The Convex Manipulation: An Alternative Technique in Surgical Treatment of 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 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 strenght of derotation maneuver, a convex manipulation through an all-level pedicle screws convex instrumentation can be performed. We report perioperative and 2-year results in a consecutive series of patients treated by convex manipulation through an all-level pedicle screws convex instrumentation. Material and Methods From January 2013 to January 2015 we surgical treated 36 consecutive patients (28 F, 8 M, mean age 13 years) affected by thoracic adolescent idiopathic scoliosis (Lenke type 1, 27 patients, and Lenke type 2, 9 patients). Mean pre-operative Cobb angle was 56°±6° in Lenke type 1 group and 51°±4° plus 32°±3° in Lenke type 2 group. We performed a posterior access only in all patients using polyaxial pedicle screws at each level on the convex side of the curve. Derotation and manipulation maneuvers were performed on the convex prebent rod. In all cases motor-evoked potentials monitoring was used. Mean follow-up time was 27 months. Results The average percentage of coronal correction was 76 ± 5% (mean post-operative Cobb angle 15°±4°), with no neurological complications. Concerning the post-operative kyphosis, we observed a slight decrease of mean values compared with pre-operative measurements (mean reduction of thoracic kyphosis 5°±2°). At 2-year follow-up no changes in coronal nor in sagittal plane were observed. The mean operative time was 210 ± 30 minutes, with a mean blood loss of 500 ± 100 ml. Using the free-hand technique, the mean time of pedicle screws positioning in the thoracic area on the convex side was 2 ± 1 minutes from T6 to T12, and 4 ± 1 minutes from T3 to T5. Whenever included in the area of arthrodesis, T2 was usually instrumented with the Universal Clamps, to reduce the stiffness of the construct. Instead, T1 has never been included in the arthrodesis area. Conclusion This case-series study shows the effectiveness and the safety of convex manipulation in Lenke type 1 and type 2 scoliosis. The coronal correction obtained with this technique is comparable to that obtained with the traditional concave derotation. Other advantages are the short operative time, the low intra-operative blood loss and, mostly, a lower risk of neurological complications.