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

STUDY DESIGN: A comparative study of 2 cohort series of surgically treated patients with adolescent idiopathic scoliosis (AIS) who were retrospectively analyzed, with level III evidence.

OBJECTIVE: 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.

SUMMARY OF BACKGROUND DATA: 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.

METHODS: 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.

RESULTS: 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).

CONCLUSION: 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.