85 - Selective Thoracolumbar Fusion in Adult Spinal Deformity (ASD) Double Curves with Circumferential Minimally Invasive Surgery (CMIS): 2-year Minimum Follow Up

Introduction: CMIS correction for ASD with double curves has typically been reserved for very experienced surgeons or considered for open surgery under recent MISDEF-2 criteria. Further, level selection for adult spinal deformity remains controversial. While selective fusion attempts have been described for fractional curves or adolescent curves, no authors have described selective thoracolumbar fusion performance for ASD with double curves.
This study evaluates the performance of selective thoracolumbar fusion for ASD double curves and investigates the compensatory response of the uninstrumented thoracic spine.

Study

Design: Retrospective Review

Methods: We retrospectively reviewed our adult spinal deformity (Cobb>20, SVA>50mm, (PI-LL)>10) database of 438 patients who underwent CMIS correction between the years 2007 and 2020. Inclusion criteria were ASD double curves (lumbar cobb >35 degrees and thoracic cobb >30 degrees), four or more levels fused, and minimum 2-year follow up. We assessed radiographic data (lumbar cobb, thoracic cobb, coronal balance, lumbar lordosis, thoracic kyphosis) as well as spinopelvic parameters (PI, PT, SS) both pre- and post-operatively. We also assessed pre- and post-intervention clinical data (VAS, ODI, SRS22, and SF36). Complications were recorded.

Results: Twenty-one ASD double curve patients underwent selective thoracolumbar correction with a mean follow up of 91 months (24-174 months, SD 43). A total of 141 levels were fused with a mean of 6.7 levels fused (4-8, SD 1.3). T10 was the most proximal and most common UIV (10/21, 48%). Pelvic fixation was performed in 12 patients (57%). Statistically significant improvements in lumbar cobb, thoracic cobb, coronal balance, lumbar lordosis, thoracic kyphosis, SVA, and PI-LL mismatch were achieved. The uninstrumented thoracic spine had a mean of 14.5 degrees of coronal correction and a mean increase of 9.4 degrees of kyphosis. Statistically significant improvements in VAS and ODI were observed. Four patients required revision surgery, which included the following: (1) a superficial wound infection requiring irrigation and debridement, (2) bilateral L5 pars fractures requiring L5-S1 ALIF and pelvic fixation, (3) adjacent segment degeneration at L5-S1 requiring ALIF and pelvic fixation, and (4) one patient developing proximal junctional kyphosis (PJK) requiring revision fusion to include the entire thoracic curve.

Conclusions: Selective CMIS thoracolumbar fusion for ASD patients with double curves can provide significant clinical improvements. Despite limiting fusion constructs to the lower thoracic and/or lumbar spine, significant correction can be observed in the uninstrumented thoracic curve. Mechanical related complications were low, but inclusion of the lumbosacral junction may limit revision surgery.