The peripheral soft tissues should not be ignored in the finite element models of the human knee joint

In finite element models of the either implanted or intact human knee joint, soft tissue structures like tendons and ligaments are being incorporated, but usually skin, peripheral knee soft tissues, and the posterior capsule are ignored and assumed to be of minor influence on knee joint biomechanics. It is, however, unknown how these peripheral structures influence the biomechanical response of the knee. In this study, the aim was to assess the significance of the peripheral soft tissues and posterior capsule on the kinematics and laxities of human knee joint, based on experimental tests on three human cadaveric specimens. Despite the high inter-subject variability of the results, it was demonstrated that the target tissues have a considerable influence on posterior translational and internal and valgus rotational laxities of lax knees under flexion. Consequently, ignoring these tissues from computational models may alter the knee joint biomechanics

An Exploration into the Relationship between Knee Shape and Kinematics Before and After Total Knee Replacement

The knee joint is unique in its design and it is thought that its articular shape is the main driver of biomechanical behaviour. Although the shape of the bony knee is acknowledged to change with osteoarthritis, the specific relationship between shape changes and function is not well understood. Deep flexion, specifically kneeling, is an ideal testing environment for the tibiofemoral joint because it is both a difficult and a desirable activity for people with knee osteoarthritis. Total knee replacement (TKR) is a surgery which attempts to restore the articular shape in order to enhance function. However, the influence of implant design on kneeling kinematics is unclear. This thesis examines the role of knee shape on kneeling kinematics before and following total knee replacement. The four aims of this thesis were to: 1) describe and quantify the main modes of shape variation which distinguish end-stage OA from age- and sex-similar healthy knees; 2) determine whether bony shape can predict deep kneeling kinematics in people with and without OA; 3) examine the published literature to determine whether there are any differences in contact patterns as a function of TKR design; and 4) to prospectively compare the six-degree-of-freedom kneeling kinematics of posterior-stabilised fixed bearing, cruciate-retaining fixed bearing and cruciate retaining rotating platform designs. Statistical shape modelling identified differences between osteoarthritic and healthy bony knee shape. Specifically: large expansions around the femoral cartilage plate; expansion and depression at the medial tibial border; and an area of corresponding bony expansion on the posterior aspect of the medial femur and tibia. Statistical shape modelling and image registration derived six degree of freedom kinematics were used to test for associations between knee shape and kneeling kinematics. The kinematic variability was described using bivariate principle component analysis. While we found weak associations between knee shape and kinematics, BMI and group (OA vs Healthy) also predicted kneeling kinematics. This indicates that factors other than bony shape are important in predicting kneeling kinematics. The third study was a systematic review with meta-analyses using quality effects models which characterised the influence of TKR implant design on kneeling contact patterns. The review found posterior stabilised designs were different to cruciate retaining designs, but the heterogeneity was high limiting any firm conclusions. The final study was a prospective randomised clinical trial examining the influence of TKR design on kneeling kinematics. The study found that posterior-stabilised fixed-bearing and cruciate-retaining rotating-platform designs had higher maximal flexion compared to cruciate retaining-fixed bearing designs. Furthermore, posterior-stabilised fixed-bearing femoral components were more posterior and the cruciate-retaining rotating-platform was in more external femoral rotation throughout flexion. However, there was substantial between-patient variability. This research breaks new ground around which aspects of bony shape are altered in osteoarthritis and how these shapes, and prosthetic design, influence kneeling kinematics. Furthermore, the methodologies employed in this thesis provide new ways of describing the variability in complex shape and kinematics datasets, which may contribute to the identification of therapeutic efficacy. Knee shape is considered to be an important driver for normal movement. However, the results of this thesis indicate that there are potentially other factors, including soft-tissue properties and patient-specific movement strategies, which might influence the kinematics of deep kneeling. The message for surgeons and other clinicians is that bony shape and TKR design are not the primary drivers of functional performance and that kneeling should be on their radar as an activity to which their patients should aspire