Modular hip joint testing apparatus : final design report

Abstract

This report details the design of a modular hip joint testing apparatus for the Concordia Hip and Knee Institute. Current methods of fatigue testing of artificial hip joints primarily focus on applying compressive axial loads onto the head of the hip joint in order examine the head/stem connection. Dr. Urs Wyss, in association with the Concordia Hip and Knee Institute, requires a testing apparatus capable of applying both compressive and tensile axial loads to the test specimen. The design of the testing apparatus focused on three aspects; mounting the top of hip joint, mounting the bottom of the hip joint, and the fluid bath that surrounds the hip joint. The top fixture consists of two plates made of 316 stainless steel that are secured together with three screws in a tripod configuration around the head of the hip joint. The bottom fixture consists of two main components; the stem holder and base, both of which are made of 316 stainless steel. The stem holder is an adjustable component that can slide along the length of the base in order to align the line of action between the top fixture and the bottom fixture. The fluid bath selected was an off-the-shelf component, a Bionix Environbath [3] courtesy of MTS Systems Corporation. The specifications for the Bionix Environbath were not available for compatibility test with the fixtures, therefore an alternative design, a fluid bath case made of acrylic glass and held together with aquarium adhesive is detailed as well. A preliminary analysis has shown that the diameter of the stem must increase in size from 14 mm to no less than 16 mm due to the high bending stress. Further analysis of the specimen and fixture using FEA software is needed to determine the actual stresses present within the stem and on the stem holder. Assuming it is compatible with the fixture, the Bionix Environbath is the best choice for the fluid bath because it incorporates the bath, circulating pump, reservoir, and temperature control in one off-the-shelf package.