In Vivo Performance of the Femoral Head-Neck Taper Connection and Development of an Electrochemical Framework for Quantitative Corrosion Investigations

Abstract

Corrosion at the modular head-neck connection in total hip arthroplasty has been shown to have deleterious biological consequences, and recent clinical observations have postulated that it may compromise the integrity of the taper connection. This dissertation summarizes the patient demographics, clinical details, and design variables of hip implants that were examined to understand their impact on the in vivo performance of taper junctions. Furthermore, it describes electrochemical assessment methods that were developed to quantitatively evaluate the effects of corrosion phenomena. In vivo taper performance was assessed using femoral components retrieved from revision surgery and from cadaveric donors. Preliminary time-to-event analyses were conducted on a collection of 5,821 retrieved joint prostheses, identifying risks factors for infection consistent with the findings of administrative databases and implant registries. The role of an activated immune system on corrosion at the head-neck taper was then explored with a subset of these explants. The results did not indicate more severe corrosion for devices revised with infection, but suggested greater corrosion severity for devices that were implanted in male patients and during primary arthroplasty procedures. Multivariable analysis of clinical and design variables did not identify an association between corrosion and the size of the modular taper, but found increased corrosion for heavier patients, longer implantation times, greater femoral head offsets and tapers with a lower flexural rigidity. Mechanical assessment of taper connection strength demonstrated that more severely corroded stem trunnions were associated with stronger taper connections. Additionally, greater corrosion was observed on retrievals from revision surgery than on those from cadaveric donors. In consideration of the electrochemical nature of corrosion processes, a new framework was devised to overcome limitations of visual corrosion assessments. Analysis using electrochemical impedance spectroscopy identified decreased impedance and increased constant phase element (CPE) capacitance as the strongest predictors of increased corrosion severity. Additionally, lower values for impedance phase angle, CPE-exponent and polarization resistance were associated with increased corrosion. From microscopic and metallographic inspection, it was found that components with subsurface damage features had significantly higher capacitance and lower impedance values than those only exhibiting surface corrosion damage features. Given that the surface area of an electrode is inversely proportional to its impedance and directly proportional to its capacitance, electrochemical analyses may provide an opportunity to identify penetrative corrosion features without destructive metallographic evaluation.Ph.D., Biomedical Engineering -- Drexel University, 201