L'objectif principal de tout dispositif médical implantable est d'améliorer l'état de santé du patient en lui assurant un risque minimum. Dans ce but, l'étude de l'implant rachidien B Dyn comporte plusieurs volets : - la réalisation d'un suivi clinique, - l’analyse et la proposition de solutions techniques (actions correctives), - la création d'un outil numérique pour des évolutions ultérieures (actions préventives).L’étude bibliographique initiale permet d'appréhender l'anatomie fonctionnelle du rachis lombaire, de comprendre les états pathologiques et leurs conséquences et enfin de faire un inventaire des techniques chirurgicales associées (résection osseuse, implantation de dispositifs...).Le suivi clinique d'une population de trente patients souligne ensuite les apports (somatiques et fonctionnels) du B Dyn dans sa conception première. Pour quelques cas, l'analyse des clichés radiographiques en position de flexion montre une détérioration naissante de l'anneau liée, probablement, à une surcharge accidentelle de l'implant. Ce constat impose une évolution de la conception de l'implant.Une analyse de la conception initiale et la caractérisation mécanique en traction, permettent de cibler les actions correctives à appliquer dans le cadre de cette évolution. La démarche mise en place s'appuie sur l'évaluation expérimentale pour sélectionner des solutions techniques satisfaisant aux critères fonctionnels ; elle conduit à une évolution du choix de matériau de l'anneau.Pour la réalisation d'évolutions ultérieures, un modèle éléments finis est créé. L’approche numérique se substitue ainsi à l’approche expérimentale contraignante et coûteuse. La caractérisation préalable des élastomères est nécessaire à l'obtention de données matériaux pour élaborer ce modèle. Les résultats des premières simulations d'un essai de traction sont comparés aux données expérimentales dans la perspective de la validation du modèle.A ce stade, l'étude du B Dyn propose une première solution d'évolution de l'implant et un outil numérique pour l'analyse future de solutions techniques. / The main focus of any implantable medical device is to improve the health of the patient by providing minimum risk. For this purpose, the study of the B Dyn spinal implant comprises several constituents: - The carrying out of a clinical follow up, - The analysis and choice of technical solutions (corrective actions) - The creation of a digital tool for further development (preventive actions).The initial bibliographical study enables to comprehend the functional anatomy of the lumbar spine, to understand the pathological states and their consequences and finally to list the associated surgical techniques (osseous resection, implantation of devices…).The clinical follow-up of a population of thirty patients then underlines the contributions (somatic and functional) of the B Dyn in its first design. For a few cases, the analysis of radiographs in flexion shows an incipient deterioration in the ring probably related to an accidental overloading of the implant. This observation requires an evolution in the design of the implant.An analysis of the initial design and the mechanical characterization in traction, allow targeting the corrective actions to be applied in the context of this evolution. The developed approach is based on the experimental evaluation in order to select technical solutions that would satisfy the functional criteria; this leads to an evolution of the choice of the ring material.To conduct subsequent developments, a finite element model is created. Thus the digital approach replaces the restrictive and expensive experimental approach. The preliminary characterization of elastomers is necessary to obtain materials data to work out this model. The results of the first simulations of a tensile test are compared to experimental data in the perspective of the model validation.At this stage, the B Dyn study provides a first solution of implant evolution and a numerical tool for the future analysis of technical solutions.

There is a need for spinal implants that have nonlinear stiffness to provide stabilization if the spine loses stiffness through injury, degeneration, or surgery. There is also a need for spinal implants to be customizable for individual needs, and to be small enough to be unobtrusive once implanted. Past and ongoing work that defines the effects of degeneration on the torque rotation curve of a functional spinal unit (FSU) were used to produce a spinal implant which could meet these requirements. This thesis proposes contact-aided inserts to be used with the FlexSuRe™ spinal implant to create a nonlinear stiffness. Moreover, different inserts can be used to create customized behaviors. An analytical model is introduced for insert design, and the model is verified using a finite element model and tests of physical prototypes both on a tensile tester and cadaveric testing on an in-house spine tester. Testing showed the inserts are capable of creating a non-linear force-deflection curve and it was observed that the device provided increased stiffness to a spinal segment in flexion-extension and lateral-bending. This thesis further proposes that the FlexSuRe™ spinal implant can be reduced in size by joining LET joint geometries in series in a serpentine nature. An optimization procedure was performed on the new geometry and feasible designs were identified. Moreover, due to maintaining LET joint geometry, the contact-aided insert could be implemented in conjunction with this new device geometry.

One of the major health problems in western societies is back pain, with a prevalence rate of 49%–80%. In many cases, the back pain is due to degenerated discs. The gold standard to treat a severely degenerated disc is spinal fusion, where the vertebral disc is replaced with a cage structure. However, fusion cages have a failure rate of 30%, hence the need for further development. The focus of this thesis is to evaluate the combination of calcium phosphate cement with titanium, for a spinal application. Mechanical tests in the form of tensile, compression and 4-point-bending were performed to study the different material properties. The obtained results was applied as material parameters for isotropic linear elastic material models, using ANSYS. This was then used to develop a cage design through topology optimisation which was further evaluated by using Finite Element Analysis. From the tensile testing of the titanium, isotropic behaviour was found. It was also found that a longer mixing time of the cement resulted in poorer mechanical properties of the calcium phosphate, however, no conclusive results were obtained from the 4-point-bending tests. The final cage geometry filled with calcium phosphate was tested under compression to see whether the cage could protect the calcium phosphate or not. MicroCT after the test confirmed that no larger cracks developed during the testing, suggesting that the cage is strong enough to protect the calcium phosphate from mechanical failure.

Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Current technology enables researchers to identify a broad spectrum of opportunities in the biomedical industry to develop new and innovative products. Imaging technology, such as Computerised Tomography (CT) scanners or Magnetic Resonance Imaging (MRI) scanners, allow doctors to visualise a patient’s internal organs and bone structure in high quality three-dimensional images. Rapid Prototyping Technology (RPT) can already produce high quality complex parts, such as concept parts for the automobile industry and medical models for preoperative planning. These parts are divided into thin layers and manufactured layer by layer. At the same time the layers are joined together to produce the desired part. Generic artificial intervertebral disc implants already exist. However, these discs are only available in standard geometrical dimensions. The possibility of using imaging technology and RPT to design and manufacture a customized, patient specific implant will be investigated. A simple design (ball and socket) is used to illustrate the design process of a customized disc. It should be noted that this project does not attempt to design a new artificial intervertebral disc implant, but rather describes the design process. The research question is: How accurate can the customised disc implant’s inverse geometry represent the geometry of the vertebrae’s endplates? A preliminary research was done and the results were used to calculate the sample size for this study. A cadaver, provided by Stellenbosch University’s Faculty of Health Sciences’ Anatomy and Histology Department, was CT scanned. The L4- and L5-vertebrae were dissected, cleaned and measured using a photogrammetry measuring machine. Meanwhile, the data gathered from the CT scan is used to design the customised disc implant. The disc is manufactured from Ti6Al4V using a RPT technique called Direct Metal Laser Sintering. After the part is manufactured it is also measured using a photogrammetry measuring machine. The photogrammetry data from the vertebrae and the manufactured customised disc implant are compared, analysed and a hypothesis is formed. It can now be determined, with a certain degree of confidence, how accurate the customised disc implant’s geometry can represent the geometry of the vertebrae’s endplates. The design of a customised disc implant demands many work hours from a qualified engineer or designer, which in turn increases the production costs. This study describes a user-friendly program which will semi-automate the design process. Only limited input from the physician will be required. This program will decrease design time, which will have a direct effect on the production costs. The manufacturing costs are investigated as well. The results from this study indicates that it is possible to design a customized prosthetic, with the help of a custom disc generator, within 27 minutes. The customized disc can then be manufactured with an accuracy of 0.37 mm using rapid prototyping. / AFRIKAANSE OPSOMMING: Huidige tegnologie maak dit vir navorsers moontlik om ʼn breë spektrum geleenthede in die biomediese bedryf te identifiseer en nuwe produkte te ontwikkel. ʼn Pasiënt kan met ʼn Gerekenariseerde Tomografie (GT) -flikkergram of ʼn Magnetiese Resonansiebeelding (MRB) - masjien geskandeer word om sodoende ʼn drie-dimensionele beeld van sy of haar interne organe en beenstrukture te verkry. Deur gebruik te maak van snelle prototiperingstegnologie (SPT) kan daar alreeds enige komplekse geometriese vorm vervaardig word. Hierdie tegnologie word ingespan om parte, ontwerp met die hulp van RGO (Rekenaargesteunde Ontwerp), te vervaardig. Die spesifieke part word in dun lae opgedeel en daarna laag vir laag vervaardig. Terselfdertyd word die lae aan mekaar geheg, totdat die gewenste vorm gegenereer is. Die moontlikheid om ʼn GT-flikkergram én SPT te gebruik, met die doel om ʼn pasklaar-vervaardigde, persoon-spesifieke implantaat te ontwerp en te vervaardig, word in hierdie projek ondersoek. Daar bestaan alreeds generiese kunsmatige intervertebrale skyf-implantate (KISI’s). Hierdie skywe word egter beperk deurdat dit slegs in standaard geometriese dimensies vervaardig word. Met dié projek word die moontlikheid van ʼn pasklaar-vervaardigde intervertebrale skyf-implantate (PVKISI) vir ʼn bepaalde pasiënt, ondersoek. ʼn Eenvoudige meganiese ontwerp (bal-en-pootjie) word gebruik om die ontwerpproses van ʼn pasklaar-skyf in hierdie projek te beskryf. Let daarop dat die projek nie poog om ʼn nuwe kunsmatige intervertebrale skyf te ontwerp nie, maar om die ontwerpproses te beskryf. Die vraag wat ondersoek word, is: Hoe akkuraat kan ʼn PVKISI die inverse geometrie van die pasiënt se intervertebrale kontakoppervlaktes voorstel? ʼn Voorafgaande ondersoek is gedoen en die resultate is gebruik om die steekproef-grootte vir hierdie studie te bepaal. ʼn Kadawer, voorsien deur die Universiteit van Stellenbosch se Fakulteit Gesondheidwetenskappe se Departement Anatomie en Histologie, is met ʼn GT-flikkergram geskandeer. Die L4- en L5-werwels is gedissekteer, skoon gemaak en met ʼn fotogrammetriemeetmasjien gemeet. Intussen is die data, verkry van die GT-flikkergram, gebruik om die PVKISI te ontwerp. Die PVKISI is van Ti6Al4V vervaardig deur Direkte Metaal Laser-Sintering (DMLS). Die part is ook met ʼn fotogrammetrie-meetmasjien gemeet. Die fotogrammetrie-data van die werwels en die PVKISI is vergelyk, geanaliseer en ʼn hipotese is daar gestel. Daar kan dus met statistiese sekerheid bepaal word hoe akkuraat die PVKISI die inverse geometrie van die intervertebrale kontakoppervlaktes kan voorstel. Die ontwerp van ʼn PVKISI vereis baie werksure van ʼn gekwalifiseerde ingenieur of ontwerper, wat veroorsaak dat die vervaardigingskoste van so ʼn implantaat kan verhoog. In dié projek word ʼn gebruikersvriendelike koppelprogram beskryf wat die ontwerpproses semi-outomatiseer. Daar sal slegs beperkte bystand van die betrokke medici vereis word. Dié koppelprogram behoort heelwat te bespaar aan die hoeveelheid werksure bestee aan die ontwerp van die PVKISI, wat direk die koste van ʼn implantaat sal verlaag. Die kostes vir die vervaardiging van die PVKISI met DMLS is ook ondersoek om te bepaal hoe kostes bespaar kan word. Daar is getoon dat ʼn pasklaar-prostese se kontakoppervlaktes met ʼn akkuraatheid van 0.37 mm, deur snelle prototipering, vervaardig kan word. Deur van die koppelprogram, wat in die studie beskryf word, gebruik te maak, sal dit moontlik wees om ʼn pasklaar-protese binne 27 minute te ontwerp.

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