Vertebral derotation in adolescent idiopathic scoliosis causes hypokyphosis of the thoracic spine.
BACKGROUND
The purpose of this study was to test the hypothesis that direct vertebral derotation by pedicle screws (PS) causes hypokyphosis of the thoracic spine in adolescent idiopathic scoliosis (AIS) patients, using computer simulation.


METHODS
Twenty AIS patients with Lenke type 1 or 2 who underwent posterior correction surgeries using PS were included in this study. Simulated corrections of each patient's scoliosis, as determined by the preoperative CT scan data, were performed on segmented 3D models of the whole spine. Two types of simulated extreme correction were performed: 1) complete coronal correction only (C method) and 2) complete coronal correction with complete derotation of vertebral bodies (C + D method). The kyphosis angle (T5-T12) and vertebral rotation angle at the apex were measured before and after the simulated corrections.


RESULTS
The mean kyphosis angle after the C + D method was significantly smaller than that after the C method (2.7 ± 10.0° vs. 15.0 ± 7.1°, p < 0.01). The mean preoperative apical rotation angle of 15.2 ± 5.5° was completely corrected after the C + D method (0°) and was unchanged after the C method (17.6 ± 4.2°).


CONCLUSIONS
In the 3D simulation study, kyphosis was reduced after complete correction of the coronal and rotational deformity, but it was maintained after the coronal-only correction. These results proved the hypothesis that the vertebral derotation obtained by PS causes hypokyphosis of the thoracic spine.
Department of Advanced Therapy for Spine and Spinal Cord Disorders, KeioUniversity, Tokyo, Japan.
Kota
K
Watanabe
Takayuki
T
Nakamura
Akio
A
Iwanami
Naobumi
N
Hosogane
Takashi
T
Tsuji
Ken
K
Ishii
Masaya
M
Nakamura
Yoshiaki
Y
Toyama
Kazuhiro
K
Chiba
Morio
M
Matsumoto
D000293:Adolescent; D001863:Bone Screws / Q000009:adverse effects*; D002648:Child; D003198:Computer Simulation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007738:Kyphosis / Q000209:etiology*; D011183:Postoperative Complications; D012399:Rotation; D012600:Scoliosis / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation; D013904:Thoracic Vertebrae / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D014057:Tomography, X-Ray Computed; D014102:Torsion Abnormality; D054159:Torsion, Mechanical; D055815:Young Adult