Cotrel-Dubousset instrumentation and vertebral rotation in adolescent idiopathic scoliosis

We have studied 34 consecutive patients receiving Cotrel- Dubousset instrumentation for a single and flexible thoracic scoliotic curve, evaluating the rib hump deformity from a single CT scan through the apical vertebra of the curve. Using two measures of rotation we found a mean improvement of 25% in the rotation of the vertebra after operation. Any, usually minor, deterioration occurred in the first six months postoperatively, and there was no significant further deterioration in 19 patients assessed over two years after surgery. Cotrel-Dubousset instrumentation can produce a significant correction of vertebral rotation and of the associated rib hump deformity.     

Mid-term effects of Cotrel-Dubousset instrumentation on the configuration of the spine and the thoracic cage in thoracic idiopathic scoliosis

Summary The effect of Cotrel-Dubousset instrumentation (CDI) on the three-dimensional spinal deformity in 24 consecutive patients with idiopathic scoliosis was investigated by posteroanterior and lateral radiographs and by computed tomography preoperatively, postoperatively, and at a mean follow-up of 3.2 years (range 2.0–5.3 years). At follow-up the mean Cobb angle was decreased by 73%, and the translation of the apical vertebra was significantly decreased by 33%. The sagittal contour was significantly improved with thoracic kyphosis T5–12 increased by 46% (6.9°) and lumbar lordosis L1–5 increased by 28% (10.3°) at follow-up. The sagittal diameter was significantly improved by 5 mm at follow-up. Although the vertebral rotation and the size of rib hump was improved postoperatively, this was followed by significant loss of correction, and at follow-up the vertebral rotation and the size of rib hump were not significantly better than preoperatively. The study indicates that while CDI improves the coronal and sagittal plane deformity permanently, the effect on vertetebral rotation and the rib hump deteriorates with time.     

Rip hump correction and rotation of the lumbar spine after selective thoracic fusion

In this study a series of 32 patients with idiopathic scoliosis, managed with selective thoracic fusion, was reviewed. Classified according to King and instrumented with the H-frame, the patients were evaluated for curve correction, rib hump correction and postoperative shift in lumbar rotation. Age and follow-up averaged 19.4 and 2.4 years, respectively. The 32 patients had an average primary and lumbar curve correction of, respectively, 66% (6.0% correction loss) and 53% (3.4% correction loss). The respective values for postoperative rib hump correction and shift in apical lumbar rotation averaged 8° and 9.4° in type II King curves, 4.4° and 3.5° in type III and 11° and-5° in Type IV. Significant differences were noted between the curve types in rib hump correction and shift in lumbar rotation. The study showed that en bloc postoperative rotation of the compensatory lumbar segment, directed towards the rib hump, positively influences rib hump correction. This en bloc rotation of the unfused lumbar segments is induced by the correcting forces applied by the instrumentation. The unfused lumbar spine of a patient with a King type II curve shows a larger lumbar rotation shift and subsequent rib hump correction than that of a patient with a King type III curve. Together with factors such as lateral angulation, rib-vertebra angles and structural limitations, the rotational dynamics of the unfused lumbar spine seem to form an important component in the understanding and surgical management of scoliosis.     

The rib hump in idiopathic scoliosis. Measurement, analysis and response to treatment.

This paper describes a simple method for the recording of rib deformity in idiopathic scoliosis. The relationships have been recorded between the measured rib hump and rib depression deformities and 1) the rotation of the vertebral bodies (as measured by the method of Nash and Moe on the standing radiograph); 2) the degree of lateral curvature (as measured by the method of Cobb on the standing radiograph); and 3) the rib-vertebra angles and their differences (as described by Mehta). No clear linear relationships were found. Many examples of irregular relationship were recorded, for example, marked spinal rotation with minimal rib hump. The response of the rib deformities to treatment by Milwaukee brace in fifty-two patients is described; the hump is little changed but the depression on the opposite side may be considerably reduced. Harrington instrumentation may have a similar effect.     

Effect of Harrington instrumentation spondylodesis on scoliotic thoracic deformity. A retrospective 5-year analysis]

INTRODUCTION AND AIM OF THE STUDY: Harrington-Instrumentation (HI) was the golden standard of scoliosis surgery for more than two decades and is still frequently used. The effects of instrumentation on rib hump reduction in long term follow-up is not well documented. 104 patients with idiopathic thoracic scoliosis were studied with a minimum follow-up of five years (min. 5 y., max. 8 years). METHODS: The rib-cage deformity was determined as rib hump index (RHi) by measuring the rib hump to the depression. The long term effect of HI was investigated using full standing AP radiographs. Measuring cobb angle (CA), translation (TA) and rotation of apical vetebra (RA) were obtained for every patient preoperatively, postoperatively and at follow-up. Patient were analysed in 3 different groups. Single curve thoracic scoliosis (n = 54) (King III and IV), double curve thoracic/lumbar scoliosis (n = 35) (King I and II) and double curve thoracic scoliosis (n = 15) (King V). RESULTS: With an average preoperative measurement of 62.7 degrees and a postoperative measurement angle of 32.9 degrees the correction of CA achieved is 47.5% (23-73%). The mean thoracic translation improved by 50% (0-100%). Rotation of the scoliosis was not reduced significant. In follow up studies no loss of correction in frontal plane deformity was obtained. The mean RHi in all groups was seen to improve by 25-30% (min. 0%, max. 60%), depending on form of scoliosis. In group of patients King II/III scoliosis (n = 52) the mean RHi increased measurably to 11.5% (min. 0%, max. 50%) correction at long term follow up. In group of patients King I/II scoliosis average RHi was increased from 31% (5-100%) to 21% correction. The mean RHi correction in the group of patients King V scoliosis correction rate of 26% (0-50%) was unchanged at long term follow up. CONCLUSION: HI leads to a permanent and stable improvement of the frontal plane including apical vertebral translation. HI does not have derotational capabilities. The effect of the rib-cage deformity was less impressive with loss of correction at follow up.     

Axial rotation component of thoracic scoliosis

The axial rotation (rotation about a vertical axis) of the vertebrae, of the ribs, and of the back surface are components of the deformity recognized clinically as the "rib hump" in thoracic scoliosis. Relationships of these rotations to the lateral deviation and lateral curvature of the spine were studied in 40 patients with idiopathic scoliosis. Stereoradiographs of the spine and rib cage were used to measure three components of axial rotation: rotation of the vertebrae, of the rib cage, and of the plane of maximum curvature of the spine. Stereotopographs of the back surface were digitized to measure the axial rotation of the back surface. In individual patients, there were high correlations of all components of axial rotation at each spinal level with the corresponding vertebral lateral deviation from the spinal axis. By regression analyses of the maximum values of each rotation in each curve, the rotation of the apex vertebra was found to be generally of lesser magnitude than the rotation of the plane of maximum curvature of the spine and in an opposite sense in kyphotic curves. The rib cage rotation was generally of lesser magnitude than the vertebra rotation, and the back surface rotation was less than both of these skeletal rotations. Vertebra rotation correlated most closely with lateral deviation of the spine. Simple segmental coupling of axial rotation and lateral bending could not be responsible for this axial rotation.     

脊柱侧凸旋转畸形的测量方法及相关性研究

目的探讨目前几种常用的测量轴向旋转方法的优缺点及其相关性。方法2005年1月～2006年12月采用后路椎弓根螺钉矫形融合术治疗了青少年特发性脊柱侧凸患者53例，MRI测量顶椎旋转角度，拍摄术前胸腰椎正侧位X线片，测量冠状位Cobb角、Nash-Moe旋转度、顶椎肋骨隆起间距（apical rib hump，RH）和肋骨弥散间距（apical ri bspread difference，ARSD）；术后拍摄胸腰椎正侧位X线片，测量术后冠状位Cobb角,RH和ARSD，比较手术前后测量指标差异。结果目前常用的Nash-Moe法、RH值和ARSD值的结果与MRI得到的结果有较好的相关性。手术矫正率与ARSD矫正率之间存在显著相关性。结论MRI扫描可以精确地测量脊柱侧凸的轴向旋转，Nash-Moe法、RH和ARSD也能够比较准确地评价顶椎的旋转，其中ARSD矫正率是评价主胸弯脊柱侧凸手术疗效的可靠指标。     

A biomechanical study on the effects of rib head release on thoracic spinal motion

Purpose

Idiopathic scoliosis is generally treated by surgical derotation of the spine. A secondary goal of surgery is minimization of the “rib hump” deformity. Previous studies have evaluated the effects of surgical releases such as diskectomy, costo-vertebral joint release, facetectomy, and costoplasty on spine mobilization and overall contribution to thoracic stability. The present study was designed to evaluate the biomechanical effects of the rib head joints alone on axial rotation, lateral bending, and segmental rotation, without diskectomy or disruption of anterior or posterior elements.

Methods

Four female cadaver thoracic spines with intact sternums and rib cages were mounted in an Instron servo-hydraulic bi-axial MTS. In a 12-step sequence, the costo-vertebral and costo-transverse ligaments were released, first unilaterally from T10–T7, then bilaterally until complete disarticulation between the rib heads and the vertebral bodies. After each release, biomechanical testing, including axial rotation and lateral bending, was performed. Vertebral body displacement was also measured using electromagnetic trackers.

Results

We found that rib displacement during axial rotation was significantly increased by unilateral rib head release, and torque was decreased with each successive cut. We also found increased vertebral displacement with sequential rib head release.

Conclusions

Our results show that sequential costo-vertebral joint releases result in a decrease in the force required for axial rotation and lateral bending, coupled with an increase in the displacement of vertebral bodies. These findings suggest that surgical release of the costo-transverse and costo-vertebral ligaments can facilitate segmental correction in scoliosis by decreasing the torso’s natural biomechanical resistance to this correction.

     

Vertebral rotation and thoracic torsion in adolescent idiopathic scoliosis: what is the best radiographic correlate?

BACKGROUND: As a result of the increased appreciation of the three-dimensional nature of scoliosis and modern spinal instrumentation's improved corrective capabilities, there has been renewed interest in the correction and measurement of vertebral rotation. Computed tomography (CT), the gold standard for accuracy, is limited in its clinical utility owing to cost, radiation exposure, and the effects of postural changes on scoliosis curves and vertebral rotation. Consequently, the Perdriolle and Nash-Moe techniques remain the standard measurements for providing a reasonable estimate of pre- and postoperative vertebral rotation because of their simplicity. However, these techniques have considerable interobserver variability, and pedicle screw instrumentation obscures the landmarks necessary for utilizing these techniques for postoperative vertebral rotation assessment. The purpose of the present study was to assess the utility of alternate radiographic measures to assess vertebral rotation and thoracic torsion when compared with conventional measures on pre- and postoperative radiographs and CT evaluation. METHODS: We reviewed the preoperative, immediate postoperative, and final follow-up radiographs, as well as the pre- and postoperative CT scans, of 19 patients (average age 15 years, 6 months) with Lenke 1 curves (average 55 degrees , range 47-66 degrees ), all treated with anterior spinal fusion. Coronal and sagittal Cobb angles as well as vertebral rotation (Perdriolle and Nash-Moe) at the superior uninstrumented, superior instrumented, apical, inferior instrumented, and inferior uninstrumented vertebrae were measured on all films, and vertebral rotation was assessed on the CT scans by a previously described method. Additionally, several measures of thoracic torsion (as a proxy for vertebral rotation and overall deformity improvement) were assessed. These included the rib-vertebral angle difference (RVAD), apical rib hump prominence (RH), apical vertebral body-rib ratio (AVB-R), and apical rib spread difference (ARSD). RESULTS: The postoperative main thoracic curve averaged 26 degrees (range 16-39 degrees , 52% correction) and 29 degrees (range 22-40 degrees , 47% correction) at final follow-up. For apical derotation, the postoperative CT improved from -11.5 degrees to -6.6 degrees and correlated significantly with the Cobb main thoracic curves (42% correction, r = 0.48, P = 0.003). There was weakly positive, but statistically significant, correlation between the pre- and postoperative CT scans and the corresponding Perdriolle and Nash-Moe measures of segmental rotation (r = 0.32-0.40, all P < 0.0001). The RVAD demonstrated poor correlation with the main thoracic curve values and correction, Perdriolle rotation and correction, and CT rotation and correction (r = -0.22-0.37, all P > 0.20). The apical RH demonstrated good correlation with the main thoracic curve (r = 0.65, P < 0.0001), apical Perdriolle rotation (r = 0.57, P < 0.0001), and CT apical rotation (r = 0.53, P = 0.002). We also found moderate correlation between the AVB-R and the main thoracic Cobb, apical Perdriolle, and CT (r = 0.57, 0.59, and 0.49, respectively; all P < 0.005). Similar relationships were found with the ARSD (r = 0.51, 0.47, and 0.43, respectively; all P < 0.02). CONCLUSIONS: The RH, AVB-R, and the ARSD-measures of thoracic torsion-demonstrated moderate to good overall correlation with the main thoracic curve Cobb angles, apical Perdriolle rotation, and apical CT rotation. These should be useful as clinical measures for assessing three-dimensional deformity correction on plane radiographs, especially for the intraoperative evaluation of vertebral derotation and thoracic symmetry restoration.     

Video-assisted thoracoscopic surgery (VATS) for the treatment of scolioticrib hump deformity

A retrospective study of 21 patients with idiopathic scoliosis who underwent endoscopic thoracoplasty was done. The objective of the study was to report and assess the morbidity and mid term outcomes of video-assisted thoracoplasty in idiopathic scoliosis. Patients with idiopathic scoliosis often present cosmetic complaints due to their rib deformity. This deformity may still exist after surgical correction of the main scoliotic curve. Endoscopic thoracoplasty has been reported as a safe method in limited cases of idiopathic scoliosis. Between 2002 and 2004, 21 patients underwent endoscopic anterior release and thoracoplasty for significant rib hump deformity associated with idiopathic scoliosis. Patients were operated on lateral position, with two endoscopic ports. Anterior release and rib resection were performed during the first stage, and instrumented posterior fusion was performed in a second stage. Patients were evaluated preoperatively, 1 week after surgery, 6 months after surgery and at their most recent follow-up with clinical and radiological measurement of the rib deformity. The mean age at surgery was 14.9 years old (range 13–17 years). The average Cobb’s angle of the main scoliotic curve was 70° (range 60°–85°). Average follow-up was 25 months (range 23–32 months). The mean number of resected ribs was five ribs (range 4–7) and the mean length of the resected rib was 4.2 cm (range 2.2–7 cm). Average operating time of endoscopic thoracoplasty (including anterior release) was 65 min (range 45–108 min). The mean preoperative height of rib hump deformity was 3.6 cm (range 2.5–5.5 cm). It was reduced to 1.5 cm at most recent follow-up. There was no significant thoracic pain necessitating medication postoperatively. No complications related to endoscopic anterior release and rib hump resection occurred in the series. Endoscopic thoracoplasty is a safe and reliable technique in idiopathic scoliosis. If indicated, the anterior release can be performed with video-assistance and the thoracoplasty can be performed on the same stage.     

Costoplasty in scoliosis surgery

The rib hump is a protrusion of the apicals ribs of the convex side of the toracic scoliosis and it is due to the torsional deformity that appears in scoliosis. It originates a great cosmetic deformity that although improves with the correction of the scoliosis, it appears again by the costal elasticity. For this reason, in cases of important deformity it is necessary to associate a costoplasty for its definitive improvement. 10 cases of Idiopatic Scoliosis with 75.5 degrees of average and rib hump of 22.1 degrees were analysed. A resection of apicals ribs without stabilization in the same surgical act were done; the correction of the curve was 34.6 degrees (55%) and of the hump 8.1 degrees (64%); there were no important complications and the postoperative evolution was normal. The average follow up was 21,9 months, only in 1 case a slight deterioration of the hump was detected, although in all the cases the ribs recovered. In conclusion, costoplasty breaks the vertebro-bicosto-esternal ring. For that reason it is effective for the improvement of the costal hump without adding morbidity to the correction of the scoliosis.     

Correction of flexible thoracic scoliosis below 65 degrees—A radiological comparison of anterior versus posterior segmental instrumentation applied to similar curves

Direct comparison of the correction of scoliosis achieved by different surgical methods is usually limited by the heterogeneity of the patients analyzed (their age, curve pattern, curve magnitude, etc.). The hypothesis is that an analysis of comparable scoliotic curves treated by different implant systems could detect subtle differences in outcome. The objective of this study was therefore: (1) to measure the 3D radiological parameters of scoliotic deformity and to quantify their postoperative changes, and (2) to compare the radiographic results achieved with one anterior and one posterior instrumentation methods applied to similar curves but representing different mechanisms of correction. Material and methods: The clinical notes and radiographs of 46 patients operated on for adolescent idiopathic scoliosis were reviewed. The inclusion criteria consisted of: a single thoracic curve, right convex, a frontal Cobb angle minimum of 45° and a maximum of 65°, flexibility on a lateral bending test of more than 30%, and a Risser test value of between 1 and 4. The operative procedures were: Cotrel-Dubousset instrumentation (CDI) for 25 patients (the CD group) and correction by anterior instrumentation (Pouliquen plate) for 21 patients (the ANT group). Preoperative and postoperative long cassette standing antero-posterior and lateral radiographs were examined. The frontal and sagittal thoracic Cobb angle, apical vertebra transposition (AVT), apical vertebra rotation (AVR), lowest instrumented vertebra (LIV) tilt, C7 vertebra shift and rib cage shift (RCS) were all compared. A computed reconstruction was produced with Rachis-91 software. Vertebral axial rotation angle was evaluated throughout the spine. Results: Postoperative assessment revealed a mean correction of the frontal Cobb angle of 37.0° for the CD group and 41.0° for the ANT group. The AVT operative correction was 45.8 and 42.7 mm, respectively, and AVR correction was 1.8 and 12.6°, respectively. The postoperative change of the sagittal Th4–Th12 Cobb angle was not significant for any method but it was significant (P=0.05) for the CD group if the curves were divided preoperatively into hypokyphotic and normokyphotic subgroups and then analyzed separately. Computed assessment demonstrated a correction of segmental axial rotation of more than 50% in the main thoracic curve in the ANT group, significantly more than that in the CD group (P<0.001). Conclusions: Anterior instrumentation provided better correction of the vertebral axial rotation and of the rib hump. CD instrumentation was more powerful in translation and more specifically addressed the sagittal plane: the postoperative thoracic kyphosis angle increased in the hypokyphotic curves and slightly decreased in the normokyphotic curves.     

Rib deformity in scoliosis

Rib deformity in scoliosis is of interest because it may help in the diagnosis, and also, in some pronounced cases, it may need correction by costoplasty. There are, however, debates about its use in diagnosis, because some authors think that rib deformity is not closely related to either the magnitude or the extent of rotation of the curve. In order to define the relation between rib deformity and scoliosis, 11 patients were recruited who were to undergo scoliosis surgery and thoracoplasty, and anteroposterior (AP) T1-S1 standing radiographs, computerized tomography (CT) scans, and three-dimensional (3D) reconstructions were obtained. From the radiographs, the most rotated vertebra, the Cobb angle, the apex and the type of the curve were determined. From the CT scans and 3D reconstructions, the exact level of the rib deformity measured was matched with the corresponding vertebral level. In this way, the most rotated vertebra and the most prominent part of the rib cage deformity were identified. The most rotated vertebra was found to be at the same level in both radiographs and CT scans in only five patients. In the rest of the patients, CT scans showed it either one level higher or lower than it appeared on the radiograph. The most prominent part of the rib cage deformity was at the same level as the most rotated vertebra in two patients, and in the rest of the patients it was one, two or three vertebral levels lower. There was no association between the Cobb angle, vertebral rotation and rib deformity. A CT scan is necessary preoperatively in patients who will undergo a costoplasty, to determine the exact levels of the prominence. However, a scanogram or a 3D reconstruction is required for exactly matching the most prominent part of the rib cage deformity to the corresponding vertebral level.     

Rib cage deformities in scoliosis: Spine morphology,rib cage stiffness,and tomography imaging

A computer-implemented biomechanical model of a thoracolumbar spine and deformable rib cage was used to investigate the influence of spine morphology and rib cage stiffness properties on the rib cage deformities that arise from scoliosis and to study the relationship of actual rib distortions with those seen on computed tomography (CT) scans. For the purposes of this study, it was assumed that rib cage deformities result from forces imposed on the ribs by the deforming spine. When a structurally normal rib cage was allowed to follow freely the imposition of scoliotic curves on the spine, different configurations of scoliosis led to substantial differences in the resulting rib cage deformities. Rib cage lateral offset correlated well with the Cobb angle of the scoliosis but not with the apical vertebral axial rotation, whereas rib cage axial rotation correlated well with apical vertebral axial rotation but not with the Cobb angle. These model-obtained findings mirror clinical findings that correction of the Cobb angle leads to correction of the lateral offset of the rib cage but does not correlate well with correction of the rib cage axial rotation. The stiffnesses of the ligamentous tissue connecting the sternum to the pelvis, of the costovertebral joints, and of the ribs themselves also influenced the rib deformities substantially. The influence of the sternopelvic ligamentous ties has not been recognized previously. The total rib cage volume remained essentially constant regardless of the severity of the resulting deformity, but the distribution of this volume between convex and concave sides varied somewhat. Simulated CT scans of model rib cages suggested that distortions of individual ribs are substantially exaggerated in such images.     

Correction of idiopathic scoliosis using the H-frame system

To determine the effectiness of posterior H-frame instrumentation for the surgical treatment of idiopathic scoliosis, 36 patients were studied. The patients underwent surgery between 1989 and 1993 and were evaluated for curve correction, hump correction, vertebral rotation, fusion level and complications. Average age at surgery was 19 years. Duration of follow-up averaged 2.5 years. Mean primary curve correction in patients with a King type I curve was 44.8% (n=4) and in patients with a type II curve 67.3% (n=9). Patients with King type III (n=17) and IV (n=6) curves achieved respective mean curve corrections of 67.8% and 63.9%. During follow-up there was a mean correction loss of 0.8% in type I, 5.4% in type II, 10.1% in type III and 2.4% in type IV curves. No significant derotation of the primary curves was noted. Rib hump correction and rotational changes of the unfused compensatory curves were significant. Fusion levels extended beyond L2 in six cases. Major neurological problems did not occur. Pseudoarthrosis developed in one patient and imbalance in two patients. The H-frame system satisfactorily achieves curve and rib hump correction with little correction loss.     

Structural vertebral changes in the horizontal plane in idiopathic scoliosis and the long-term corrective effect of spine instrumentation

Summary The rotation and structural changes of the apex vertebra in the horizontal plane as well as of the thoracic cage deformity were quantified by measurements on computed tomography (CT) scans from patients with right convex thoracic idiopathic scoliosis (IS). The CT scans were obtained from 12 patients with moderate scoliosis (mean Cobb angle 25.8°, r 13°–30°) and from 33 with severe scoliosis (mean Cobb angle 46.2°, r 35°–71°). In addition, CT scans of thoracic vertebrae from 15 patients without scoliosis were used as reference material. Ten of the scoliotic cases had had Cotrel-Dubousset instrumentation (CDI) and posterior fusion and had entered a longitudinal study on the effect of operative correction on the re-modelling of the apical vertebra. An increasingly asymmetrical vertebral body, transverse process angle, pedicle width and canal width were found in the groups with scoliosis as compared with the reference material. Vertebral rotation and rib hump index were significantly larger in patients with early and advanced scoliosis than in normal subjects. The modelling angle of the vertebral body, the transverse process angle index and the vertebral rotation in relation to the middle axis of the thoracic cage were significantly greater in patients with severe than with moderate scoliosis. The results of this longitudinal study suggest that the structural changes of the apical vertebra regress 2 years or more after CD instrumentation.     

Does lateral vertebral translation correspond to Cobb angle and relate in the same way to axial vertebral rotation and rib hump index? A radiographic analysis on idiopathic scoliosis

The deformity in idiopathic scoliosis (IS) is three dimensional in nature and effective correction involves all three planes. Even though the vertebral translation (VT) is an accepted element in the deformity along with vertebral rotation(VR) as reported by Asher and Cook (Spine (Phila Pa 1976) 20(12):1386–1391, 1995), Kotwicki et al. (Study Health Technol Inf 123:164–168, 2006) and Kotwicki and Napiontek (Pediatr Orthop 28(2):225–229, 2008), rib hump (rib hump index (RI)) and Cobb angle as reported by Aaro and Dahlborn (Spine (Phila Pa 1976) 6(6):567–572, 1981), it was assumed that VT was represented by adequately by Cobb angle and it was not analysed individually. We hypothesized that the Cobb angle and the VT measured in axial plane on CT scan and may not represent the same measurement and factors like coronal plane vertebral tilt,VR and vertebral deformation might affect them in different ways. Hence, VT should be considered as a separate variable and its relationship with VR, RI and Cobb angle should be investigated. Since the newer implants depend on curve translation and derotation for correction studying the role of VT and the relationships is important. VT, VR and RI were measured in CT scans of 75 patients with IS and correlated with Cobb angle. Regression analysis was used to identify the influence of the variables on each other. All the variables significantly correlated with one another but the correlation of Cobb and VT is not perfectly linear and it cannot be used to represent VT. VT influences RI much more than Cobb angle or VR. VT, therefore, merits further study treating it as an independent variable.     

Derotation of the spine

Idiopathic scoliosis is a three-dimensional deformity: lateral deviation in the coronal plane, thoracic hypokyphosis in the sagittal plane, and rotation in the transverse plane affecting the ribs and trunk. With pedicle screw fixation and modern corrective techniques, derotation of the spine can now be accomplished. The goals of vertebral derotation are to achieve true three-dimensional correction of the spinal deformity and reverse the torsional asymmetry induced by scoliosis. Intuitively, in typical thoracic adolescent idiopathic scoliosis, this would mean optimal coronal correction, restoration of thoracic kyphosis, and realignment of thoracic torsion by lifting the concavity out of the chest and reducing the convex rib deformity without the need for thoracoplasty.     

The effect of sublaminar wires on the rib hump deformity during scoliosis correction manoeuvres

Introduction

During thoracic curve correction, the tightening of the sublaminar wires through concavity creates a medial and a dorsal translation of the spine. However, little is known about the effect of the sublaminar wires on the axial plane.

Methods

This is prospective case series analysis of 30 consecutive surgical patients with main thoracic adolescent idiopathic scoliosis. All of the patients were fused with hybrid instrumentation (apical concavity–sublaminar wires) and differential rod contouring (over-kyphosis concavity/under-kyphosis convexity). The degrees of the rib hump were measured with a scoliometer placed at the apex of the deformity at five different times: (1) preoperatively through the Adam’s test, and during surgery (sterilised scoliometer), (2) with the patient lying prone, (3) after the Ponte osteotomies, (4) after the apical sublaminar tightening, and (5) after convexity apical derotation and compression manoeuvres.

Results

(1) Preoperatively, the Adam’s test was 16.3° ± 4.6. (2) Lying prone and under general anaesthesia, it decreased to 11.4° ± 3.9. (3) After exposure and Ponte osteotomies, it was 7.1° ± 4. (4) After the wire tightening, it was 10.8° ± 4.7. (5) After the convexity manoeuvres, it was 4.8° ± 3.7. The degrees of the rib hump final correction were 11.6° ± 4 (70 % correction). The tightening of the sublaminar wires increased the rib hump by 3.5°.

Conclusions

The sublaminar wire tightening towards the concave rod seemed to create an effect opposite of the desired effect, increasing the apical rotation and the thoracic rib hump deformity. Convexity manoeuvres (apical screw derotation and compression) are necessary and must be coupled with an under-bending of the convex rod to neutralise this effect.