Polyethylene prostheses

Grobbelaar C.J., T.A. Du Plessis, and F. Marais. 1978. The radiation improvement of polyethylene prostheses A preliminary study. Bone Joint Surg 60-B 370-374. 

Grobbelaar CJ, du Plessis TA, Marais F. The radiation improvement of polyethylene prostheses. A preliminary study. J Bone Joint Surg Br 1978 60-B(3) 370-4. 

Residual free radicals trapped in the polyethylene are knovm to cause longterm stability problems in implanted polyethylene prosthesis. The free radicals can react with oxygen to form unstable hydroperoxides, which can decompose to carbonyls. The latter are readily susceptible to chain scission and subsequent loss of mechanical properties. The only known method of directly measuring residual free radicals is by electron spin resonance (ESR) spectroscopy (also... 

The materials used in a total joint replacement ate designed to enable the joint to function normally. The artificial components ate generally composed of a metal piece that fits closely into bone tissue. The metals ate varied and include stainless steel or alloys of cobalt, chrome, and titanium. The plastic material used in implants is a polyethylene that is extremely durable and wear-resistant. Also, a bone cement, a methacrylate, is often used to anchor the artificial joint materials into the bone. Cementiess joint replacements have mote tecentiy been developed. In these replacements, the prosthesis and the bone ate made to fit together without the need for bone cement. The implants ate press-fit into the bone. 

These include attempts by surgeon M.N. Smith-Petersen in 1925, Robert and Jean Judet in 1938, and Dr. Edward J. Haboush in 1953. However, the first successful hip prosthesis was not developed until 1961 when Dr. Chamley made a hip prosthesis out of a high molecular weight polyethylene cup. Today, artificial hip joints are implanted in over 200,000 people each year in the USA (Ratner, 2004). 

Figure 26. Reconstruction of the tunica intima on the inner surface of a clinically used polyethylene terephtalate vascular prosthesis. A non-modified inner surface of the prosthesis, B immobilization of defined assemblies of protein molecules (e.g., collagenfiarninin or collagen+fibrin) on the inner surface of the graft, C immunofluorescence of von Willebrand factor, a marker of the identity a differentiation of vascular endothelial cells, in human saphenous vein endothelial cells in cultures on the inner surface of a prosthesis coated with collagen and larninin, D detail of a layer of endothelial cells growing on a layer of collagen and fibrin. Note well developed talin-containing focal adhesion plaques. A, B conventional optical microscope, C, D confocal microscope Leica DM 2500 [30,31].

Dentures acrylic, ultrahigh molecular weight polyethylene (UHMWPE), epoxy Facial prosthesis acrylic, PVC, polyurethane (PUR)... 

Orthopaedic prosthesis Mechanism of wear of Ultra-high molecular weight polyethylene currently used in total hip and knee joint implants— see J. Mater. Set. 28 1045-1058 (1993). 

The application of polymeric materials in medicine is a fairly specialized area with a wide range of specific applications and requirements. Although the total volume of polymers used in this application may be small compared to the annual production of polyethylene, for example, the total amount of money spent annually on prosthetic and biomedical devices exceeds 16 billion in the United States alone. These applications include over a million dentures, nearly a half billion dental fillings, about six million contact lenses, over a million replacement joints (hip, knee, finger, etc.), about a half million plastic surgery operations (breast prosthesis, facial reconstruction, etc.), over 25,000 heart valves, and 60,000 pacemaker implantations. In addition, over AO,000 patients are on hemodialysis units (artificial kidney) on a regular basis, and over 90,000 coronary bypass operations (often using synthetic polymers) are performed each year (]J. 

Miscellaneous. Many other organs sometimes become diseased or defective, and some artificial device has been used to replace them. For example, the gastrointestinal (GI) tract has often been replaced, totally or partially, by some type of plastic tubing. Such a prosthesis does not perform the normal GI tract functions but merely connects existent, nondiseased tubular parts in the body. Many materials have been used such as polyamides, polyesters, polysilicones, and polyethylene. In a similar manner, various ducts have been replaced by plastic tubing. Finally, the bladder, trachea, ureter, and similar organs have been replaced by nonfunctional plastic tubing (]J. 

The first implanted synthetic polymeric biomaterial appears to be PMMA, which was used as a hip prosthesis in 1947 (see USP XVIII, The Pharmacopia of the USA, (18th Revision), US Pharmacopoeial Convention, Inc., Rockville, MD, 1 September 1980). Polyethylene, and then other polymers, were used as implants in the middle ear in the early 1950s, yielding good initial results, but local inflammation limited the use of these materials. 

For hip surgeries, the protection of the acetabulum is provided by a deposit on the metal of the prosthesis of a layer of polyethylene with a very high cross-linked mass using y radiation. Inguinal hernias are treated by the introduction of a polypropylene membrane. Cataracts are treated by the extraction of the natural crystalline lens, and replacing it with a substitute in polymethylmethacrylate. 

Ultrahigh molecular weight polyethylene (UHMW PE) is most commonly used for articulation surfaces in joints. It is also used for prosthesis components in total hip replacement. In the latter application, it may be reinforced with carbon fibers to increase wear properties. 

Minneapolis, MN.) (b) Chitra tilting disc valve prosthesis with the occluder made of ultra high molecular weight polyethylene. (Courtesy of Sree Chitra Tirunal Institute for Medical Sciences and Technology, India.)... 

Total knee replacements can be implanted with or without cement, the latter relying on porous coating for fixation. The femoral components are typically made of CoCr alloy and the monolithic tibial components are made of UHMWPE. In modular components, the tibial polyethylene component assembles onto a titanium alloy tibial tray. The patellar component is made of UHMWPE, and a titanium ahoy back is added to components designed for uncemented use. The relatively small size of the pateUar component compared to the forces that travel through the extensor mechanism, and the small area of bone available for anchorage of the prosthesis, make the pateUa vulnerable. 

The use of polymeric materials in the medical field is growing and gives rise to problems peculiar to the mode of application. Prosthesis is one of the major medical interests, and certain plastic replacement parts are now commonly used. High-density polyethylene is a successful replacement part for damaged hip joints and is employed as the socket, which accommodates a steel ball cemented to the femur using... 

Another ophthalmologic application of polymeric biomaterials is the development of ocular prosthesis and biologically inspired compound eyes [197,198]. Such prostheses, commonly fabricated from porous polyethylene, are designed to serve as nonfunctional artificial substitutes for enucleated eyeballs [199]. 

Flip prosthesis 1962 1 000 000 Ultrahigh-molecular-weight polyethylene... 

The foimdation that Neer laid for shoulder replacement can be seen today in many ways. The continued production and use of the 1973 version of his humeral component as the Neer II and the many other humeral and glenoid components based on this original design is testament to its stature in the surgical community. The basic concepts included in the Neer prosthesis such as all-polyethylene and metal-backed keeled glenoid components and wire... 

The reverse total shoulder prosthesis design concept is one in which the humeral head is replaced with a concave polyethylene bearing surface and the glenoid face is augmented by a convex articular metal component. As the name implies, this reverses the normal anatomic geometries of the humeral head and glenoid face. An example of this prosthesis concept is shown in Figure 9.12. 

Reverse shoulder prosthesis system components. The metal screw-fixed ball is implanted in the scapula to replace the glenoid, and the concave polyethylene component mounted on the stem is implanted into the proximal humerus to replace the humeral head (image courtesy of Encore Medical, Austin, TX). 

Composed of ultra-high-molecular-weight polyethylene fibers. Spectra cable is another option that is available to body-powered prosthesis designers and users. Spectra cable is now widely used at almost all major upper-limb fitting... 

Rose, R.M., Ries, M.D., Paul, I.L., Crugnola, A.M. and Ellis, E. (1984) On the true wear rate of ultrahigh molecular weight polyethylene in the total knee prosthesis, J. Biomed. Mater. Res., 18, 207-224. 

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