Wednesday, September 26, 2018 7:35 AM–9:00 AM ePosters: P35. Implant sonication versus tissue culture for the detection of spinal implant infection

BACKGROUND CONTEXT Diagnosing a spinal implant infection (SII) remains a challenge. We have previously shown that implant sonication followed by culture is more sensitive than peri-implant tissue culture for the microbiologic diagnosis of SII. In this follow-up study, we analyzed the largest sample size available in the literature to compare these two culture methods. PURPOSE To compare implant sonication versus tissue culture for the detection of spinal implant infection. STUDY DESIGN/SETTING Restrospective case series. METHODS We compared peri-implant tissue culture to the vortexing-bath sonication technique which samples bacterial biofilm on the surface of retrieved spinal implants. We established different thresholds for sonicate positivity and assessed the sensitivity and specificity of these culture methods for the diagnosis of SII. RESULTS A total of 153 patients were studied. With 100 colony forming units (CFU) as a threshold for sonicate culture positivity, there were 47 patients with SII. At this level, the sensitivites of peri-implant tissue and sonicate fluid culture were 66.0% and 70.2% (p=.6); the specificities were 88.7% and 93.4%, respectively. With 50 CFU as a threshold, there were 51 patients with SII. The sensitivies of peri-implant tissue and sonicate fluid culture were 68.6% and 76.5% (p=.47); the specificities were 92.2% for both methods. Finally, with 20 CFU as a threshold, there were 52 patients with SII. The sensitivies of peri-implant tissue and sonicate fluid culture were 69.8% and 83.0% (p=.09); the specificities were 94.0% and 92.0%, respectively. CONCLUSIONS When compared to peri-implant tissue culture, implant sonication followed by culture remains a sensitive and specific method for the diagnosis of SII. Lower thresholds for defining sonicate fluid culture positivity allow for increased sensitivity with a minimal decrease in specificity, further enhancing the clinical utility of implant sonication.