Diagnosis of occult infection using Fracture Related Infection criteria at the time of nonunion repair.

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To apply the recently developed Fracture-Related Infection criteria to patients presenting for repair of fracture nonunion and determine the incidence and associated organisms of occult infection in these patients. Retrospective. Tertiary referral trauma center. Patients presenting with fracture nonunion after operative intervention. Demographic variables, injury characteristics, culture results, and physical exam and laboratory values at time presentation. A total of 270 nonunion patients were identified. Sixty-eight percent (n=184) had no clinical or laboratory signs of infection at presentation, prior to nonunion repair. Following operative intervention, 7% (n=12/184) of these clinically negative patients had positive intraoperative cultures indicating occult infection. The most common organisms causing occult infection were low virulence Coagulase-negative Staphylococcus (83%) and Cutibacterium acnes (17%). Thirty-two percent (n=86/270) of patients presented with clinical and/or laboratory signs of infection at presentation prior to nonunion repair, with 19% (n=16/86) of these patients having negative cultures. The most common organisms in this group of patients with positive clinical signs and intra-operative cultures were Methicillin-resistant Staphylococcus Aureus (21%) and gram-negative rods (29%). Patients with nonunion of the tibia were significantly more likely to have high virulence organism culture results (p<0.001) . Based on this analysis, occult infection occurs in 7% of patients presenting with nonunion and no clinical or laboratory signs of infection. We recommend that all patients should be carefully evaluated for infection with intraoperative cultures regardless of presentation. Organisms associated with occult infection at the time of nonunion repair were almost exclusively of low virulence (CoNS and C. Acnes) and were more likely to present in the upper extremity. Patients with nonunion of the tibia were more likely to have infection secondary to high virulence organisms and demonstrate clinical or laboratory signs of infection at the time of presentation.