Reyes, Justin L.

Study Design: Single-center retrospective cohort study. Objective: To determine if the 4-rod construct (4RC) is protective against the occurrence of rod fractures when compared with the 3-rod construct (3RC) in adult spinal deformity (ASD) patients with long fusions to the sacrum. Summary of Background Data: Past studies have explored the different outcomes in subjects with dual-rod versus multirod constructs. There is a lack of literature distinguishing the ramifications of 3RC versus 4RC, particularly in the prevalence of rod fractures and rod fractures requiring subsequent revision surgery as a result of pseudarthrosis. Methods: ASD patients undergoing long instrumented fusions to the sacrum were dichotomized between the 3RC and 4RC cohorts. Outcomes of interest include the occurrence of rod fractures (RFs) and RFs requiring revision (RFR). Two-tailed independent-sample t test with Welch's correction and χ 2 /Fisher exact test were used for continuous and categorical variables, respectively. Multivariable logistic regression analysis was performed to assess whether the 4RC is protective against rod fractures when compared with the 3RC. Results: One hundred forty-five patients with a minimum 2-year follow-up were included (3RC=57, 4RC=88). Four RC had a greater body mass index (BMI) ( P =0.002), longer operating room (OR) time ( P =0.002), greater estimated blood loss (EBL) ( P =0.002), total instrumented levels (TIL) ( P =0.028), and more 3-column osteotomies (3COs) performed ( P =0.028). Four RC had greater baseline coronal vertical axis (CVA) (28.2±24.9 vs. 18.5±16.9 mm, P =0.006) and sagittal vertical axis (SVA) (55.1±64.8 vs. 30.4±41.8 mm, P =0.006). Three RC had a greater rate of RF (28.1% vs. 14.8%, P =0.0506) and RFR (14.9% vs. 10.2%, P =0.486) when compared with 4RC, but these findings were not statistically significant. After controlling for BMI, the use of 3-column osteotomies, total instrumented levels, change in coronal alignment (∆CVA), change in sagittal alignment (∆SVA), use of bone morphogenetic protein, and number of interbody fusions, 3RC was associated with 4.93× greater odds of experiencing RFs ( P =0.0078). However, significance fell short when adjusting for the occurrence of RFR [OR=2.58 (0.60–11.19), P =0.2067]. Conclusion: ASD patients having long fusions to the sacrum with 4RC across the lumbosacral junction are shown to be at lesser risk of developing rod fractures but not revision surgery as compared with 3RC at 2-year follow-up.

Background: The Spinal Cord Shape Classification System (SCSCS) class has been associated with spinal cord monitoring data loss during spinal deformity surgery. The objective of the current study was to prospectively validate the SCSCS as a predictor of spinal cord monitoring data loss during spinal deformity surgery. Methods: A prospective cohort study of consecutive patients who were undergoing primary deformity surgery at a single institution from 2018 to 2023 and whose major curve was in the spinal cord region was undertaken. Spinal cord morphology at the apex of the major curve on preoperative axial T2-weighted magnetic resonance imaging was used to categorize patients into 3 spinal cord shape types based on the SCSCS. The primary outcome was intraoperative neuromonitoring (IONM) data loss related to spinal cord dysfunction. Demographics and surgical and radiographic variables were compared between patients with IONM data loss and those without loss. Predictors of IONM loss were determined using bivariate and multivariable logistic regression analyses. Results: A total of 256 patients (168 adult, 88 pediatric) were included and were separated into 3 SCSCS types: 110 (43.0%) with Type I, 105 (41.0%) with Type II, and 41 (16.0%) with Type III. IONM loss was observed in 30 (11.7%) of the 256 patients, including 7 (6.4%) of 110 with SCSCS Type I, 7 (6.7%) of 105 with Type II, and 16 (39.0%) of 41 with Type III. IONM loss was associated with SCSCS Type III, the preoperative deformity angular ratio, performance of 3-column osteotomies, greater operative time, greater transfusion volume, and greater postoperative sagittal corrections. SCSCS type was the strongest independent predictor of IONM data loss. SCSCS Type III had the greatest odds of IONM loss (odds ratio [OR] = 6.68, 95% confidence interval [CI] = 2.45 to 18.23 compared with Types I and II combined). The overall predictive performance with respect to IONM loss (area under the receiver operating characteristic curve = 0.827) was considered excellent. Conclusions: This prospective cohort study of patients undergoing spinal deformity correction confirmed that patients with a Type-III spinal cord shape had greater odds of IONM loss. Inclusion of the SCSCS in preoperative risk stratification and intraoperative management of spinal deformity corrective surgery is recommended. Level of Evidence: Prognostic Level II . See Instructions for Authors for a complete description of levels of evidence.