Objective Little information is available to guide treatment strategies regarding patients with unexpected positive cultures (UPC),including Propionibacterium acnes (PA),without overt signs of infection in revision shoulder arthroplasty (RSA).The purpose of our study was to analyze the prevalence,clinical meaning,treatment and prognosis of UPC in RSA.Data sources and study selection We performed a systematic review of the literature between 1950 and 2013 for all studies reporting on UPC for PA.Studies with the prevalence and prognosis of patients with UPC in RSA were analyzed.Results Six studies meeting our inclusion criteria yielded data for 1 402 patients who underwent a total of 1405 RSA.Based on the available data,following RSA 235 shoulders had UPCs with a pooled percentage of 16.7％ (235/1405).The most commonly isolated bacteria from shoulders following RSA with UPCs was PA with pooled percentages of 63.4％ (149/235).Occurrence of true infection from UPCs after RSA was seen in 24 shoulders (24/235,10.2％).Antibiotic use did not influence the rate of the occurrence of true infection from UPCs (P=0.498).Conclusions Our study showed a low risk of having a true infection from UPCs after RSA without clinical signs of preoperative infection at the time of the surgery.Therefore,prolonged antibiotic therapy may not be necessary in these patients.