الفهرس 
Evolution of Total Knee ArthroplastyOnly 14 pages are availabe for public view
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Abstract
Total Knee Replacement surgery is one of the most common and successful solutions for degenerative knee arthritis and painful knee conditions. A concept of replacing destroyed worn out surfaces with new uniform surfaces by replacing the Femoral condyles, the Tibial plateau and their cartilages with biomaterials as plastic and metal to form a knee joint that simulate the function and the movement of the human knee.
The advent of Total Knee Replacement Surgeries was an important milestone in the history of othropedic surgery starting in the early 1970’s at which both surgeons and engineers have developed the cornerstone principles of knee arthroplasty, their early designs heading to their evolution till this day.
Biomaterial selection is one of the most challenging issues due to requirements and biocompatibility, so it has been of major interest to material designers in recent years.
The subject of biomaterials entails an understanding of the interaction of artificial man made materials for use within the human body, In Total Knee arthroplasty, a strong emphasis is placed on the ability of the materials to bear loads and resist material degradation for long periods of time.
In recent years, improvements in materials promise to reduce wear and improve the durability of TKA further.
In this essay we have discussed the three main types of biomaterials that are widely used in Total Knee arthroplasty as bearing surfaces which are Metallic alloys, Polyethylene and Ceramic alloys regarding their composition, manufacture, properties, advantages and disadvantages of each of these materials.
The metallic alloys most widely used in knee prosthesis are, Low carbon grade authentic stainless steels, Titanium and titanium base alloys and Cobalt chrome alloys.
Cobalt chrome has an increased stability and excellent material properties such as corrosion resistance which are advantageous for a long term durability and thus a promising material for total joints, though on the other hand, the possible toxicity of released Ni ions from Co-Ni-Cr and their limited frictional properties have been a matter of concern in using these alloys as an articulating components, which explains why Co-Cr-Mo alloys is usually the dominant alloy for total joint arthroplasty.
For stainless steels, there are more than 60 grades, however Stainless steel 316L is the type mainly used for biomedical implication such as joint replacements.
The success of stainless steel material is based on the fact, that it has one unique advantage, the chromium in the stainless steel has a great affinity for oxygen, forming a film of chromium oxide that resist corrosion.
Nickel Titanium (NiTi) from the point of view of practical application, can have three different forms, martensite, stress induced martensite and austenite, fully austenitic NiTi material generally has suitable properties for surgical implant.
NiTi has an ability to be highly damping and vibration attenuating, which is from the orthopedic point of view, this property could be useful in dampening the stress between bone and the articular prosthesis, and this is besides the high wear resistance that has been reported compared to CoCrMo
Although NiTi carries a lot of favorable properties, yet the medical applications has been hindered due to the lack of knowledge of the biocompatibility of NiTi still, and only very few well monitored studies have been published in journals, while no controlled or randomized studies have been published so far.
Titanium and Titanium alloys had been used for more than thirty years for implants, as it is the most biocompatible of all materials because of its resistance and tolerance to body fluids. The high strength, low weight and outstanding corrosion resistance, by Titanium and Titanium alloys has led to this diversified range of successful applications, this higher strength to weight ratio have made it more successful compared to stainless steel.
Polyethylene is the most common material as a bearing surface for Total Knee Arthroplasty, due to its unique properties of nontoxicity, abrasion resistance, low coefficient of friction, high impact resistance, energy absorption capacity at high loading rates, resistance to stress cracking, and high ductility have made it an optimum material to withstand the stress of joint articulation.
On the other hand wear and damage to UHMWPE components for knee replacement is not a new phenomenon and has been clinically observed since the 1970s
Osteolysis which may be provoked by exposure of bone to particles of UHMWPE, has been a major concern for hip replacement, however only recently has osteolysis been regarded as an important complication for TKA
Another complication is Backside wear which have thus far been concerned primarily with wear at the articulating surface between the femoral condyles and the UHMWPE tibial insert. Recently however, researches have drawn attention to backside articulation (i.e between the tibial insert and the metallic tray or base plate)
Alumina and Zirconia ceramics have been used in THA for many years, and both materials have a lower coefficient of friction than metal.
Ceramics are hard biomaterials with a superior surface finish, high compressive strength, and increased resistance to third body wear.
The Lower coefficient of friction of ceramic surfaces means that ceramics will produce less polyethylene particles by abrasive wear than cobalt chromium alloys.
The hydrophilic nature of ceramic surfaces generates a fluid film surface that minimizes adhesive wear in ceramic polyethylene articulations, in THA, the use of ceramic femoral heads articulating against polyethylene results in significant wear reduction compared to metal femoral heads, these properties of ceramics make them suitable for the counter surface material in TKA, if polyethylene wear is to be minimized.
Failure of Ceramic bearings in vivo, while rare, is a serious concern for their profound consequences towards patients, surgeons and orthopedic implant industry
The clinical problems are more often due to implant loosening caused by the release of an excessive number of wear particles into the biological environment.
The aim of further research is to obtain further advances in technology that will help the human being with incapacities to live a more normal life with the help of joint replacements, and in this essay we have analyzed different facets which are needed in the development of an optimum knee prosthesis.