Viscoelastic characteristics of the canine cranial cruciate ligament complex at slow strain rates.

Rosti Readioff,Eithne Comerford,Brendan Geraghty,Ahmed Elsheikh

doi:10.7717/peerj.10635

Abstract

Ligaments including the cruciate ligaments support and transfer loads between bones applied to the knee joint organ. The functions of these ligaments can get compromised due to changes to their viscoelastic material properties. Currently there are discrepancies in the literature on the viscoelastic characteristics of knee ligaments which are thought to be due to tissue variability and different testing protocols.The aim of this study was to characterise the viscoelastic properties of healthy cranial cruciate ligaments (CCLs), from the canine knee (stifle) joint, with a focus on the toe region of the stress-strain properties where any alterations in the extracellular matrix which would affect viscoelastic properties would be seen. Six paired CCLs, from skeletally mature and disease-free Staffordshire bull terrier stifle joints were retrieved as a femur-CCL-tibia complex and mechanically tested under uniaxial cyclic loading up to 10 N at three strain rates, namely 0.1%, 1% and 10%/min, to assess the viscoelastic property of strain rate dependency. The effect of strain history was also investigated by subjecting contralateral CCLs to an ascending (0.1%, 1% and 10%/min) or descending (10%, 1% and 0.1%/min) strain rate protocol. The differences between strain rates were not statistically significant. However, hysteresis and recovery of ligament lengths showed some dependency on strain rate. Only hysteresis was affected by the test protocol and lower strain rates resulted in higher hysteresis and lower recovery. These findings could be explained by the slow process of uncrimping of collagen fibres and the contribution of proteoglycans in the ligament extracellular matrix to intra-fibrillar gliding, which results in more tissue elongations and higher energy dissipation. This study further expands our understanding of canine CCL behaviour, providing data for material models of femur-CCL-tibia complexes, and demonstrating the challenges for engineering complex biomaterials such as knee joint ligaments.

Highlights

Ligaments play a major role in stifle joint stability (Budras, 2007; Levangie & Norkin, 2005), with part of the primary support being provided by the cranial cruciate ligament (CCL) (Carpenter & Cooper, 2000; Slatter, 2002)
CCL samples The CCL samples (n = 6 paired stifle joints) used to investigate mechanical properties of the ligament were of mixed gender and the bodyweight of the cadavers were in the range of 17–25.5 kg (20.68 ± 3.85 kg)
The current study focused on the viscoelastic behaviour, such as strain rate dependency, hysteresis and recovery of canine CCLs at slow strain rates to better understand the tissue behaviour at the toe region where the constituents of the extracellular matrix makes a major contribution to ligament mechanics

Summary

Introduction

Ligaments play a major role in stifle (knee) joint stability (Budras, 2007; Levangie & Norkin, 2005), with part of the primary support being provided by the cranial cruciate ligament (CCL) (Carpenter & Cooper, 2000; Slatter, 2002). There is a large economic cost associated with managing canine CCLR, for example in the United States alone the economic cost was estimated to be at least one billion dollars in 2003 (Wilke et al, 2005) Both human and canine CCL failure significantly increases the incidence of age-associated joint degeneration (Lee et al, 2014; Liu et al, 2003; Peters et al, 2018) and so understanding the tissue’s fundamental material properties can assist with the prediction and effective management of ligament injuries. There is a relatively large deformation of the tissue with little increase in load and this permits initial joint deformations with minimal tissue resistance (Amis, 2004; Dale & Baer, 1974; Fratzl et al, 1998; Wingfield et al, 2000) (Fig. 1)

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