Shock machine for the mechanical behaviour of hip prostheses: a description of performance capabilities

TL;DR

This paper describes a shock testing machine for hip prostheses that simulates in vivo conditions, revealing fracture mechanisms and wear patterns, and demonstrating its capability to reproduce real-world implant degradations.

Contribution

The study introduces a new shock machine capable of replicating in vivo conditions for testing hip prostheses and analyzing their failure modes.

Findings

Only dry condition cups failed under shock testing.

Fractures observed were intergranular and transgranular.

Wear stripes and surface roughness were characterized.

Abstract

The aim of this study was to describe the behaviour of a shock machine designed for testing hip prostheses. A microseparation between head and cup occurs inducing a shock of several times the body weight, leading to fracture of ceramic femoral components. Femoral heads and cups of diameter 32 mm manufactured from alumina were tested in dry and wet conditions. Implants were subjected to shocks with a load profile of 9 kN load at 2 Hz and various microseparations. Position is monitored and force is measured with two acquisition systems. The working range and the device capabilities were investigated. Only cups tested in dry conditions failed. Observations by scanning electron microscopy revealed intergranular and transgranular fractures. Two wear stripes were observed on the heads. Three-dimensional roughness of wear stripes was measured. Since experimental results are in good agreement with retrieved femoral heads, the shocks machine reproduces the in vivo degradations.