Mid-Thoracic Upper Instrumented Vertebrae in Adult Spinal Deformity: A Viable Stopping Point?

Abstract

Single-institution retrospective cohort study. To compare patients undergoing ASD surgery with an upper instrumented vertebrae (UIV) in the upper-, mid-, or lower-thoracic spine regarding: 1) preoperative factors, 2) perioperative variables, and 3) and postoperative outcomes. The classic teaching in adult spinal deformity surgery (ASD) is to avoid stopping a construct in the mid-thoracic spine; however, this theory remains untested. Patients undergoing ASD surgery from 2009-21 with 2-year follow-up were reviewed. Standard demographic, radiographic, and perioperative data were collected. The primary independent variable was UIV location: upper-thoracic: C7-T4, mid-thoracic: T5-T8, and lower-thoracic: T9-L2. Outcomes included mechanical complications, reoperations, and patient-reported outcome measures. Of 190 patients, UIV region was: 29 (15.3%) upper-thoracic UIV, 42 (22.1%) mid-thoracic, and 119 (62.6%) lower-thoracic. Preoperatively, mid-thoracic UIV patients were older than upper-thoracic UIV (71.7±10.8 vs. 60.6±14.1, P<0.001). Perioperatively, mid-thoracic UIV had higher estimated blood loss than both upper- (P=0.047) and lower-thoracic (P<0.001) groups. Radiographically, C7-plumb line (C7PL) correction was greater in mid- vs. lower-thoracic UIV (27.9±28.0° vs. 16.8±17.7°, P=0.045). Postoperatively, mid-thoracic UIV had higher rates of pseudarthrosis (47.6% vs. 20.7%, P=0.021), reoperation for mechanical complications (50.0% vs. 20.7%, P=0.012), and reoperation for any reason (52.4% vs. 20.7%, P=0.007) versus upper-thoracic UIVs. Compared to lower-thoracic UIVs, mid-thoracic UIVs had higher rates of pseudarthrosis (47.6% vs. 28.6%, P=0.025) and rod fracture (38.1% vs. 20.2%, P=0.021). No difference was found in proximal junctional kyphosis/failure or PROMs. Mid-thoracic UIVs had higher rates of pseudarthrosis and both mechanical and all-cause reoperations compared to upper-thoracic UIVs, as well as higher rates of pseudarthrosis and rod fractures compared to lower-thoracic UIVs. The only superior outcome of a mid-thoracic UIV was greater coronal C7PL correction versus lower-thoracic UIV. These findings suggest stopping ASD constructs in the mid-thoracic spine may yield worse outcomes and should be approached cautiously.