Higher Intraoperative Blood Loss is Associated with Increased Risk of Intraoperative Neuromonitoring Data Loss for the Type 3 Spinal Cord Shape During Spinal Deformity Surgery

Introduction: Within the spinal cord shape classification system(SCSCS), type 3 spinal cords (actual cord deformation on apical axial MRI scan) have been shown to be associated with much higher risk of intraoperative neuromonitoring(IONM) data loss. The current study is to identify whether there are variables among type 3 cord shapes that further predicts the likelihood of IONM changes within this subgroup.

Methods: This is a retrospective cohort study of consecutive patients with type 3 spinal cords undergoing spinal deformity surgery from a single academic institution between 2016-2023. The primary outcome examined was whether there was IONM data loss. Demographic, clinical, operative, and radiographic variables were compared in those patients with and without IONM data loss.

Results: A total of 79 patients with type 3 spinal cords meeting the inclusion criteria were identified. Of these, 30 pts(38%) had IONM data loss, while 49 pts(62%) did not. In comparing the IONM loss group with the no IOMN change group, there were no differences between the groups in age or BMI. There were no significant differences in the mean preoperative coronal deformity angular ratio(C-DAR), sagittal DAR(S-DAR), or total DAR(T-DAR). In addition, there were no significant differences in the mean change in C-DAR, S-DAR, or T-DAR between the groups when comparing the postoperative versus preoperative measurements. There was no difference in proportion of patients with a vertebral column resection(VCR), or in the mean instrumented number of levels. However, there was a significantly higher estimated blood loss (EBL) (1320±614 vs 1049±468,p=0.03) in the IONM loss group.

Conclusion : In this largest reported cohort patients with type 3 spinal cords undergoing spinal deformity surgery, somewhat surprisingly, the only factor found to be significantly associated with risk of IONM data loss was higher EBL. Thus this is important for deformity surgeons to realize when treating this specific group of high risk patients.