Not sure if this will help or not, but a quick pubmed search turned up a paper which evaluated synovial fluid aspirated at the time of surgery for 10 primary TKAs (osteoarthritic fluid) and 8 revisions (periprosthetic fluid). So this may help you in that it characterizes post-replacement fluid. There are several papers cited that discuss synovial fluid in this context, you may be able to make use of some of them. I am not sure if any of them go into the natural history of the fluid.

Pubmed ID 16898218

Hope that helps, good luck.