Browsing by Author "Nortje, B. D."

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    Feasibility of additive manufacturing for patient-specific knee replacements.
    (2021-12) Nortje, B. D.; Van der Merwe, J. H.; Becker, Thorsten Hermann
    ENGLISH ABSTRACT: Osteoarthritis causes the degradation of the articular cartilage of the knee. This results in a loss of function of the joint. With a total knee replacement surgery, these articular surfaces are removed and replaced with artificial components. The ability to integrate patient-specific implant components can improve the results of a total knee replacement. The focus of this research is to investigate the feasibility of manufacturing methods required for a femoral knee replacement component for patient-specific implants. Through understanding what has been accomplished in literature, a multi-directional pin-on-flat wear tester is developed. This machine is based on the motion that is observed by the knee articulation in specific. A cross-shear ratio is designed to achieve similar wear characteristics to that seen in a knee replacement. This development is validated through the use of Co-Cr-Mo samples. The developed and implemented machine is utilised to perform an assessment of laser powder bed fusion, a powder bed based additive manufacturing technique, for use in patient-specific femoral knee replacements. Focus is placed on the use of Ti-6Al-4V and Co-Cr-Mo; where the latter is used for a benchmark to indicate the relative wear properties of the former. The average wear rates that resulted after 3 x 106 cycles were 2.58 mg/MC and 2.63 mg/MC for Co-Cr-Mo and Ti-6Al-4V, respectively. Additive manufacturing provides the ability to manufacture a near net shape component that is suited for the patient’s geometry. Orthopaedic surgeons consider the full and natural functioning of the replaced joint to be an indication of the operation’s success. The unsatisfactory performance of an implant can be attributed to the incorrect tension of the ligaments surround- ing the joint; this is often found to be a result of geometric intolerances of the standard implant sizes in relation to the patient’s natural joint. This can be rectified through the use of additive manufacturing which provides the ability to manufacture components of high geometric tolerances. A feasibility analysis is done with regards to cost and suitability of man- ufacturing processes for patient-specific femoral knee replacements. Additive manufacturing is compared to CNC machining to assess the feasibility of pur- suing a patient-specific femoral knee replacement that is manufactured from Ti-6Al-4V. The device that was developed illustrated satisfactory performance in ac- cordance to what is expected from literature. Through these tests, Ti-6Al-4V displayed suitable wear properties for use in articulating joints. The study places focus on the knee joint, but can be adapted for many other articulating joints with lower loading. It can then be shown that additive manufacturing may not be a feasible option for manufacturing based on cost, but may prove beneficial for reasons such as geometry complexities, surface finish, accuracy and extent to which the surfaces can be altered.