Shoulder arthroplasty has been performed by many years for the treatment of several conditions such as osteoarthritis, umeral head avascular necrosis and proximal umeral fractures following traumas. Surgical site infection (SSI) following shoulder arthroplasty remains a challenge, which increases morbidity including reoperations, implant removal, poor mobility, and raises extra medical costs. Identification of risk factors may help implementing adequate strategies to prevent infection. We aim to identify pre- and intra-operative risk factors associated with deep infections in shoulder arthroplasty. An age and sex-matched case control study was conducted to describe the prevalence rate, clinical and microbiological findings and to evaluate patient and surgical risk factors for shoulder arthroplasty-associated infections (SAIs), among 158 patients who underwent shoulder replacement surgery due to any reason, from 1988 to 2011 at a tertiary public university institution. To evaluate risk factors from SAI we performed uni- and multivariate analysis by multiple logistic regression. We analyzed 168 prosthetic shoulder replacement surgeries from 158 patients, with an overall infection rate of 9.5%, (16/168 cases). Gram-positive cocci and Gran-negative bacilli were equally isolated in 50% of cases, however the most common bacteria detected (18.8%) was Pseudomonas aeruginosa. Univariate analysis identified neither specific comorbidity nor pre-operative risk factors, but American Society of Anesthesiologists (ASA) score higher than 2 (odds ratio [OR] = 5.30, 95% confidence interval [CI] = 1.58 to 17.79; p=0,013) to be significant preoperative patient-related predisposing factor for SAI. On univariate analysis, the only surgery-related factor significantly associated with higher risk of SAIs was the presence of surgical haematoma (OR = 7.1, 95% CI = 1.1 to 46; p=0.04). On multivariate analysis ASA score higher than two (OR = 4.7, 95% CI = 1.3 to 16.9; p=0.01) was the only independent predictor for periprosthetic shoulder infection. This study identified unusual pathogens and confirmed previously patient-related known factors such as higher ASA score that predispose to SAIs.
