Pedicle screw instrumentation in adolescent idiopathic scoliosis (AIS)

Abstract

Introduction: Pedicle screw instrumentation in AIS has advantages of rigid fixation, improved deformity correction and a shorter fusion, but needs an exacting technique.

Materials and methods: The author has been using the K-wire method with intraoperative single PA and lateral radiographs, because it is safe, accurate and fast. Pedicle screws are inserted in every segment on the correction side (thoracic concave) and every 2-3 on the supportive side (thoracic convex). After an over-bent rod is inserted on the corrective side, the rod is rotated 90° counterclockwise. This maneuver corrects the coronal and sagittal curves. Then the vertebra is derotated by direct vertebral rotation (DVR) correcting the rotational deformity. The direction of DVR should be opposite to that of the vertebral rotation. A rigid rod has to be used to prevent the rod from straightening out during the rod derotation and DVR. The ideal classification of AIS should address all curve patterns, predicts accurate fusion extent and have good inter/intraobserver reliability. The Suk classification matches the ideal classification is simple and memorable, and has only four structural curve patterns; single thoracic, double thoracic, double major and thoracolumbar/lumbar. Each curve has two types, A and B. When using pedicle screws in thoracic AIS, curves are usually fused from upper neutral to lower neutral vertebra. Identification of the end vertebra and the neutral vertebra is important in deciding the fusion levels and the direction of DVR. In lumbar AIS, fusion is performed from upper neutral vertebra to L3 or L4 depending on its curve types.

Conclusions: Rod derotation and DVR using pedicle screw instrumentation give true three dimensional deformity correction in the treatment of AIS. Suk classification with these methods predicts exact fusion extent and is easy to understand and remember.

Fig. 1

a Intraoperative PA and lateral radiographs after K-wires are inserted. b Magnified T8-10. Exact pedicle entry points are marked

Fig. 2

a A 15-year-old girl with a single thoracic AIS, type A, in which the NV is the same as the EV. The distal fusion level is T12 (NV) and the direction of the DVR of the distal NV is the opposite direction compared with the thoracic DVR. b The patient is treated with the rod derotation and DVR, and the postoperative radiographs show a well balanced spine

Fig. 3

a A 14-year-old girl with a single thoracic AIS, type B, in which the NV is located at the EV + 3. The distal fusion level is the NV-1 (L2) and the direction of the DVR of the two lowest instrumented vertebrae is the same direction compared with the thoracic DVR. b The patient is treated with the rod derotation and the DVR method

Fig. 4

a A 13-year-old girl with a double thoracic AIS. The distal fusion level is the NV, which is L1, and the direction of the DVR is the opposite direction compared to the thoracic DVR. b Both thoracic curves are fused with four rods, rod derotation and DVR. c The preoperative unequal shoulder height is well corrected postoperatively

Fig. 5

a A 13-year-old girl with a double major curve of AIS. The DVR direction of the lumbar curve is the opposite to the direction of the thoracic DVR. b Bending radiographs show that L3 is cross mid-sacral line and L3 rotation is less than grade 2 (type A). This is fused to the NV-1 (L3). c Both thoracic and lumbar curves are treated with two rods, the translation and DVR

Fig. 6

a A 17-year-old girl with a double major curve, type B. The DVR direction of the lumbar curve is the opposite to the direction of the thoracic DVR. b Bending radiographs show that L3 not cross mid sacral line and L3 rotation is more than grade II (type B), which is fused to the NV (L4). c The patient is treated with two rods, rod derotation and DVR

Fig. 7

a A 12-year-old girl with a thoracolumbar curve with fusion of the TL curve only. The direction of DVR is the same in both the thoracic and the lumbar curve. b Bending radiographs show L3 cross the mid-sacral line and L3 rotation is less than grade II (type A) on bending film. c The patient is fused to the NV-1 (L3) with rod derotation (S bended rod) and DVR

Fig. 8

a A 15-year-old girl with a thoracolumbar curve. b Bending radiographs show that L3 is not cross the mid-sacral line and L3 rotation is more than grade II (type B). c The patient is fused to the NV(L4) with rod derotation (S bent rod) and DVR

Fig. 9

Type A & B for the distal fusion levels. Thoracic curve type A; the neutral vertebra (NV) is located 1 level distal from the end vertebra (EV), fuse to the NV. Thoracic curve type B; the NV is located 3 levels distal from the EV, fuse to the NV-1. Lumbar curve type A; L3 cross the central sacral line and rotation is less than G2, fuse to the L3. Lumbar curve type B; L3 not cross central sacral line and rotation is more than G2, fuse to the L4