Sagittal plane analysis of adolescent idiopathic scoliosis: The effect of anterior versus posterior instrumentation

Study Design. Radiographic analysis of anterior and posterior instrumentation for adolescent idiopathic scoliosis. Objectives. To compare effects of anterior versus posterior instrumentation on sagittal plane parameters. Summary of Background Data. The sagittal plane is critical to the long-term success of scoliosis surgery, but few studies have compared the effect of anterior versus posterior instrumentation. Methods. Standing, full spine lateral radiographs of 110 consecutive patients (mean age 14 years) who had surgery for adolescent idiopathic scoliosis between 1996 and 1998 at one institution with a minimum 24-month (mean 32 months) follow-up were evaluated. Fifty patients were instrumented anteriorly with single screw-rod constructs. Sixty patients were instrumented posteriorly with segmental implants (5.5 mm; hooks, wires, and/or pedicle screws). Results. At the final follow-up, the proximal junctional measurement (measured between the proximal instrumented vertebra and the segment two levels cephalad) increased most with posterior instrumentation (+7° increase for posterior thoracic vs. +1° increase for anterior thoracic instrumentation, P = 0.02; +9° increase for posterior thoracic and lumbar instrumentation vs. +4° for anterior thoracolumbar instrumentation, P = 0.03). Thoracic kyphosis (T5-T12) increased significantly with anterior versus posterior thoracic instrumentation (+4° vs. -2° change, P = 0.04). Lumbar lordosis (T12-S1) was enhanced with either anterior or posterior instrumentation. No significant changes in distal junctional measurement (measured between the distal instrumented vertebra and the segment two levels caudal) were noted. The C7 sagittal plumbline remained negative in all groups at the final follow-up. Conclusion. Anterior and posterior instrumentation had differential effects on the sagittal plane in patients with adolescent idiopathic scoliosis. However, the overall magnitude of the differences was small. Properly performed, both approaches can result in acceptable sagittal profiles.