The impact of lower thoracic versus upper lumbar upper instrumented vertebra in minimally invasive correction of adult spinal deformity

OBJECTIVE The goal of this study was to compare the impact of using a lower thoracic (LT) versus upper lumbar (UL) level as the upper instrumented vertebra (UIV) on clinical and radiographic outcomes following minimally invasive surgery for adult spinal deformity. METHODS A multicenter retrospective study design was used. Inclusion criteria were age ≥ 18 years, and one of the following: coronal Cobb angle > 20°, sagittal vertical axis > 50 mm, pelvic tilt > 20°, pelvic incidence–lumbar lordosis mismatch > 10°. Patients were treated with circumferential or hybrid minimally invasive techniques at ≥ 3 spinal levels and had a 2-year minimum follow-up. They were then divided into 2 groups depending on whether the UIV was in the UL region, defined as a UIV location of L1–2, or the LT region, defined as T10–12. RESULTS A total of 114 of 223 patients met the inclusion criteria (68 LT and 46 UL). The UL group was older (67.5 vs 62.3 years; p = 0.015). Preoperative spinopelvic parameters were similar, except for sacral slope, which was higher in the UL group (30.5° vs 26.5°; p < 0.001). The percentage of patients with fixation crossing the lumbosacral junction was also similar (70.6% vs 67.4%; p = 0.717). Postoperative lumbar lordosis (42.5° vs 35.5°; p = 0.01) and change in coronal Cobb angle (−23.2° vs −9.6°; p < 0.001) were greater in the LT group, but other changes in postoperative spinopelvic parameters and changes in health-related quality-of-life scores were similar between groups. Reoperation rates were lower in the UL group (17.4% vs 36.8%; p = 0.025), largely associated with fewer radiographic failures (UL = 10.9% vs LT = 26.5%; p = 0.042); however, overall complication rates were not significantly different (UL = 43.5% vs LT = 60.3%; p = 0.077). CONCLUSIONS Selecting a UL vertebra for UIV in minimally invasive surgical correction of adult spinal deformity results in lower reoperation rates compared to extending fixation to the LT region. This choice also correlates with shorter operating room times and reduced estimated blood loss. Although extending fixation to the LT region is associated with slightly greater lumbar lordosis and a greater change in the coronal Cobb angle, clinical outcomes were similar between the LT and UL groups for UIV.