Development of an intervertebral disc implant, biomodelling methodology and a femoral endoprosthesis
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The intervertebral discs of the lumbar spine can be damaged as a result of trauma, disease or deformity. If an intervertebral disc becomes too compromised the current surgical solution is to fuse the vertebra at the affected spinal level. Spinal fusion presents its own complications which can limit its short and long term success. One of the key limiting factors is the loss of mobility at the affected level, this causes additional loading and accelerated degradation of the adjacent intervertebral discs. Therefore, the aim of this project was to develop an intervertebral disc implant which allowed natural motion at the affected level. The implant developed consists of a fluid filled welded bellows assembly. This arrangement is similar to a healthy intervertebral disc in which the fluid nucleus pulpous is contained by the annulus fibrosus. The proposed implant also incorporates overload and motion-restricting features to prevent the implant and spinal column being damaged. Artificial disc implants have been developed by other researchers. The implant developed in this project is unique as it does not generate any wear debris. This is significant as wear debris can cause a macrophage response and osteolysis, thus ultimately limiting the long term viability of implants which do produce wear debris. This thesis also details the development of BioModelling methodology for producing graphical reconstructions from medical scan data. These reconstructions can be used to produce plastic and metallic models for pre-operative planning purposes and implants for in-vivo use. While originally intended for the spinal implant work, it was ultimately used for other tasks. A case study illustrates its use in producing a maxilla implant. The final component of this project was to design and produce a femoral endoprosthesis for a patient with Osteogenesis Imperfecta. The patient's existing implants had failed and as a result an implant was required which could fully support all the applied loads whilst still allowing the patient's healthy hip and knee joints to be retained.