Background: It’s has been recently accepted that the posterior segmental spinal system is one of the best instruments in scoliosis correction. Since Cotrel introduced the CD system the use of this system is widely performed. Most reports verify moderate to good correction of coronal deformity with the Cobb’s angle correction range from 60 to 70%. However, many authors reported little degrees of vertebral derotation ranging from 0 to 20%. Wood found that actually the derotation occurred outside the segment of instrumentation and many authors demonstrated no or minimal apical derotation in the CD system. Recently the development of posterior pedicular screws system especially on vertebral derotation. This study reported the efficacy of RSS which is one of the pedicular screw system designed specifically for 3D idiopathic scoliosis correction.

Objective: To study the efficacy of RSS in idiopathic scoliosis correction

Methodology: We prospectively collected the data from April 1998 to March 1999. There were 25 patients who had the diagnosis of idiopathic scoliosis and underwent the posterior spinal correction and fusion with RSS. Inclusion criteria: all patients who had the Dx of AIS and underwent posterior spinal correction and fusion with RSS. Exclusion criteria: Juvenile scoliosis and in patient who had the indication for combined anterior and posterior approach.

We recorded the data both preoperatively and postoperatively as follow: Standing height, Cobb’s angle, Kyphotic angle (T5 to T12), coronal trunk balance (plumb line), shoulder height difference, Rib hump difference, vertebral rotation, alignment index, coronal hump difference.

Regarding vertebral rotation, we use the CT scan measurement by the method introduced by Aaro and Dahlborn and the angle we use was called RaMI which is defined by the angle formed between 2 lines, one line drawn from the sternum to the most posterior corner of the spinal canal and the other drawn from the most posterior aspect of the spinal canal and extending anteriorly to equally bisect the vertebral body. The alignment index is calculated by the equation as follow: -AI=|apex-(T+B)/2| where AI = alignment index, apex = average apical RaMI rotation angle, T= average upper end vertebral Raml rotational angle and B = average lower end vertebral Raml rotation. This represented the overall segmental vertebral rotational alignment, the closer the value to zero, the better the alignment. Coronal hump difference is used to evaluate the rib cage deformity and is measured from CT-scan film by first create the Raml line and the second line was made perpendicular to Raml line and touch the posterior aspect of the more prominent rib cage as shown in figure. We measure the distance from point B to rib cage on the less prominent hump in mm and this is the virtual coronal hump difference which can converted back to coronal hump difference by magnificating factor.