Culture positivity in primary total shoulder arthroplasty.

Background: The clinical significance of positive cultures in shoulder surgery remains unclear. This study determined the rate and characteristics of positive intraoperative cultures in a cohort of patients undergoing primary shoulder arthroplasty.

Methods: From February 2015 to March 2016, 94 patients, without prior surgery, underwent primary shoulder arthroplasty. Before surgery, all shoulders were prospectively enrolled and consented to obtain standardized intraoperative cultures. All patients received standard preoperative antibiotic prophylaxis. Standardized fluid and tissue locations were sampled and sent for aerobic and anaerobic cultures and held for 13 days. Patients and surgeon were blinded to the culture results.

Results: Average age at surgery was 70.5 years (range, 50-91 years), and 41 patients (47%) were male. At least 1 positive culture was found in 33 shoulders (38%), with 17 patients (19%) having ≥2 positive cultures. Cutibacterium (formerly Propionibacterium) acnes was the most common organism (67%), followed by coagulase-negative Staphylococcus (21%), Staphylococcus aureus (3%), and other organisms (18%). The rate of positive culture was higher in men (51%) than in women (26%, P = .016). Cutibacterium acnes was more common in men with positive cultures (95% vs. 17%, P < .001) and coagulase-negative Staphylococcus and Staphylococcus epidermidis were more common in women with positive cultures (42% vs. 10%, P = .071).

Conclusion: Positive deep tissue cultures develop in a high percentage of patients undergoing primary shoulder arthroplasty despite antibiotic prophylaxis. The long-term clinical implication of this finding requires further study, especially with regard to the risk of late failures of shoulder arthroplasty.