Property changes of UHMW polyethylene hip cup endoprostheses during implantation

Abstract

In this study it is demonstrated that the combined chemical and mechanical influences of the implant situation cause property changes of ultra-high-molecular-weight polyethylene (UHMW PE) hip joint cups. Nearly 30 out of 48 loosened cups, retrieved 3 weeks to 11 years after implantation, were investigated. Density measurements show a density increase with implantation time and a dependence of these changes from implant position and loading conditions. The rate of extractable constituents also increases with course of time. An increased in vivo conditioned oxidation of the UHMW PE can be demonstrated by infrared (IR) spectrometry. The density increase can be explained by post-crystallization, which is the result of oxidative chain scission. This leads to a reduction of the average molecular weight of the PE and to an increased extractability of constituents. Since these changes have been recognized as the reasons for aging and failing of UHMW PE, the methods of material characterization used in this study for retrieved implants will help to develop suitable in vitro testing and simulating methods. They are the prerequisite for the necessary improvements of the material properties of UHMW PE.

Gamma Inert Sterilization: A Solution to Polyethylene Oxidation?

“…In vivo degradation was first studied by Eyerer, Grood, and colleagues in the 1980s 8,9 . However, until recently, historical polyethylene acetabular liners were not widely recognized to be susceptible not only to shelf aging but also to in vivo oxidation associated with a characteristic regional variation pattern 10,11 .…”

Behavior of Adsorbed Albumin Film on CoCrMo Alloy under <I>In-situ</I> Observation

“…The friction and wear properties of UHMWPE are affected among other parameters by the chemistry of periprosthetic synovial fluid [1,2] and in particular by proteins and phospholipids. Long immersion periods in the synovial fluid change the mechanical properties of UHMWPE [3,4]. Proteins and phospholipids affect the corrosion and the surface chemistry of the metallic alloy [5,6].…”

Ultra High Molecular-Weight Polyethylene (Uhmwpe) in Total Knee Replacement: Fabrication, Sterilisation and Wear

“…Both of these processes depend on the local temperature and the time for which pressure is applied 7,[8][9][10][11][12] and both may be done well or badly. 11,13,14 In the past voids have been shown to be present in badly compacted materials possibly causing inferior mechanical properties in the resulting mass. 7,8,[15][16][17] Foreign inclusions have also been demonstrated because of impurities in the equipment processing the powder.…”

“…5,6 Research has resulted in improvement in the morphology of consolidated UHMWPE. [11][12][13][14]18,19 Compaction can be achieved by one of three processes: ram extrusion, slab compression moulding or direct compression moulding of a component [4][5][6][7]12 which, in general, produce equivalent material. The disadvantage of ram extrusion and slab compression moulding is that they may not produce uniform conditions in the compacted mass.…”

“…Bond scission followed by oxidation changes UHMWPE into material of lower molecular weight 14,19,23,25,[30][31][32] which is less resistant to wear and, specifically, to delamin ation. 9,[33][34][35] Once the process of oxidative chain scission has started it is self-perpetuating because further alkyl radicals are generated which in turn react with any oxygen that may be present.…”