Influence of retrieved hip- and knee-prosthesis biomaterials on microbial detection by sonication.

Microorganisms' ability to adhere and form a biofilm differs among biomaterials; however, clinical data are conflicting. Microbial adherence and biofilm formation on different biomaterials of explanted joint prosthesis components were investigated. Consecutive patients with explanted joint prosthesis were prospectively included. The bacterial load dislodged from retrieved prosthetic components was evaluated qualitatively and quantitatively in sonication-fluid cultures. For comparison between groups, one-way ANOVA and Wilcoxon signed-rank test were used. A total of 112 components originating from 58 knee and 54 hip prostheses were retrieved from 40 patients. Components were made of titanium alloy in 42 cases, cobalt-chromium alloy in 38 and polyethylene in 32. Bacteria in sonication-fluid cultures grew in all polyethylene components (100 %), followed by titanium alloy (79 %) and cobalt-chromium components (71 %). Larger bacterial counts were found on polyethylene than on titanium (p < 0.013) or cobalt-chromium alloy (p = 0.028). Coagulase-negative Staphylococcus aureus and Streptococcus species were most commonly isolated. In conclusion, polyethylene showed larger biofilm burden than metal alloys, indicating their higher microbial adhesion affinity in vivo. Sonication of polyethylene liners, rather than the whole prosthesis, was sufficient for diagnosis of prosthetic joint infection. Moreover, bacterial counts were larger after sonication of polyethylene liners than of metal alloys, suggesting intrinsic differences in the ability for biofilm formation on various biomaterials. Polyethylene liners allowed the diagnosis of prosthetic joint infections (PJIs) in all investigated cases, suggesting that sonication of polyethylene liners rather than of the complete prosthesis was sufficient for pathogen detection in PJIs.