Cobalt-chromium-molybdenum (CoCrMo) alloy-based metal-on-metal prostheses have been the implant of choice for total hip replacement in younger patients. However 6.2% of patients require revision of their CoCrMo total hip replacement (THR) implant within five years of surgery and their use was restricted in 2013. We aimed to determine if there were individual differences in the immune response to wear debris that might indicate a poor outcome with a CoCrMo prosthesis. Blood from 22 donors was incubated with CoCrMo particles (>99.9% less than 10 μm diameter) generated by a wear simulator for 24 h. T cell phenotype was assessed by immunostaining and secretion of 8 different pro- and anti-inflammatory cytokines was measured using multiplex technology. Clear differences were seen between individuals in the induction of Th17 and Th1 responses, with some donors showing pro-inflammatory responses (increased IL17 or IFNγ) and others showing anti-inflammatory responses (decreased IL17 or IFNγ). The only differences seen for gender and age related to increased IL-10 expression from T cells in females (p = 0.008) and a trend towards decreased IL-6 expression systemically for older donors (p = 0.058). We conclude that individuals show differential responses to CoCrMo wear debris and that these responses could give early indications of the suitability of the patient for a metal-on-metal prosthesis.
Metals
on metal implants have long been used in arthroplasties
because of their robustness and low dislocation rate. Several relatively
low-corrosion metals have been used in arthroplasty, including 316L
stainless steel, titanium, and cobalt–chromium–molybdenum
alloy. Debris from these implants, however, has been found to cause
inflammatory responses leading to unexpected failure rates approaching
10% 7 years surgery. Safety assessment of these materials traditionally
relies on the use of simple two-dimensional assays, where cells are
grown on the surface of the material over a relatively short time
frame. It is now well-known that the composition and stiffness of
the extracellular matrix (ECM) have a critical effect on cell function.
In this work, we have evaluated how cobalt ions influence the assembly
of type I collagen, the principle component of the ECM in bone. We
found that cobalt had a significant effect on collagen matrix formation,
and its presence results in local variations in collagen density.
This increase in heterogeneity causes an increase in localized mechanical
properties but a decrease in the bulk stiffness of the material. Moreover,
when collagen matrices contained cobalt ions, there was a significant
change in how the cells interacted with the collagen matrix. Fluorescence
images and biological assays showed a decrease in cell proliferation
and viability with an increase in cobalt concentration. We present
evidence that the cobalt ion complex interacts with the hydroxyl group
present in the carboxylic terminal of the collagen fibril, preventing
crucial stabilizing bonds within collagen formation. This demonstrates
that the currently accepted toxicity assays are poor predictors of
the longer-term biological performance of a material.
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