertip force is also greater in the semi-physiological condition, implying a more efficient grip function. Inter-individual variation is observed in the radioulnar orientation of the force experienced by the metacarpal bone, the fingertip force, and the strain patterns on the metacarpal shaft.ConclusionThis study demonstrates a new method for measuring force and strain experienced by the metacarpal, and fingertip force in cadaveric digits that can, in turn, inform computation models. Inter-individual variation in loads experienced by the third digit suggest that there are differences in joint contact and/or internal bone structure across individuals that are important to consider in clinical and evolutionary contexts.

Highlights

IntroductionDifferent manipulative and locomotor behaviours lead to varied biomechanical loading of the hand and affect the external morphology (e.g. entheses) and internal structure (e.g. cortical thickness, trabecular architecture) of bones
Different manipulative and locomotor behaviours lead to varied biomechanical loading of the hand and affect the external morphology and internal structure of bones
We present the results of net force and strain experienced by the metacarpal bone and fingertip force of the three test subjects in each tendon path condition

Summary

Introduction

Different manipulative and locomotor behaviours lead to varied biomechanical loading of the hand and affect the external morphology (e.g. entheses) and internal structure (e.g. cortical thickness, trabecular architecture) of bones. It has been used to infer hand function in the past, including the evolution of tool-use behaviours and precision grip abilities in fossil hominins (Skinner et al, 2015; Stephens et al, 2018) These functional interpretations are almost always based on loose estimates of joint posture at a predicted, but often unknown, point of peak loading during different manipulative (Key, 2016; Rolian, Lieberman & Zermeno, 2011; Williams, Gordon & Richmond, 2012) and, locomotor behaviours (Richmond, 2007; Wunderlich & Jungers, 2009). The setup allows for the measurement of fingertip force as well We tested this experimental setup using three cadaveric human third digits in which the flexor tendons were loaded in two tendon pathways: (1) parallel to the metacarpal bone shaft, with bowstringing; (2) a semi-physiological condition in which the tendons were positioned closer to the bone shaft. Inter-individual variation in loads experienced by the third digit suggest that there are differences in joint contact and/or internal bone structure across individuals that are important to consider in clinical and evolutionary contexts

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