Predictors of increased length of stay and cost in readmissions for spinal surgical site infections.

BACKGROUND

Surgical site infection (SSI) following spinal surgery remains a costly and morbid complication, frequently necessitating hospital readmission and operative management. While prior studies have characterized the overall economic burden of spinal SSI, the specific drivers of cost during SSI-related readmissions are poorly defined. The primary research question of this study was to identify clinical, operative, and microbiologic factors associated with increased hospital cost, length of stay, and financial margins during readmission for operative management of spinal SSI.

METHODS

We performed a retrospective cohort study of adult patients readmitted for surgical management of spinal SSI at a single tertiary academic center between 2015 and 2022. Demographic, clinical, operative, microbiologic, and payer-related variables were extracted from the electronic medical record. Itemized direct hospital costs, payments, and net revenue were obtained from institutional financial databases. The primary outcome was direct hospital cost during the SSI readmission. Multivariable Gamma generalized linear models with log link were used to identify independent predictors of cost, while secondary analyses evaluated contribution margin, margin rate, and length of stay using linear and negative binomial regression models.

RESULTS

A total of 123 patients were included, with a mean age of 63.2 years and a mean readmission length of stay of 15.9 days. Mean direct hospital cost during readmission was $25,713±$21,128. Length of stay was strongly correlated with cost (r=0.695, p<.001). In a streamlined multivariable model retaining the full cohort (n=123), each additional hospital day increased cost by 4.8% (+$1,207/d; p<.001), and staged index procedures were associated with 45.0% higher costs (p<.001). PSO/VCR was paradoxically associated with 33.6% lower cost (p=.001); a sensitivity analysis excluding LOS showed this association strengthened, not attenuated (-51.7%), indicating confounding by surgical case selection rather than LOS. Private insurance was associated with lower direct costs and higher contribution margins and margin rates compared with government payers.

CONCLUSIONS

Hospital length of stay is the dominant driver of cost during readmission for spinal SSI, with operative complexity and staged procedures contributing additional financial burden. Strategies focused on reducing inpatient duration and optimizing perioperative efficiency may substantially mitigate the economic impact of spinal SSI.