Effectiveness and Safety of Convex Derotation in Thoracic Adolescent Idiopathic Scoliosis

Abstract

Introduction Concave derotation is the traditional correction maneuver in adolescent idiopathic scoliosis surgery. However, the positioning of thoracic pedicle screws at the concave side of the curve can be quite challenging, because of the small pedicle size and the wide variation in its morphological characteristics, due to the vertebral dystrophy observed in scoliotic patients. Then, to reduce risks of neural damages and ensure the same strength of derotation maneuver, a convex derotation through an all-level pedicle screws convex instrumentation can be performed. We report perioperative and 1-year results in a consecutive series of patients treated by convex derotation through an all-level pedicle screws convex instrumentation. Materials and Methods From January 2013 to January 2014, we surgically treated 24 consecutive patients (18 female patients and 6 male patients, mean age 13 years) affected by thoracic adolescent idiopathic scoliosis (Lenke Type 1, 19 patients, and Lenke Type 2, 5 patients). Mean preoperative Cobb angle was 56 ± 6 degrees in Lenke Type 1 group and 51 ± 4 degrees plus 32 ± 3 degrees in Lenke Type 2 group. We performed a posterior access only in patients using polyaxial pedicle screws at each level on the convex side and two sublaminar acrylic loops (universal clamps) at the upper instrumented vertebra, to reduce the stiffness of the construct. Derotation maneuver was performed on the convex prebent rod. In all cases, motor-evoked potential monitoring was used. Mean follow-up time was 15 months. Results The average percentage of coronal correction was 76 ± 5% (mean postoperative Cobb angle 15 ± 4 degrees), with no neurological complications. Regarding the postoperative kyphosis, we observed a slight decrease in mean values compared with preoperative measurements (mean reduction of thoracic kyphosis 5 ± 2 degrees). At 1-year follow-up, no changes in coronal or sagittal plane were observed. The mean operative time was 210 ± 30 minutes, with a mean blood loss of approximately 500 ± 100 mL. Using the free-hand technique, the mean time of pedicle screws positioning in the thoracic area on the convex side was approximately 2 ± 1 minutes from T6 to T12 and approximately 4 ± 1 minutes from T3 to T5. Whenever included in the area of arthrodesis, T2 was usually instrumented with the universal clamps. Instead, T1 has never been included in the arthrodesis area. Conclusion This case-series study shows the effectiveness and safety of convex derotation in Lenke Type 1 and 2 scoliosis. The coronal correction obtained with this technique is comparable to that obtained with the traditional concave derotation. Other advantages are short operative time, low intraoperative blood loss, and, mostly, a reduced risk of neurological complications.