The radiographic resolution of beads from porous coated joint prostheses

While there have been reports of the 750 microns chrome-cobalt beads disassociating from the PCA type prosthesis, failure of the 200 microns bead has not been documented despite reports of failed prosthesis, which use the smaller bead. As a result of the negative reports, the hypothesis was posed as to the limit of resolution in the image of the standard clinical radiographical film. To test the hypothesis, chrome-cobalt beads, ranging in size from 200 to 700 microns, in differing configurations were placed adjacent to a femoral prosthesis that had been implanted into a cadaveric specimen. Using standard clinical radiographic technique, differing exposures were made of the configurations. The results demonstrated that beads or a conglomerate of beads smaller than 300 microns could not be resolved and were therefore invisible and unrecordable. The clinical significance is to question whether all porous-coated prostheses shed metal alloy particles, some of which are radiographically undetectable due to the limitations of their resolvable size.