Date of Award

2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Program

Biomedical Engineering

Track

Biomaterials and Regenerative Technology

Research Advisor

William Mihalko

Committee

Dennis DiAngelo; Jessica Jennings

Keywords

CoCrMo, corrosion, electrochemistry, synovial fluid, total knee arthroplasty

Abstract

Introduction. Cobalt-chromium-molybdenum (CoCrMo) femoral components are widely used in total knee arthroplasty (TKA). However, recent retrospective clinical trials associate moderate adverse local tissue reactions (ALTRs) with CoCrMo release in the knee. Additionally, gaps persist in our understanding of the fundamental corrosion processes that occur at the CoCrMo-synovial fluid interface. The first study investigates the electrochemical behavior of CoCrMo in human synovial fluid obtained at the time of primary TKA, using CoCrMo in phosphate-buffered saline (PBS) as a comparison. The second study compares the synovial fluid properties, both physical and electrochemical, in necropsy TKA and contralateral (native) knee specimens. Methods. In the first study, synovial fluid was collected from 118 patients immediately before arthroplasty (IRB approval number: 16-04802-XP and 21-08403-XP). In the second study, synovial fluid was collected from 20 deidentified pairs of necropsy TKA and native knees (IRB approval number: 22-09069-XP). Synovial fluid volume was recorded for each patient/necropsy specimen Synovial fluid from each respective study was then transferred to a three-electrode electrochemical cell with a wrought CoCrMo alloy working electrode. To quantify electrochemical properties, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and linear polarization (LP) tests were run. Specifically for the first study, 10 comparison tests using PBS were run using the same methodology. For the first study, A Welch’s t-test (α=0.05) was used to determine significant differences between human synovial fluid and electrochemical data. A Pearson’s correlation test was used to determine if a correlation existed between the two group’s electrochemical data and to determine if a correlation existed between the human synovial fluid’s pH and electrochemical data. For the second study, a Wilcoxon signed-rank test was performed ot determine differences in the physical and electrochemical properties of human synovial fluid. Results. For the first study, synovial fluid electrochemical properties varied on a patient-by-patient basis and significantly differed (p< 0.05) from comparison tests performed in PBS. In human synovial fluid, OCPs ranged between -0.38 and 0.15 V and corrosion potentials (Ecorr) values ranged between -0.95 and -0.2 V. Additionally, instantaneous corrosion rates (1/Rp) spanned nearly four orders of magnitude. For the second study, synovial fluid volumes from the TKA specimens were significantly higher than in native knee specimens (p=0.0001). Synovial fluid pH was found to be more acidic in the TKA specimens than the native knee specimens (n=15, p=0.048). Significant differences in OCP values were not identified (p>0.05). Approximate instantaneous corrosion rates were significantly higher in TKA specimens than native knee specimens (p=0.007). Conclusion. For the first study, synovial fluid properties varied by a patient-by-patient basis which could suggest that the electrochemical properties of CoCrMo implants may depend on the patient’s local physiological environment, influenced by the biological and chemical components of synovial fluid. The second study compared the physical and electrochemical properties of synovial fluid from necropsy TKA and native knee specimens. In the TKA group, synovial fluid volume and 1/Rp values were significantly higher than their native counterparts. Additionally, the pH tended to be more acidic in the TKA group. Future research will investigate the metal ion content in the synovial fluid to find correlations in metal ion content and the physical and electrochemical properties of synovial fluid.

ORCID

https://orcid.org0009-0007-9384-768X

DOI

10.21007/etd.cghs.2025.0693

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