Engineering Materials in Medicine - Knee Implant Study Material
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Added on 2020-10-03
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This study material covers the design, materials, and 3D printing of knee implants. It also includes a market survey and medical applications of Nitinol. The knee joint, its key functions, and the need for knee replacement are discussed. The study material also covers the requirements for bio-materials and the selection of materials. The metallic biomaterials used in knee implants are compared, and porous Nickel-Titanium is selected for the femoral and tibial components. The study material is for ME6505 course under Prof. Seeram Ramakrishna and Assoc Prof. Thian Eng San at Desklib.
Engineering Materials in Medicine - Knee Implant Study Material
Added on 2020-10-03
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ENGINEERING MATERIALS IN MEDICINEME6505GROUP PROJECTProf. Seeram Ramakrishna Assoc Prof. Thian Eng San TEAM 8: KNEE IMPLANTSubmitted by,Dai Zhenwei Kalaiselvan Vimareesan Mullapudi Sneha Sree Pan Bo Rajagopalan Eswaran Ramasamy Vignesh Raveendra Ramgopal Shi Zhirui Suhail Mohammed Hussain Wang Haiming
1 CONTENTS 1. Introduction ........................................................................................................................................................2 1.1. Key functions of the Knee ...........................................................................................................................2 1.2. Need for Knee replacement ...........................................................................................................................2 2. Knee Replacement Prosthesis ....................................................................................................................................... 3 2.1. Knee Implant Designs............................................................................................................................................... 32.2. Implant Fixation .............................................................................................................................................3 3. Bio-materials................................................................................................................................................................... 4 3.1. Requirements for Bio Material............................................................................................................................... 4 3.2. Selection of Material .....................................................................................................................................5 4. 3D printing of Knee implant ..............................................................................................................................7 4.1. Printing of Tibial Insert / Spacer and Patellar Component ..........................................................................7 4.2. Printing of Femoral and Tibial Component ..................................................................................................8 5. Issues ....................................................................................................................................................................9 5.1. Biocompatibility of Nitinol ..........................................................................................................................9 5.2. Issues in 3D printing NiTi using SLM ..........................................................................................................9 6.Medical Applications of Nitinol .......................................................................................................................10 7. Market Survey for 3D printed knee implants ...................................................................................................10 8. Conclusion ........................................................................................................................................................11 9. References .........................................................................................................................................................11
2 1. Introduction The knee joint is one of the most critical, largest and strongest joint in the human body. It helps in joining the lower leg with the thigh and enables the former to move relative to the latter while supporting the body’s weight at the same time. There are three bones which constitute a knee joint which are the femur, the patella, and the tibia. The patella is otherwise called as knee cap. The femur and the tibia are also referred to as thigh bone and the main bone of the lower leg respectively. The meniscus, which is a layer of tough, rubbery fibrocartilage between tibia and femur, functions as a shock absorbing element for preventing collision between the leg bones during jumping, running and other activities. The joint capsule contains the synovial membrane which produces the synovial fluid to lubricate the knee. [1] 1.1.Key functions of the Knee The knee is a joint comprising of complex movements in various directions with the help of multiple bones. The movements include bending (flexion), straightening (extension), gliding of femur on top of the tibia in forward and backward directions (translation) and also inward rotation of femur (internal rotation) or in outward direction (external rotation) with respect to the tibia. Range of motion (ROM) measurements helps to evaluate the functioning of a joint and is measured with functional and passive measurements which differ depending upon gender and age. The ROM values for a normal knee are, flexion from 0 to 160o and extension up to 0o and in some cases up to -10o which condition is referred to as hyperextension. The maximum patellar compression force generally is 7 fold of one’s body weight and the maximum compressive load on the tibial and femoral component would be 5.6 times body weight (values taken during squatting activity). [6] [7]Figure 1. Knee joint and its parts 1.2.Need for Knee replacement Knee replacement, otherwise termed as knee arthroplasty, is a surgery performed to relieve disability and pain by replacing the weight bearing surfaces of the knee joint (Figure 2). Osteoarthritisis one of the most common knee diseases which is caused by rubbing of the bones against one another resulting in severe knee pain. Knee deformity, severe knee pain or stiffness, swelling and chronic knee inflammation do not become better with basic treatments like lubricating injections, medications and physical therapies and thus requiring total knee replacement. [2] Figure 2. Osteoarthritis causing bone spursFigure 3. Total knee replacement implant
3 2.Knee Replacement Prosthesis The total knee replacement prosthesis or knee implant consists of three main components. They are the femoral component, the tibial component and the spacing made of plastic (usually polyethylene) between the two components, as shown in Figure 3. The femoral component is attached to the lower end of the femur and is grooved to allow for smooth movement of knee cap against the bone. The tibial component, attached to the tibia on its upper end, is basically a flat metal platform with a plastioc spacer as a cushion on the top and a stem at the bottom that fits into the centre of the tibial bone. [3] 2.1.Knee Implant Designs There are several knee implant designs in the market. But the most common knee implant designs are [4][5]: 1.Posterior-Stabilized Designs This design is the most commonly used, which involves the removal of posterior cruciate ligaments and replacing it with the parts of implant. The tibial component has a raised surface with an internal post that fits into the cam of the femoral component (Fig. 4a). This is usually prescribed for patients with knee cap removed previously, severe flexion contracture and severe deformity. 2.Cruciate-Retaining DesignsThis design retains the posterior cruciate ligament and it involve the removal of anterior cruciate ligament (Fig. 4b). This type of implant design is prescribed for those patients with healthy posterior cruciate ligament. 3.Bicruciate-Retaining Designs The bicruciate-retaining design implant is a new implant design under study which involves the retaining of both the posterior and anterior cruciate ligament of the knee which is aimed to make the knee function like a normal and a non-replaced knee(Fig. 4c). 4.Unicompartmental Implant The unicompartmental implant is used for partial knee replacement. This type of implant is used only when one side of the knee joint is damaged and when that part alone has to be resurfaced (Fig. 4d). (a)(b)(c)(d)Figure 4. (a) Posterior-Stabilized Design, (b)Cruciate-Retaining Design, (c)Bicruciate-Retaining Design, (d)Unicompartmental Implant 2.2.Implant Fixation There are basically three types of fixation to help in fixing knee implants to the bone [4]: ●Cemented Fixation-This type of fixation involves fixing the metal components to the respective bones by means of fast-curing bone cement like polymethylmethacrylate. ●Cementless Fixation-This method involves the usage of interference fits or press fits or even augmenting with screws. Cementless implants are usually made of materials that initiate growing of new bones into the surface of implant to facilitate fixation.●Hybrid Fixation-This is a combination of both cemented and cementless type of fixation. It involves the femoral component inserted into the thigh bone without the use of cement whereas the patellar and the tibial components rely on cement for connecting them to their respective bones.
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