Development and validation of a novel thoracic spinal stenosis surgical invasiveness index: a single-center study based on 989 patients

Background context Surgical invasiveness indices have been established for general spine surgery (surgical invasiveness index [SII]), spine deformity, and metastatic spine tumors; however, a specific index for thoracic spinal stenosis (TSS) has not been developed. Purpose To develop and validate a novel invasiveness index, incorporating TSS-specific factors for open posterior TSS surgery, which may facilitate the prediction of operative duration and intraoperative blood loss, and the stratification of surgical risk. Study design A retrospective observational study. Patient sample Overall, 989 patients who underwent open posterior TSS surgeries at our institution during the past 5 years were included. Outcome measures The operation duration, estimated blood loss, transfusion status, major surgical complications, length of hospital stay, and medical expenses. Methods We retrospectively analyzed the data of 989 consecutive patients who underwent posterior surgery for TSS between March 2017 and February 2022. Among them, 70% (n=692) were randomly placed in a training cohort, and the remaining 30% (n=297) automatically constituted the validation cohort. Multivariate linear regression models of operative time and log-transformed estimated blood loss were created using TSS-specific factors. Beta coefficients derived from these models were used to construct a TSS invasiveness index (TII). The ability of the TII to predict surgical invasiveness was compared with that of the SII and assessed in a validation cohort. Results The TII was more strongly correlated with operative time and estimated blood loss (p<.05) and explained more variability in operative time and estimated blood loss than the SII (p<.05). The TII explained 64.2% of operative time and 34.6% of estimated blood loss variation, whereas the SII explained 38.7% and 22.5%, respectively. In further verification, the TII was more strongly associated with transfusion rate, drainage time, and length of hospital stay than SII (p<.05). Conclusions By incorporating TSS-specific components, the newly developed TII more accurately predicts the invasiveness of open posterior TSS surgery than the previous index.