These authors spought to investigate the value of implant sonication fluid cultures in the diagnosis of shoulder periprosthetic joint infection (PJI) compared with tissue culture. They conducted a retrospective case-control study analyzing all patients who underwent a revision surgery for any kind of suspected septic or aseptic event due to failed shoulder arthroplasty.
Of the 72 patients, a total of 28 (38.9%) were classified as infected. Of the 28 infected patients, 20 (71.4%) had an identified organism by tissue cultures.
Of all infected patients, 71.4% (20/28 patients) had an identified organism by tissue cultures, and C acnes was the most commonly isolated pathogen, in 13/28 patients (46%), followed by coagulase-negative staphylococci (5/28, 17.9%), Staphylococcus aureus (2/28, 7%), Finegoldia magna (1/28, 3.6%), Streptococcus agalactiae (1/28, 3.6%), Enterococcus faecalis (1/28, 3.6%), and Peptoniphilus asaccharolyticus (1/28, 3.6%).
The sensitivities of sonicate fluid (50 CFU/mL) and periprosthetic tissuebculture for the diagnosis of periprosthetic shoulder infection were 36% and 61% (P . .016), and the specificities were 97.7% and 100%, respectively. If no cutoff value was used in sonication culture, the sensitivity increased to 75% whereas the specificity dropped to 82%. Although there was no significant difference in sensitivity between tissue culture and the no-cutoff sonication fluid culture (61% vs. 75%), the specificity of tissue culture was significantly higher (100% vs. 82%,).
The authors concluded that tissue culture showed a higher sensitivity and specificity than implant sonication in the diagnosis of shoulder PJI and should remain the gold standard for microbiological diagnosis of shoulder PJI.
Comment: It is not a question of either explant or tissue cultures. We have found that both tissue and explant cultures are of importance in the detection of a periprosthetic infection. In their study it is possible that the authors missed the opportunity to recover bacteria in over 25% of their cases because in some cases they only submitted two specimens to the laboratory.
Because Cutibacterium are not evenly dispersed throughout an infected shoulder it is critical that five deep specimens be submitted for culture, in that even if the shoulder is infected, some specimens may show no growth. Recall that titanium alloy provides a surface that is attractive for Cutibacterium biofilm formation; this in some cases the explant cultures are positive while the tissue cultures are negative.
Our routine is to culture synovium, collar membrane, humeral membrane, and all explanted prostheses. Explants are vortexed in 3 cc of saline to remove the biofilm, but sonication has not been shown to be of added value.
Here is a relevant poster from a recent American Shoulder and Elbow Surgeons meeting
Should Explants Be Cultured at Revision Shoulder Arthroplasty?
Background:Surgeons revising a failed arthroplasty need to know whether or not bacteria are present around the implanted components. The specimen harvesting and culturing practices used to recover bacteria at revision surgery vary among surgeons, some including only tissue and others including both tissue and removed component explants. Culturing explants has the potential benefit of revealing organisms residing in biofilms on their surface that might otherwise be overlooked. The purpose of this study was to assess the added value of culturing explants in seeking evidence of Propionibacteriumat revision arthroplasty. We sought to answer three questions:
1. Does culturing of explants (in addition to tissue cultures) facilitate the recovery of Propionibacteriumfrom revised shoulder arthroplasties?
2. In Propionibacteriumculture-positive shoulders, how does the Propionibacteriumload from explant cultures compare with the load from tissue cultures?
3. In Propionibacteriumculture-positive shoulders, are some anatomic areas more likely to have positive cultures?
Methods:From December 2015 until March 2018, 122 revision arthroplasties were consented for inclusion in a revision shoulder arthroplasty database. Specimens were submitted for standardized Propionibacterium culturing of tissue from the collar membrane, humeral canal, and periglenoid area as well as explants of the humeral head, humeral stem, and glenoid components. In this analysis we included only those shoulders that had both tissue and explant culture results from three anatomically similar locations: 1) HEAD region: collar membrane tissue and humeral head explant (n=86), 2) STEM region: humeral canal tissue and humeral stem explant (n=58), or 3) GLENOID region: periglenoid tissue and glenoid explant (n=45). Tissue samples were placed in a stomacher with saline, and the saline was streaked onto three different anaerobic and aerobic media and observed for 21 days. Explanted components were vortexed with saline, and the saline was streaked in a similar fashion. Semiquantitative culture results were reported for each specimen as the Specimen Propi Value (SpPV). We analyzed the results for two threshold values: SpPV>0 and for SpPV≥1.
Results:For both thresholds, inclusion of explant cultures increased the percentages of cultures that were positive.
Importantly, explants were culture positive in shoulders in which the tissue specimens were negative in 6 of 30 (20%) HEAD specimens, 8 of 24 (33%) STEM specimens, and 9 of 19 (47%) GLENOID specimens. The PropionibacteriumSpPVs were similar between positive explant and tissue specimens in the HEAD region (tissue 1.0 ± 0.8 vs. explant 1.5 ± 1.1, p=0.144), STEM region (tissue 1.2 ± 1.0 vs. explant 1.3 ± 1.1, p=0.873), and GLENOID region (tissue 1.0 ± 0.6 vs. explant 0.8 ± 0.8). The percentage of positive tissue or explant specimens were similar between anatomic sites: the HEAD specimens were positive in 30 of 86 (35%) samples, STEM 24 of 58 (41%), and GLENOID 19 of 45 (42%).
Conclusion:In this study, inclusion of explant cultures increased the percentages of cultures positive for Propionibacteriumat each of three anatomic sites. These findings suggest that the identification of Propionibacterium in revision arthroplasty is more likely if removed implants are submitted for culture. This increase may be due to the detection of bacteria in implant biofilms in cases where it was not detectable in tissue samples.
And here are some related studies
Performance of implant sonication culture for the diagnosis of periprosthetic shoulder infection
Sonication versus Vortexing of Implants for Diagnosis of Prosthetic Joint Infection
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