Characteristics and Outcomes of Occult Infections in Presumed Aseptic Nonunions: A Retrospective Cohort Study.

OBJECTIVES

To determine (1) the rate of positive cultures in presumed aseptic nonunions, (2) the rate and microbial spectrum of positive cultures that represented occult infection, and (3) rates of nonunion healing.

DESIGN

Retrospective cohort study.

SETTING

Tertiary referral center.

PATIENTS SELECTION CRITERIA

Adult patients with a presumed aseptic nonunion treated with single-stage revision between 2002 and 2022.

OUTCOME MEASURES AND COMPARISONS

The rate of positive cultures compared for 2 protocols: old: 1-2 samples cultured 7 days versus new: 5 samples cultured 14 days. The rate of positive cultures meeting occult infection criteria with the new protocol (≥2 samples with phenotypically indistinguishable microorganisms, or ≥1 sample with a high virulent microorganism). Nonunion healing rates between protocols and between groups based on culture results with the new protocol.

RESULTS

One hundred seventy-nine patients were included. The rate of positive cultures was 14% (n = 15/105) with the old protocol and 51% (n = 38/74) with the new protocol (P < 0.001). With the new protocol, the rate of positive cultures meeting occult infection criteria was 19% (n = 14/74), and coagulase-negative staphylococci (48%) and Cutibacterium acnes (38%) were the most common microorganisms. Nonunion healing rates after the primary revision did not differ between protocols (old: 82% vs. new: 86%, P = 0.41) and groups based on culture result (sterile: 86% vs. occultly infected: 93%, P = 0.66). The final overall nonunion healing rate was 97%.

CONCLUSIONS

Occult infections were identified in 1 in 5 presumed aseptic nonunions using a standardized protocol with 5 intraoperative samples cultured 14 days and were predominantly caused by slow growing, gram-positive microorganisms. The local spectrum and antimicrobial sensitivity of occult infections should be considered when developing empiric antimicrobial protocols. Patients with presumed aseptic nonunions can expect high healing rates, regardless of the culture result.

LEVEL OF EVIDENCE

Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.