Variation in joint fluid composition and its effect on the tribology of replacement joint articulation

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2003.Page 286 blank.Includes bibliographical references.Polyethylene wear is a significant clinical problem limiting the long-term survival of joint replacement prostheses, particularly in total hip arthroplasty (THA) and total knee arthroplasty (TKA). Although the tribology of joint replacement has consequently become an area of significant research, the effect of joint fluid on lubrication in the replaced joint has been largely overlooked. Several factors that affect the tribology of metal on polyethylene articulation in joint prostheses stem from the fluid lubricating the joint. In particular, the properties and composition of joint fluid likely contribute to fluid film lubrication and boundary lubrication in joint replacements, as they do in natural joints. The primary objective of this thesis is to examine the effect of natural variation in joint fluid composition and properties on friction, lubrication, and wear in joint arthroplasty. To achieve this goal, several parameters relating to the composition and mechanical properties of joint fluid are determined. Steady shear viscosity and linear viscoelastic properties of joint fluid are evaluated as indicators of its mechanical properties. Furthermore, concentrations of the hyaluronic acid, protein, and phospholipid in joint fluid are measured using standard biochemical techniques.(cont.) The molecular weight of hyaluronic acid is also determined using size exclusion chromatography. These properties and components are evaluated in joint fluid from patients undergoing TKA and from patients undergoing surgical revision of an existing TKA (as well as from other patient groups). Results are considered in the context of previous studies of healthy and diseased synovial fluid. Correlations between and among components and flow properties are determined. Friction tests are performed on articulations between ultra-high molecular weight polyethylene (PE) and cobalt-chromium-molybdenum alloy (Co-Cr), materials commonly used in total joint replacement prostheses. These tests evaluate joint fluid samples as well as synthetic joint lubricants that are composed based on the range of compositions and properties determined. Certain components are found to increase friction in this articulation relative to water lubrication, but some joint fluid samples performed as well as bovine serum.(cont.) Significant differences in tribology demonstrated by these experiments indicate that the composition of joint fluid affects the tribology of Co- Cr on PE joint prostheses, though the variability in friction could not be explained by physiological variation in the components examined. In related work, the relative importance of contact area and normal load is evaluated in the wear of a Co-Cr on PE articulation. Within a relevant range of contact stress, volumetric wear rate increased with increasing contact area, and was independent of normal load. The results of these tribological investigations are brought together in a conceptual framework under which to consider the wear of PE in TJA.by Dan Mazzucco.Ph.D