# A comparison of the clinical characteristics and outcomes of aerobic and anaerobic prosthetic joint infections (PJIs): a single-center retrospective review

## TL;DR

This study compares the clinical features and outcomes of anaerobic and aerobic prosthetic joint infections, finding that anaerobic infections often present with chronic symptoms and require more invasive treatments.

## Contribution

The study highlights the under-recognized role of anaerobic organisms in prosthetic joint infections and provides insights into their distinct clinical presentation and management.

## Key findings

- Anaerobic PJIs had longer symptom duration and more sinus tracts compared to aerobic PJIs.
- Shoulder PJIs were more frequently anaerobic, and anaerobic cases were more likely to require two-stage exchange.
- Anaerobic PJIs showed lower ESR and CRP levels and similar recurrence rates compared to aerobic infections.

## Abstract

Background: Prosthetic joint infection (PJI) is an uncommon but serious complication of joint arthroplasty, associated with significant morbidity and healthcare costs. Anaerobic organisms are an under-recognized cause of PJI, either as sole pathogens or within polymicrobial infections, and data on their clinical impact are limited. This study compared clinical presentation and outcomes of anaerobic vs. aerobic PJIs. Methods: This is a retrospective review of 284 patients who met Musculoskeletal Infection Society (MSIS) criteria for PJI from 2014 to 2020 at the University of Iowa Hospitals and Clinics (UIHC). A total of 38 had anaerobic PJI; 268 had aerobic PJI. Statistical analyses were performed using Pearson's
χ2
, a Fisher exact test, and a
t
test. Results: Anaerobic PJIs represented 13.4 % of PJIs in our institution. Compared to aerobic cases, anaerobic PJIs had longer symptom duration (19.4 vs. 10.9 weeks,
p=0.005
), more sinus tracts (23.7 % vs. 6.1 %,
p<0.001
), fewer fevers (13.2 % vs. 31.3 %,
p=0.022
), more radiographic abnormalities (44.7 % vs. 29.3 %,
p=0.024
), and lower ESR and CRP (ESR: 49.0 vs. 67.4 mm h−1; CRP: 6.6 vs. 12.3 mg dL−1; both
p=0.003
). Shoulder PJIs were more often anaerobic (39.5 % vs. 4.9 %,
p<0.001
). Anaerobic PJIs were more likely to be treated with two-stage exchange (65.8 %), while aerobic cases more often underwent debridement and implant retention (44.7 %). Recurrence rates were similar. Conclusion: Anaerobic PJIs tend to present with features such as shoulder involvement, prolonged or chronic symptoms, sinus tract formation, and radiographic signs of infection, whereas aerobic PJIs are more commonly linked to acute presentations. For this reason, both aerobic and anaerobic cultures should be performed routinely to optimize diagnostic yield.