The predictive value of the fulcrum bending radiograph in spontaneous apical vertebral de-rotation in adolescent idiopathic scoliosis

Abstract

SUMMARY: Apical vertebral rotation (AVR) and Cobb angles (CA) were measured in patients suffered from thoracic adolescent idiopathic scoliosis before and after posterior spinal fusion and instrumentation without direct apical de-rotation maneuver. Spontaneous apical vertebral de-rotation occurred with correction of scoliosis deformity. The difference in AVR between fulcrum bending radiograph (FBR) and postoperative assessment was statistically insignificant. This amount of spontaneous apical de-rotation can be predicted with FBR and should be considered when assessing the de-rotational effects with different surgical strategies. 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 have considered the spontaneous coupling effect on vertebral de-rotation produced by correction of coronal deformity, in particular utilizing the predictive capacity of the preoperative fulcrum bending radiograph (FBR). METHODS: Twenty-five Lenke type 1 AIS patients 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 FBR 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 CT-based AVR values on preoperative supine, FBR, and postoperative supine were 17.7, 9.8, and 8.1 degrees. The mean AVR degree difference on CT between preoperative FBR and postoperative supine assessment was 1.7 degrees (p=0.056). The preoperative FBR approximated a mean 82.7% of postoperative apical vertebral de-rotation. Preoperative supine CT-based AVR was positively correlated with FBR (r=0.55; p=0.011). 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). CONCLUSION: The amount of spontaneous apical vertebral de-rotation in AIS patients can be predicted with FBR. Such spontaneous de-rotation should be considered when assessing the effects with different implants and surgical strategies. Significance: Most of the apical vertebral rotation in AIS can be corrected spontaneously with correction of scoliosis deformity. The amount of spontaneous apical de-rotation can be predicted with fulcrum bending radiograph and should be considered when assessing de-rotational effects with different surgical techniques.