Synovial Fluid Electrochemical Properties Are Altered After Total Knee Arthroplasty: A Necropsy Retrieval Study

Abstract

Background: Primary total knee arthroplasty (TKA) relies on cobalt chrome alloy (CoCrMo) implants to replace the degraded joint and restore patient function. However, retrieval analysis documents wear processes on femoral components, associated with metal accumulation in the periprosthetic tissue. It remains unclear how TKA affects synovial fluid and whether arthroplasty promotes oxidation within the joint capsule. To address these gaps, we asked, does TKA alter the synovial fluid's physical and electrochemical properties?

Methods: Synovial fluid was aspirated from 18 pairs of deidentified necropsy TKA and native contralateral knee specimens. The aspirated volume and pH were recorded. Then synovial fluid was transferred into an electrochemical cell consisting of a wrought CoCrMo working electrode, an Ag/AgCl reference electrode, and a platinum counter electrode. To assess electrochemical properties, open circuit potential, impedance spectra, and linear polarization data were acquired. After data collection, impedance spectra were circuit fitted, and the inverse of the oxide polarization resistance (R_p^-1) was calculated to measure the instantaneous corrosion rate.

Results: In necropsy TKA synovial fluid samples, we documented increased synovial fluid volumes (6 ± 2.77 versus 1.75 ± 1.41 mL, P < 0.001) and higher instantaneous corrosion rates (1.70 x 10^-7 ± 1.03 x 10^-7 versus 8.61 x 10^-8 ± 1.17 x 10^-7, P = 0.012) when compared to the native knee cohort.

Conclusions: Our results show how the synovial fluid after TKA can change, increasing in volume and decreasing the resistance of the CoCrMo oxide film. The mechanisms that promote these physical and chemical changes remain unclear. Future research is needed to investigate correlations between increased synovial fluid corrosion rates and metal release.

Level of evidence: Level II, prospective cohort study.

Keywords: cobalt chrome alloy implant; corrosion; electrochemical properties; synovial fluid; total knee arthroplasty.