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.