JSES - 2026-05-13 - Journal Article
Evaluation of the International Consensus Meeting (ICM) Diagnostic Categories for Shoulder Periprosthetic Joint Infection: C. Acnes Predominates even in Definite Infections.
Ricchetti ET, Collins AP, Khazzam MS, Wright TW, Entezari V, Orvets ND, Whitson AJ, Hsu JE, American Shoulder and Elbow Surgeons (ASES) Revision Arthroplasty / Periprosthetic Joint Infection (PJI) Multicenter Group
Topics
Key Takeaway
C. acnes was the most common organism in both Definite (25%) and Non-Definite (27%) shoulder PJI categories using the 2018 ICM diagnostic framework across 490 revision arthroplasty cases.
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Summary
This multicenter prospective cohort evaluated 490 consecutive revision shoulder arthroplasties using the 2018 ICM PJI diagnostic categories to characterize case distribution, demographics, and microbiology across Definite (14%), Probable (11%), Possible (18%), and Unlikely (57%) PJI groups. Gross purulence was the most common Definite PJI criterion (65%), and the Probable PJI group was significantly younger, male-predominant (80.8%), lower ASA class, and on fewer narcotics than the Definite group. C. acnes predominated in both Definite and Non-Definite categories, challenging the conventional virulent/low-virulence organism dichotomy embedded in current diagnostic scoring.
Key Limitation
The study lacks treatment and outcome data, so it cannot determine whether ICM category assignment translates into differential management decisions or affects eradication rates.
Original Abstract
INTRODUCTION
Consensus-derived diagnostic criteria for shoulder periprosthetic joint infection (PJI) were established at the 2 nd International Consensus Meeting (ICM) on Musculoskeletal Infection in 2018. Data is still limited, however, on the clinical presentation and distribution of shoulder PJI cases with regards to ICM diagnostic categories. The purpose of this study was to utilize data from a multicenter prospective cohort of revision shoulder arthroplasties to evaluate the frequency of cases meeting criteria for each ICM PJI category and to examine the distribution of demographic data, microbiology, and positive criteria in each category.
METHODS
Data were prospectively collected on consecutive revision shoulder arthroplasty cases in the American Shoulder and Elbow Surgeons (ASES) Revision Shoulder Arthroplasty and PJI Multicenter Research Group. Standardized collection was performed for patient demographics, microbiology, major diagnostic criteria for the Definite PJI category, and minor criteria for the Probable, Possible, and Unlikely PJI categories in the ICM classification. Variations in demographic data, microbiology, and frequency of major and minor criteria were then evaluated within each PJI category for associations and differences.
RESULTS
490 cases were evaluated, including 71 (14%) Definite PJI, 52 (11%) Probable PJI, 87 (18%) Possible PJI, and 280 (57%) Unlikely PJI. Male sex was significantly more common in the Probable PJI group (80.8%) compared to Definite (63.3%), Possible (59.8%), or Unlikely PJI (43.2%) (p<0.001). The Probable PJI group was also more likely to be younger (p=0.010), on less narcotics (p=0.014), and of lower ASA class (p=0.004) than the Definite PJI group. Gross intra-articular purulence was the most common Definite PJI criteria (65%). Across Non-Definite PJI groups, the mean ICM PJI score and mean number of positive tissue cultures were significantly higher in the Probable PJI group (p<0.001) and remained statistically significant even after adjusting for amount of testing performed. C. acnes was the most commonly cultured bacteria in both Definite PJI (25%) and Non-Definite PJI (27%) groups.
CONCLUSION
C. acnes was the most common bacteria present in Non-Definite PJI as well as Definite PJI cases, suggesting that classification of bacteria as "virulent" and "low virulence" may need reconsideration. Significant differences were seen in demographic characteristics, presence of minor criteria, and growth of positive cultures across Non-Definite PJI groups, even when adjusted by amount of testing performed. These findings support the usefulness of these diagnostic categories and criteria. Data from this multicenter effort will help refine ICM PJI categories and determine how they guide treatment decision-making.
LEVEL OF EVIDENCE
Level I, Prospective Cohort Design, Epidemiology Study.