[Introduction]
Adolescent idiopathic scoliosis (AIS) Lenke type 5 has been reported to have a problem of wedging of the caudal end of the lower instrumented vertebrae after posterior corrective surgery, and one of the risk factors is L4 end vertebra. The purpose of this study was to compare the lumbar curves of AIS Lenke types 1 and 5 using three-dimensional polygonal models and to characterize the type 5 lumbar curve in three dimensions.
[Methods]
The participants were 30 AIS patients operated on at our hospital, divided into three groups: group A (six patients with Lenke classification type 1A), group BC (12 patients with types 1B and C), and group 5C (12 patients with type 5). Cobb angle of TL/L, L4 tilt angle, and L3/4 and 4/5 intervertebral angles were measured on simple standing whole spine posterior-anterior radiographs and compared among the three groups. 3-dimensional polygonal models of each lumbar vertebra (L1~5) were created from the preoperative CT images. The translation and rotation angles of each vertebral body in the anterior, sagittal, and vertical axes were measured based on the center of gravity of each vertebra and compared among the three groups.
[Results]
The mean Cobb angle of TL/L was 30 degrees in group A, 42 degrees in group BC, and 49 degrees in group 5C; the L4 tilt angle was 2.8 degrees in group A, 15.1 degrees in group BC, and 22.3 degrees in group 5C; the L3/4 intervertebral angle was 3.9 degrees in group A, 3.7 degrees in group BC, and 5.4 degrees in group 5C; the L4/5 intervertebral angle was 1.1 degrees in group A, 4 degrees in group BC, and 8.7 degrees in group 5C. In the 3-dimensional evaluation, compared to group A, group BC had left lateral axial rotation at L3/4 and lateral shift to the left at L3/4 and 4/5. Group 5C had axial rotation and lateral shift to the left at L1/2 and 2/3 and lateral bending to the left at L3/4 and 4/5, in addition to changes in group BC.
[Discussion]
Compared to the Lenke type 1 lumbar spine, the type 5 lumbar spine had more lateral flexion deformity in the lower lumbar spine from the Cobb angle, the L4 tilt angle, and the L4/5 intervertebral angle on simple radiographs. It also had more axial rotation and lateral deviation in the upper lumbar spine, as well as more lateral flexion deformity in the lower lumbar spine. We considered that these are the morphological characteristics of the type 5 lumbar spine and that not only the lateral flexion deformity of the lower lumbar spine but also the rotation angle and amount of lateral deviation of the upper lumbar spine may be factors that determine the Lenke type 5 TL/L curve and may serve as indicators for predicting curve progression and understanding pathophysiology.