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Significance and Use
3.1 This guide uses a weight-loss method of wear determination for the polymeric components used with hip joint prostheses, using serum or demonstrated equivalent fluid for lubrication, and running under a dynamic load profile representative of the human hip-joint forces during walking (1,2).5 The basis for this weight-loss method for wear measurement was originally developed (3) for pin-on-disk wear studies (see Practice F732) and has been extended to total hip replacements (4,5) femoral-tibial knee prostheses (6), and to femoropatellar knee prostheses (6,7).
3.2 While wear results in a change in the physical dimensions of the specimen, it is distinct from dimensional changes due to creep or plastic deformation, in that wear generally results in the removal of material in the form of polymeric debris particles, causing a loss in weight of the specimen.
3.3 This guide for measuring wear of the polymeric component is suitable for various simulator devices. These techniques can be used with metal, ceramic, carbon, polymeric, and composite counter faces bearing against a polymeric material (for example, polyethylene, polyacetal, and so forth). This weight-loss method, therefore, has universal application for wear studies of total hip replacements that feature polymeric bearings. This weight-loss method has not been validated for high-density material bearing systems, such as metal-metal, carbon-carbon, or ceramic-ceramic. Progressive wear of such rigid bearing combinations generally has been monitored using a linear, variable-displacement transducers or by other profilometric techniques.
1.1 This guide describes a laboratory method using a weight-loss technique for evaluating the wear properties of materials or devices, or both, which are being considered for use as bearing surfaces of human-hip-joint replacement prostheses. The hip prostheses are evaluated in a device intended to simulate the tribological conditions encountered in the human hip joint, for example, use of a fluid such as bovine serum, or equivalent pseudosynovial fluid shown to simulate similar wear mechanisms and debris generation as found in vivo, and test frequencies of 1 Hz or less.
1.2 Since the hip simulator method permits the use of actual implant designs, materials, and physiological load/motion combinations, it can represent a more physiological simulation than basic wear-screening tests, such as pin-on-disk (see Practice F732) or ring-on-disk (see ISO 6474).
1.3 It is the intent of this guide to rank the combination of implant designs and materials with regard to material wear-rates, under simulated physiological conditions. It must be recognized, however, that there are many possible variations in the in vivo conditions, a single laboratory simulation with a fixed set of parameters may not be universally representative.
1.4 The reference materials for the comparative evaluation of candidate materials, new devices, or components, or a combination thereof, shall be the wear rate of extruded or compression-molded, ultra-high molecular weight (UHMW) polyethylene (see Specification F648) bearing against standard counter faces [stainless steel (see Specification F138); cobalt-chromium-molybdenum alloy (see Specification F75); thermomechanically processed cobalt chrome (see Specification F799); alumina ceramic (see Specification F603)], having typical prosthetic quality, surface finish, and geometry similar to those with established clinical history. These reference materials will be tested under the same wear conditions as the candidate materials.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D883 Terminology Relating to Plastics
F75 Specification for Cobalt-28 Chromium-6 Molybdenum Alloy Castings and Casting Alloy for Surgical Implants (UNS R30075)
F86 Practice for Surface Preparation and Marking of Metallic Surgical Implants
F136 Specification for Wrought Titanium-6Aluminum-4Vanadium ELI (Extra Low Interstitial) Alloy for Surgical Implant Applications (UNS R56401)
F138 Specification for Wrought 18Chromium-14Nickel-2.5Molybdenum Stainless Steel Bar and Wire for Surgical Implants (UNS S31673)
F370 Specification for Proximal Femoral Endoprosthesis
F565 Practice for Care and Handling of Orthopedic Implants and Instruments
F603 Specification for High-Purity Dense Aluminum Oxide for Medical Application
F648 Specification for Ultra-High-Molecular-Weight Polyethylene Powder and Fabricated Form for Surgical Implants
F732 Test Method for Wear Testing of Polymeric Materials Used in Total Joint Prostheses
F799 Specification for Cobalt-28Chromium-6Molybdenum Alloy Forgings for Surgical Implants (UNS R31537, R31538, R31539)
G40 Terminology Relating to Wear and Erosion
ISO StandardISO6474 Implants for Surgery-Ceramic Materials Based on Alumina Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
ICS Number Code 11.040.40 (Implants for surgery, prothetics and orthotics)
UNSPSC Code 42321700(Hip joint implants)