Anaerobes in Late-Onset Prosthetic Joint Infection (PJI) and Colorectal Carcinoma

Background: Late-onset anaerobic prosthetic joint infection (PJI) is uncommon but may indicate underlying, previously asymptomatic colorectal malignancy. While the association between Streptococcus bovis group (SBG) bacteremia and colorectal cancer is well established, links between anaerobic PJIs and colorectal neoplasia are rarely reported. Anaerobic organisms originating from the gastrointestinal tract may translocate via the hematogenous route, and their presence in PJI should prompt clinicians to consider occult colorectal pathology. Methods: All periprosthetic arthroplasty infection cases between 2015 and 2025 were reviewed. Clinical records, diagnostic findings, microbiological data, and treatment outcomes were analyzed. Results: Three female patients (mean age 76.3 years) presented with late-onset PJI occurring at least five years after primary total knee arthroplasty. Causative organisms included Bacteroides fragilis, Morganella morganii, and Klebsiella pneumoniae. All patients underwent two single-stage revision surgeries and one debridement, antibiotics and implant retention (DAIR) procedure. Cross-sectional computed tomography imaging of the abdomen and pelvis (CT-AP) performed to evaluate hematogenous sources of infection consistently revealed previously undiagnosed colorectal malignancy. One patient had additional metastatic disease. Postoperative complications included one case of pulmonary embolism; no other major complications were observed. Conclusions: Anaerobic PJIs are rare, and their association with colorectal malignancy is not well established. These cases highlight the importance of evaluating potential gastrointestinal sources, including occult colorectal cancer, in patients presenting with late-onset anaerobic PJI.