Determination of distal fusion level with segmental pedicle screw fixation in single thoracic idiopathic scoliosis

A retrospective study was conducted. To determine the exact distal fusion level in the treatment of single thoracic idiopathic scoliosis (King Types 3 and 4) with segmental pedicle screw fixation. Pedicle screw fixation effectively shortens the distal fusion extent by improved three-dimensional deformity correction. However, the selection of distal fusion extent remains controversial in single thoracic idiopathic scoliosis. This study analyzed 42 patients with single thoracic adolescent idiopathic scoliosis (32 King 3 patients and 10 King 4 patients) who underwent segmental pedicle screw fixation and had a minimum follow-up period of 2 years (range, 2-6 years). The patients were grouped according to the distal fusion level with reference to the standing neutral rotated vertebra (NV) for comparison of deformity correction and spinal balance using standing radiographs. Failure to restore an adequate trunk balance and progression or extension of the primary curve (adding on) was considered unsatisfactory. Preoperative 50 degrees +/- 11 degrees of thoracic deformity was corrected to 13 degrees +/- 5 degrees, for a curve correction of 74%. Preoperative 23 degrees +/- 7 degrees of lumbar deformity was corrected to 2 degrees +/- 8 degrees, for a curve correction of 93%. Curve correction was not significantly affected by King type or distal fusion level (P > 0.05). Postoperative unsatisfactory results were obtained in 14 patients. When the preoperative NV was the same or one level distal to end vertebra (EV), fusion down to NV was satisfactory (14/14). When the preoperative NV was more than two levels distal to EV, fusion down to one level shorter than NV (NV-1) also was satisfactory (9/9). However, when fusion down to NV-2 or shorter was performed, the chances of adding on were higher (14/19; P < 0.01). Preoperative 17 degrees +/- 8 degrees of thoracic kyphosis was improved to 24 degrees +/- 7 degrees. In single thoracic idiopathic scoliosis, NV is an important factor for the determination of fusion level. When preoperative NV and EV show no more than two-level gap differences, the curve should be fused down to NV. When the gap is more than two levels, fusion down to NV-1 is satisfactory, saving one or two motion segments, as compared with fusion extending to the stable vertebra.