Background:

Contrary to lower limb infection, POstoperative Shoulder Infection (POSI) often involves Cutibacterium acnes (C. acnes). Our aim was to describe patient characteristics and pathogens retrieved in POSI to guide initial empiric antibiotic selection with suspected infection during revision. We also compared microorganisms in infection following trauma, arthroplasty (AP) and arthroscopy (AS).

Methods:

A multicenter retrospective study from 2010 to 2016 reviewed laboratory databases and medical records to identify patients with a previous shoulder surgery and a confirmed shoulder infection. The following procedures were included: AP, AS, fracture fixation (FF) or another open surgery (OS). A confirmed shoulder infection was defined as two positive cultures or more of the same microorganism, or clear clinical infection with one positive culture or more.

Results:

Among the five hospitals and 28 surgeons involved, 94 POSI cases were identified. Mean age was 59 years at index surgery (Range: 22 – 91) with a majority of men (n = 70, 74 %). Among POSI cases, AP was the most common index surgery (n=41), followed by FF (n=27), AS (n=16) and OS (n=10). The median time between index surgery and the first positive sample was five months and the mean was 23 months, (min 6 days – max 27 years), illustrating a positively skewed distribution. Cutibacterium spp. were identified in 64 patients (68%), including 59 C. acnes patients (63%), which was the most frequent germ in all four surgical groups. In 86 % of cases, C. acnes was identified at the first revision. The other two most common germs were: Staphylococcus epidermidis and Staphylococcus aureus, with 29 % and 17 %, respectively. Polymicrobial infection was present in 30% of patients. Gender analysis revealed that C. acnes was twice as frequent in males (male = 52/70; female = 7/24, p<0.001). S. epidermidis was more prevalent in women (n=11, 46 %) compared to men (n= 16, 21%) (p=0.032). C. acnes infection was most frequent in arthroscopic surgery (n=14, 70%, p=0.049). S epidermidis was three times more prevalent in chronic than in acute cases.

Conclusion:

Empiric antimicrobial therapy following POSI, while waiting for culture results, should cover C. acnes, S. epidermidis and S. aureus. There is a significant gender difference regarding POSI culture results. C. acnes is more frequent in men, but should still be covered in women as it was found in 29% of cases.