In-vivo demonstration of spontaneous apical vertebral derotation in thoracic adolescent idiopathic scoliosis

Abstract

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a three-dimensional coupling deformity. Various studies have reported vertebral rotational effects with different implant constructs and surgical techniques for AIS. However, none of them has considered the spontaneous coupling effect on vertebral de-rotation produced by correction of coronal deformity. METHOD: Twenty-five AIS patients with Lenke type 1 with Cobb angles greater than 45° who underwent posterior spinal fusion with instrumentation without direct apical de-rotation were prospectively assessed. Cobb angles (CA) and apical vertebral rotations (AVR) in standing, supine and fulcrum bending positions preoperatively, and in supine position postoperatively, were assessed on x-rays and CT scans. RESULTS: The study entailed 80% females and 20% males (mean age, 15.5 years). The mean preoperative CA (AVR) in standing, supine and fulcrum bending positions were 56 (24), 41 (18), and 20 (10) degrees, respectively. The differences were statistically significant (p<0.05). The mean postoperative CA (AVR) was 15 (8) degrees. The mean difference in AVR between fulcrum bending and post-operation was 2 degrees (p=0.06). The postoperative supine AVR was significantly positively correlated with postoperative CA (r=0.82), and negatively correlated with change in curve magnitude (r=-0.49), correction rate (r=-0.83) and fulcrum bending correction index (r=-0.45) (p<0.05). CONCLUSIONS: Spontaneous apical de-rotation occurred concomitantly with correction of the coronal deformity. The amount of spontaneous AVR correction can be predicted with fulcrum bending radiographs. Such spontaneous de-rotation should be considered when assessing the effects with different implants and surgical strategies.