Development of incrementally formed patient-specific titanium knee prosthesis

Eksteen, Pieter De Waal (2013-03)

Thesis (MScEng)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Osteoarthritis (OA), also known as degenerative joint disease is a progressive disorder of the joints caused by gradual loss of cartilage and resulting in the development of bony spurs and cysts at the margins of the joints. The degradation of the musculoskeletal system, which is mainly caused by joint injury, obesity (leading to musculoskeletal fatigue) and aging can also lead to osteoarthritis. The hands, feet, spine, and large weight-bearing joints, such as the hips and knees are commonly affected. The only medical solution to severe cases of osteoarthritis is the surgical reconstruction or replacement of a malformed or degenerated joint, better known as arthroplasty. Arthroplasty makes use of biomedical implants and replacements to restore functionality of the joints. Biomedical engineering in arthroplasty is an ever increasing field of interest as a result of its innovative improvements to surgical quality. Certain cases of partial osteoarthritis require less surgical action. Partial knee replacement surgery, also known as unicondylar (or unicompartmental) knee arthroplasty involves a covering which is placed over the affected area to resurface the affected bone and protect the patient from further degeneration. Advantages of partial replacement include faster recovery time and less post-operative pain. The biomedical implants used for these operations consist of a standardized implant that is fit onto the bone by modifying (cutting away) the outer structure of the bone. The result is known to cause post-operative discomfort among some patients. The problem with these standard designs includes the requirement of the removal of unaffected (healthy) bone matter, leading to induced trauma and pain for patients during the recovery phase of the operations. A preferred alternative to the standard design would be to create a custom implant for every patient, reducing the need to remove parts of unaffected bone matter. The implementation of this proposed method tends toward Minimally Invasive Surgery (MIS). MIS is normally preferred as it reduces the risk of various negative consequences of normal arthroplasty such as nerve or tendon damage during surgery. It could be argued that the proposed method may cause less damage to the fragile tendon, bloodflow, and nerve networks of the knee. Increasing material costs of metal products introduce great interest in more cost efficient forming processes to reduce the loss of redundant blank material. Incremental Sheet Forming (ISF), a relatively new class of forming process, has the potential to meet the need for this more efficient forming process. The ISF process is highly flexible, can be developed in normal milling machines, and can reduce production cost by up to 90% in comparison to processes such as stamping. The ISF process is a non-patented process, as the existing patents are referred to the designed machines and not the process. The availability of the ISF process contributes greatly to its attractiveness. ISF can be implemented in any facility that has access to a three- or more-axis CNC machine. The advantage of ISF implemented in CNC machines is that CNC technology has already reached a mature stage in development, contributing to the accuracy and methodology (such as feed rate or angular velocity of the tool) of the ISF process. The forming of valuable lightweight materials is well covered by ISF processes. A variety of studies contribute to research on the forming of titanium and titanium based alloys as part of ISF of lightweight materials. The ISF process utilizes the functionality of commercial CNC machines, improving the process availability of many manufacturing companies. The ISF process offers fast setup times and flexibility of the forming process. The purpose of this project is to define a process chain for creating a customized biomedical implant as well as determining the validity of the process chain by applying each step. The design and development procedure of a titanium based biomedical arthroplasty implant using innovative Incremental Sheet Forming (ISF) techniques will be documented, as well as an investigation of the financial cost and potential gain that this implant can offer.

AFRIKAANSE OPSOMMING: Osteoartritis is 'n gewrig siekte wat degeneratiewe newe-effekte behels in die gewrigte. Hierdie siekte lei to die geleidelike verlies van kraakbeen en lei tot die onreelmatige ontwikkeling van abnormale beengroei. Osteoartritis kan ook deur beserings in die gewrig veroorsaak word. Die hande, voete, ruggraat, en enige groter gewigdraende gewrigte, soos die heupe en knieë kan geaffekteer word. Die enigste mediese oplossing tot ernstige gevalle van die siekte is chirurgiese rekonstruksie of vervanging van die gewrig, meer bekend as artroplastie. Artroplastie maak gebruik van biomediese implantate om funksionaliteit van die gewrig te herstel. Biomediese ingenieurswese in artroplastie is 'n toenemende navorsingsveld as gevolg van die innoverende aspekte om chirurgiese kwaliteit te verhoog. Sekere gevalle van gedeeltelike osteoartritis vereis veel minder chirurgiese behandeling. Gedeeltelike knie vervanging chirurgie, meer bekend as unikompartementele knie artroplastie, behels 'n bedekking wat slegs die geaffekteerde been bedek, om die pasiënt van verdere degenerasie te beskerm. Voordele van gedeeltelike vervanging sluit vinniger herstel tyd en minder pyn in. Die biomediese implantate wat gebruik word vir hieride operasies bestaan uit standaard ontwerpe wat aan die been gepas word deur die wysiging (of wegsny) van die buitenste beenstruktuur. Die nagevolg van hierdie chirurgie is lang herstel periodes en kan ongemaklikheid in die knie veroorsaak. Die probleem met die bogenoemde standaard is dat die prosedure die verweidering van selfs ongeaffekteerde (of gesonde) been in sluit, wat lei tot verdere kniepyn en ongemak vir pasiënte lei tydens die herstelperiode. 'n Verkiesde alternatief tot die standaard ontwerpe is om 'n persoonlikke implantaat vir elke pasiënt te skep, en so kan die behoefte om dele van ongeaffekteerde been te behou moontlik wees. Die toepassing van die voorgestelde metode neig na Minimale Skade Chirurgie (MSC). MSC word gewoonlik verkies om die risiko van verskeie negatiewe nagevolge te verminder, en skade aan die tendon, bloed- en senunetwerke van die knie te beperk. Die toenemende materiaalkoste vand metal produkte lei tot 'n groot belangstelling in meer koste besparing vormings prosesse, om sodoende die verlies van oortollige materiaalverlies te verminder. Inkrementele Plaat Vervorming (IPV), 'n relatiewe nuwe klas van vervorming, is 'n waardige kanidaat om hierdie doel te bereik. Die IPV proses is baie toepaslik, en kan deur die gebruik van Rekenaar Numeriese Kontrole (RNK) masjienerie toegepas word. Verder sal dit vervaardigingskoste kan verlaag met soveel as 90% in vergelyking met ander prosese soos die stempel metode. Die beskikbaarheid van die IPV proses dra grootliks by tot die proses se aantreklikheid in die industrie. IPV kan geimplementeer word in enige fasiliteit wat toegang tot 'n drie-as RNK masjien het. Die voordeel van dit is die feit dat RNK masjienerie klaar ontwikkel en volwasse is, wat kan bydra tot goeie akkuraatheid in die vormingsproses. Die vervaardiging van laegewig materiale soos titaan of aluminium is gedokumenteer. 'n Verskeidenheid van studies dra waarde tot navorsing van die vormingsproses van titaan as deel hiervan. Die IPV proses bied vinnige opstel tye en goeie buigsaamheid met die vormingsproses, veral met behulp van 'n vyf-as masjien. Die doel van hierdie projek is om 'n proses ketting te ontwerp. Die proses ketting, wat uit vele stappe bestaan, sal die ontwerp en vervaardigingsproses van 'n persoonlike biomediese knie implantaat bevestig deur middel van die IPV vormings tegniek. Validasie van die proses ketting sal dus plaasvind deur die stappe van die voorgestelde proses ketting uit te voer. 'n Finale ondersoek sal die finansiele en regalutoriese aspekte van die projek aanspreek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80397
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