Predicting the Outcome of Selective Thoracic Fusion in False Double Major Lumbar “C” Cases With Five- to Twenty-Four-Year Follow-up

Abstract

Retrospective radiographic and clinical study. To examine the long-term outcome of selective thoracic fusion (STF) performed for lumbar "C" modifier curves in adolescent idiopathic scoliosis. The efficacy of STF in lumbar "C" false double major curves is controversial. We examined the 5- to 24-year outcomes of patients with "C" lumbar curves who underwent STF at a single institution to determine which factors help predict successful outcome. Thirty-two patients (age, 14.8 ± 2.0 years) with a lumbar "C" modifier underwent primary STF and had minimum 5-year follow-up (mean, 6.8 years). All patients were fused distally to either T12 or L1. At latest follow-up, 18 were considered successful (group S), 2 required reoperation to accommodate worsening deformity (group R), and 12 were considered marginal outcomes (group M), as defined by >3 cm coronal imbalance (n = 5), >5 mm worsening of lumbar apical vertebra translation compared with preoperative (n = 4), >1 Nash-Moe grade worsening of lumbar apical vertebra rotation (n = 1), >10° thoracolumbar junction kyphosis which was at least 5° worse than preoperative (n = 5), and lumbar Cobb angle >5° worse than preoperative (n = 2). Clinical outcomes were determined by Scoliosis Research Society (SRS)-30 at final follow-up. Of the multiple factors considered, 2-month postoperative standing lumbar sagittal alignment was most predictive for long-term outcome (P < 0.019 by Kruskal-Wallis ANOVA). Satisfactory outcomes had statistically significantly greater T12-S1 lordosis than those that were marginal (64.8° (group S) vs. 52.0° (group M); P = 0.014) or required reoperation (64.8° [group S] vs. 38.0° [group R]; P < 0.001). Traditionally considered variables such as apical vertebra rotation, apical vertebra translation, Cobb angle magnitudes, coronal and sagittal balance, and their respective thoracic-to-lumbar ratios were not independently significant. Selective thoracic fusions performed for lumbar "C" modifier scoliotic deformities generally have excellent long-term radiographic and SRS-30 outcomes at 5- to 24-year follow-up. Care should be taken to ensure that overcorrection of the thoracic curve is not performed beyond the ability of the lumbar curve to compensate. Furthermore, consideration of selective thoracic fusion should not be ruled out simply because the patient may have a somewhat stiff lumbar curve based on side-bending radiographs.