Tieteellinen tutkimus ORTON Invalidisäätiö ORTON. Engineer in hospital. Sami Sainio - PDF

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Engineer in hospital Sami Sainio Masters thesis from own subject Masters thesis done to Hospital ORTON about hip implants wear and how to measure the wear Subject: Discussion with

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Engineer in hospital Sami Sainio Masters thesis from own subject Masters thesis done to Hospital ORTON about hip implants wear and how to measure the wear Subject: Discussion with orthopedists led to given subject as it combines the interests of the doctor as well as the engineer and is useful for the hospital Why is there a engineer at the hospital? We are needed at the hospital in other things than just electronics and devices: Implant materials and their compatibility Wear measurements from the implants Material selections for the tools during the surgery What does the engineer need at the hospital? Medical environment demands: Terminology, doctors speak a language of their own Socials skills, you need to be humble You will have to follow the orders and/or suggestions of the nurses even if they are below your education in the hierarchy of yours Patience and ability to explain things for a specialist of different field. It is adamant that the message is understood correctly! What is expected of the engineer? Ability to answer questions related to your own field, for example material sciences Is it materials wize OK to use Vitallium (CoCr) with stainless steel, or should titanium be used? When working with joint replacements it is necessary to know some anatomy and physiology, but If hospital needs another doctor, they will hire a doctor, not an engineer! Engineering skills are the main thing! Implant (THR total hip replacement) wear and measuring the wear Sami Sainio Background Hip prosthesises needed more and more when the population ages In Finland THR amounts are increasing 1990 about over 8000 Yearly expenses roughly 55 B Material combinations used Metal-polymer Ceramic-polymer Ceramic-ceramic Metal-metal Hip prosthesises In addition to the traditional cemented installation, there are a large number of MoM (Metal on Metal) and CoC (Ceramic on Ceramic) bearing surface implants Wear and bodys reaction to wear particles is significantly different depending on the materials used Exercise (20 min) 1) What materials are used in the given hip? 2) Which of the materials is being worn during use? 3) How would you measure the wear? Linear and volymetric wear per year? 4) Which factors rule the measuring accuracy (error limits)? How precise can the measurements be from an x-ray? 5) Which factors pay role in the wear process? 6) Which particles are the most harmful to the tissue? Polymer -, ceramic - or metal particles? Materials Materials: Cup, acetabulum: UHMWPE (Ultra High Molecular Weight Polyethylene) Femur: CoCrMo (Cobalt Chrome Molybdenum) Today: Acetabulum: HXLPE (Highly Crosslinked Polyethylene) along with E-vitamin doped polymers Femur: still CoCr/CoCrMo, 316L or Ti6Al4V where bearing surface is coated with CoCrMo Polymer is the component being worn Metal is so hard compared to polymer, that this bearing surface will not really be worn at all Measurement procedure Hip in x-ray Y-axis Acetabulum X-rays Z-axis Femur Factors affecting the precision of the measurement Patients position Hip tilt angle affect to measurement when penetration directly towards Y-axis Tilt angle Femur and acet. positions True wear Measured & error % Where the image is taken It is important to take image the same way every time Wear direction Direction of the wear is significant when measuring the wear! Measurement accuracy and error amount Measurement accuracy is also affected by the radiological artefacts Metal components often have slight halo around them making the edge to be hard to define Human mistakes Margin of error atleast ±0,4 mm Yearly wear Linear wear, depending on patient activity 0,01 0,25 mm / year Volumetric wear = Wear is always cylinderical approcimanetly 100 mm 3 / year Cup Head Cup Head How does the wear affect the body? Wear particles causes tissue and bone to degrade, possibly so badly that the implant will loosen and fall off (osteolysis) Implant needs to be changed, revision surgery Metal particles may cause other reactions as well, such as system wide problems May lead to pseudotumors Implants mechanical funtionality is totally lost when the bearing surface is worn through Tissue reaction to wear particles Ceramic particles the least dangerous Polymer particles are harmful Metal particles are the worst Metal-metal bearing surface linear wear is on micrometer scale (fex. 10 µm per year) Metal-polymer wear is millimeter scale (fex. 0,1 mm per year) From which combination the amount of particles is the highest? Tissue reaction to wear particles Metal-metal bearing surface generates much more particles, because the particles are so small Polymer particles are about the size of 0,1 50 µm Metal particles are about the size of nm Wear amount is not as significant as the tissue reaction to the particles! Which factors affect the wear amount? Most important thing is the position where the implant is installed None of the bearing surfaces will last if they are improperly installed Wear amount is mainly controlled by the patient activity, not weight! If the implant is installed to a bad position it will cause other problems as well Right position for the implant Inclination Inclination angle (abduction angle) Anteversion Patient anatomy is the key! Anteversion angle Questions or comments? Thank you!
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