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Separating the study of kinematic geometry of the human knee from the study of its behaviour under load provides insight into the complex relationship between form and function at the joint. The development of a three-dimensional mathematical model which examines the mobility and stability of the joint in sequence is described in this thesis. A previously proposed model of knee mobility, in which the ligaments and ar- ticular surfaces act as rigid constraints between the bones in a single degree-of- freedom spatial mechanism, was re-examined and its limitations addressed. A new geometric-numerical approach to solving the model kinematics, capable of handling both idealised and more anatomical representations of the articular surfaces, was developed. A database of specimen-specific motion and geometry was established, based on cadaver studies. Articular contact kinematics and ligament length patterns were also quantified. In experiment, all components of passive knee movement were found to be coupled to the flexion angle, providing justification for the underlying concept of the model of knee mobility. Specimen-specific models of mobility were successful in predicting the main fea- tures of passive knee motion through a full range of flexion. Incorporation of second order tibial articular surfaces permitted the prediction of physiological motion com- patible with more realistic contact point movement. Through incorporation of continuous three-dimensional arrays of extensible lig- ament fibres, a preliminary model of knee stability was formulated. Although in need of further refinement, sample predictions of joint behaviour during a/p drawer and axial rotation have demonstrated the potential of the model in highlighting the subtleties of ligament mechanics. It was concluded that the sequential approach is appropriate for the study of joint behaviour in three dimensions and that, based on the success of the analogous two-dimensional theory, it provides an invaluable tool in the study of joint mechanics in activity and in the design and assessment of surgical procedures for treating knee injury and disease.

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Graduation date: 1998

M.Ing. / Grade 350W structural steel was introduced into the South African steel market to replace its predecessor 300W structural steel. 350W structural steel has a 50 MPa increase in its minimum yield strength. Currently, little or no experimental data exists that describes the behaviour of full scale 350W structural sections. No extensive comparisons between 350W and 300W, as to their structural behaviour, exist. The main aim of this investigation was firstly to determine if the minimum yield strength was fully realised throughout typical sections and if the increase in yield strength changed the yielding behaviour of the material. Secondly, the effect that the increased yield strength has on the structural resistance of axial compression members. The investigation largely consisted of an evaluation of firstly the material and then secondly the structural behaviour of full scale member sections as axial members. It was found that all the sections tested complied with the minimum specified yield strength of 350 MPa. In general, 350W hot rolled structural steel yields more gradually than 300W hot rolled structural steel. This increase is small and seems to be of little significance as far as the overall behaviour is concerned. In general, the increase in minimum yield strength from 300 MPa to 350 MPa has realised an increase in critical buckling strength well into the medium slenderness ratio region and is beneficial for members of short and intermediate lengths. The data seems to indicate that SANS 10162-1:2005 can be used with confidence when designing axial compression members in 350W hot rolled structural steel.