Analysis of intravertebral axial rotation in adolescent idiopathic scoliosis using three-dimensional MRI

This paper reports a pilot study analysing axial rotation in patients with adolescent idiopathic scoliosis using three-dimensional MR. The objective w as to define the proportion of segmental axial rotation that occurs due to intravertebral deformity in patients with adolescent idiopathic scoliosis. Ten patients with adolescent idiopathic scoliosis with right thoracic curve (Cobb angle 44 degrees - 78 degrees) selected sequentially from clinic wer e included in the study. Patients were imaged with a Siemens 1T impact scan ner using dual echo steady state gradient echo T2-weighting (TR 30msec/ TE 9/45 msec/ 40 degrees). Three-dimensional volume images of the apical ten v ertebrae were obtained in the axial plane and were post-processed through m ultiplanar reconstruction, allowing axial reconstructions to be obtained in the plane of each endplate. Axial rotation was measured, and an absolute v alue determined by reference to a neutrally-rotated vertebra. The proportio n of intravertebral and intervertebral deformity within each scoliotic curv e was subsequently determined. Overall change in observed axial rotation fr om end vertebra to apical vertebra ranged from:20 degrees to 34 degrees, wi th a mean of 28 degrees. The mean proportion of axial rotation within the o verall scoliotic curve occurring due to intravertebral basis was 34%, with a range of 9% - 76%. It was concluded that a significant but variable amoun t of the overall scoliotic deformity in patients with adolescent idiopathic scoliosis occurs as a result of intravertebral rotation, contributing over 45% of the total scoliotic axial rotation in half of the patients imaged. This study implies that assessment of axial rotation in the plane of indivi dual endplates with three-dimensional MRI may be a useful means for identif ying a subgroup of patients in whom derotational surgery is likely to be of limited benefit.