Comparative study of cultures and next-generation sequencing in the diagnosis of shoulder prosthetic joint infections.

BACKGROUND: Serum and synovial markers used to diagnose lower extremity prosthetic joint infection (PJI) have performed poorly for shoulder PJI. As a result, diagnosis is commonly reliant on the accuracy of positive or negative cultures. Next-generation sequencing (NGS) can sequence an entire bacterial genome. This study was conducted to determine the correlation between NGS and routine cultures in revision shoulder arthroplasty.

METHODS: All patients undergoing revision shoulder arthroplasty were prospectively enrolled. In a standardized manner, tissue samples were transferred immediately into sterile specimen containers and transported for culture and NGS (MicroGen Dx, Lubbock, TX, USA). Infection definitions using culture and NGS were analyzed for concordance.

RESULTS: There were 44 total revision arthroplasty cases included. There were no cases of polymicrobial culture results. Cutibacterium (formerly Propionibacterium) acnes was the most common bacterial species cultured (8 of 13 [61.5%]) and identified by NGS (12 of 17 [70.1%]) in cases of definite and probable infection. The concordance (κ) between the 2 diagnostic criteria for defining infection that included culture or NGS was 0.333 (fair). There were significantly more cases of probable contaminants when cultures (10 of 44 [22.7%]) were used in the definition of infection compared with NGS (0 of 44 [0%]; P = .001).

DISCUSSION: Culture data from revision shoulder arthroplasty cases commonly yields monomicrobial results; whereas, NGS data suggests that bacterial loads in revision arthroplasty are most commonly polymicrobial. In addition, a definition of infection that uses cultures is more prone to "probable contaminants" than NGS. Significant uncertainty remains about our current methods of diagnosing shoulder PJI.