# Characterization of Micro-Threaded Stem Taper Surfaces of Cementless Hip Endoprostheses

## TL;DR

This study examines how micro-threaded stem tapers in hip implants affect failure rates and corrosion, finding that ceramic heads reduce corrosion and implant failures.

## Contribution

The study introduces a novel analysis of micro-threaded stem tapers in cementless hip implants, linking taper corrosion to implant failure and infection.

## Key findings

- Ceramic heads reduce taper corrosion and implant failure rates.
- Low corrosion rates were observed in both new and aseptically loosened tapers.
- Infected tapers showed higher corrosion rates compared to non-infected ones.

## Abstract

We investigated micro-threaded stem taper surface and its impact on premature failures, aseptic loosening, and infection in cementless hip endoprostheses. Our study focused on the fretting, and crevice corrosion of micro-threaded tapers, as well as the characterization of the microstructure and surface properties of two new and three retrieved Zweymüller stem tapers. The retrieved samples were selected and examined based on the head–stem taper interface being the sole source of modularity with a metallic component, specifically between the Ti alloy taper stem and the ceramic head. To determine the surface chemistry and microstructures of both new and retrieved hip endoprostheses stem taper titanium alloy, scanning -electron microscopy (SEM) was employed for morphological and microstructural analyses. Energy dispersive spectroscopy (EDS) was utilized for characterizing chemical element distribution, and electron backscattered diffraction (EBSD) was used for phase analysis. The roughness of the micro-threated stem tapers from different manufacturers was investigated using an optical profilometer, with standard roughness parameters Ra (average surface roughness) and Rz (mean peak to valley height of the roughness profile) being measured. Electrochemical studies revealed no fretting corrosion in retrieved stem tapers with ceramic heads. Consequently, three retrieved tapers and two new ones for comparison underwent potentiodynamic measurements in Hank’s solution to determine the corrosion rate of new and retrieved stem taper surfaces. The results showed a low corrosion rate for both new and prematurely failed retrieved samples due to aseptic loosening. However, the corrosion rate was higher in infected and low-grade infected tapers. In conclusion, our study suggests that using ceramic heads reduces taper corrosion and subsequently decreases the incidence of premature failures in total hip arthroplasty.