Hip simulator wear testing of the taper-trunnion junction and bearing surfaces of modular hip prostheses

Abstract

Adverse reaction to metal debris (ARMD) released from the taper-trunnion junction of modular total hip replacements (THRs) is an issue of contemporary concern, not only in metal-on-metal (MoM) but in ceramic-on-ceramic (CoC) and metal-on-cross linked polyethylene (MoP) THRs. Moreover, there is no consensus in the literature regarding the mechanisms behind material loss at the taper-trunnion junction. The aim of this research work to investigate the material loss, if any, at the taper-trunnion junction of modular CoC and MoP THRs under physiological walking cycles. Following ISO-14242, material loss from the bearing surfaces was also quantified alongside surface topographical and microscopic analysis. After 5 million cycles, the mean material loss from the ceramic bearing surfaces was 0.25mm3, and from the metallic trunnions, it was 0.29mm3 in the CoC hip simulator test. The three-dimensional surface roughness (Sa) of the trunnions on the unworn and worn areas showed a statistically significant decrease from 0.558 ± 0.060 to 0.312 ± 0.028μm respectively (p < 0.001). In the MoP hip simulator test, the mean material loss from the polymeric liners, metallic tapers and trunnions were 14.28, 0.22 and 0.24mm3 respectively. The Sa of the femoral tapers on the unworn and worn areas showed a statistically significant increase from 0.510 ± 0.068 to 0.867 ± 0.233μm respectively (p < 0.001). Until this research, no long-term hip simulator tests had quantified material loss from the taper-trunnion junction of commercially available modular CoC and MoP THRs. Metallic material loss from the taper-trunnion junctions of CoC and MoP THRs may explain the ARMD reported in the literature for these THRs. Material loss at the taper-trunnion junction needs to be measured in preclinical testing using the hip simulator to avoid ARMD and further increase the longevity of modular THRs. Based on the results, the mechanisms responsible for the material loss at the metallic taper still a multivariable process.