Surprise positive culture rate in the treatment of presumed aseptic long-bone nonunion: a systematic review with meta-analysis of 2397 patients

Introduction In pre-operatively presumed aseptic nonunions, the definitive diagnosis of infection relies on intraoperative cultures. Our primary objective was to determine (1) the rate of surprise positive intraoperative cultures in presumed aseptic long-bone nonunion (surprise positive culture nonunion), and (2) the rate of surprise positive cultures that represent infection vs. contamination. Secondary objectives were to determine the healing and secondary surgery rates and to identify cultured micro-organisms. Materials and Methods We performed a systematic literature search of PubMed, Embase and Cochrane Libraries from 1980 until December 2021. We included studies reporting on ≥ 10 adult patients with a presumed aseptic long-bone nonunion, treated with a single-stage surgical protocol, of which intraoperative cultures were reported. We performed a meta-analysis for: (1) the rates of surprise positive culture nonunion, surprise infected nonunion, and contaminated culture nonunion, and (2) healing and (3) secondary surgery rates for each culture result. Risk of bias was assessed using the QUADAS-2 tool. Results 21 studies with 2,397 patients with a presumed aseptic nonunion were included. The rate of surprise positive culture nonunion was 16% (95%CI: 10–22%), of surprise infected nonunion 10% (95%CI: 5–16%), and of contaminated culture nonunion 3% (95%CI: 1–5%). The secondary surgery rate for surprise positive culture nonunion was 22% (95%CI: 9–38%), for surprise infected nonunion 14% (95%CI 6–22%), for contaminated culture nonunion 4% (95%CI: 0–19%), and for negative culture nonunion 6% (95CI: 1–13%). The final healing rate was 98% to 100% for all culture results. Coagulase-negative staphylococci accounted for 59% of cultured micro-organisms. Conclusion These results suggest that surprise positive cultures play a role in the clinical course of a nonunion and that culturing is important in determining the etiology of nonunion, even if the pre-operative suspicion for infection is low. High healing rates can be achieved in presumed aseptic nonunions, regardless of the definitive intraoperative culture result.