Chronic Septic Arthritis of a Native Elbow Caused by Cutibacterium acnes: A Case Report

Abstract

Introduction: Cutibacterium acnes is a slow-growing, aerotolerant anaerobic, gram-positive organism most often discussed in shoulder surgery and implant-associated infection. Native elbow septic arthritis due to C. acnes is rare and can be missed when cultures are not held long enough. Case Presentation: An 18-year-old right-hand dominant male landscaper presented with six weeks of atraumatic left elbow pain, swelling, stiffness, and night sweats after failing a one-week course of oral sulfamethoxazole/trimethoprim and cephalexin. White blood cell count was normal at 9,000/microliter, whereas ESR was 59 mm/hr and CRP was 8.9 mg/dL. Radiographs showed elbow effusion without osseous abnormality, and MRI demonstrated a complex loculated effusion with surrounding soft tissue inflammation. Initial arthrocentesis was nondiagnostic because less than 2 mL of bloody fluid was obtained, leaving insufficient fluid for analysis or culture. Because symptoms persisted despite empiric inpatient intravenous antibiotics, the patient underwent open irrigation and debridement through a posterior triceps-split approach. Purulent material was encountered, multiple intraoperative specimens were deliberately sent for prolonged incubation, and at least two separate intraoperative cultures grew C. acnes on postoperative days 9 and 11. Formal antimicrobial susceptibility results were not available in the source record. The patient was discharged on oral ciprofloxacin and linezolid for two weeks until outpatient follow-up under the treating clinical team. At two-week follow-up, he had no early wound complication and range of motion improved to 5 to 120 degrees. Discussion: This case illustrates an indolent native-joint infection with normal peripheral leukocyte count, elevated inflammatory markers, initially nondiagnostic aspiration, and delayed culture positivity after extended incubation. Antibiotic exposure before operative sampling and the absence of susceptibility data limit interpretation. Conclusion: C. acnes should be considered in chronic atraumatic monoarthritis of the elbow. Multiple operative specimens and prolonged culture incubation are important when routine evaluation is nondiagnostic.