The Surgical Treatment of Double Thoracic Curves in Adolescent Idiopathic Scoliosis – Factors Involved in the Decision to Perform a Selective Fusion of the Main Thoracic Curve Versus a Posterior Fusion

Summary: After analyzing factors affecting the outcome of selective ASF of MT curve versus nonselective PSF of both curves in double thoracic curves, we found that with a larger MT/PT Cobb ratio, greater PT curve flexibility, and a minimal preoperative T1 tilt, selective ASF of MT curve can be considered but limited correction is recommended. With a smaller MT/PT ratio, less PT curve flexibility, and greater preoperative T1 tilt, PSF of both curves is recommended.

Introduction: Double thoracic (Lenke 2) adolescent idiopathic curves traditionally require posterior spinal fusion (PSF) of both main thoracic (MT) and proximal thoracic (PT) curves. In certain situations, selective anterior spinal fusion (ASF) of MT curve can be considered.

Purpose: To analyze factors involved in the decision to perform selective ASF versus nonselective PSF of both curves.

Methods: A retrospective multi-center review of 112 patients with Lenke 2 curves was performed. Multiple coronal and sagittal measurements were obtained pre and postoperatively.

Results: The pre- and postoperative instrumented MT curves were almost identical in both groups. MT/PT Cobb ratio averaged 1.66 in ASF and 1.46 in PSF (p=0.004). Postoperatively, the instrumented PT correction following PSF was consistently greater than the spontaneous PT correction following ASF. The mean T1 tilt increased following ASF but decreased following PSF. The patients were divided into 4 subgroups according to post-op T1 tilt. There was a trend for Group A to have a larger MT/PT ratio, a larger flexibility index, and a smaller pre-op T1 tilt. Similar trend existed between Group C versus Group D. With similar instrumented MT correction, the spontaneous PT correction in Group A was significantly larger than Group B, and the instrumented PT correction in Group C was significantly larger than Group D. The mean pre-op sagittal Cobb measurements were statistically equivalent. Postoperatively, in ASF group, T2-5 became less kyphotic, T5-12 became more kyphotic, and T2-12 kyphosis increased. Conversely, in PSF group, T2-5 became more kyphotic, T5-12 became less kyphotic, and T2-12 kyphosis decreased.

Conclusion: With a larger MT/PT ratio, greater PT curve flexibility, and minimal preoperative T1 tilt, selective ASF of MT curve can be considered. With a smaller MT/PT ratio, less PT curve flexibility, and greater preoperative T1 tilt, PSF of both PT and MT curves is recommended.

FDA Diclosure Cleared: No ** Thoracic Pedicle Screws