Clinical Characteristics of Delayed-Onset Surgical Site Infection during Instrumented Spinal Surgery

<p>Introduction: The purpose of this study was to elucidate the clinical characteristics of delayed-onset surgical site infections (SSI) compared with those of early-onset SSIs.</p><p>Methods: Of the 1555 patients who underwent spinal instrumentation surgery, 31 (2.0%) required additional surgery because of surgical site infection. Background factors, such as age, gender, medical history, surgical factors, clinical findings at the time of onset (including wound appearance, imaging, and blood tests), causative microorganisms, presence of implants, and duration until normalization of C-reactive protein (CRP) were investigated. Delayed-onset SSIs were defined as those occurring after 30 days postoperatively and were compared with early-onset SSIs.</p><p>Results: A total of 35% of the cases were classified as delayed-onset SSIs, with a median onset period of 79 days. Compared with early-onset SSIs, delayed-onset SSIs exhibited a lower incidence of visible wound abnormalities and lower CRP levels. In delayed-onset SSIs, imaging studies revealed significant differences in lytic changes on CT scans and bone marrow edema on MRI. P. acnes was the predominant causative microorganism in delayed-onset SSIs (early-onset vs. delayed-onset: 2 cases/20, 5 cases/11), and the rate of implant preservation was significantly lower in delayed-onset cases (early-onset vs. delayed-onset: 100%, 45%). However, no significant difference was observed in the time to CRP normalization or treatment duration between the two groups.</p><p>Conclusions: Delayed-onset SSIs often manifest with subtle clinical signs, progress insidiously to cause bone destruction, and exhibit marked instability when detected, often requiring implant removal. In patients with persistent postoperative back pain and delayed bone union, consideration of this clinical condition is essential.</p>