OBJECTIVESTo quantify the changes of the spatial relations between the vertebral body and the thoracic aorta in main right thoracic adolescent idiopathic scoliosis (AIS) following anterior and posterior instrumentation and fusion.

METHODSTwenty-nine patients with main right thoracic AIS were divided into 2 groups. Group A included 13 females and 1 male with an average age of 14.3 years old and average main thoracic Cobb angle of 44.9 degrees, these patients underwent mini-incision thoracic anterior spinal fusion. Group B included 12 females and 3 males with an average age of 14.2 years old and average main thoracic Cobb angle of 46.4 degrees, all of them were treated with posterior spinal fusion. Patients underwent CT scanning from T5 to T12 Pre-and post-operatively. Five parameters pertaining to the spatial relations between the vertebral body and the thoracic aorta including the angle for safety screw placement (gamma), the angle of the aorta relative to the vertebral body (beta), vertebral rotation angle (gamma), distance from the aorta to the closest point of the vertebral body cortex (a) and distance from the posterior wall of the aorta to the anterior edge of the left rib head (b) were analyzed and were correlated with the curve correction.

RESULTSIn Group A, the alpha angle and 3 angle increased while gamma decreased after curve correction, and significant difference were found at T8 and T9 levels (P < 0.05); the a value decreased and b value increased after curve correction and reached significant difference at T9 (P < 0.05). No significant change of these parameters was found in Group B post-operatively. In Group A, the increment of alpha angle, beta angle and b value show great correlation with the decrement of gamma angle (P < 0.01). At the periapical the increment of alpha angle, beta angle and b value show great correlation with decrement of apical vertebral translation, while decrement of a value show great correlation with increment of kyphosis from T5 to T12 (P < 0.01).

CONCLUSIONSUnder anterior instrumentation and correction, the aorta moved anteromedially toward vertebral body on CT scanning. The factors contributing to the aorta shifting included releasing of aorta from vertebrae, vertebral derotation and curve correction.