Deep SSI after posterior spinal fusion with instrumentation is a troublesome and undesired complication, which may result in pseudarthrosis, spondylodiscitis, correction loss, spinal instability, adverse neurological sequelae, and implant removal if not treated timely . Early diagnosis and aggressive surgical therapy are critical to eradicate infection, retain implant, decrease morbidity, restore spinal stability, and obtain satisfactory wound healing . In terms of surgical treatments for early deep SSI after posterior spinal instrumentation, continuous irrigation suction system and VAC system following debridement are two common methods [4, 9, 20].
The application of a continuous irrigation suction system can improve local microcirculation, remove necrotic tissues and inflammatory factors, decrease the bacterial adhesion and recontamination, avoid secondary wound closure, and reduce the number of postoperative operating room visits. Lian et al.  reported that 23 patients with early postoperative deep SSI after spinal fusion with instrumentation were treated with thorough debridement and continuous irrigation suction system. The instrumentation and cages of all patients were retained successfully, and 21 patients (91.3%) had good wound healing with a mean of 12 days of continuous irrigation. Yuan et al.  reported 11 patients with early deep SSI after thoracolumbar instrumentation that underwent debridement and continuous irrigation suction system, and 3 patients required placement of the continuous irrigation suction system for a second time until wound healing. Rohmiller et al.  respectively studied 21 patients developing acute infections following posterior spinal fusion and instrumentation and found that 14 patients achieved complete resolution of their infection without recurrence after placement of the initial suction irrigation system during the follow-up period. However, there are some complications from a continuous irrigation suction system. First, the continuous irrigation suction system severely restricts the patient’s movement and functional exercise in bed. Besides, irrigation saline or drainage is likely to leak from inflow or outflow tubes, further resulting in wetting of the wound dressing, further increasing the frequency of dressing changes and the risk of retrograde infection.
The VAC system has been widely used to treat deep SSI after posterior spinal instrumentation because of its advantages of reducing tissue edema, promoting granulation tissue formation and angiogenesis, increasing blood flow, decreasing bacterial presence in the wound, and removing necrotic tissue [1, 4, 8, 9, 18]. Canavese et al.  reviewed 14 patients with early deep SSI after spinal instrumentation for scoliosis treated with a VAC system and identified that the VAC system was a reliable and useful tool for the spinal surgeon to eradicate the infections since all patients’ wounds healed with retention of the instrumentation and no loss of spinal correction or recurrent infection occurred. In the study performed by Zeng et al. , 16 patients with deep SSI after lumbar surgery with instrumentation underwent the treatment of the VAC system. The VAC dressing was replaced 2.4 times on average before secondary wound closure. All patients significantly improved the Japanese Orthopaedic Association scores and reduced the Oswestry disability index without recurrence of infection at the last follow-up. Nevertheless, the VAC system has some disadvantages. Jones et al.  ever reported five major complications related to the VAC system in four patients, including hemorrhage in two patients, one of whom died of unstable hemodynamics. Under some circumstances, granulation tissue may grow into the VAC dressing, thus affecting the efficacy of the VAC system. Webb  described that 2.2% of patients developed rash because of contact with the VAC dressing. Additionally, patients using the VAC system require a secondary closure, which adds to the patient’s pain and the extra cost.
In recent years, unlike many previous clinical applications of the VAC system for secondary wound closure, the incisional VAC system following primary wound closure has been successfully used for the prevention of SSI in spine surgery [11, 12]. However, there have been no reports about the application of incisional VAC system following a one-stage incision suture to treat deep spinal SSI. In this study, we treated 21 patients with early deep SSI after posterior lumbar fusion with instrumentation by using an incisional VAC system following a one-stage incision suture combined with continuous irrigation and obtained satisfactory results. To the best of our knowledge, this study is the first report to apply incisional VAC system following one-stage incision suture combined with continuous irrigation to the treatment of deep spinal SSI.
The treatment method we adopt in this study combined the advantages of a continuous irrigation suction system and VAC system and eliminated the disadvantages of each other. In our study, the incisional VAC system application can remove drainage and infectious material around the closure wound, prevent fluid leakage from inflow or outflow tubes, avoid skin erosion around inflow or outflow tubes, decrease the risk of retrograde infection, increase microcirculation and tissue regeneration, protect the closure wound from external infectious sources as a sterile barrier, decrease lateral tissue tension, and promote incisional apposition in case of dehiscence . All the patients were cured and retained implants with an average of 1.9 times of VAC dressing replacement and an average of 10.2 days of continuous irrigation. No patients need to be transferred to the operation room for a second debridement. Only one patient developed a back skin rash with itching around the wound during treatment. There was no recurrent infection or other complications during follow-up. The postoperative VAS scores for back pain were significantly improved in all patients. The satisfactory rate was 90.5% according to Kirkaldy-Willis functional criteria .
With regard to laboratory testing related to SSI, ESR and CRP, as inflammatory markers, are two commonly used indicators to indicate improvement or progression of infection, especially CRP with more sensitivity [3, 26]. Under normal circumstances, peak ESR levels can be found up to 5–7 days and normalize within 4–6 weeks after surgery. CRP levels typically peak at 3 days and reduce within 10–14 days after surgery . Therefore, the analyses of ESR and CRP levels must be interpreted in terms of the time since the index surgery. In the study by Yuan et al. , all the 23 patients with postoperative deep SSI showed increased CRP levels before debridement, and 21 patients (91.3%) presented with increased ESR levels. Zeng et al.  reported that all the 31 patients with postoperative deep SSI before debridement had elevated CRP levels, and 21 patients showed increased ESR levels. In our study, CRP and ESR levels increased in all patients with early deep SSI. Their levels dropped significantly after a series of aggressive treatments and returned to normal within 3 months in most patients.
Many scholars [3, 14, 26] have identified various risk factors for SSI after spine surgery, which can be classified as those intrinsic to patient-specific, procedure-related, and perioperative care. In this study, we took elderly (age > 70 years), body mass index > 30, smoking, diabetes mellitus, coronary artery disease, chronic obstructive pulmonary disease, anemia, low serum albumin, operation time > 3h, and perioperative blood loss > 500 ml as the risk factors for SSI and found that 18 patients (85.7%) had at least one of the above risk factors. In order to prevent postoperative SSI, we suggest as follows: First, surgeons should carefully consider patient’s potential risk factors for SSI and modify them as much as possible before surgery. Second, simplification of complex surgery and improvement of surgical technique are required to decrease operative time and intraoperative bleeding. Futhermore, postoperative careful incision care and timely correction of anemia or low serum albumin are also important to prevent complications of SSI.
We acknowledge there are some limitations to this study. First, the sample size of early deep SSI patients was relatively small. Second, there was no control group to further highlight the advantages of the treatment protocol in the study. Furthermore, this is a single-center retrospective study. To overcome these shortcomings, a multicenter prospective randomized controlled trial with a larger sample size should be performed to identify the efficacy of the treatment protocol used in this study.