Investigation of Modular Taper Material and Design Factors That Affect Mechanically Assisted Crevice Corrosion at the Femoral Head-Stem Junctions in Total Hip Arthroplasties
Authors:   , Kocagöz Sevi Berna , Kurtz Steven M. 
Published: July 2021

Modularity in total hip arthroplasty (THA) designs allows intraoperative flexibility for the surgeon to adapt leg length and femoral offset to the individual anatomy and gives the option to keep a well-fixed femoral stem and revise femoral head and acetabulum, as needed. In early designs, modularity was only used in the femoral head-stem tapers. In the 1980s-1990s, researchers detected corrosion at this interface; however, the clinical significance was unclear at this time, and the use of modularity continued. Recent design changes to THA include the use of multiple modular interfaces on the stem, and adapter sleeves for additional intraoperative flexibility. Large head metal on metal (LHMOM) bearings had gained popularity to eliminate polyethylene debris from the articulating surfaces and provide improved range of motion. The clinical use of these designs led to increased reports of adverse local tissue reactions (ALTRs), and release of metallic material and corrosion at the modular tapers became a clinical concern. ALTR due to corrosion is also observed in total knee arthroplasty cases. Taper corrosion still poses a clinical risk for all components that employ any modular connections. There is a need to systematically investigate the factors that increase the risk of taper corrosion. The process leading to corrosion and metallic particle release from modular connections is mechanically assisted crevice corrosion (MACC). The severity of MACC depends on a combination of mechanical, electrochemical, geometrical, material and solution conditions. Previous researchers have investigated the device design and material factors that may lead to variations in these conditions; however, there still does not exist any manufacturing standards for the design and materials of tapers. The goals for this doctoral research were to: 1. Investigate the difference of visual fretting-corrosion damage in the femoral head-stem taper in a matched cohort study comparing THA with ceramic and CoCrMo femoral heads. 2. Develop a method for measuring taper angle clearance. Use developed method to measure retrievals and compare taper corrosion between ceramic and CoCr heads in retrievals using a matched cohort study design as a function of taper angle clearance. 3. Develop and validate a quantitative method to estimate volumetric material lost from the taper surfaces. Use developed method to compare taper corrosion between ceramic and CoCr heads in retrievals using a matched cohort study design as a function of volumetric material loss. 4. Investigate fretting-corrosion behavior of PEEK-metal interfaces and compare with metal-metal interfaces using a previously developed in vitro pin-on-disk fretting-corrosion test system. Explore potential mitigation of taper fretting-corrosion using alternative materials. The key findings of this research have shown that there was no correlation between taper angle clearance and volumetric material loss. There was a significant correlation between femoral head material and volumetric material loss. Using ceramic heads reduced the total volumetric material loss from femoral head-stem taper junctions. The volumetric material loss from femoral head taper surfaces was higher compared to their mated femoral stem taper surfaces in THAs using CoCrMo alloy femoral heads. Lastly, the fretting currents generated between PEEK-metal material couples was lower compared to metal-metal material couples tested in vitro using a tribocorrosion pin-on-disk test setup.