In this project techniques for measuring and describing the relative motion between two bodies have been applied to the measurement and description of the human tibio-femoral joint. A three-dimensional computer simulation of this joint was developed to describe and analyse clinical instabilities of the knee joint.

The techniques for measuring and describing knee joint motion in the literature are reviewed and analysed with regard to the clinical instability of the knee joint associated with anterior cruciate ligament rupture known as the 'pivot shift'.

An electromagnetic measurement device was assessed and found to be suitable for measuring the three-dimensional motion of the tibio-femoral joint. This was used to measure the pivot shift under different loading conditions in cadaveric knees. It was found that the pivot shift could be described in terms of tibial rotations versus angle of knee flexion. The pivot shift could be elicited after isolated sectioning of the anterior cruciate ligament, with combined valgus moments and loading on the iliotibial tract.

A software package was identified and a protocol developed which could be used to simulate the relative motion between two bodies. A simulation was created with the geometry, load-displacement data and kinematics of an intact knee as input. This also used data on the force-extension characteristics of the individual ligament fibre bundles, that provided the tensile restraints between the bones.

As a single application, this was used to predict the forces within ligaments during knee motion, in particular the pivot shift motion. This technique can now be used to analyse other structures within the knee joint.

The knowledge derived from the work in this thesis will help to improve surgical intervention in knee joint instabilities.