Molecular Weight Polyethylene Wear Debris Research Articles

Ultra-high molecular weight polyethylene wear debris generated in vivo and in laboratory tests; the influence of counterface roughness.

The objective of this study was to investigate the effect of counterface roughness and lubricant on the morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris generated in laboratory wear tests, and to compare this with debris isolated from explanted tissue. Laboratory tests used UHMWPE pins sliding against stainless steel counterfaces. Both water and serum lubricants were used in conjunction with rough and smooth counterfaces. The lubricants and tissue from revision hip surgery were processed to digest the proteins and permit filtration. This involved denaturing the proteins with potassium hydroxide (KOH), sedimentation of any remaining proteins, and further digestion of these proteins with chromic acid. All fractions were then passed through a 0.2 micron membrane, and the debris examined using scanning electron microscopy. The laboratory studies showed that the major variable influencing debris morphology was counterface roughness. The rougher counterfaces produced larger numbers of smaller particles, with a size range extending below 1 micron. For smooth counterfaces there were fewer of these small particles, and evidence of larger platelets, greater than 10 microns in diameter. Analysis of the debris from explanted tissues showed a wide variation in the particle size distribution, ranging from below 1 micron up to several millimetres in size. Of major clinical significance in relation to osteolysis and loosening is roughening of the femoral components, which may lead to greater numbers of the sub-micron-sized particles.

Comparison of the size and morphology of UHMWPE wear debris produced by a hip joint simulator under serum and water lubricated conditions

This paper investigates the effect of lubricant on the size and morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris produced by a hip joint simulator. Bovine serum and water were chosen as the lubricants for comparison. When bovine serum was used as lubricant, the majority of the wear debris produced was submicron sized and equiaxed or elongated in shape; no transfer film was found on the femoral heads. When water was used as lubricant, large pieces of thin UHMWPE flakes about 2–3 mm across were produced and patches of transfer films were observed on the femoral heads. These large flakes were comprised of numerous smaller thin flakes compacted together. While the size and shape of the wear debris produced with serum lubrication are similar to those reported from clinical studies in total hip replacement, the debris produced with water lubrication bears no resemblance to what has been seen clinically.

The effect of transfer film and surface roughness on the wear of lubricated ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) wear debris is now recognised as one of the major contributing factors of the loosening and failure of total artificial joints. In water-lubricated laboratory tests the volume of UHMWPE wear debris generated is highly dependent on changes in counterface topography caused by polymer transfer film and the subsequent changes in wear rate have been determined under different conditions. In tests with deionised water as a lubricant, initially smooth surfaces became rougher and increased the wear rate of the UHMWPE, while there was some smoothing of the initially rough counterfaces. A change in the effective surface roughness, R A, of 0·02–0·04 μm caused by polymer transfer produced a seven-fold increase in the wear rate of UHMWPE. The use of protein-containing lubricants greatly reduced the amount of polymer transfer film, the counterface roughness remained constant and there was little change in the average wear rate throughout the tests. This was considered more representative of conditions in the body. It is more appropriate to use protein-containing lubricants in laboratory tests, which inhibit polymer transfer film formation and produce more consistent and reliable wear results.

Fate of Ultrahigh Molecular Weight Polyethylene (UHMW-PE) Wear Debris in Patients with Hip Implants

The process of ultrahigh molecular weight polyethylene (UHMW-PE) breakdown, started at the articular surface of the cup, continues in small fragments after generation. An assiduous interaction between the UHMW-PE particles and the host cells leads to oxidative changes of the UHMW-PE and to size reduction of the particles simultaneous with transporting them toward, and finally by, lymphatic or blood vessels. The particles are mobilized by means of enzymatic, extracellular matrix-degrading activity of cells that have phagocytosed them or adhered to them. Together, these characteristics indicate an attempt by the natural cellular immunity system to eliminate the implant wear debris. Macrophages are the main effector cells acting as scavengers; however, excessive amount of the wear debris evokes phagocytic activity of cells other than macrophages as well.