Doctoral Degrees (Industrial Engineering)

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Browsing Doctoral Degrees (Industrial Engineering) by Subject "Arthroplasty"

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    Development of a process chain for digital design and manufacture of patient-specific intervertebral disc implants with matching endplate geometries
    (Stellenbosch : University of Stellenbosch, 2011-03) De Beer, Neal; Van der Merwe, A. F.; Scheffer, C.; Dimitrov, D. M.; University of Stellenbosch. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: Back pain is a common concern amongst a growing population of people across the world today, where in most cases the pain can become unbearable resulting in major lifestyle adjustments. Seventy to eighty percent of the population of the Western world experiences low-back pain at one time or another. Pain can be produced as a worn disc becomes thin, narrowing the space between the vertebrae. Pieces of the damaged disc may also break off and cause irritation to the nerves signalling back pain. Depending on the severity of a patient’s condition, and after conservative treatment options have been exhausted, a disc replacement surgery (arthroplasty) procedure may be prescribed to restore spacing between vertebrae and relieve the pinched nerve, while still maintaining normal biomechanical movement. Typical complications that are however still observed in some cases of disc implants include: anterior migration of the disc, subsidence (sinking of disc) and lateral subluxation (partial dislocation of a joint). Issues such as function, correct placement and orientation, as well as secure fixation of such a disc implant to the adjacent vertebrae are highly important in order to replicate natural biomechanical behaviour and minimise the occurrence of the complications mentioned. As various imaging and manufacturing technologies have developed, the option for individual, patientspecific implants is becoming more of a practical reality than it has been in the past. The combination of CT images and Rapid Manufacturing for example is already being used successfully in producing custom implants for maxilla/facial and cranial reconstructive surgeries. There exists a need to formalise a process chain for the design and manufacture of custom-made intervertebral disc implants and to address the issues involved during each step. Therefore this study has investigated the steps involved for such a process chain and the sensible flow of information as well as the use of state-of-the-art manufacturing technologies. Strong emphasis was placed on automation of some of the processes as well as the user-friendliness of software where engineers and surgeons often need to work together during this multi-disciplinary environment. One of the main benefits for customization was also investigated, namely a reduction in the risk and potential for implant subsidence. Stiffness values from pressure tests on vertebrae were compared between customized implants and implants with flat endplate designs. Results indicated a statistically significant improvement of customized, endplate matching implants as opposed to flat implant endplates. Therefore it may be concluded that the use of customized intervertebral disc implants with patient specific endplate geometry may decrease the risk and potential for the occurrence of subsidence.
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    Laser powder bed fusion-centred approach to enable local drug delivery from a cementless hip stem
    (Stellenbosch : Stellenbosch University, 2021-03) Bezuidenhout, Martin Botha; Damm, Oliver; Sacks, Natasha; Dicks, Leon Milner Theodore; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: Periprosthetic joint infection (PJI) resulting from colonisation of implant surfaces by pathogenic bacteria and subsequent biofilm formation is a devastating complication following total hip arthroplasty. It significantly reduces a patient’s quality of life and, in severe cases, can result in amputation or mortality. Treatment of PJI is associated with a substantial burden on healthcare and economic resources. The importance of research towards innovations in PJI prevention and treatment is emphasised. Local delivery of antimicrobial drugs is an effective approach to prevent and treat PJI as it enables high local drug concentrations while avoiding systemic side effects. Current practice is considered sub-optimal and appreciable research exists on the improvement of local drug delivery strategies. For cementless hip stems the focus tends to be on coatings and conditioning of the external implant surface. A significant research gap exists between external and internal drug delivery strategies where ‘internal’ refers to the incorporation of reservoir structures within the implant. Therefore, a prototype strategy utilising the internal volume of a cementless stem for a reservoir from which an antimicrobial drug can be delivered directly to the implant surface was investigated. The challenge of fabricating a cementless hip stem with intricate internal geometries can be effectively addressed through metal additive manufacturing (MAM). Industry is steadily incorporating MAM into process chains as the main production technology for the fabrication of high-value functional components. Laser powder bed fusion (LPBF) was applied in this study as MAM technology to fabricate a Ti6Al4V ELI demonstrator cementless hip stem with local drug delivery functionality. This required an interdisciplinary approach, for which a problem solving framework has been synthesised to aid in process chain development from an LPBF-centred perspective. The overall problem was decomposed into integrated partial and single problems which were systematically investigated through literature study and experimentation. An LPBF-centred solution was developed for the direct integration of permeable structures in a dense part using an in-process assembly method. Different levels of porosity were induced into permeable thin walls according to a systematically identified window for ranges of the process parameters, laser power and scanning speed. This resulted in tailorable release profiles for the model antibiotic vancomycin from an aqueous formulation. Released vancomycin retained its antibiotic efficacy against Staphylococcus aureus Xen 36 (methicillin sensitive) and Staphylococcus aureus Xen 31 (methicillin resistant), representing two of the most frequent pathogens in PJI. Solutions for single problems were recomposed for integrated solutions to partial problems, and subsequently for an overall prototype solution. The overall solution cementless hip stem prototype effectively prevented surface colonisation by Staphylococcus aureus Xen 31, confirming the efficacy of the developed local drug delivery strategy. These results were used to inductively refine the LPBF-centred interdisciplinary problem solving framework. The original contribution of the research corresponds to the experimentation and framework development phases respectively. This involves the systematic investigation of LPBF to enable local drug delivery and an LPBF-centred approach for interdisciplinary problem solving. Lastly, it contributes to the advancement of LPBF by demonstrating the application efficacy of the prototype solution.