Introduction

In the last few years corrosion was increasingly observed at head-neck interfaces of artificial hip joints, especially in joints with larger heads. There has always been evidence of some corrosion at modular junctions of artificial joints, but except for few designs, it was not seen as a real problem. It is important to better understand the factors contributing to corrosion at modular interfaces, so that necessary improvements can be made to minimise or completely avoid corrosion, in order to avoid possible adverse tissue reactions.

Patients and Methods

This retrieval analysis compared the corrosion and fretting behaviour of 40 mm femoral heads (n = 13) to monopolar hemiarthroplasty heads (n = 17 for a diameter < 50 mm; n = 6 for a diameter ≥ 50 mm) such that all implants had a minimum implantation period of three months, a 12/14 mm taper, and the heads and stems consisted of CoCr alloy. The 40 mm heads articulated with a polyethylene cup whereas the monopolar hemiarthroplasty heads articulated with cartilage. The 40 mm heads were manufactured from one company whereas the monopolar hemiarthroplasty heads were manufactured from four different companies. Corrosion and fretting damage were assessed using a previous technique [1]. Table 1 lists the patient information and reasons for revision whereas Table 2 provides the implant information.

The Mann Whitney U test and the Kruskal-Wallis test were performed for identifying significant differences for corrosion and fretting scores that were not normally distributed (α = 0.05). An unpaired student's t-test was conducted for comparing the head corrosion scores for the two head size groups of monopolar hemiarthroplasty implants since these scores were normally distributed.