Olanlokun, Kola Folorunsho; (1999) Control of Knee Stability by Internal Devices. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This work is aimed at identifying the factors that determine the anterior/posterior stability of knees that have prosthetic articulations. It is also aimed at clarifying the manner in which each of the factors contributes to the determination of knee stability: and at determining ways in which anterior/posterior instability of the knees can be prevented. The subject of knee stability and previous contributions to knee modelling and related empirical work were reviewed, and the limitations of current orthopaedic practice and research were identified. Stability-determining methods of engineering, physics, and mathematics were also reviewed; and a method was selected for the purpose of this thesis. With femorotibial motion restricted to the sagittal plane, a wide range of knees that have prosthetic articulations were represented by a generalized mechanical system. On the basis of this system, nonlinear analytical models were developed on the knee's kinematic constraint, energy, quasi-static force versus deflection, stiffness and anterior/posterior stability. Model-based simulations were carried out to show the effects of specific system configuration variables, input load-parameters, and 'constants' on the anterior/posterior stability of the knee. Graphical results on the anterior/posterior force versus deflection and anterior/posterior stiffness versus deflection behaviour of the knee were plotted. The anterior/posterior stability maps that correspond to these graphs were also plotted. The stability maps show regions at which the knee will be stable, and regions at which it will be unstable. The validity of the anterior/posterior equilibrium equations and knee stability models was investigated. The anterior/posterior stability of a knee that has prosthetic articulations is determined by the algebraic sign of the anterior/posterior stiffness of the system constituted by the knee and its inputs. The factors that determine the stability of the knee are the configuration variables, input load-parameters and 'constants' of the system constituted by the knee and its inputs. The manner in which designers of prosthetic articulations, knee surgeons, physiotherapists and the patient can help in preventing anterior/posterior instability of the knee has been identified. Also, the relationships between anterior/posterior laxity, stiffness and stability of the knee have been established.

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