Preservation of Thoracic Kyphosis Is Critical to Maintain Lumbar Lordosis in the Surgical Treatment of Adolescent Idiopathic Scoliosis

Study Design. Retrospective analysis of prospectively collected multicenter series. Objective. To evaluate the sagittal profile of surgically treated adolescent idiopathic scoliosis (AIS) patients. Summary of Background Data. With the increasing popularity of segmental pedicle screw spinal instrumentation, thoracic kyphosis (TK) is often sacrificed to achieve coronal and axial plane correction. Methods. Radiographs of AIS patients with a Lenke type 1 deformity and minimum 2-year follow-up after selective thoracic fusion (lowest instrumented vertebra of T11, T12, or L1) were evaluated. Changes in TK were correlated with changes in lumbar lordosis (LL). Patients were divided according to approach (open/thoracoscopic anterior vs. posterior). Analysis of variance was used to compare pre and postoperative radiographic measures. Results. Two hundred fifty-one patients (age: 14 +/- 2 years) were included. Sixty seven percentages of the patients had anterior surgery (97 open anterior, 71 thoracoscopic) and 33% (83 patients) had posterior spinal fusion. A decrease in postoperative TK was significantly correlated (P <= 0.001) with a decrease in LL at first erect (r = 0.3), 1 year (r = 0.4) and 2 years (r = 0.4), independent of surgical approach. LL decreased significantly at the first erect regardless of approach (P = 0.003); however, at 2-year postoperative TK and LL were significantly decreased after a posterior approach (P <= 0.001) when compared with an anterior approach that added kyphosis. The decrease in LL (5.6 degrees +/- 9.7 degrees) was nearly twice the decrease in TK (2.8 degrees +/- 11.4 degrees) in the posterior group at 2-years. Conclusion. Given that thoracic AIS is often associated with a preexisting reduction in TK, ideal surgical correction should address this deformity. Procedures which further reduce TK also reduce LL. It is unclear if the loss of LL from thoracic scoliosis correction will compound the loss of LL that occurs with age and lead to further decline in sagittal balance. With this concern, we recommend a posterior column lengthening and/or an anterior column shortening to achieve restoration of normal TK and maximal LL.