PhD Thesis Proposal: Audrey J. Martin

Monday, July 24, 2017, 2:00–4:00pm

Jackson Conference Room, Cummings Hall

“Corrosion Kinetics of Orthopedic Implant Alloys: The Roles of Crevice Geometry and Strain”

Abstract

Total hip arthroplasty is a successful procedure performed to restore function to painful or diseased joints. However, recent reports of poor clinical outcomes due to corrosion have raised alarm within the orthopedic community. Corrosion has been observed and studied within the orthopedic community since the 1970s, but in the last decade, there has been increasing evidence to suggest that corrosion by-product can lead to adverse local tissue reactions and has driven a need to further characterize corrosion mechanisms. The purpose of this proposed work is to study corrosion behavior of orthopedic alloys, specifically identifying effects of (1) crevice geometry and (2) applied strain on degradation behavior.

Modern joint replacements are designed modular to facilitate customizability for the patient and allow for less invasive revision surgeries. This naturally gives rise to concerns around crevice corrosion. Early studies on crevice corrosion of orthopedic biomaterials indicated negligible effects from crevice corrosion mechanisms, but outside of the orthopedics literature, the characterization of crevice corrosion has become more sophisticated. Total hip replacements primarily consist of a combination of cobalt chromium- and titanium-based alloys, both of which attribute their corrosion resistance to a strong passivating oxide layer. This has led to an increased interest in mechanically assisted corrosion mechanisms which would fracture the oxide layer to initiate corrosion. Meanwhile the effect of changes in crevice chemistry as a function of crevice geometry remains poorly characterized.

Furthermore, modular junctions rely on a taper locking mechanism to join modular components during surgery, resulting in residual stresses at the interface. Joint forces also result in the application of cyclic stresses during gait. While speculated to contribute to corrosion mechanisms at the taper, there has yet to be an experimental evaluation of corrosion in response to stress and subsequent strain.

While retrieval studies continue to formulate hypotheses regarding corrosion behavior in total joint arthroplasty, there is a clear need for in vitro studies to test these hypotheses and further an understanding of the basic science behind corrosion mechanisms seen in vivo. Results from this work may help inform future implant design and performance testing to facilitate better clinical outcomes for patients.

Thesis Committee

For more information, contact Daryl Laware at daryl.a.laware@dartmouth.edu.