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`Source : Spine journal
`
`Volume: 29
`
`Issue:
`
`Date: 2004
`
`~:343-349
`
`Author: Lee et al
`
`Title : Direct Vertebral Rotation: A New Technique of Three-Dimensional Deformity Correction With Segmental Pedicle Screw Fixation in
`Adolescent Idiopathic Scoliosis
`
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`

`SPINE Volume 29, Number 3, pp 343-349
`@2004, Lippincott Williams & Wllkins, Inc.
`
`II Direct Vertebral Rotation: A New Technique of
`Three-Dimensional Deformity Correction With
`Segmental Pedicle Screw Fixation in Adolescent
`Idiopathic Scoliosis
`
`Sang-Min Lee, MD. PhD. Se-ll Suk. MD, PhD, and Ewy-Ryong Chung. MD. PhD
`
`Study Design. A prospective study.
`Objeetives. To introduce a new technique, direct ver(cid:173)
`tebral rotation, and to compare the surgical results of
`direct vertebral rotation with those of simple rod
`derotation.
`Summary of Background Data. Pedicle screw fixation
`with a simple rod derotation maneuver enables a power(cid:173)
`ful coronal and sagittal plane correction in scoliosis sur(cid:173)
`gery. However, the ability of achieving rotational correc(cid:173)
`tion is still unclear.
`Methods. Thirty-eight adolescent idiopathic scoliosis
`patients treated with segmental pedicle screw fixation
`were analyzed. The first group (n = 17) was treated by
`direct vertebral rotation; the second group (n = 21) was
`treated by simple rod derotation. All patients had a min(cid:173)
`imum follow-up of 2 years. Having similar preoperative
`curve patterns, both groups were evaluated for the defor(cid:173)
`mity correction, lower instrumented vertebral tilt, and spi(cid:173)
`nal balance. Apical vertebral rotation was evaluated by
`computed tomography scans. Surgical techniques of di(cid:173)
`rect vertebral rotation were as follows: a precontoured
`rod was inserted into segmental screws on the concave
`side in thoracic scoliosis; a simple rod derotation was
`performed; and then the screws on the juxta-apical ver(cid:173)
`tebrae, both on concave and convex sides, were rotated
`opposite direction to the rod derotation. Then, all the
`screws were sequentially tightened.
`Results. In the direct vertebral rotation group, the av(cid:173)
`erage preoperative apical vertebral rotation of 16.7° was
`corrected to 9.6°, showing 42.5% correction, whereas in
`the simple rod derotation group, the correction was neg(cid:173)
`ligible from 16.1 o to 15.7° (2.4%). In the direct vertebral
`rotation group, the average preoperative thoracic curve of
`55° was corrected to 12° (79.6%), and the lumbar curve of
`39° was corrected to 7° (80.5%). In the simple rod derota(cid:173)
`tion group, the preoperative thoracic curve of 53• was
`corrected to 17° (68.9%), and the lumbar curve of 39° was
`corrected to 16° (62.2%). The average lower instrumented
`vertebral tilt correction was 80.6% and 66.3% in the di(cid:173)
`rectvertebral rotation and the simple rod derotation
`group, respectively. There were statistically significant
`
`From the Seoul Spine Institute, Inje University, Sanggye Paik Hospital,
`Seoul, Korea.
`Acknowledgment date: October 15, 2002. First revision date: February
`3, 2003. Second revision date: May 9, 2003. Acceptance date: August
`18,2003.
`The manuscript submitted does not contain information about medical
`device(s)/drug(s).
`No funds were received in support of this work. No benefits in any
`form have been or will be received from a commercial party related
`directly or indirectly to the subject of this manuscript.
`Address correspondence and reprint requests to Sang-Min Lee, MD,
`and, PhD, Seoul Spine Institute, Inje University Sanggye Paik Hospital,
`761-1 Sanggye Dong, Nowon-Ku, Seoul 139-707, Korea; E-mail:
`snoopy5@unitel.co.kr
`
`differences in the coronal curve, lower instrumented verte(cid:173)
`bral tilt, and rotational correction (P < 0.05, Mann-Whitney
`U test). Thoracic kyphosis was improved in both groups.
`Conclusions. Segmental pedicle screw fixation with
`"direct vertebral rotation" showed better rotational and
`coronal correction than "simple rod de rotation." [Key
`words: idiopathic scoliosis, pedicle screw fixation, rota(cid:173)
`tional correction, direct vertebral rotation] Spine 2004;29:
`343-349
`
`Idiopathic scoliosis is a three-dimensional deformity.
`The spine deviates laterally in the coronal plane and an(cid:173)
`teriorly with thoracic hypokyphosis in the sagittal plane.
`It also rotates in the transverse plane by intravertebral
`and intervertebral rotation.
`The ideal correction system should provide rigid fix(cid:173)
`ation and should get maximal correction with minimal
`fusion levels. Moreover, it should correct all three di(cid:173)
`mensions of the scoliotic deformity. Using the hooks in
`the upper and lower stable vertebra, Harrington instru(cid:173)
`mentation applied distraction and/or compression forces
`for the correction and fixation of the curve. For many
`years, it was used throughout the world as a treatment of
`choice in scoliosis correction and fusion. Actually, Har(cid:173)
`rington instrumentation with compression-distraction
`did make some coronal correction, but there was a major
`complication in the sagittal plane, such as flat back de(cid:173)
`formity. Other significant complications included loss of
`curve correction, long fusion levels and pseudarthroses.
`Harrington instrumentation is no longer the gold stan(cid:173)
`dard for treating scoliosis surgery. Since the advent of
`Harrington instrumentation, several new instrumenta(cid:173)
`tion systems and corrective methods have been devel(cid:173)
`oped with a goal of three-dimensional correction. In the
`early 1980s, Cotrel-Dubousset instrumentation with rod
`derotation was introduced to enable a three-dimensional
`correction in scoliosis surgery. Early papers of Cotrel(cid:173)
`Dubousset upholders reported that the derotation ma(cid:173)
`4
`neuver could induce a three-dimensional correction.1
`-
`However, recent reports question the rotational correc(cid:173)
`tion even though they generally find the corrections are
`satisfactory in both coronal and sagittal planes.5- 14 The
`authors have used segmental pedicle screw fixation and
`the derotation maneuver in most scoliosis surgeries for a
`decade. As a result of our many experiences, we were
`convinced that the rod derotation had a powerful pos(cid:173)
`teromedialization effect on the curve, but doubtful about
`the rotational correction. In 1999, we described a new
`
`343
`
`

`

`344 Spine • Volume 29 • Number 3 • 2004
`
`method, "direct vertebral rotation," which was designed
`to enable satisfactory rotational correction, especially in(cid:173)
`tervertebral rotational correction during idiopathic sco(cid:173)
`liosis surgery.
`
`Principle of Direct Vertebral Rotation
`There are two forces induced by the rod derotation. First,
`the vector of "rod derotation" is directed posteriorly and
`medially. This force corrects both coronal and sagittal
`plane deformities, but not that in the transverse plane.
`Second, the rod also rotated about 90° on its own axis
`during the rod derotation. This may affect the vertebral
`rotation in scoliosis.
`In the severe or rigid scoliosis cases, for example, there
`is great amount of friction between the rod and the pedi(cid:173)
`cle screws during the rod derotation. In those cases, the
`rotational force of the rod would increase the rotational
`deformity. If there is no friction between the rod and
`screws, the screws will glide on the rod. In this situation,
`the rotational deformity may be corrected depending on
`the angle between the pedicle screws and the vector of the
`rod derotation. This might be similar to rod derotation in
`very flexible, mild curves (Figure 1A). Clinically, the ef(cid:173)
`fect of the rod derotation on the rotational correction is
`negligible because there always exists some amount of
`friction between the screws and the rod during the rod
`derotation,
`The concept of direct vertebral rotation (DVR) is sim(cid:173)
`ple: correction of vertebral rotation by application of a
`posterior force in the direction opposite to that of the
`deformity. The pedicle screw enters the pedicle posteri(cid:173)
`orly and traverses to the anterior vertebral body. This
`makes it possible to transmit the rotational force to the
`entire vertebral body and thus to correct the rotational
`deformity. Other posterior instrumentations such as
`hooks or wire systems cannot deliver a sufficient torque
`anteriorly to enable the vertebral rotation because the
`axis of fixation is posterior to that of vertebral rotation.
`The torque is applied to the pedicle screw using long
`screw derotators on both concave and convex sides of
`the curve. Direct vertebral rotation corrects the interver(cid:173)
`tebral rotation, which means it enables a three(cid:173)
`dimensional correction in scoliosis surgery. The direc(cid:173)
`tion of DVR is opposite to that of the vertebral rotation.
`In the right thoracic curve, apical and juxta-apical verte(cid:173)
`brae are rotated clockwise in the transverse plane. The
`direction of DVR must be opposite to the rotational de(cid:173)
`formity, i.e., counter-clockwise rotation in the transverse
`plane. On the lowermost one or two screws, however,
`the direction of DVR depends on the rotation of vertebra
`in the compensatory lumbar curve. We address this more
`in the discussion. Compression or distraction should not
`be performed, because there are no distractive or com(cid:173)
`pressive forces acting on the vertebra in scoliosis. Com(cid:173)
`pressive or distractive forces applied to improve correc(cid:173)
`tion may increase the risk of iatrogenic complications;
`such as postoperative decompensation or flat back
`deformity.
`
`a) severe, rigid scoliosis
`
`b) mild, flexible scoliosis
`
`vertebral rotation
`
`vertebral rotation
`
`Direction of vertebral rotation =
`Direction of rod rotational axis
`
`Gliding between screw and rod
`
`a
`
`d
`
`e
`
`Figure 1. A. Diagram of the apical vertebral rotation during the rod
`derotation in the transverse plane: black long arrow = direction of
`rod derotation, black short arrows = direction of vertebral rota(cid:173)
`tion, and hollow arrows = direction of pedicle screw inserted onto
`the apical vertebra. a, In the severe or rigid scoliosis, the vertebral
`rotation will be aggravated during the rod de rotation because high
`amounts of friction occurred between the pedicle screws and the
`rod. b, In the very flexible, mild curves, the screw will glide on the
`rod. The vertebral rotation depends on the angle between pedicle
`screws and vector of the rod derotation. B, Diagram of DVR in the
`transverse plane. a, Insert the screws on the correction sides. b
`and c, Derotate the rod (counter-clockwise rotation). d, Insert the
`screw derotators onto the pedicle screws. e and f, Rotate the
`screw derotators opposite direction (clockwise rotation) to the rod
`derotation.
`
`• Materials and Methods
`
`Seventeen adolescent idiopathic scoliosis (AIS) patients under(cid:173)
`went DVR with pedicle screw fixation (DVR group) from 1999
`to 2000. They were compared with 21 AIS patients having
`similar preoperative curve patterns and magnitudes treated
`with simple rod derotation (SRD group). Using the King clas(cid:173)
`sification, the DVR group had 3 patients in Type I; 7 in Type II;
`4 in Type III; 1 in Type IV; and 2 in Type V. The SRD Group
`had 5 patients in Type I; 8 in Type II; 7 in Type III; and 1 in
`Type IV. Patients treated by combined anterior release and
`posterior procedures were excluded. Thoracolumbar or lum(cid:173)
`bar scoliosis patients treated with either SRD or anterior sur(cid:173)
`geries were also excluded. There were no exclusionary criteria
`forDVR.
`
`

`

`In the DVR group, male to female ratio was 1 to 16, with an
`average age at surgery of 14.7 years (range 12.2-19.1).1n the
`SRD group, male to female ratio was 1 to 20, and the age was
`14.6 years (range 11.1-17.3). The patients had a minimum
`follow-up of 2 years. Evaluation parameters were: coronal and
`sagittal Cobb angle, lower instrumented vertebral tilt (UVf)
`by standing radiographs, apical rotational correction, and lo(cid:173)
`cation of the plumb line. The apical vertebral rotational cor(cid:173)
`rection (rotational angle to sacrum, RAsac) was evaluated by
`computed tomography (CT) scans. When the plumb line from
`first thoracic vertebra deviated more than 2 em from the center
`of sacrum, it was considered decompensation.
`In the DVR group, the average preoperative thoracic curve
`was 55 ± 15° (range 40-96°), lumbar curve was 39 ± 12°
`(range 22-62°), and uvr was 24 ± 8° (range 13-42°).1n the
`SRD group, the average preoperative thoracic curve was 53 ±
`11° (range 40-78°), lumbar curve was 39 ± 14° (range 18-
`680), and the average LIVT was 23 ± 7° (range 12-40°), The
`average preoperative apical vertebral rotation checked by CT
`scans (RAsac) was 16.7 ± 5.7° in the DVR group and 16.1 ±
`6.1 o in the SRD group. Preoperative thoracic kyphosis (T5-
`T12) was 16 ± 3° and 18 ± 3° in the DVR group and the SRD
`group, respectively.
`In the statistical analysis using the Mann-Whitney U test,
`there were no statistical differences in the preoperative thoracic
`and lumbar Cobb angle, thoracic kyphosis, LIVT, and apical
`vertebral rotation between the two groups (all P > 0.05).
`
`Surgical Procedure. Fusion was carried out from upper neu(cid:173)
`tral to distal neutral vertebra with a few exceptions. There was
`no difference in the determination of fusion level between the
`DVR and SRD group. Rigid rods (Cotrel-Dubousset 7.0 mm,
`stainless) were used to minimize rod deformation for the defor(cid:173)
`mity correction.
`Surgical procedures of DVR were as follows (Figure 1B):
`1. Insert the pedicle screws at each segment on the correc(cid:173)
`tion sides (thoracic concave) and every second or third on the
`support sides (thoracic convex) of the curves.
`2. Rotate the precontoured rod on the correction sides
`(counter-clockwise) without any compression or distraction
`(SRD).
`3. Insert the screw derotators (4-8 derotators) onto the
`pedicle screws of the juxta-apical vertebrae both on the con(cid:173)
`cave and convex sides.
`4. During or after the rod derotation, rotate the screw der(cid:173)
`otators to the opposite direction (clockwise) of rod derotation
`(Figure 2C).
`5. Rotate the lowermost pedicle screw(s) depending on the
`unfused lumbar curve (details in discussion).
`6. After locking the concave rod in the corrected position, a
`rod contoured to the corrected curve is placed on the convex
`side and is locked in situ.
`7. The two rods are then connected by two cross-links. Fol(cid:173)
`lowing instrumentation, posterior fusion with autogenous
`bone and allograft is performed.
`
`Three-Dimensional Deformity Correction in AIS • Lee et al 345
`
`after the operation and was 12 ± 5° at the last follow-up,
`showing 79.6% of curve correction. In the SRD group,
`the average preoperative curve of 53 ± 11° was corrected
`to 16 ± go just after the operation and was 17 ± go at the
`last follow-up, showing 6g,9% of curve correction.
`There was a statistically significant difference in thoracic
`curve correction between the two groups (P = 0.001,
`Mann-Whitney U test).
`In the DVR group, the average thoracic curve correc(cid:173)
`tion was g3.0% in King Type I, 80.6% in Type II, 77.7%
`in Type III, 76.7% in Type N, and 75.9% in Type V. In
`the SRD group, the average thoracic correction was
`66.g% in King Type I, 64.1% in Type II, 74.2% in Type
`III, and 80.4% in Type N. The patients' numbers in each
`type were too small for statistical analysis.
`2) Lumbar curve correction.
`In the DVR group, the average preoperative lumbar
`curve of 39 ± 12° was corrected to 7 ± 4° at the last
`follow-up, showing 80.5% of curve correction. In the
`SRD group, the average preoperative curve of 39 ± 14°
`was corrected to 16 ± 9° at the last follow-up, showing
`62.2% of curve correction. There was a statistically sig(cid:173)
`nificant difference in lumbar curve correction between
`the two groups (P = 0.001, Mann-Whitney U test).
`Excluding the King Type I curve, the patients sub(cid:173)
`jected to the selective thoracic fusion were analyzed for
`the spontaneous lumbar curve correction. In the DVR
`group, the average preoperative lumbar curve of 36 ±
`10° was spontaneously corrected to 9 ± 5° just after the
`operation and was 7 ± 5° at the last follow-up, showing
`78.8% of curve correction. In the SRD group, the aver(cid:173)
`age preoperative curve of 33 ± 10° was corrected to
`13 ± go just after the operation and was 14 ± 9° at the
`last follow-up, showing 61.g% of curve correction.
`There was a statistically significant difference in the
`spontaneous lumbar curve correction between the two
`groups (P = 0.001, Mann-Whitney U test).
`
`2. Sagittal Colt'ection in Thoracic Curve
`The average thoracic sagittal correction was kyphosis of
`7° in the DVR group and kyphosis of 5° in the SRD
`group, without a statistically significant difference (P >
`0.05, Mann-Whitney U test).
`
`3. Lower Instrumented Vertebral Tilt Correction
`The average LIVT correction was 80.6% in the DVR
`group and 66.3% in the SRD group, respectively. There
`was a statistically significant difference between the two
`groups (P = 0.025, Mann-Whitney U test).
`
`• Results
`The results of surgical correction are shown in Table 1.
`1. Coronal Curve Correction
`1) Thoracic curve correction.
`In the DVR group, the average preoperative thoracic
`curve of 55 ± 15° (SD) was corrected to 11 ± 6° just
`
`4. Apical Vertebral Rotation Correction
`The average rotational correction of the apical vertebral
`was 42.5% in the DVR group and 2.4% in the SRD
`group, with a statistically significant difference (P <
`0.001, Mann-Whitney U test). In the SRD group, post(cid:173)
`operative A VR had no significant difference from the
`preoperative A VR (P > 0.05, Mann-Whitney U test).
`
`

`

`346 Spine • Volume 29 • Number 3 • 2004
`
`Rgure 2. A and B, A 14.6-year-old girl with AIS with 96° of right thoracic and 54° of left lumbar curves. C, The patient was treated by DVR
`and selective thoracic fusion without anterior release (view from the caudal). 0, The apical vertebral angle was checked 34° after simple
`rod derotation. It was decreased to 25° after DVR. The thoracic hump also decreased after DVR (arrow). E and F, Two years' follow-up
`radiographs show that the thoracic curve was corrected to 23° and the lumbar curve was spontaneously corrected to 4° with balanced
`spine. The lumbar rotation was also improved after surgery (arrows). G and H, Preoperative thoracic apical vertebral rotation of 19.6° was
`improved to 10.4°, showing 46.9% of rotational correction by DVR. I, Preoperative and postoperative medical photos.
`
`5. Spinal Balance
`Spinal balance was improved after surgery in both
`groups. Improved thoracic curve correction did not
`cause the postoperative decompensation in the DVR
`group (Figure 2).
`
`6. Complication
`There was one case of a hemothorax that required a chest
`tube insertion in the SRD group. In this patient, the rib
`periosteum was lacerated during the thoracoplasty pro(cid:173)
`cedure. The chest tube was removed 5 days after the
`
`

`

`Table 1. The Results of Surgical Correction
`
`Group I (n = 17)
`
`Group II (n = 21)
`
`PValue
`
`55± 15°
`12± 5°
`79.6%
`
`39 ± 12°
`7 ± 4°
`80.5%
`
`16±3°
`23 ± 4°
`
`24 ± 8°
`4 ± 30
`80.6%
`
`16.7 ± 5.7°
`9.6 ± 5.6°
`42.5%
`
`Thoracic curves
`Preoperative
`Postoperative*
`Correction
`lumbar curves
`Preoperative
`Postoperative*
`Correction
`Thoracic kyphosis
`Praoperativa
`Postoperative
`LIVT
`Preoperative
`Postoperative*
`Correction
`AVR
`Preoperative
`Postoperative*
`Correction
`Decompensation
`4/17 (23.5%)
`Preoperative
`2/17 (11.8%)
`Postoperative
`* Significant difference in Mann-Whitney U test.
`LIVT = lower instrumented vertebral tilt; AVA = apical vertebral rotation.
`
`>0.05
`0.001
`
`>0.05
`0.001
`
`>0.05
`>0.05
`
`>0.05
`0.025
`
`>0.05
`<0.001
`
`53± 11°
`17 ± 8°
`68.9%
`
`39 ± 14°
`16 ±go
`62.2%
`
`18 ± 3°
`23±3°
`
`23± 7°
`7 ±5°
`66.3%
`
`16.1 ± 6.1°
`15.7 ± 6.2°
`2.4%
`
`5/21 (23.8%)
`2/21 (9.5%)
`
`operation without any other problems. There were no
`major (vascular or neurologic) complications related to
`pedicle screw fixation. There was no pedicle breakage or
`screw pullout during the SRD or DVR procedures. At the
`final follow-up, all patients demonstrated solid fusion.
`
`• Discussion
`
`Idiopathic scoliosis is a complex three-dimensional de(cid:173)
`formity, in the coronal, sagittal and transverse planes.6
`Rod derotation has been known to have a three(cid:173)
`dimensional deformity correction in idiopathic scoliosis
`4
`surgery.1
`15 The powerful posteromedialization effect
`-
`•
`of the rod derotation is generally accepted in these days.
`However, its reports on the rotational correction are
`variable. Pollock and Pollock, Jr, 12 described that 30° of
`the rotational correction could be achieved using Cotrel(cid:173)
`Dubousset hooks, and Krismer et af16 reported a little
`correction could be achieved without significant differ(cid:173)
`ences. Lenke et al17 showed 11 o of rotational improve(cid:173)
`ment, but later Bridwell et af18 said that only a limited
`amount of rotational correction could be achieved. Using
`an FEM model, Gardner-Morse and Stokes6 reported
`that go of vertebral rotation were aggravated after the
`rod derotation.
`Vertebral rotation in scoliosis can be evaluated by
`simple radiographs19 or by CT scans.5
`16 Our former
`•
`study4 of rod derotation checked by simple radiographs
`seemed to show a significant rotational correction; how(cid:173)
`ever, a recent study using CT scans (RAsac)20 showed
`little rotational correction in scoliosis surgery. There
`were several other reports that rod derotation had little
`12
`effect on rotational correction.10
`16 They claimed that
`-
`•
`posterior instrumentation with hook system could not
`generate a sufficient torque for the vertebral rotation be-
`
`Three-Dimensional Deformity Correction in AIS • Lee et al 347
`
`cause the axis of hook fixation was posterior to that of
`vertebral rotation.
`Compared to hooks, treatment by pedicle screw fixa(cid:173)
`tion offers an enhanced three-dimensional deformity cor(cid:173)
`rection and preservation of motion segments by reducing
`fusion extents. Despite the advantages of pedicle screws
`over other spinal implants, many spine surgeons hesitate
`to use them in the treatment of spinal diseases for fear of
`causing neurologic injuries, especially in the thoracic
`spine surgery. These complications can be avoided by
`adherence to sound pedicle insertion techniques and
`careful confirmation of the pilot hole before insertion of
`the pedicle screws. Using pedicle screws, the selection of
`fusion levels was usually from upper neutral vertebra to
`lower neutral vertebra. In single thoracic curves that
`have more than two levels' discrepancy between the
`lower end vertebra and neutral vertebra, the distal fusion
`level can be performed one level proximal to the neutral
`vertebra without causing trunk decompensation after
`surgery. In lumbar or double major scoliosis, the distal
`fusion level is usually reduced to the lower end vertebra.
`However, it is generally accepted that posterior instru(cid:173)
`mentation and correction methods are to be less effective
`in the rotational correction than anterior systems.
`In early 1999, the authors described DVR that was
`designed to improve rotational correction in idiopathic
`scoliosis. The authors planned to compare the surgical
`results with SRD. The first author operated five consec(cid:173)
`utive cases of DVR, and the second author operated all
`the SRD cases until mid 2000. Then, the authors were
`convinced that DVR did correct rotational deformity.
`Since then, nearly all patients with AIS have been treated
`by the DVR.
`Direct vertebral rotation is accomplished using pedi(cid:173)
`cle screw fixation, because it is the only instrumentation
`system that effectively uses the pedicle and vertebral
`body as anchors for fixation. In this procedure, a rota(cid:173)
`tional force is transmitted through the pedicle screws
`from the posterior pedicle to the anterior vertebral body.
`The transverse rotation can be easily corrected using
`long lever-arm screw derotators fixed to both concave
`and convex sides. This will distribute the rotational
`torque among several pedicles to help prevent pedicle
`breakage. There is little chance of canal intrusion due to
`pedicle breakage during DVR when the screws are in(cid:173)
`serted correctly because the medial wall of pedicle is
`three times stronger than the lateral wall.
`The direction of DVR on the juxta-apical vertebrae is
`opposite to the rotation of the vertebrae in the transverse
`plane. During or after the rod is derotated 90° counter(cid:173)
`clockwise, DVR on the juxta-apical screws should be
`rotated clockwise. On the lowermost one or two screws,
`there are two options depending on the distal uninstru(cid:173)
`mented lumbar curve. These screws have an important
`role in regulating the compensatory lumbar curve. When
`the preoperative compensatory lumbar curve crosses the
`center sacral vertical line with a significant rotation (for
`example, King Type II or Lenke Type IC), the two low-
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`348 Spine • Volume 29 • Number 3 • 2004
`
`ermost screws should he rotated opposite to the direction
`of the thoracic DVR, that is, the direction of lessening
`lumbar rotation. One reason for this is that the remnant
`thoracic rotational deformity inhibits the ultimate rota(cid:173)
`tional correction in the lumbar curve, even though a sig(cid:173)
`nificant amount of lumbar rotation is spontaneously cor(cid:173)
`rected. In this situation, the lumbar rotation is improved
`by rotating the lowermost screws to the opposite direc(cid:173)
`tion of thoracic DVR. Second, when the preoperative
`curve is a single thoracic scoliosis of hanging curve (for
`example, King Type III, Type N; Lenke Type lA, IB),
`there is no need to perform DVR on the lowermost
`screws because lumbar rotation is spontaneously cor(cid:173)
`rected during the thoracic DVR.
`In our study, the evidences of the rotational correction
`could be detected in various ways. The average thoracic
`A VR correction using the CT scans (RAsac) was 42.5%.
`In the surgical field, the angle between the vertical line
`and nut driver that was fixed onto the apical screw was
`decreased after DVR (Figure 2D). Also, the screw length
`checked by intraoperative anteroposterior radiographs
`was also decreased after DVR. All the above indicate that
`the rotational deformity was improved, which means,
`DVR enables three-dimensional correction in scoliosis
`surgery.
`At first, it was thought that the method would only
`give better rotational correction than simple rod derota(cid:173)
`tion. However, it was apparent that the coronal correc(cid:173)
`tion was more improved both in the instrumented tho(cid:173)
`racic and the uninstrumented lumbar curve than when
`simple rod derotation was employed. It was an unex(cid:173)
`pected benefit of DVR. As was mentioned previously, the
`rotational deformity in the simple rod derotation case
`was not corrected and prevented a part of the ultimate
`coronal and sagittal curve correction. Exaggerated coro(cid:173)
`nal correction in the thoracic curve has a high risk of
`postoperative decompensation, because the unfused
`lumbar curvature with retaining rotational deformity
`cannot reciprocally follow the proximal curve correc(cid:173)
`tion. However, the retaining rotational deformity to pre(cid:173)
`venting lumbar curvature improvement is appeased by
`DVR.
`In our study, the average thoracic Cobb angle was
`improved more in the DVR group (79.6% of curve cor(cid:173)
`rection) than in SRD group (68.9% of curve correction),
`a statistically significant difference. The lumbar coronal
`curve also showed far better correction in the DVR
`group (80.5%) than in the SRD group (62.2%). The
`lumbar curve progressed a little after surgery in the SRD
`group because a significant lumbar rotation remained.
`On the other hand, follow-up radiographs showed lum(cid:173)
`bar curve improvement in the DVR group. Contrary to
`an abrupt correction in the thoracic fused segments, the
`unfused compensatory lumbar curve was improved little
`by little as the rotational remnants decreased. This sug(cid:173)
`gests that the rotational correction in the thoracic curve
`spontaneously unwinds the rotation in lumbar curve.
`Therefore, DVR enables better thoracic and lumbar
`
`curve correction than simple rod derotation with re(cid:173)
`duced problems of trunk decompensation after surgery.
`Though DVR has a great effect on the rotational cor(cid:173)
`rection, we recommend further study to achieve im(cid:173)
`proved rotational correction and to determine the exact
`fusion levels. There still remains a significant interverte(cid:173)
`bral (about 50%) and intravertebral rotational defor(cid:173)
`mity that cannot he corrected by surgery. Besides these,
`the rotational correction in one vertebral segment is
`small because of the strong bonds of ligaments and disc.
`The correction is smaller if the curve is rigid. Despite
`these limitations, it is the authors' opinion that DVR is
`the best posterior procedure to correct the three(cid:173)
`dimensional deformity in the idiopathic scoliosis.
`The authors also checked the correction of the lower
`instrumented vertebral tilt (LIVT). This could be another
`index for a feasible estimation of early degenerative
`change in lumbar curve. In the DVR group, LIVT
`showed far better correction than in the SRD group,
`which means there is less chance of degenerative change
`in the unfused lumbar curve. In our series, two patients
`were decompensated after surgery in the DVR group.
`Both patients were improved in spinal balance compared
`to the preoperative state, but they were considered de(cid:173)
`compensated after surgery as their plumb line deviated
`more than 2 em from center sacral vertical line.
`In conclusion, simple rod derotation has significant
`coronal and sagittal correction with posteromedializa(cid:173)
`tion of curve, but with little effect on rotational correc(cid:173)
`tion. Direct vertebral rotation (DVR) is a new and effec(cid:173)
`tive method that gives a true three-dimensional
`deformity correction in idiopathic scoliosis surgery,
`making better coronal and rotational correction than the
`simple rod derotation.
`
`• Key Points
`
`• Thirty-eight patients with AIS treated with seg(cid:173)
`mental pedicle screw fixation were prospectively
`analyzed for the rotational correction of scoliosis
`according to the correction mechanism; the first
`group (n = 17) treated by direct vertebral rotation
`and the second group (n = 21) treated by the sim(cid:173)
`ple rod derotation.
`• The average thoracic AVR correction was
`42.5% in the DVR group and 2.4% in the SRD
`group. There was a statistically significant differ(cid:173)
`ence between the two groups (P < 0.001, Mann(cid:173)
`Whitney U test). In the SRD group, postoperative
`A VR had no significant difference from the preop(cid:173)
`erative A VR.
`• The DVR group also showed better coronal curve
`and UVT correction than the SRD group.
`
`References
`1. Cotrel Y, Dubousset J, Guillaumat M. New universal instrumentation in
`spinal surgery. Clin Orthop 1988;227:10-23.
`
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`Three-Dimensional Deformity Correction in AIS • Lee et al 349
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`2. Muschik M, Schlenzka D, Robinson PN, et al. Dorsal instrumentation fw:
`idiopathic adolescent thoracic scoliosis: rod rotation versus translation. Eur
`Spine] 1999;8:93-9.
`3. Suk Sl, Lee CK, Chung SS. Comparison of Zielke ventral dcrotation system
`and Cotrcl-Dubousset instrumentation in the treatment of idiopathic lumbar
`and thoracolumbar scoliosis. Spine 1.9.