Abstract
Introduction
In THA, fretting corrosion at the head-stem taper junction has emerged as a clinical concern that may result in adverse local tissue reactions, even in patients with a metal-on-polyethylene bearing [1]. Taper junctions that employ a ceramic head have demonstrated reduced corrosion at the interface [2]. However, during revision surgery with a well-fixed stem, a titanium sleeve is used in conjunction with a ceramic head to ensure proper fit of the head onto the stem and better stress distribution. In vitro testing has suggested that corrosion is not a concern in sleeved ceramic heads [3]; however, little is known about the in vivo fretting corrosion of the sleeves. The purpose of this study was to investigate fretting corrosion in sleeved ceramic heads.
Materials and Methods
Between 2001 and 2014, 35 sleeved ceramic heads were collected during revision surgery as part of a multi-center retrieval program. The sleeves were all fabricated from titanium alloy and manufactured by 4 companies (CeramTec (n=14), Smith & Nephew (Richards, n=11), Stryker (n=5), and Zimmer (n=5)). The femoral heads were made from 3 ceramics (Alumina (n=7), Zirconia (n=11), and Zirconia-toughened Alumina (n=17)). Sleeve dimensions (length and thickness) were measured using calibrated calipers. Fretting corrosion of the sleeves and available associated stems was scored using a 4-point, semi-quantitative scoring system [4], with 1 being little-to-no damage, and 4 corresponded to severe fretting corrosion. Five sleeves could not be extracted; thus the external surface was not scored.
Results
Moderate-to-severe fretting corrosion scores (Score ≥ 2) were observed in 97% (34/35) of internal tapers (sleeve-femoral stem contact), 57% (17/30) of external tapers (sleeve-femoral head contact), and 65% (11/17) of the stems. The internal sleeve had higher fretting corrosion scores than the external taper (Mean Score Difference [MSD] = 1.1; p = 0.001) and stem (MSD = 0.7; p = 0.016). Fretting corrosion scores were correlated with implantation time at all surfaces (Rho ≥ 0.53; p ≤ 0.015). Scores were not correlated with sleeve dimensions (p > 0.05). Fretting corrosion scores of the external sleeve correlated directly with activity level (p = 0.005) and inversely with patient age (p = 0.03).
Discussion
The retrieval data shows that fretting corrosion can occur in these components, particularly on the internal surface of the sleeve. The corrosion scores were similar to levels observed in prior studies of tapers in CoCr heads [2]. Implantation time was the main predictor of increased fretting corrosion. The impact of ceramic material and sleeve design currently remain unclear as the analyses were confounded with implantation time. Thus, more detailed and quantitative analyses are required to fully determine the factors that influence fretting corrosion of sleeved ceramic heads in THA.
