Objective: new method of evaluating the thoracic modifier in adolescent idiopathic scoliosis using true lateral digital x-ray views of the fifth thoracic vertebra and the twelfth thoracic vertebra.

Methods: prospective study included thirty patients with adolescent idiopathic scoliosis. Lenke classification type I, II, III, IV were included in this study. Every patient was subjected to thorough clinical and radiological examination including Plain x-ray long standing Antero-posterior view. From this view, Coronal tilt angle of T5 and T12 was calculated . According to the CTA of T5 and T12, Two lateral view images were obtained, one focusing on T5 and the other on T12 to measure the degree of sagittal tilt of T5 and T12. Thoracic modifier using the new method is calculated using cobb's method in which cobb angle is equal to summation of T5 STA and T12 STA. All mentioned angles were measured using Surgimap.

Results: T5 STA ranged from -14.70º to 28.80º with a mean of 6.50 ± 10. T12 STA ranged from 3.40º to 41.10º with a mean of 21.40 ± 8.49. Total thoracic modifier ranged from 3.40º to 41.10º with a mean of 21.40 ± 8.49.