Orthopedic UHMWPE

Orthopedic UHMWPE has a molecular mass of 2 10" a.m.u. or higher. In this state, the polymer has a high viscosity, even in the molten state. Thus, macroradicals have very low mobility, either in the molten or in the solid state, while the H radical, which has a diameter smaller than 1 A, can migrate in the polymer mass, even in the crystalline phase, where distances between C atoms are in the order of 4 A. H radicals resulting from Reaction 3 are very mobile and they can extract other H atoms intermolecularly or intramolecularly producing hydrogen, following Scheme 2. 

TABLE 3.4 Oxidation and Hydroperoxide Content in Unexpired, Gamma Sterilized Orthopedic UHMWPE Implants from the Torino Packaging Survey, Adapted from [1]... 

In the 1990s, some researchers showed that a biocompatible stabilizer could have been useful, or even necessary, to stabilize orthopedic UHMWPE [37, 71, 72]. 

In summary, over the past decade the small punch test has been extensively developed to perniit direct assay of the mechanical properties of orthopedic UHMWPE bearings. 

H. Schmotzer, Method for producing implant parts from highly cross-linked uhmwpe and implant parts for human medicine, US Patent 7 364 685, assigned to Plus Orthopedics AG (Rotkreuz, CH), April 29, 2008. 

Ultrahigh molecular weight polyethylene (UHMWPE) is an engineering plastic which has a wide spectrum of applications, particularly as a material for orthopedic prostheses due to its high strength, high resistance to chemicals and physical abrasion, high wear... 

Bergstrom, J. S., Rimnac, C. M., and Kurtz, S. M., Molecular Chain Stretch is a Multiaxial Failure Criterion for Conventional and Highly Crosslinked UHMWPE. Submitted to J. Orthopedic Research (2003)... 

Since 1962, UHMWPE also has been used in orthopedics as a bearing material in artificial joints. Each year, about 1.4 million joint replacement procedures are performed aroimd the world. Despite the success of these restorative procedures, UHMWPE implants have only a finite lifetime. Wear and damage of the UHMWPE components is one of the factors limiting implant longevity. 

The ultra-high molecular weight polyethylene used in orthopedic applications is a type of polymer generally classified as a linear homopolymer. Our first task is to explain what is meant by all of these terms. Before proceeding to a definition of UHMWPE, one needs to first understand what constitutes a linear homopolymer. 

The second part of the Handbook is focused on the use of UHMWPE as an ortiiopedic biomaterial. Chapter 4 reviews tire clinical origins of UHMWPE in hip replacement, which was introduced to orthopedics in 1962 by Sir John Chamley. Although several variants of UHMWPE have been investigated since the 1960s, UHMWPE remains the gold standard orthopedic bearing material still widely used today in joint replacements around the world. Chapter 5... 

The topics outlined in this Handbook may be used as a resource in imder-graduate, as well as graduate, courses in biomaterials and orthopedic biomechanics. Students in these disciplines can learn a great deal from exposure to the historical development of total joint replacements within the context of UHMWPE. The first two main sections of this book, which cover tire fimda-mentals of UHMWPE and clinical applications in the spine and upper and lower extrenrities, are intended as a resource for imdergraduate instruction. 

The orthopedics literature contains numerous references to different trade names for UHMWPE, which fall into two categories 1) GUR resins currently produced by Ticona and 2) the 1900 resins, previously produced by Basell. The UHMWPE grades currently used in the orthopedic industry are summarized in Table 2.2. 

After molding, the sheet is typically turned into rods or other preform shapes to facilitate subsequent machining operations by orthopedic manufacturers. Thus, the final shape of UHMWPE stock material today is not necessarily dictated by the conversion method. 

Today only a few converters supply medical grade, GUR 1020 and 1050 ram extruded UHMWPE to the orthopedic industry. Medical grade extrusion facilities for Poly Hi Solidur and Westlake Plastics are based in the United States, whereas Perplas Medical s medical grade extrusion is in England. 

The choice of conversion method (and converter) is at least as important a decision as the choice of resin for an UHMWPE component, because both factors introduce a subtle change in the morphology and material properties of the consolidated polymer. However, there is currently no consensus as to which resin and conversion method would be imiversally superior for all orthopedic applications. Consequently, it is left to each orthopedic manufacturer to determine which conversion method (and resin) is most appropriate for applications in hip, knee, shoulder, and spine implants. 

Bimkraut H.W 1991. Synthesis of UHMWPE. In Ultra-high molecular weight polyethylene as a biomaterial in orthopedic surgery. H.G. Willert, G.H. Buchhom, and P. Eyerer. Eds. Lewiston, NY Hogrefe Huber. 

Muratoglu O.K., M. Jasty, and W.H. Harris. 1997. High resolution synchrotron infra-red microscopy of the structure of fusion defects in UHMWPE. Transactions of the 43rd Orthopedic Research Society 22 773. 

Schmidt M.B., and J.V. Hamilton. 1996. The effects of calcium stearate on the properties of UHMWPE. 42nd Orthopedic Research Society 21 22. 

The purpose of this chapter is to review historical and contemporary packaging and sterilization methods for UHMWPE. Obviously, all of the sterilization methods currently employed by the orthopedic community fulfill their intended purpose, namely the eradication of bacterial agents, which may result in sepsis and premature revision. The diverse sterilization methods in current use reflect the lack of scientific consensus as to which of the currently favored sterilization methods provides the most advantageous long-term UHMWPE product for the ultimate user, namely the patient. 

Summary of Contemporary Barrier Packaging Techniques Used for Gamma Sterilization of UHMWPE Among Major Orthopedic Manufacturers (as of January 2003)... 

Contemporary Gamma Vacuum Foil (GVF) barrier packaging for gamma sterilization of UHMWPE components, used by DePuy Orthopedics (Warsaw, IN). 

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