Published Article / Rapid Manufacturing (RM) has emerged over the past few years as a potential technology to successfully produce patient-specific implants for maxilla/facial and cranial reconstructive surgeries. However, in the area of spinal implants, customization has not yet come to the forefront and with growing capabilities in both software and manufacturing technologies, these opportunities need to be investigated and developed wherever possible. The possibility of using Computed Tomography (CT) and Rapid Manufacturing (RM) technologies to design and manufacture a customized, patient-specific intervertebral implant, is investigated. Customized implants could aid in the efforts to reduce the risk of implant subsidence, which is a concern with existing standard implants. This article investigates how accurately the geometry of a customized artificial intervertebral disc (CAID) can represent the inverse geometry of a patient's vertebral endplates. The results indicate that the endplates of a customized disc implant can be manufactured to a calculated average error of 0.01mm within a confidence interval of 0.022mm, with 95% confidence, when using Direct Metal Laser Sintering.

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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