Cervical and thoracic sagittal misalignment after surgery for adolescent idiopathic scoliosis: a comparative study of all pedicle screws versus hybrid instrumentation.

Abstract

A comparative study of 2 cohort series of surgically treated patients with adolescent idiopathic scoliosis (AIS) who were retrospectively analyzed, with level III evidence. To compare the effect on the cervical sagittal balance of 2 AIS correction constructs, namely, all pedicle screws and hybrid instrumentation using hooks and pedicle screws. An inverse relationship between cervical and thoracic kyphosis in AIS has been found in pediatric patients after concave derotation using hybrid constructs with pedicle screws and hooks. Two series of 25 nonconsecutive patients with Lenke type-I AIS who underwent spinal fusion were retrospectively reviewed. In 1 series, the patients were treated with all thoracic pedicle screw constructs. In the other series, the correction was achieved by using hybrid constructs. Preoperative and 2-year follow-up radiographical examinations were evaluated, measuring the following parameters: C2-C7 sagittal angle, displacement of C2-C7 plumb line, T1 sagittal tilt, T1-T5 and T5-T12 sagittal profile, and C7-S1 global sagittal balance. In both groups, there was a lordotic effect on the T5-T12 kyphosis after surgery, with an average loss of 6.1° for hybrid and 7.7° for pedicle screws. When the postoperative data were compared, the intergroup differences were found only in the sagittal C2-C7 Cobb angle, showing a mean kyphotic trend (-5.2°) in the pedicle screws group compared with a mean lordotic trend (1.8°) in the hybrid group (P < 0.05). In both techniques, the patients with upper-instrumented vertebra at T4 or below showed a lordotic effect that was more evident in the hybrid constructs (+9.4° ± 11.3 vs. +0.3° ± 11.4). In those with the upper-instrumented vertebra at T3 or higher levels, both techniques had a kyphotic effect that was more severe in the patients of the pedicle screws group (-7.0° ± 12.6 vs. -2.8° ± 10.5). Independent of the surgical technique used, the cervical spine had a tendency to decompensate and acquire a kyphotic sagittal profile. Constructs based on all pedicle screws have a stronger hypokyphotic effect on the thoracic spine, with a predisposition to greater decompensation of the cervical spine. Kyphotic changes in the C2-C7 sagittal alignment induced by scoliosis correction are correlated with the level of the upper-instrumented vertebra.