Non-destructive wear analysis of aged polyethylene hip inserts: Comparison of gravi-metric investigations with three-dimensional microstructure analysis in micro-CT after 10 million cycles

Abstract

The hip joint is the most frequently implanted artificial joint in humans. The most important parameter is the durability, i.e. the time until a replacement operation. The most common reason for material failure is mechanical abrasion/wear as a limiting factor and significantly determines the survival time of the implant. [1, 2]. In the case of the acetabular cup, the plastic insert is often the most affected. The hip model examined here is characterized by a metal sleeve into which the plastic insert is pressed. This assumes an optimal fit of the insert in the cup in order to create conditions for the lowest possible abrasion. Unfortunately, it is not yet possible to test the abrasion of this system non-destructively. The abrasion of the hip is tested on so-called simulators by biomechanical loading according to ISO standard 14 242 over 5 million cycles [3, 4]. Additional scenarios with increased loading of the cup are required, such as artificial aging of the plastic as a "worst-case" scenario. A non-destructive analysis of the polyethylene has not been possible so far; up to now, the plastic has been knocked out of the metal sleeve with a hammer blow (with force) under strong deformation (Fig.1: destroyed back side by mechanical deformation on the left, plastic insert on the right). This study is the first to enable non-destructive testing of the plastic after aging and biomechanical stress by X-ray microcomputed tomography (XCT) examination. This will be compared to conventional gravimetric examinations and surface scanning results and tested for routine use. The second goal is to test wear abrasion not after 5 million cycles but after 10 million cycles.