Impact relief ability of Metal-on-Metal artificial hip joint with multi-garter spring using drop impact tester for practical use

Toshiaki Kaneeda, Xinming Zhao and Hiroshi Matsuura

Metal-on-metal (MoM) joints can provide better wear properties than hard-on-polymer joints, leading to reducing osteolysis. However during gait, MoM hip joints have no material to relieve impact. These impacts can cause severe pain in postoperative patients. Kaneeda proposed double-shell MoM artificial hip joints in which multi garter springs were inserted between the inner and outer acetabular shell as an impact relief device. The proposed double-shell metal-on-metal artificial hip joint is composed of two layers, as shown in Fig. 11).

A garter spring is usually used when by loading and a compression stress from the outside to the center axis. In the model testing for garter spring, it is demonstrated that garter spring had impact relief ability, then using dual garter springs could lead to better impact relief ability than single one2).

In this work, the impact relief ability of model hip joint were investigated by using the Instron CEAST 9340 machine as shown in Fig. 2. The machine is a floor standing impact system designed to deliver 0.30–405J of energy and equipped with precise locating system for height. A holding device of double-shell cup was made to fix the right position. A shape of drop impact weight was modified for this experiment. The model hip joint was applied vertical load over 6000N, which is estimated to be equal to maximum vertical load during jumping. The ability in the case of single garter spring and dual garter springs was evaluated in the model hip joint, comparing with UHMWPE liner in the same size of femur head. Each testing was conducted 10 times.

Fig. 3 shows load-time curve detected. From the results, it can be seen that in both case Load L gradually rise with Time T, then reach maximum values, finally L gently drop: maximum impact load as well as maximum impact load arriving time also presented nearly the same values. Much differences in shape of the curve between model hip joint with dual garter springs and UHMWPE liner could not be recognized. The model hip joint with dual garter springs may has enough impact relief ability.