Indications of proximal thoracic curve fusion in thoracic adolescent idiopathic scoliosis: recognition and treatment of double thoracic curve pattern in adolescent idiopathic scoliosis treated with segmental instrumentation.

STUDY
DESIGN: A retrospective study.
OBJECTIVES: To determine the indications of fusing the proximal thoracic curve when treating idiopathic thoracic scoliosis with segmental instrumentation. SUMMARY OF BACKGROUND DATA: Failure to recognize a significant proximal thoracic curve often results in postoperative shoulder asymmetry due to relative overcorrection of the lower thoracic curve. With segmental instrumentation that enhances the correction of the instrumented curve, the double thoracic curve pattern that needs fusion of both the proximal and the distal thoracic curves should be redefined.
METHODS: Forty patients with thoracic adolescent idiopathic scoliosis with a right lower thoracic curve of more than 40 degrees and a left proximal thoracic curve of more than 25 degrees treated by segmental pedicle screw instrumentation were analyzed after a minimum follow-up of 2 years.
RESULTS: Of the 40 patients, 18 were treated by fusion of both the proximal and the distal curves, whereas 22 were treated by fusion of the distal curve only. The postoperative shoulder height difference (SHD, in millimeters) was 0.9 x preoperative SHD + 5.3 for the fusion of both curves and 0.6 x preoperative SHD + 12 for the distal curve fusion (linear regression), showing that proximal thoracic curve fusion improved the SHD when the left shoulder was level with or higher than the right.
CONCLUSIONS: Idiopathic thoracic scoliosis with a proximal thoracic curve of more than 25 degrees and level or elevated left shoulder should be considered a double thoracic curve pattern and should be treated by fusing both the proximal and the distal curves when using segmental instrumentation.