Study design: A prospective study using intraoperative stereophotogrammetry to analyze change during the correction of scoliosis.
Objective: To examine the relation between the number of hooks used during segmental instrumentation and the amount of correction achieved.
Summary of background data: An intraoperative stereophotogrammetric technique was developed at our center. Vertebral translations and rotations can be measured at several stages during scoliosis surgery.
Methods: Thirty-two patients with right thoracic adolescent idiopathic scoliosis were studied using our stereophotogrammetry technique during surgical correction. Correlations were determined between apical vertebral movements and the hook ratio (number of vertebrae/number of hooks used).
Results: Mean curve Cobb angle correction was 66%. Correction occurred in all three planes but primarily along the x and y axes. Scoliotic deformity was corrected by translation of the vertebra along the y axis and rotation about the x; physiologic kyphosis was restored by translation along the x axis and rotation about the y. The plane of maximum deformity as compared with the sagittal plane of the patient corrected from 57 degrees to 25 degrees as an indication of detorsion of the scoliotic deformity.
Conclusions: Increasing the number of hooks per vertebral segment significantly enhances the correction of the coronal scoliotic deformity and enhances the z axis derotation, but does not significantly change the reestablishment of the kyphosis, nor does it result in significant elongation of the spine.