Tribological Investigation of Articular Cartilage Substitution in the Medial Compartmental Knee

In the development of any cartilage substitution device, an understanding of the
tribological response of the natural joint, as well as the treated joint is of upmost
importance. Many previous studies have investigated the tribology of potential cartilage
substitution therapies, using small scale pin on plate experiments. The aim of the
current study was to develop an anatomical and physiological simulation of the medial
compartmental bovine knee joint and to use this simulation to investigate a number of
cartilage substitution therapies for damaged or diseased knee joints.
A pendulum friction simulator was used to apply physiological loading and motion to
medial compartmental knees. The wear of the cartilage was characterised following the
experiments using three different techniques: surface topography analysis, volumetric
wear quantification using µMRI scans and histological assessment. Three main
interventions were investigated using this novel anatomical simulation - the tribological
response of meniscectomy, the effect of conformity of tibial hemiarthroplasty designs,
and finally, a number of potential cartilage substitution materials were investigated as
osteochondral repair devices in the femoral condyle.
In the first two studies, the removal of the meniscus and a decrease of tibial
hemiarthroplasty conformity, resulted in an elevation of the coefficient of friction,
contact stress, friction shear stress and subsequently the wear and degradation of
cartilage. In the defect repair study, biphasic defect repair materials (hydrogels) had a
superior tribological performance to non-compliant single phase materials (stainless
steel). Across the three studies, the use of non-biphasic materials and/or the loss of
joint congruity resulted in a more rapid decrease of cartilage interstitial fluid
pressurisation and biphasic fluid load support, resulting in increased cartilage solid-solid
contact and increased wear.
This tribological simulation can be used to investigate many potential knee joint
intervention, from uni- or hemi-arthroplasty, cartilage defect repair, meniscus
substitutes or tissue engineered substitutes. This simulation can be used to further our
understanding of the tribological characteristics of more satisfactory and conservative
therapies for damaged and diseased synovial joints.