SSI is one of the most frequent healthcare-associated infections.11 It significantly hampers the benefits of surgical management in addition to reducing satisfaction from patients.12–14 As we know, frequent symptoms of spinal postoperative SSI, including incision pain, fever, and oozing, can rarely be identified at early stages. Delayed diagnosis of SSI may eventually result in surgical failure. Identification of SSI for early intervention becomes valuable in clinical practice since infection control should be lunched as early as possible. In this study, we tried to distinguish the likely SSI at very early stages and prevent it from developing into confirmed SSI.
In current study, we found a likely SSI rate of 10.7%, which is relatively higher than the results from previous studies.11,15−17 This can be explained by the fact that, the enrolled criteria in current study are actually wider than the standard diagnosis criteria of SSI. Actually there are variations in the definitions of SSI and the frequency of SSI after spine surgery varied according to different definitions.18,19 Positive microbiological evidence is needed to diagnose a SSI in most international criteria, while here in this study we used evidence of clinical signs and symptoms of infection. We noticed that most of the patients did not have culture positive laboratory values in our study. A possible reason is that, in order to have a positive microbiological test, it requires a certain number of bacteria to be grown in those cultures. While in our study the infection was identified and treated at early stages, results in a relative small number of bacterial colonization, which is not enough for a positive culture result.
Previous studies showed that the majority of SSI become apparent within 30 days of an operative procedure, and longer in instrumented surgeries. While some cases had their infections present clinically even after the initial 3-month period.12,17 In this study, we differentiated those patients at very early stages. The average elapsed time from operation to the diagnosis of likely SSI is 7.1 ± 1.3 days, which is significant earlier than that of published studies.
On the other hand, we looked at the changing tendency of different inflammatory biomarkers during the irrigation treatment. CRP and ESR values were significantly higher than the normal level before the start of irrigation and dropped rapidly during the following treatment. It seems that CRP and ESR are closely correlated with the severity of infection. This is consistent with the work from Eiichiro et al, among which they looked at CRP in 11 cases of SSI and 130 cases of non-SSI following instrumented spinal fusion.20 They concluded that CRP at day 7 post-operation had high predictive value of an SSI.
Furthermore, treatment options reported in published studies composed of extensive debridement and prolonged antibiotic therapy guided by antimicrobial susceptibility of the isolated bacteria.8,10 Those methods always come with multiple debridements, secondly wound closure and even removal of the implant. However, reopen the incision and doing multiple debridements is painful and leading to a lengthy hospital stay. It is even more difficult to decide whether to preserve or remove the implant in those situations because cage removal is technically demanding and results in total segmental instability and neurological compromise.13
Lee et al.8 found 31% of SSI patients had implant loosening with both pedicle screws and cages at the time of diagnosis. During their treatment, all implants including cages were removed and re-implantation of auto-iliac bone blocks were performed. Tsubouchi et al.13 investigated the risk factors for implant removal after spinal SSI based on data from seven spine centers, they observed that 40% of SSI patients had their implant removal. Study from Mirovsky et al.21 reported that 33.3% of patients with SSI have their cages repositioned in the face of infection, and they concluded that in postoperative uncontrolled deep infection with cages, removal of all hardware including the interbody cages is the treatment of choice. Kim et al.22 reported 10 patients who were referred to them during a 1-year period for deep SSI after OPLS with cages. All 10 patients underwent cage removal via an anterior surgical approach. However, none of the likely SSI patients enrolled in current study had implant loosening and none of them required removal of the instrumentation during the whole treatment.
On the other hand, compared with the prolonged antibiotic therapy (usually 4 to 6 weeks of intravenous antibiotic therapy followed by another 6 to 9 weeks of oral antibiotic administration) in previous studies, the average time of antibiotics administration in our study is only 13.8 ± 4.3 days, which is significant shorter. It is also known that deep SSI leads to a lower incidence of solid fusion.23–26 However, the fusion rate at 6-months and 12-moths in our study are 84.7% and 97.2% respectively, which is significantly higher than most other studies. By notes, the average medical cost of enrolled patients is 13,274 ± 3,471 US dollars, much cheaper than the cost reported by published studies.27–30
Hence, compared with traditional reported methods, we believe this early infection control treatment may help preventing the formation of SSI, decreasing the dose of antibiotic administration, reducing the length of hospitalization or medical costs, and increasing the fusion rate without removing the implant in most patients.4,27,31
Limitations to this study should be noted. First of all, it is a bedside invasive procedure, which means it may trigger secondary infections without carrying out strict septic manipulation. Trained personnel are needed to perform the insertion of the irrigation/draining devices sterilely. Second, it needs a nurse who has received relative training stay beside the patient and control the “T” type valve during the irrigation. Third, the tube is relatively thin and soft, makes it easily twisted or blocked by the debris from the incision, which results to recurrent leaking/oozing and dressing changes.
In conclusion, early identification and control of likely SSI following OPLS is valuable in clinical practice and the bedside irrigation system seems to be a safe and effective choice. Future large sample-sized control studies are awaited to provide stronger evidence for its efficacy.