Unexpected positive cultures after revision shoulder arthroplasty -does it affect outcome?

Abstract Background Several studies have confirmed a high rate of unexpected positive cultures (UPCs) after presumably aseptic revisions of shoulder arthroplasties; however, the impact on the outcome is still unclear. The purpose of this prospective study is to compare the patient-reported outcomes of standard revisions with and without the emergence of UPCs. Methods During a 3-year period, we included all patients who were revised for reasons other than suspicion of infection from two orthopedic centers. Five biopsies were obtained from every revision, and only cultures with the same bacteria in at least three biopsy specimens were classified as UPCs. All patients were assessed using the Oxford Shoulder Score (OSS) and range of motion preoperatively and after at least a two-year follow-up. Results In this study, 124 patients were included, with a median follow-up of 29 months (range 29–32), and UPCs emerged after 27 revisions (22%), with Cutibacterium acnes (C. acnes) accounting for 67% (18/27). At baseline, the OSS was 22 in both the culture-negative and UPC groups (p = 0.46). Then, at follow-up, the OSS was 37 in the culture-negative group and 35 in the UPC group (p = 0.91). The forward elevation increased significantly by 44° and 41° respectively in the two groups, but no statically significant difference between the culture-negative group and the UPC group was found (p = 0.66). In contrast, the external rotation was unchanged after the revision, and again, no difference in the change between the culture-negative and UPC groups (p = 0.54) was observed. Subgroup analyses stratified by different implant designs revealed equal patterns with no statistical differences in outcome. Conclusion We did not find a difference in outcome after a presumed aseptic revision regardless of the emergence of UPCs. Similarly, we could not demonstrate that patients with UPCs presented with poorer function at baseline compared to culture-negative patients. The clinical relevance of UPCs thus requires further evaluation, especially in the case of C. acnes as a potential pathogenic contra merely colonizing microbe.