Wear in Total Hip and Knee Replacements

Abstract

Before the advent of total joint replacement, patients who had end-stage arthritis of the lower extremities had unremitting pain and a greatly decreased functional capacity. In addition, they often were confined to a wheelchair and were dependent on the care of others. Today, the outcomes of primary total hip and knee replacement are predictable and usually excellent 35,45,57,64,212,221 . Prosthetic joint replacement has dramatically improved the lives of millions of people worldwide.As the fixation of total joint implants has become more reliable and durable and as the technology of total joint replacement has been applied to younger and more active patients, the current limitations of total joint arthroplasty are related to the wear of the components 248 . Wear is the removal of material, with the generation of wear particles, that occurs as a result of the relative motion between two opposing surfaces under load. In complex mechanical-biological systems such as total hip and knee replacements, there can be many types of wear. Although the mechanical consequences of wear, such as progressive thinning of polyethylene components, can limit the functional life of a joint replacement, the clinical problems from wear more frequently are due to the release of an excessive number of wear particles into a biological environment. When particles within a certain size-range are phagocytized in sufficient amounts, the macrophages enter into an activated state of metabolism, releasing substances that can result in periprosthetic bone resorption. Progressive loss of periprosthetic bone can necessitate a reoperation, which is the definitive measure of clinical failure of a joint arthroplasty. Wear ModesIt is important to distinguish among the fundamental mechanisms of wear (adhesion, abrasion, and fatigue); the changes in the appearance (the morphological characteristics) of the bearing surfaces, which are referred to as wear damage; and the conditions under which the prosthesis was functioning when the wear occurred, which have been termed the wear modes 156 . Adhesion involves bonding of the surfaces when they are pressed together under load. Sufficient relative motion results in material being pulled away from one or more surfaces, usually from the weaker material. Abrasion is a mechanical process wherein asperities on the harder surface cut and plow through the softer surface, resulting in removal of material. When local stresses exceed the fatigue strength of a material, that material then fails after a certain number of loading cycles, releasing material from the surface. One or more of the classic mechanisms of wear may be operating on the prosthesis in a particular wear mode, and a prosthesis may function in several wear modes over its in vivo service life. The predominant type of wear of one prosthetic joint can differ from that of another. Furthermore, in a specific joint, there may be different types of wear occurring at different times over the service life of the implant. The damage to an implant is a result of a...

Application of magnetic field assisted finishing process for nanofinishing of freeform femoral knee joint and performance analysis of finished surface

“…13 A 10-fold rise in the wear rate of UHMWPE is reported with the threefold increase in the roughness of femoral countersurface. 14 In the laboratory tests, with a threefold surge in counterface roughness, a 20-fold rise in wear rate of UHMWPE is observed. 15 Also, the wear volume and number of generated wear particles depend on the surface roughness of the counterface.…”