Anterior Instrumentation Improves Correction of Severe Lumbar Lenke C Curves in Double Major Idiopathic Scoliosis

Summary: Fourteen skeletally immature patients with adolescent idiopathic scoliosis and double major curves with large (greater than 70 degrees) lumbar curves with notable L5 obliquity were studied. Those fixed with anterior instrumentation with the anterior release had significantly better coronal plane angulation in the distal unfused segments and saved unfused levels compared with posterior instrumentation alone or anterior release without instrumentation.

One of the primary goals in treating adolescent idiopathic scoliosis surgically is to preserve as many mobile levels as possible as well as maintaining normal coronal and sagittal segmental alignment in those unfused distal segments. Modern instrumentation strategies effect significant coronal plane correction, however with double major curves with large lumbar componenets (> 70 degrees and notable L5 obliquity), instrumentation posteriorly typically must include L4, leaving only two moble segments, often with concomitant coronal plane malalignment (tilting). Initial anterior release may limit the posterior fusion to L3, but over time, the coronal plane segmental alignment distally can be lost. We retrospectively reviewed fourteen individuals, six of whom had initial anterior release to L3 fixed with segmental anterior instrumentation (group A), and compared them with an identical group treated with anterior release to L3, without instrumentation, or posterior instrumentation alone to L4 (group B). The average thoracic curvatures for the groups were similar (Group A: 81 degrees, group B: 73 degrees) as was the lumbar curve (77 degrees group A; group B 72 degrees). There were no significant diffeences in terms of curve flexibility, l3, L4 or L5 tilt, vertebral rotation, apical translation, coronal or sagittal balance. All were skeletally immature (Risser 2 or less; half were Risser 0). At 4.5 years follow-up (2.5 - 7 years), curve correction, balance, fusion rates were not statistically different. The LIV horizontal angle as well as the coronal plane angles of the distal unfused segments were significantly normalized in those treated with anterior instrumentation. In cases of severe lumbar curvatures (> 70 degrees), it appears that adding anterior instrumentation to an initial anteior release and fusion, not only saves a level compared with a traditional posterior fusion to L4, but also maintains normal coronal segmental alignment over time; thereby theoretically reducing the risk of of late degenerative changes.