An analysis of metal ion levels in the joint fluid of symptomatic patients with metal-on-metal hip replacements

Abstract

We retrospectively analysed concentrations of chromium and cobalt ions in samples of synovial fluid and whole blood taken from a group of 92 patients with failed current-generation metal-on-metal hip replacements. We applied acid oxidative digestion to our trace metal analysis protocol, which found significantly higher levels of metal ion concentrations in blood and synovial fluid than a non-digestive method. Patients were subcategorised by mode of failure as either 'unexplained pain' or 'defined causes'. Using this classification, chromium and cobalt ion levels were present over a wider range in synovial fluid and not as strongly correlated with blood ion levels as previously reported. There was no significant difference between metal ion concentrations and manufacturer of the implant, nor femoral head size below or above 50 mm. There was a moderately positive correlation between metal ion levels and acetabular component inclination angle as measured on three-dimensional CT imaging. Our results suggest that acid digestion of samples of synovial fluid samples is necessary to determine metal ion concentrations accurately so that meaningful comparisons can be made between studies.

Metal-on-metal hip prostheses: Correlation between debris in the synovial fluid and levels of cobalt and chromium ions in the bloodstream

“…The correlation is statistically significant both for Co and Cr but is slightly higher for the ion cobalt. In the absence of particles in the synovial fluid, the circulating values of Cr or Co are lower than 7 ppb in 15 cases out of 16 and establishing values slightly higher than that proposed by Estey et al [15], suggesting 4 ppb as normal threshold level of ions for asymptomatic subjects. With the increase of the number of Co-Cr particles isolated in the synovial fluid, the level of circulating ions increases.…”

“…Davda et al measured the levels of Co and Cr ions present in the synovial fluid of patients with prostheses without evaluating the presence of particles; they therefore showed that the analytical method foreseeing acid oxidative digestion causes a significant increase in metal ions measured in the fluid, therefore indirectly proving that nanoparticles are present in the fluid and contribute to the total local content of cobalt and chromium [16].…”

“…Recently, many reports have shown several cases of patients with MoM hip prostheses where a remarkable increase of Co and Cr concentrations in blood and joint synovial fluid has been reported [15,16].…”

“…Fluid from the hip joint is the first biological fluid into which the debris are released, but such samples are more difficult to retrieve compared to venous blood, and their diagnostic value must therefore be carefully considered [16]. For this reason many authors have verified the existence of the correlation between blood and synovial fluid levels of these ions [8,17,18].…”

Osteocyte physiology and response to fluid shear stress are impaired following exposure to cobalt and chromium: Implications for bone health following joint replacement

“…In well‐functioning prostheses at 10‐year follow‐up, median Co and Cr concentrations in the circulation have been reported to be 0.75 μg/L (range: 0.3–50.1 μg/L) and 0.95 μg/L (range: 0.3–58.6 μg/L) respectively 17. Periprosthetic concentrations are several fold higher (median Co, 113 μg/L; median Cr, 54 μg/L),18 while patients with failing prosthesis have reported Co and Cr concentrations as high as 528 μg/L (range: 0–13,000 μg/L) and 1,844 μg/L (range: 0–38,600 μg/L), respectively 19. We recently demonstrated that exposure to Co 2+ and Cr 3+ adversely affects both osteoclast and osteoblast survival and function, including the mineralization of prosthesis surfaces in vitro, at concentrations equivalent to those found clinically 20, 21, 22…”