Journal List > J Korean Soc Spine Surg > v.10(2) > 1035575

Lee, Suk, and Chung: Direct Vertebral Rotation (DVR): A New Technique of 3-D Deformity Correction with Segmental Pedicle Screw Fixation in Adolescent Idiopathic Scoliosis (AIS)

Abstract

Study Design

A prospective study.

Objectives

To introduce a new technique, direct vertebral rotation (DVR), and to compare the surgical results with those of a simple rod derotation (SRD).

Summary of Background Data

Pedicle screw fixation, with a simple rod derotation maneuver, enables powerful coronal and sagittal plane corrections in scoliosis surgery. However, the ability for rotational correction is still unclear.

Methods

Thirty- eight A IS patients, treated with segmental pedicle screw fixation, were analyzed. The first group (n=17) was treated by DVR, and the second (n=21) by SRD. Having similar preoperative curve patterns, both groups were evaluated for the deformity correction and spinal balance.

Results

In the DVR group, the average preoperative A VR of 16.7° was corrected to 9.6°, showing a 42.5% correction, while in the SRD group, the correction was negligible, from 16.1° to 15.7° (2.4%). In the DVR group, the preoperative thoracic curve of 55° was corrected to 12° (79.6%), and the lumbar curve from 39° to 7° (80.5%). In the SRD group, the preoperative thoracic curve of 53° was corrected to 17° (68.9%), and the lumbar curve from 39° to 16° (62.2%). The average LIVT correction was 80.6 and 66.3% in the DVR and SRD group, respectively. There were statistically significant differences in the coronal curve, LIVT and rotational correction (p<0.05, Mann- Whitney u test).

Conclusions

The segmental pedicle screw fixation with ‘ direct vertebral rotation’ showed better rotational and coronal corrections than the ‘ simple rod derotation’.

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Fig. 1.
A. Two forces induced by the rod derotation. First, the vector of ‘ rod derotation’ is directed posteriorly and medially. Second, the rod also rotated about 90 degrees on its own axis during the rod derotation. This may affect the vertebral rotation in scoliosis B. a) In the severe or rigid scoliosis, there are high amounts of frictions between the pedicle screws and the rod. The vertebral rotation will be aggravated during the rod derotation because the direction of vertebral rotation will be same to the direction of the rod rotational axis. b) In the very flexible, mild curves, the screw would glide on the rod. Rod derotation might have some effect on the vertebral rotation, depending on the angle between pedicle screws and vector of the rod derotation. C. Diagram of direct vertebral rotation (DVR). During or after rod derotation (a-c), rotate the screw derotators to the opposite direction (d-f).
jkss-10-180f1.tif
Fig. 2.
A. Simple rod derotation. Derotate the pre-contoured rod on the correction sides (counter-clockwise rotation). B. DVR. Insert the screw derotators onto the pedicle screws both in concave and convex sides. Rotate the screw derotators to the opposite direction (clockwise rotation of the rod derotation. C. Model picture of DVR.
jkss-10-180f2.tif
Fig. 3.
A, B. A 14.6 year-old AIS girl with 96° of right thoracic and 54° of left lumbar curves. C, D. The patient was operated by DVR and selective thoracic fusion without anterior release. Two years follow up standing radiographs show that the thoracic curve was corrected to 23°and the lumbar curve was spontaneously corrected to 4° with balanced spine. The rotation of lumbar curve was also improved postoperatively (arrows). E, F. Preoperative and postoperative medical photos.
jkss-10-180f3.tif
Fig. 4.
A, B. Preoperative apical vertebral rotation of 19.6°(RAsac.) was improved to 10.4°, showing 46.9% correction by DVR. C, D. In the surgical field, the angle between the vertical line and nut driver that was fixed onto the apical screw was 34° after simple rod derotation. It was significantly decreased (25°) after DVR. The right thoracic hump also decreased after DVR (arrow). E. The screw length checked by intraoperative antero-posterior radiographs was 22mm after simple rod derotation. It was decreased (18mm) after DVR, which means the apical vertebral rotation was improved. F. Preoperative narrow disc spaces on the concave side of the curvature were spontaneously widened after DVR without any distraction or compression.
jkss-10-180f4.tif
Table 1.
The results of surgical correction.
  Group I (n=17) Group II (n=21) p value
Thoracic Curves      
  Preoperative 55± 15° 53± 11° >0.05
  Postoperative∗ 12± 5° 17± 8° 0.001
  Correction 79.6% 68.9%  
Lumbar Curves      
  Preoperative 39± 12° 39± 14° >0.05
  Postoperative∗ 7± 4° 16± 9° 0.001
  Correction 80.5% 62.2%  
Thoracic Kyphosis      
  Preoperative 16± 3° 18± 3° >0.05
  Postoperative 23± 4° 23± 3° >0.05
LIVT        
  Preoperative 24± 8° 23± 7° >0.05
  Postoperative∗ 4± 3° 7± 5° 0.025
  Correction 80.6% 66.3%  
AVR        
  Preoperative 16.7± 5.7° 16.1± 6.1° >0.05
  Postoperative∗ 9.6± 5.6° 15.7± 6.2° 0.000
  Correction 42.5% 2.4%  
Decompensation      
  Preoperative 4 / 17 5 / 21  
  Postoperative 2 / 17 2 / 21  

AVR:apical vertebral rotation.

LIVT:lower instrumented vertebral tilt

∗ Significant difference in Mann-Whitney u test

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