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Ph.D., Faculty of Health Sciences, University of the Witwatersrand, 2008. / Lumbar disc replacement is a rapidly expanding surgical treatment modality for longstanding back and leg pain due to intervertebral disc degeneration. Compared to fusion surgery, it has the advantage of preserving segmental mobility, but convincing evidence of superiority over fusion surgery is missing. As part of this research project, I participated in the development of a new intervertebral disc prosthesis, with several international patents attached to the design of the prosthesis, the instrumentation and the insertion technique. The Kineflex (Centurion) lumbar disc is a mechanical, un-constrained, re-centering disc prosthesis developed in South Africa. After the development and manufacturing of the disc, prototype test racks were custom-made at the premises of the manufacturer and the disc was extensively tested for mechanical wear and fatigue. The first implantation took place in October 2002. I prospectively captured all cases performed by our centre, with documentation including demographic data, co-morbidities, clinical history, symptoms and signs. The completed consent forms were filed. The outcome was monitored, pre-operatively and in follow-up, with complete radiological documentation of all radiographs on JPEG files. Clinical outcome results were documented using two different internationally validated questionnaires as well as our own questionnaire, which expands further on work and demographic details, previous operative and conservative treatment, and satisfaction with the treatment outcome. The aim of the this project was to develop a disc prosthesis that is suitable and safe for human implantation into the lumbar spine disc space, even in severely advanced disc degeneration and to verify this in the outcome studies presented in this thesis. Existing indications and contra-indications for artificial disc replacement were critically evaluated regarding their validity for this particular implant. Results: Chapter 3 elaborates on the extensive pre-clinical mechanical wear and fatigue testing protocol to which the Centurion (Kineflex) lumbar disc prosthesis was subjected. The results of this testing protocol, together with our early clinical outcome results, formed the basis for the awarding of the European quality recognition (CE-Mark). In these extensive in vitro studies, we were able to show the durability of the Kineflex disc prosthesis in the long term. This, together with our initial clinical outcome results, formed the basis for the acceptance into a “prospective, randomized, multicenter Food and Drug Administration investigational device exemption study of lumbar total disc replacement with the KINEFLEX Lumbar Artificial Disc versus the CHARITÉ™ Artificial Disc”. Chapter 4 is compiled from an invited submission to a new book on motion preservation surgery in the human spine, edited by leading spine surgeons in the field (James J. Yue, Rudolf Bertagnoli, Paul McAfee, and Howard An) and published by Elsevier Publishers: Chapter 42: Kineflex. In this chapter, an overview is given of the ideas behind the Kineflex disc development, as well as of the insertion instrumentation used for disc implantation. It further reports on early clinical outcome results of the first patients implanted with the device in our centre (the first 40 implantations worldwide were all performed by me). Chapter 5, our first peer reviewed international publication, reports on clinical and radiological 2-year outcome results of our first 100 patients. With the Kineflex implant, we could demonstrate equally good radiological placement accuracy in patients with severe and less severe disc degeneration of the index level, rendering the implant suitable even in severe degeneration of a spinal motion segment. Chapter 6 and Chapter 7 of this thesis consist of two further peer-reviewed publications. They both report on so-called “off-label” patient sub-groups in our disc replacement series. In Chapter 6 we present the second published series on a larger group of patients presenting with adjacent segment disease after previous lumbar fusion surgery as well as the first publication, which investigated the radiological changes in alignment parameters secondary to the disc replacement surgery in this patient group. Chapter 7 consists of the first published series on patients with “degenerative spondylolisthesis” treated with disc replacement surgery. A detailed description of the operative reduction technique is provided, which is unique to the Kineflex disc and its insertion instrumentation. In this pilot study, two-year results on a limited patient group are presented. This thesis concludes with the overall discussion in Chapter 8. It outlines the current knowledge on artificial disc replacement and places my results into perspective with recent discoveries published in the literature. It finishes with my assessment of what future research should concentrate on.

Developing computational models of the human spine has been a hot topic in biornechanical research for a couple of decades in order to have an understanding of the behaviour of the whole spine and the individual spinal parts under various loading conditions. The objectives of this thesis are to develop a biofidefic multi-body model of the whole human spine especially for dynamic analysis of impact situations, such as frontal impact in a car crash, and to generate finite element (FE) models of the specific spinal parts to investigate causes of injury of the spinal components. As a proposed approach, the predictions of the multi-body model under dynamic impact loading conditions, such as reaction forces at lumbar motion segments, were utilised not only to have a better understanding of the gross kinetics and kinematics of the human spine, but also to constitute the boundary conditions for the finite element models of the selected spinal components. This novel approach provides a versatile, cost effective and powerful tool to analyse the behaviour of the spine under various loading conditions which in turn helps to develop a better understanding of injury mechanisms.

3-D computational modelling of the human spine provides a sophisticated and cost-effective medium for bioengineers, researchers, and ergonomics designers in order to study the biomechanical behaviour of the human spine under different loading conditions. Developing a generic parametric computational human spine model to be employed in biomechanical modelling introduces a considerable potential to reduce the complexity of implementing and amending the intricate spinal geometry. The main objective of this research is to develop a 3-D parametric human spine model generation framework based on a command file system, by which the parameters of each vertebra are read from the database system, and then modelled within commercial 3-D CAD software. A novel data acquisition and generation system was developed as a part of the framework for determining the unknown vertebral dimensions, depending on the correlations between the parameters estimated from existing anthropometrical studies in the literature. The data acquisition system embodies a predictive methodology that comprehends the relations between the features of the vertebrae by employing statistical and geometrical techniques. Relations amongst vertebral parameters such as golden ratio were investigated and successfully implemented into the algorithms. The validation of the framework was carried out by comparing the developed 3-D computational human spine models against various real life human spine data, where good agreements were achieved. The constructed versatile framework possesses the capability to be utilised as a basis for quickly and effectively developing biomechanical models of the human spine such as finite element models.