Sustained Postoperative Fever Without Evident Cause After Spine Instrumentation as an Indicator of Surgical Site Infection

Abstract

Background: Surgical site infection after spinal instrumentation increases morbidity and mortality as well as medical costs and is a burden to both patients and surgeons. Late-onset or sustained fever increases the suspicion for comorbid conditions. This retrospective, exploratory cohort study was conducted to identify the rate of and risk factors for sustained or late-onset postoperative fever after spinal instrumentation operations and to determine its relationship with surgical site infection. Methods: Five hundred and ninety-eight patients who underwent lumbar or thoracic spinal instrumentation were retrospectively reviewed. The patients were divided according to (1) whether or not they had had a sustained fever (SF[+] or SF[-]) and (2) whether or not they had had a surgical site infection (SSI[+] or SSI[-]). Clinical characteristics, surgical factors, prophylactic antibiotic usage, fever pattern, and laboratory/imaging findings were recorded for all patients by electronic medical chart review. Results: In total, 68 patients (11.4%) had a sustained fever. The rate of surgical site infection was significantly higher when the patient had sustained fever (13.2% [9 of 68] compared with 0.9% [5 of 530]; p < 0.001). Comparison of the patients who had a sustained fever but no surgical site infection (SF[+], SSI[-]) and those with both a sustained fever and surgical site infection (SF[+], SSI[+]) showed that continuous fever, an increasing or stationary pattern of inflammatory markers, and a C-reactive protein (CRP) level of >4 mg/dL on postoperative days 7 to 10 were diagnostic clues for surgical site infection. The sensitivity and specificity of postoperative magnetic resonance imaging (MRI) for the detection of surgical site infection were 40.0% and 90.9%, respectively, when MRI was performed within 1 month after surgery. Conclusions: Although most patients with sustained fever did not have surgical site infection, fever was significantly related to surgical site infection. Continuous fever, increasing patterns of inflammatory markers, and high CRP on postoperative days 7 to 10 were diagnostic clues for surgical site infection. This study demonstrated provisional results for factors that can discriminate febrile patients with surgical site infection from febrile patients without infection. Further investigation with a larger sample size is warranted for clarification.