In the present study of patients receiving posterior instrumented spinal fusion, prophylactic ciNPWT use significantly decreased the rate of wound dehiscence by 36.9% and SSI by 60.7% compared with standard surgical dressings. This is despite the ciNPWT cohort being significantly biased towards increased risk factors for SSI, including older age, greater likelihood of diabetes, more instrumented levels, and EBL, and more operations for deformity correction [5, 7,8,9, 18].

Use of ciNPWT through VAC is an established means of reducing rates of SSI for surgical wound healing by primary closure [19]. Primary mechanisms of action attributed to the action of VAC devices used for ciNPWT include: (1) wound contraction (macrodeformation), (2) stabilization of wound environment, (3) removal of extracellular fluid, and (4) microdeformation at the foam-wound interface [10]. These primary changes yield the secondary changes desired by the surgeon, including enhanced angiogenesis and granulation tissue formation, favorable changes in wound biochemistry and the systemic inflammatory response, and a decrease in pathogen burden [10]. Individual reports have produced conflicting results regarding the efficacy of ciNPWT in reducing the incidence of SSI in spinal fusion surgery [4, 11, 13,14,15].

A prospective study among 274 patients by Mueller et al. supported the use of ciNPWT as a means of reducing rates of SSIs, especially among patients (instrumentation, deformity, and malignancy) and surgeries at higher risk, as well as patients with diabetes and higher EBL [15]. While there was no statistical difference in surgeries with decompression alone (4.2% vs. 9.1%, p = 0.63), there was a significant reduction in instrumented surgeries (3.4% vs. 10.9%, p = 0.02) [15]. A retrospective comparative study limited to spinal trauma patients by Mehkri et al. reported an independent association between ciNPWT use and decreased 90-day SSI and wound-related returns to the operating room [4]. This was despite a tendency towards ciNPWT patients possessing greater risk factors such as significantly older age, diabetes, and increased BMI. Cumulative 2022 meta-analysis reported that ciNPWT could significantly reduce the incidence of postoperative SSI, but there was no significant benefit on reducing the incidence of wound dehiscence or reoperation [13].

SSIs represent a significant cause of healthcare-acquired morbidity, mortality, and healthcare resource expenditure [1,2,3]. Annually in the United States, there are an estimated 158,000 SSIs at a cost of up to $10.07 billion in 2009 USD [20]. Spine surgeries account for more than 1 million procedures annually and neurosurgical SSIs incur the highest costs among surgical specialties, indicating an opportunity for significant harm and healthcare costs reduction [21]. Costs for treatment of postoperative spine surgery SSI range from $16,242 to $31,245 [3, 4]. In the present study, the NNT with ciNPWT to prevent one SSI was 8 patients. The incurred costs of using prophylactic ciNPWT ($4,560) to prevent one SSI requiring operative intervention ($26,222) amounts to a potential cost savings of $21,662 per SSI prevented. Per 100 patients receiving posterior instrumented spinal fusion, the potential mean cost-savings related to SSI prevention is $270,775. Mehkri et al. previously reported a potential cost-savings of $163,492 per 100 patients treated for spinal trauma [4]. The increased cost-savings in the present study may be attributed to inclusion of patients operated on for deformity, tumor, and infection, which carry a high risk of wound-related complications [14, 22,23,24,25]. Compared with Mehkri et al., patients in the present study possessed an even greater tendency towards risk factors including older age (60.58 vs. 52.42 years), increased BMI (31.34 vs. 28.44 kg/m2), cancer (17.9% vs. 2.9%), and chronic steroid use (9.6% vs. 0.5%) [4]. Increased age, including age > 60 years, has been shown to be significant preoperative risk factor [7,8,9]. These factors in addition to the inclusion of high-risk patients with infectious and oncologic surgical indications may account for the substantially greater cost-savings in the present study. Cost-benefit ratio in cases with lesser index surgery cost and risk of infection, such as decompression alone compared to instrument surgeries, may not warrant the higher surgical dressing costs. Further investigation should assist in developing an algorithm for the selective use of ciNPWT for increasingly complex cases (i.e. length of fusion, staged procedure) and higher-risk patient populations (neoplastic or infectious etiology) [14].

This is a retrospective study of a single surgeon’s experience among 229 patients that was not randomized and whose total cohort number resulted from an observational study and was not based on sample size calculation. Therefore, it is likely that our control group is underpowered to determine statistical significance of less frequently occurring demographic categories and clinical outcomes, including subgroup analysis of the effect of ciNPWT depending on surgical indication. The selection of patients to receive a standard surgical dressing versus ciNPWT was not based on a standardized algorithm and thus was subject to selection bias. However, patients in the ciNPWT group were higher risk for SSI due to significantly older age, higher incidence, diabetes, more levels of instrumented fusion, and EBL, the latter two being likely markers of increased surgical complexity. The present study also includes high-risk patients with infection, tumor, and deformity, who were notably excluded from some prior studies [4, 13]. In particular, the ciNPWT group had significantly more surgeries for deformity than controls. Additionally, surgeries involved long constructs with an average of 5 intervertebral levels instrumented across for all patients. Despite these predisposing factors placing patients at high risk for infection, the overall reported infection rate in the present study (13.1%) does not differ substantially from previously reported studies involving posterior instrumentation by Adogwa et al. (13.67%) and Mehkri et al. (14.42%) [4, 12]. Overall incidence of infection in the present study is high, and therefore the attributed effect of ciNPWT may not be applicable to practices with lower risk patients/surgeries. The use of hospital costs as an outcome is complicated by significant variations in costs across time, region, and hospital system. Its importance, however, cannot be understated given the significant financial and healthcare resource investment associated with both the index spine surgery as well as management of wound dehiscence and SSI. Future studies should evaluate which patient populations and surgical modifiers may receive the greatest from application of an ciNPWT.