The estimated incidence of septic arthritis in developed countries is 6 cases per 100,000 population per year.[1]Tarkowski A. Infection and musculoskeletal conditions: infectious arthritis. Best Pract Res Clin Rheumatol. 2006 Dec;20(6):1029-44.
http://www.ncbi.nlm.nih.gov/pubmed/17127195?tool=bestpractice.com
In patients with underlying joint disease or with prosthetic joints the incidence increases approximately 10-fold, to 70 cases per 100,000 of the population.[2]Kaandorp CJ, Dinant HJ, van de Laar MA, et al. Incidence and sources of native and prosthetic joint infection: a community based prospective survey. Ann Rheum Dis. 1997 Aug;56(8):470-5.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1752430/pdf/v056p00470.pdf
http://www.ncbi.nlm.nih.gov/pubmed/9306869?tool=bestpractice.com