Surface analyses of orthopedic fixation screws submitted different artificial rest soil

Implantable plates, screws and wires are frequently held in the surgical instrument tray, and are reprocessed every time the instruments are used. There have been questions raised about this practice but there is a lack of data to demonstrate organic residuals on reprocessed implantable plates, screws or wires. The objective of this study was to determine is surface analysis techniques could be used to detect such residual organic material on stainless steel malleolus screws.

New malleolus screws were compared to ones that had been coated in purified lipopolysaccharide or Artificial Test Soil (ATS) containing lipopolysaccharide. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and surface time-of flight secondary ion mass spectrometry (TOF-SIMS) were used to assess the fixation screws.

Organic material was visualized on the LPS and ATS-LPS inoculated screws but not on the new unsoiled screws. This was further supported by the peaks observed at masses between 40 – 100 D on TOF-SIMS spectra of the LPS inoculated and ATS-LPS inoculated screws. After deconvolution of high resolution XPS analyses, the LPS inoculated screws showed a carbon and oxygen oxidized state whereas the ATS-LPS inoculated screws showed predominantly C-NO (nitroso).

In conclusion, our data demonstrated that surface analysis can detect organic residuals present in fixation screws. The XPS data confirmed that LPS reacted predominantly with positively charged surface metallic ions (Fe+ and Cr+) whereas proteins reacted with the surface oxide layer of fixation screws forming C-NO. The application of these surface analysis techniques will be helpful in determining if the reprocessing of such items results in an accumulation of organic material that might lead to aseptic loosening when implanted.