Can we trust intraoperative culture results in nonunions?

OBJECTIVES: To identify the presence of bacterial biofilms in nonunions comparing molecular techniques (multiplex polymerase chain reaction and mass spectrometry, fluorescent in situ hybridization) with routine intraoperative cultures.

METHODS: Thirty-four patients with nonunions were scheduled for surgery and enrolled in this ongoing prospective study. Intraoperative specimens were collected from removed implants, surrounding tissue membrane, and local soft tissue followed by standard culture analysis, Ibis's second generation molecular diagnostics (Ibis Biosystems), and bacterial 16S rRNA-based fluorescence in situ hybridization (FISH). Confocal microscopy was used to visualize the tissue specimens reacted with the FISH probes, which were chosen based on the Ibis analysis.

RESULTS: Thirty-four patient encounters were analyzed. Eight were diagnosed as infected nonunions by positive intraoperative culture results. Ibis confirmed the presence of bacteria in all 8 samples. Ibis identified bacteria in a total of 30 of 34 encounters, and these data were confirmed by FISH. Twenty-two of 30 Ibis-positive samples were culture-negative. Four samples were negative by all methods of analysis. No samples were positive by culture, but negative by molecular techniques.

CONCLUSIONS: Our preliminary data indicate that molecular diagnostics are more sensitive for identifying bacteria than cultures in cases of bony nonunion. This is likely because of the inability of cultures to detect biofilms and bacteria previously exposed to antibiotic therapy.

LEVEL OF EVIDENCE: Diagnostic Level I. See Instructions for Authors for a complete description of levels of evidence.