Apical instrumentation alters the rotational correction in adolescent idiopathic scoliosis

The aim of this study was to retrospectively evaluate the effect of apical vertebral instrumentation in the axial plane in the surgical treatment of idiopathic scoliosis. Seventy-six consecutive patients with King type II idiopathic scoliosis, treated with posterior spinal instrumentation, were included in the study. The mean age of the patients was 14.5 years (range 10-18 years), and the mean follow-up was 49 (range 28-74) months. Preoperative radiological evaluation was performed with postero-anterior, lateral, traction and side-bending radiographs. Vertebral rotation was measured with a Perdriolle torsion meter. Patients were retrospectively divided into two groups according to the presence of apical vertebra instrumentation. Group 1 consisted of 43 patients in whom the upper and lower neutral and intermediate vertebrae of thoracic curves had been instrumented on the concave side. Group 2 consisted of 33 patients who had received instrumentation of the apical vertebra on the concave side in addition to the instrumentation configuration of group 1. Posterior fusion was added in all patients. Cobb and Perdriolle measurements were compared between the two groups preoperatively and at the last follow-up. Preoperative age and gender distribution, Cobb angle and rotational measurements, and correction ratios on side-bending films were similar in the two groups. Although the differences between the two groups in preoperative mean values of both Cobb angle and apical rotation were not statistically significant (P>0.05), mean values of apical rotation were significantly different postoperatively (P<0.05). At the same time, apical derotation ratios differed significantly between the two groups (P=0.000). We conclude that instrumentation of the apical vertebra provides better derotation at the apex.