J Korean Soc Spine Surg.  2005 Dec;12(4):275-280.

The Comparison of Rigid and Semi-rigid Rod for the Correctability of the Thoracic Hypokyphosis of the Idiopathic Scoliosis

• Park WW
• Ahn SJ
• Park JH

Abstract

STUDY DESIGN: The analysis was based on the sagittal and coronal correction of 64 cases of thoracic hyphokyphosis that were due to idiopathic scoliosis. PURPOSE: We wanted to compare the three pedicle screws and rod systems (using either a semirigid and rigid rod) from the view points of the coronal and sagittal plane correction during the surgical treatment of idiopathic scoliosis. SUMMARY OF LITERATURE REVIEW: There haven't been any reports that have compared the differences and their significance between the semirigid and rigid rod systems for correcting the thoracic hypokyphosis of idiopathic scoliosis.
MATERIALS AND METHODS
After a minimum follow-up of 1 year, the results of the frontal and sagittal correction of each study group were compared. There were a total of 52 females and 12 males. The mean age at the time of surgical intervention was 16.4 (age range: 12~24). CD instrumentation with a rigid stainless steel rod (7 mm in diameter and 1200 N/mm for its stiffness) was used in group I (36 patients), and 4-CI instrumentation with a titanium alloy rod (6.35 mm in diameter and 1200 N/mm for its stiffness) was used in group II (18 patients). Xia instrumentation with a semi-rigid rod (6 mm in diameter and 600 N/mm for its stiffness) was used in group III (10 patients). For all patients undergoing the segmental pedicle screw fixation procedure, pedicle screws were inserted into every vertebra on the concave side, in the end of each vertebra and then alternately in every other vertebra on the convex side. We measured the preoperative and postoperative magnitude of the major and compensatory curves, the thoracic kyphotic angle on the standing radiographs and the flexibility of the curve. We statistically compared the correctability of thoracic kyphotic angle between the rigid and semi-rigid rods.
RESULTS
The differences of preoperative and postoperative major curves in groups I, II and III were 47.3 degrees/12.7 degrees, 51.6 degrees/12.3 degrees and 49.6 degrees/13.3 degrees respectively. The thoracic kyphotic angle was 22.6 degrees/26.6 degrees, 22.0 degrees/26.9 degrees and 23.8 degrees/22.8 degrees, respectively. There was no significant difference for the correction of the coronal angle in each group, but groups I and II were superior to group III for the rate of correcting the kyphotic angle.
CONCLUSION
The rod should be stiff enough to pull the spine posteromedially when using the derotation technique for the surgical treatment of idiopathic scoliosis.

Keyword

Idiopathic scoliosis; Thoracic hypokyphosis; Semirigid and rigid rod; Pedicle screw fixation

MeSH Terms

Alloys
Female
Follow-Up Studies
Humans
Male
Pliability
Scoliosis*
Spine
Stainless Steel
Titanium
Alloys
Stainless Steel
Titanium

Figure

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  Fig. 1. (A) In group I (CD instrumentation), Preoperative major thoracic curve was 59° and kyphotic angle was 8°. (B) In the fifth postoperative year, Major curve was corrected to 21° and thoracic kyphosis was improved from 8° to 19°.

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  Fig. 2. (A) In group II(4-CIS instrumentation), Double thoracic curve was 37° & 50°, thoracic kyphosis was 33°. (B) In the second postoperative year, major curve was corrected to 20°, 18° and thoracic kyphosis was improved from 33° to 36°.

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  Fig. 3. (A) In group III (XIA instrumentation), Preoperative major thoracic curve was 65° and kyphotic angle was 18°. (B) In the second postoperative year, major curve was corrected to 17° but thoracic kyphosis worsened from 18° to 16°.

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