JBJS | Adolescent Idiopathic Scoliosis. Correction of Vertebral Rotation with Use of Wisconsin Segmental Spinal Instrumentation*

The Journal of Bone & Joint Surgery, Volume 78, Issue 11

Articles | November 01, 1996

Adolescent Idiopathic Scoliosis. Correction of Vertebral Rotation with Use of Wisconsin Segmental Spinal Instrumentation*

J. G. JARVIS, M.D., F.R.C.S.(C)†; R. N. GREENE, M.D.†OTTAWA, ONTARIO, CANADA

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Investigation performed at the University of Ottawa, Children's Hospital of Eastern Ontario, Ottawa

The Journal of Bone & Joint Surgery. 1996; 78:1707-12

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Abstract

We retrospectively reviewed the results of use of Wisconsin segmental spinal instrumentation in twenty-four patients who had adolescent idiopathic scoliosis. Our purpose was to determine whether there had been any correction of the rotational component. The mean age at the time of the operation was thirteen years and eight months (range, eleven to seventeen years). Computerized tomography was used to measure the degree of vertebral rotation relative to the midline of the body and relative to the mid-sagittal plane in thirty curves that had been treated with instrumentation and in fifteen that had not. According to the criteria of King et al., five patients had a type-I curve; fourteen, a type-II curve; four, a type-III curve; and one, a type-V curve.The mean correction in the coronal plane was 23 degrees (43 per cent; range, 20 to 69 per cent) for the curves that had been treated with instrumentation and 15 degrees (35 per cent; range, 11 to 77 per cent) for those that had not. The mean derotation of the apical vertebra, in relation to the midline of the body, in twenty-two curves that had been treated with instrumentation and that had had a mean initial rotation of 26 degrees (range, 8 to 53 degrees) was 6 degrees (range, 1 to 29 degrees). For seven curves, with a mean initial rotation of 25 degrees (range, 21 to 35 degrees), rotation increased a mean of 3 degrees (range, 1 to 7 degrees) after instrumentation. The rotation of the apical vertebra did not change in one curve treated with instrumentation. Derotation was seen in twelve of the fifteen curves that had not been treated with instrumentation.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

The treatment of scoliosis has been directed toward stabilizing or reducing the lateral curve. Adams⁴, in 1865, noted that scoliosis was a combination of lordosis and rotation; today, it is considered a three-dimensional deformity^13-15,30,39. Operative correction and stabilization of the lateral curve has been accomplished with a variety of spinal instrumentation systems; however, correction of vertebral rotation received little attention until the introduction of Cotrel-Dubousset instrumentation in the mid-1980's^8,11,36,37.

Wisconsin segmental spinal instrumentation¹⁷ is a hybrid system comprising Harrington distraction rods, Luque rods, and button-wire constructs. The wires are passed through the spinous processes to encircle the rods and, when tightened, pull the spine to the midline. The technique is simple, relatively easy, of short duration, and less expensive than many of the currently available systems²⁰. Since 1985, we have used this instrumentation in the treatment of idiopathic scoliosis at our tertiary-care medical center.

We performed this study to determine whether use of the Wisconsin segmental spinal instrumentation system can decrease vertebral rotation in patients who have scoliosis.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Division of Orthopaedic Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario KIH 8L1, Canada. Please address requests for reprints to Dr. Jarvis.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Division of Orthopaedic Surgery, University of Ottawa, Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario KIH 8L1, Canada. Please address requests for reprints to Dr. Jarvis.

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Figs. 1-A and 1-B: Computerized tomographic images showing the points used to measure vertebral rotation. Fig. 1-A: Vertebral rotation relative to the midline (RAml).

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Vertebral rotation relative to the mid-sagittal plane (RAsag).

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Figs. 2-A through 2-D: Graphs of preoperative and postoperative rotation, showing four patterns of changes that can occur in curves treated with and without instrumentation. The levels treated with instrumentation lie between the dark horizontal lines. Fig. 2-A: Graph of a type-II curve²³, showing an increase in rotation of the apical vertebra in the curve treated with instrumentation and a decrease in the compensatory curve.

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Graph of a type-III curve²³, showing no change in either the curve treated with instrumentation or the compensatory curve.

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Graph of a type-III curve²³, showing no change in either the curve treated with instrumentation or the compensatory curve.

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Graph of a type-I curve²³, showing a change in vertebral rotation at the level of the Harrington hook.

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TABLE I VERTEBRAL ROTATION

*The values are given as the mean, with the range in parentheses.†In one curve, the rotation of the apical vertebra did not change.

	In Relation to Midline				In Relation to Mid-Sagittal Plane
	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*
		(Degrees)	(Degrees)	(Degrees)		(Degrees)	(Degrees)	(Degrees)
All curves
With instrumentation	30†				30†
With derotation	22	26 (8—53)	6 (1—29)	—	17	16 (8—24)	6 (1—19)	—
With increased rotation	7	25 (21—35)	—	3 (1—7)	12	15 (19—24)	—	5 (1—15)
Without instrumentation	15				15†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	3	12 (14—18)	—	4 (1—8)	5	10 (6—13)	—	3 (1—7)
Type-II curves²³
With instrumentation	14†				14
With derotation	10	30 (16—53)	7 (1—29)	—	7	16 (10—24)	8 (4—19)	—
With increased rotation	3	23 (21—26)	—	3 (1—5)	7	15 (19—22)	—	6 (1—15)
Without instrumentation	14				14†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	2	11 (4—18)	—	1 (1—2)	4	10 (6—13)	—	2 (1—4)

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TABLE I VERTEBRAL ROTATION

*The values are given as the mean, with the range in parentheses.†In one curve, the rotation of the apical vertebra did not change.

	In Relation to Midline				In Relation to Mid-Sagittal Plane
	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*
		(Degrees)	(Degrees)	(Degrees)		(Degrees)	(Degrees)	(Degrees)
All curves
With instrumentation	30†				30†
With derotation	22	26 (8—53)	6 (1—29)	—	17	16 (8—24)	6 (1—19)	—
With increased rotation	7	25 (21—35)	—	3 (1—7)	12	15 (19—24)	—	5 (1—15)
Without instrumentation	15				15†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	3	12 (14—18)	—	4 (1—8)	5	10 (6—13)	—	3 (1—7)
Type-II curves²³
With instrumentation	14†				14
With derotation	10	30 (16—53)	7 (1—29)	—	7	16 (10—24)	8 (4—19)	—
With increased rotation	3	23 (21—26)	—	3 (1—5)	7	15 (19—22)	—	6 (1—15)
Without instrumentation	14				14†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	2	11 (4—18)	—	1 (1—2)	4	10 (6—13)	—	2 (1—4)

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Between 1988 and 1994, twenty-four patients who had adolescent idiopathic scoliosis had a posterior spinal arthrodesis with use of Wisconsin segmental spinal instrumentation. The vertebrae included in the arthrodesis were selected according to the criteria of King et al.²³. Preoperative anteroposterior and lateral radiographs, made with the patient standing, and side-bending radiographs, made with the patient supine, were measured with use of the Cobb method. The degree of correction in the coronal plane was measured on the first available anteroposterior radiograph made with the patient standing, after removal of the cast.

Transaxial computerized tomographic images were made, preoperatively and one week postoperatively, through the apex, top, and bottom of each structural and compensatory curve, with use of the method of Aaro and Dahlborn^1,3. A single cut through the pelvis was made to serve as a baseline. Vertebral rotation was measured relative to two parameters: the midline of the body (RAml, Fig. 1-A) and the mid-sagittal plane (RAsag, Fig. 1-B).

Results

Introduction | Materials and Methods | Results | Discussion | References

There were twenty-four patients (twenty-one girls and three boys). The mean age at the time of the operation was thirteen years and eight months (range, eleven to seventeen years). Five patients had a type-I curve, according to the criteria of King et al.²³, fourteen had a type-II curve, four had a type-III curve, and one had a type-V curve. Preoperatively, the curves that were treated with instrumentation averaged 55 degrees (range, 36 to 90 degrees) and the compensatory lumbar curves, 44 degrees (range, 24 to 72 degrees). Postoperatively, the mean correction in the coronal plane was 23 degrees (43 per cent; range, 20 to 69 per cent) for the curves that were treated with instrumentation and 15 degrees (35 per cent; range, 11 to 77 per cent) for the lumbar curves that were not treated with instrumentation.

Curves Treated with Instrumentation

Rotation of a vertebra toward a neutral position is medial derotation. Rotation away from neutral, which increases rotation, is lateral rotation. In twenty-two of the thirty curves, the apical vertebra was medially derotated a mean of 6 degrees (range, 1 to 29 degrees) in relation to the midline of the body. There was a mean of 3 degrees (range, 1 to 7 degrees) of increased rotation of the apical vertebra in seven curves. There was no change in rotation relative to the midline of the body in one curve. The degree of derotation relative to the mid-sagittal plane was 6 degrees (range, 1 to 19 degrees) in seventeen curves, and twelve curves had a mean increase in rotation of 5 degrees (range, 1 to 15 degrees). There was no change relative to the mid-sagittal plane in one curve (Table I).

Patients who had a type-II curve had a greater degree of derotation than those who had the other types of curves, regardless of the method of measurement. The mean derotation in relation to the midline in ten of the fourteen type-II curves, which had had a mean initial rotation of 30 degrees (range, 16 to 53 degrees), was 7 degrees (range, 1 to 29 degrees) (Table I), compared with 5 degrees (range, 1 to 10 degrees) for the other types of curves, which had had a mean initial rotation of 23 degrees (range, 8 to 32 degrees).

Curves Not Treated with Instrumentation (Compensatory Curves)

The mean medial derotation of the apical vertebra in relation to the midline of the body was 8 degrees (range, 2 to 20 degrees) in twelve of the fifteen curves. Twelve of the fourteen type-II curves were derotated in relation to the midline (mean, 8 degrees; range, 2 to 20 degrees) and nine were derotated in relation to the sagittal plane (mean, 5 degrees; range, 1 to 10 degrees) (Table I).

Patterns of Vertebral Rotation

Analysis of vertebral rotation relative to the mid-sagittal plane, according to vertebral level, showed four typical patterns: a decrease in rotation of the apical vertebra of the curve treated with instrumentation toward neutral and no change in the compensatory curve (Fig. 2-A), an increase in rotation of the apical vertebra of the curve treated with instrumentation and a decrease in rotation of the compensatory curve (Fig. 2-B), no change in either curve (Fig. 2-C), and a change in vertebral rotation at the level of the Harrington hook (Fig. 2-D).

Discussion

Introduction | Materials and Methods | Results | Discussion | References

Stokes et al.^38,39 showed that maximum axial rotation occurred either at the apex of the curve or at the two adjacent vertebrae. Several methods have been used to quantify vertebral rotation. With the Cobb method¹⁰, the image of the spinous process is evaluated in relation to the vertebral body. With the method of Nash and Moe²⁶, the image of the pedicle is evaluated in relation to the vertebral body. Perdriolle and Vidal^27-30 devised a template to measure vertebral rotation by assessing the position of the pedicle. Several other methods have been developed^9,16,39, but they have been shown to be inaccurate for the measurement of severe curves and to be difficult to use after spinal instrumentation, which obscures osseous landmarks on radiographs^5,7,21,32,33. Suzuki et al.⁴⁰ used ultrasound to measure axial rotation of the spine and found a close relationship to the Cobb angle in untreated patients but not in those who were managed with a brace. Ultrasound has not been widely used to measure vertebral rotation. Computerized tomography has been recognized as the most accurate method of determining vertebral rotation⁴³, and several methods of assessment have been developed^21,22,24,43. The most widely accepted method, devised by Aaro and Dahlborn^1,3, involves the use of transaxial tomographic slices and was employed in the current study.

Several different instrumentation systems have been used in attempts to correct the rotational component of scoliosis^{6,11,12,18,19,22,25,34,36,37,42}. The results of Harrington-rod instrumentation with regard to correction of rotation have been reported, but many of these studies involved the use of plain radiographs³¹ and were done before the advent of computerized tomography⁶. Aaro and Dahlborn² evaluated thirty-three patients who had been managed with Harrington instrumentation and found that the mean angle of rotation relative to the mid-sagittal plane had decreased a mean (and standard deviation) of 1.8 ± 7.1 degrees; they concluded that Harrington instrumentation did not derotate the spine. Marchesi et al.²⁵ used computerized tomography to assess vertebral rotation in four patients who had been managed with Harrington instrumentation and in seven who had been managed with Luque instrumentation; the mean derotation of the apical vertebra was 16 and 12 per cent, respectively. In three patients who had combined Harrington and Luque sublaminar instrumentation, the mean apical derotation was 13 per cent. These authors²⁵ reported that the most derotation occurred at the end vertebrae and outside of the levels that had been treated with instrumentation, indicating that derotation of the spinal segments treated with instrumentation induced changes in the segments that had not been so treated.

Several authors, using different radiographic measurements, reported that Cotrel-Dubousset instrumentation derotated the axial deformity from 9 to 40 per cent (in 250¹¹, thirty-four¹², thirty¹⁸, thirty¹⁹, twenty-four²², thirty-three³⁴, seventy^36,37, and ten⁴² patients). Shufflebarger³⁵ thought that attempts should be made to decrease vertebral rotation and noted the wide variation in the degree of derotation obtained with Cotrel-Dubousset instrumentation. Shufflebarger et al.^36,37 used computerized tomography to measure rotation in relation to the mid-sagittal plane in seventy patients, and they reported vertebral derotation of 37 to 39 per cent for the thoracic apical vertebrae and 22 per cent for the lumbar apical vertebrae as measured with the method of Perdriolle. Ecker et al.¹⁹, using the same method, found an improvement of only 14 per cent, with increased rotation in twelve of thirty-six thoracic curves. Transfeldt et al.⁴¹ studied the effect of Cotrel-Dubousset instrumentation on vertebral rotation within and three segments beyond the levels that were treated with instrumentation in fifteen patients; they reported some degree of apical vertebral derotation in thirteen. However, there were numerous changes, including various amounts of en bloc rotation of entire spinal segments and intersegmental rotation or uncoupling, particularly at the cervicothoracic and thoracolumbar junctions. The small number of patients in that series precludes any conclusions.

Wood et al.⁴², using the method of Aaro and Dahlborn, found that Cotrel-Dubousset instrumentation did not consistently or predictably derotate the apical segments of the thoracic spine relative to the pelvis. All four type-II curves in their series derotated, a mean of 26 per cent (range, 2 to 50 per cent); however, four of the six type-III curves had a mean increase in rotation of 10 per cent (range, 3 to 20 per cent). Wood et al. noted more segmental rotation beyond the levels of instrumentation and thought that type-II curves may be better suited to absorb the transmitted rotational force and preserve a balanced spine. They also postulated that type-III curves, with more rigid segments, were resistant to derotation and that, although excellent correction was obtained in the coronal plane with use of Cotrel-Dubousset instrumentation, this was simply because of rotation of the entire trunk about the axial plane and not because of derotation of the vertebrae. We found that type-II curves had a greater degree of derotation than other curves.

Cundy et al.¹² also used the method of Aaro and Dahlborn to study the effects of Cotrel-Dubousset instrumentation on rotation, in thirty-four patients. They found a mean derotation of 24 per cent in relation to the midline. They attributed better results in relation to the midline to the fact that this measurement reflects not only the degree of vertebral rotation but also the degree of displacement of the vertebrae toward the midline. We also found a greater degree of correction in relation to the midline. Transfeldt et al.⁴¹ believed that this change in vertebral rotation is related to uncoupling of the vertebra (or intersegmental rotation) and not to en bloc rotation.

Our findings are consistent with those of Transfeldt et al.⁴¹, who reported derotation of most compensatory curves. Transfeldt et al. believed that derotation of the vertebrae not included in the instrumentation may be a factor in decompensation after Cotrel-Dubousset instrumentation. We are unable to comment on intersegmental rotation or uncoupling as, in order to minimize the dose of radiation, we did not make computerized tomographic images at all thoracic and lumbar levels. We are also unable to comment on the rotational effects at the level of the Harrington hooks until more patients have been enrolled in the study.

All of our patients had improvement in the coronal plane. Derotation was most pronounced in type-II curves. The magnitude of rotational correction was equal to or better than that reported in association with other instrumentation systems^{2,6,11,12,18,19,22,25,31,34,36,37,42}.

References

Introduction | Materials and Methods | Results | Discussion | References

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Drummond, D.; Guadagni, J.; Keene, J. S.; Breed, A.; and |and |Narechania, R.: Interspinous process segmental spinal instrumentation. J. Pediat. Orthop.,4: 397-404, 1984.4397 1984 [CrossRef]

Dubousset, J.; Graf, H.; Miladi, L.; and |and |Cotrel, Y.: Spinal and thoracic derotation with CD instrumentation. Orthop. Trans.,10: 36, 1986.1036 1986

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Herndon, W. A.; Sullivan, J. A.; Gruel, C. R.; and |and |Yngve, D. A.: A comparison of Wisconsin instrumentation and Cotrel-Dubousset instrumentation. J. Pediat. Orthop.,13: 615-621, 1993.13615 1993

Ho, E. K.; Upadhyay, S. S.; Ferris, L.; Chan, F. L.; Bacon-Shone, J.; Hsu, L. C.; and |and |Leong, J. C.: A comparative study of computed tomographic and plain radiographic methods to measure vertebral rotation in adolescent idiopathic scoliosis. Spine,17: 771-774, 1992.17771 1992 [PubMed][CrossRef]

Hopf, C., and |and |Schaub, T.: Eine computertomographische Analyse zur Wirbelrotation vor und nach der operativen Korrektur der idiopathischen Skoliose. ROFO: Fortschr. Geb. Röntgen,151: 408-413, 1989.151408 1989 [CrossRef]

King, H. A.; Moe, J. H.; Bradford, D. S.; and |and |Winter, R. B.: The selection of fusion levels in thoracic idiopathic scoliosis. J. Bone and Joint Surg.,65-A: 1302-1313, Dec. 1983.65-A1302 1983

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Marchesi, D. G.; Transfeldt, E. E.; Bradford, D. S.; and |and |Heithoff, K. B.: Changes in vertebral rotation after Harrington and Luque instrumentation for idiopathic scoliosis. Spine,17: 775-780, 1992.17775 1992 [PubMed][CrossRef]

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Scheid, D. K.; Akbarnia, B. A.; Merenda, J. T.; and |and |Graviss, E. R.: Radiographic evaluation of idiopathic scoliosis correction using Cotrel-Dubousset instrumentation. Orthop. Trans.,13: 243, 1989.13243 1989

Shufflebarger, H.: Cotrel-Dubousset instrumentation. In The Pediatric Spine: Principles and Practice, p. 1564. Edited by S. L. Weinstein. New York, Raven Press, 1994.

Shufflebarger, H. L., and |and |Clark, C.: Cotrel-Dubousset instrumentation in adolescent idiopathic scoliosis. Orthop. Trans.,11: 97, 1987.1197 1987

Shufflebarger, H. L.; Ellis, R. D.; and |and |Clark, C. E.: Cotrel-Dubousset instrumentation (CDI) in adolescent idiopathic scoliosis: minimum 2 year follow-up. Orthop. Trans.,13: 79-80, 1989.1379 1989

Stokes, I. A. F.: Axial rotation component of thoracic scoliosis. J. Orthop. Res.,7: 702-708, 1989.7702 1989 [PubMed][CrossRef]

Stokes, I. A.; Bigalow, L. C.; and |and |Moreland, M. S.: Measurement of axial rotation of vertebrae in scoliosis. Spine,11: 213-218, 1986.11213 1986 [PubMed][CrossRef]

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Wood, K. B.; Transfeldt, E. E.; Ogilvie, J. W.; Schendel, M. J.; and |and |Bradford, D. S.: Rotational changes of the vertebral-pelvic axis following Cotrel-Dubousset instrumentation. Spine,16(8S): 404-S408, 1991.16(8S)404 1991

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Figs. 1-A and 1-B: Computerized tomographic images showing the points used to measure vertebral rotation. Fig. 1-A: Vertebral rotation relative to the midline (RAml).

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Vertebral rotation relative to the mid-sagittal plane (RAsag).

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Graph of a type-III curve²³, showing no change in either the curve treated with instrumentation or the compensatory curve.

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Graph of a type-III curve²³, showing no change in either the curve treated with instrumentation or the compensatory curve.

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Graph of a type-I curve²³, showing a change in vertebral rotation at the level of the Harrington hook.

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TABLE I VERTEBRAL ROTATION

*The values are given as the mean, with the range in parentheses.†In one curve, the rotation of the apical vertebra did not change.

	In Relation to Midline				In Relation to Mid-Sagittal Plane
	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*
		(Degrees)	(Degrees)	(Degrees)		(Degrees)	(Degrees)	(Degrees)
All curves
With instrumentation	30†				30†
With derotation	22	26 (8—53)	6 (1—29)	—	17	16 (8—24)	6 (1—19)	—
With increased rotation	7	25 (21—35)	—	3 (1—7)	12	15 (19—24)	—	5 (1—15)
Without instrumentation	15				15†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	3	12 (14—18)	—	4 (1—8)	5	10 (6—13)	—	3 (1—7)
Type-II curves²³
With instrumentation	14†				14
With derotation	10	30 (16—53)	7 (1—29)	—	7	16 (10—24)	8 (4—19)	—
With increased rotation	3	23 (21—26)	—	3 (1—5)	7	15 (19—22)	—	6 (1—15)
Without instrumentation	14				14†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	2	11 (4—18)	—	1 (1—2)	4	10 (6—13)	—	2 (1—4)

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TABLE I VERTEBRAL ROTATION

*The values are given as the mean, with the range in parentheses.†In one curve, the rotation of the apical vertebra did not change.

	In Relation to Midline				In Relation to Mid-Sagittal Plane
	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*	No. of Curves	Initial Rotation*	Derotation*	Increased Rotation*
		(Degrees)	(Degrees)	(Degrees)		(Degrees)	(Degrees)	(Degrees)
All curves
With instrumentation	30†				30†
With derotation	22	26 (8—53)	6 (1—29)	—	17	16 (8—24)	6 (1—19)	—
With increased rotation	7	25 (21—35)	—	3 (1—7)	12	15 (19—24)	—	5 (1—15)
Without instrumentation	15				15†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	3	12 (14—18)	—	4 (1—8)	5	10 (6—13)	—	3 (1—7)
Type-II curves²³
With instrumentation	14†				14
With derotation	10	30 (16—53)	7 (1—29)	—	7	16 (10—24)	8 (4—19)	—
With increased rotation	3	23 (21—26)	—	3 (1—5)	7	15 (19—22)	—	6 (1—15)
Without instrumentation	14				14†
With derotation	12	17 (6—29)	8 (2—20)	—	9	14 (3—23)	5 (1—10)	—
With increased rotation	2	11 (4—18)	—	1 (1—2)	4	10 (6—13)	—	2 (1—4)