Future surgery after revision shoulder arthroplasty: the impact of unexpected positive cultures.

Background: The clinical implications and treatment of unexpected positive cultures (UPCs) in revision shoulder arthroplasty are not well defined. The purpose of this study was to describe results of patients with and without UPCs after revision shoulder arthroplasty.

Methods: A single institutional database was used to retrospectively identify all revision shoulder arthroplasties performed between January 1, 2011, and December 31, 2013. Patients with preoperative suspicion of infection were excluded. Multivariable regression analysis was used to identify risk factors for future surgery after revision shoulder arthroplasty.

Results: There were 117 revision shoulder arthroplasties without preoperative suspicion of infection. There were 28 of 117 (23.9%) with UPCs, of which 15 (57.1%) were Propionibacterium acnes; 18 of 28 (64.3%) patients received antibiotics for 6 weeks postoperatively without complications compared with 10 of 28 (35.7%) who received a routine 2-week empirical antibiotic regimen; 2 of 28 (7.1%) patients with UPCs required future surgery, and only 1 (3.6%) had a recurrent infection. Comparatively, 18 of 89 (20.2%) patients without UPCs (P = .109) required 25 additional surgeries. Average time to UPC was 4.3 years after index revision. Multivariable regression analysis of patient demographics, comorbidities, surgical procedure, and presence of UPCs found no independent predictors of reoperation.

Discussion: Nearly one-quarter of our institution's revision shoulder arthroplasties had UPCs. The patients without UPCs had a nonsignificantly higher risk of reoperation compared with those with UPCs. We did not identify clinical or demographic variables that independently correlated with reoperation. Further study will be necessary to determine the true clinical benefit of routine culture acquisition in cases with low suspicion for prosthetic joint infection.