10100802
Fixed lumbar apical vertebral rotation predicts spinal decompensation in lenke type 3c adolescent idiopathic scoliosis after selective posterior thoracic correction and fusion
Retrospective radiographic review of surgically treated double major curves (Lenke type 3C) in adolescent idiopathic scoliosis. To evaluate the role of selective posterior thoracic correction and fusion in double major curves with third generation instrumentation and to identify preoperative radiographic parameters that predict postoperative coronal spinal decompensation. Traditionally the surgical treatment of double major curves consists of fusion of both the thoracic and the lumbar curve. Few attempt to perform selective thoracic fusion in this curve pattern because of the potential to create spinal imbalance. Thirty-six patients with Lenke type 3C curves underwent a selective posterior thoracic correction and fusion with either Cotrel–Dubousset instrumentation or the Universal Spine System. Radiographs were evaluated to assess coronal and sagittal balance, curve flexibility, and curve correction at a minimum follow up of 2 years. Postoperative coronal spinal decompensation was investigated with respect to preoperative radiographic parameters on standing anteroposterior (AP), standing lateral radiographs, thoracic and lumbar supine side-bending radiographs. Coronal spinal decompensation was defined as plumbline deviation of C7 of more than 2 cm with respect to the centre sacral vertical line (CSVL) within 2 years of surgery. Twenty-six patients (72%) showed satisfactory frontal plane alignment patients (28%) showed coronal spinal decompensation. Significant group differences, however, were identified for lumbar apical vertebral rotation, measured according to Perdriolle (La scoliose. Son êtude tridimensionnelle. Maloine, Paris, pp 179, 1979) (A 16°, B 22°, P = 0.02), percentage correction (derotation) of lumbar apical vertebrae in lumbar supine side-bending films in comparison to standing AP radiographs (A 49%, B 27%, P = 0.002) and thoracic curve flexibility (A 43%, B 25%, P = 0.03). High correlation was noted between postoperative decompensation and derotation of lumbar apical vertebrae in pre-operative lumbar supine side-bending films with a critical value of 40% (Pearson correlation coefficient; P = 0.62, P < 0.001). Ten of 36 patients (28%) with Lenke type 3C adolescent idiopathic scoliosis showed coronal spinal decompensation of more than 2 cm after selective posterior thoracic correction and fusion. Lumbar apical vertebral derotation of less than 40% provided the radiographic prediction of postoperative coronal spinal imbalance. We advise close scrutiny of the transverse plane in the lumbar supine bending film when planning surgical strategy.
31279453
Long-term follow-up of fused and unfused idiopathic scoliosis.
We reviewed 77 unfused and 91 fused patients with idiopathic scoliosis who first attended between 1949 and 1965. Both groups were re-examined at least 10 years after reaching skeletal maturity, with attention to progression of the Cobb angle, increased in vertebral rotation, back pain and psychosocial problems. We found that spinal fusion protects the scoliotic spine from further deterioration during adult life except for those with severe curves and marked rotation. Fusion also significantly reduced the incidence of severe pain and allowed patients to carry out heavy physical work, but did not confer complete immunity from backache. Surgery improved the appearance, but patients were not always completely satisfied with the cosmetic result.
25659381
Surgical treatment of double major scoliosis. Improvement of the lumbar curve after fusion of the thoracic curve.
We have evaluated two methods of surgical treatment of adolescent idiopathic double major scoliosis in 59 patients. In group 1, 31 patients were treated by fusion of the upper curve only. In group 2, 28 patients had lumbar fusions also including most of the lower curve. The magnitude of the lower curve and the correction obtained in traction were good indicators of the correction achieved postoperatively. Forty-four patients were reviewed at a minimum of 10 years after operation. Those in group 1 showed sustained improvement of the lower curve with minimal stiffness and pain. Group 2 patients had lumbar curves of similar severity at review, but had significantly more low back pain and stiffness. The number of lumbar segments which remained mobile appeared to be a critical factor in determining the outcome. Selective fusion of the upper curve in double major scoliosis produces satisfactory results if the lumbar curve is less than 50 degrees. It may also be appropriate for flexible lumbar curves of larger angle.
36528949
The selection of fusion levels in thoracic idiopathic scoliosis.
From the material and data reviewed in our study of 405 patients, it appears that postoperative correction of the thoracic spine approximately equals the correction noted on preoperative side-bending roentgenograms. Selective thoracic fusion can be safely performed on a Type-II curve of less than 80 degrees, but care must be taken to use the vertebra that is neutral and stable so that the lower level of the fusion is centered over the sacrum. The lumbar curve spontaneously corrects to balance the thoracic curve when selective thoracic fusion is performed and the lower level of fusion is properly selected. In Type-III, IV, and V thoracic curves the lower level of fusion should be centered over the sacrum to achieve a balanced, stable spine.
20399299
Coronal Decompensation Produced by Cotrel—Dubousset “Derotation” Maneuver for Idiopathic Right Thoracic Scoliosis
From 1985 to 1987,82 patients with idiopathic scoliosis followed 12 to 44 months underwent selective fusion and correction of their right thoracic curves by Cotrel—Dubousset instrumentation using the “derotation” maneuver. Preoperative, postoperative, and follow-up standing anteroposterior roentgenograms of the spine were analyzed. For curves in which there was deviation from the midline (plumb line) and rotation of the lumbar segments, an increased incidence of decompensation was produced after surgery, when posterior Cotrel—Dubousset instrumentation and fusion were carried to the “stable” vertebra with one rod bend and hook alignment on the left sided derotation rod. Previous guidelines established for selective fusion with conventional posterior instrumentation (Harrington or Luque rods) may not be applicable to derotation with Cotrel—Dubousset instrumentation.
45692009
Choosing Fusion Levels in Progressive Thoracic Idiopathic Scoliosis
The selection of fusion levels in thoracic idiopathic scoliosis was subjected to multicenter retrospective review to test the validity of the classification system and recommendations of King et al. The 253 patients reviewed were treated by posterior fusion and Harrington instrumentation. Bending films were of little help in selecting fusion levels. Standing radiographs alone were usually adequate. King Type II curves may yield better lumbar correction if the lumbar curve is partially included in the fusion. Type IV curves may be safely fused one level proximal to the stable vertebrae.
26102744
Analysis of factors related to truncal decompensation following Cotrel-Dubousset instrumentation.
Spinal imbalance following Cotrel-Dubousset (CD) instrumentation for adolescent idiopathic scoliosis is a problem that is recognized with increasing frequency. We reviewed the clinical records and radiographs of 41 consecutive patients treated with CD instrumentation and attempted to identify factors related to postoperative worsening of spinal balance. Spinal balance was determined by the perpendicular distance of C7 to the center sacral line. Twenty-five were decompensated postoperatively. Sixteen patients had balance that was worse relative to the preoperative films. Eleven of 16 patients with worsened balance postoperative were King type III curves. Of 16 patients with worsened balance postoperatively, 13 had been fused to or below the lower neutral vertebra. Overcorrection of either the primary curve or the composite curve (sum of the measurable curves) relative to the preoperative bending films was not related to postoperative worsening of spinal balance. Fusion to the neutral or stable vertebra with CD instrumentation runs a high risk for postoperative worsening of spinal balance when the derotation maneuver is used. Consideration should be given to avoiding the derotation maneuver in larger type II curves in order to preserve spinal balance and avoid extension of instrumentation into the middle or lower lumbar spine.
21777407
Preventing Decompensation in King Type II Curves Treated With Cotrel‐Dubousset Instrumentation. Strict Guidelines for Selective Thoracic Fusion
Between 1985 and 1988, 50 adolescent idlopathic scoliosis patients with either King Type II (n = 19) or III (n = 31) curves were treated with Cotrel-Dubousset instrumentation and had a minimum of 2-year follow-up. Five of these patients had early postoperative decompensation, and have provided important lessons for the future prevention and treatment of these imbalances. Most problematic was distinguishing betwean King Type II and double major curve patterns. Proper Identification of King Type II curves, which may be successfully treated with selective thoracic fusion, requires careful analysis of the standing preoperative coronal radiograph as well as the side benders. Thus, we now define Type II curves based on the differential between the thoracic and lumbar curve magnitude, apical vertebral deviation from the midline, and apical vertebral rotation on the standing coronal radiograph in addition to a positive flexibility index.
9760590
Criteria for Selective Fusion in Idiopathic Scoliosis Using Cotrel‐Dubousset Instrumentation
Spinal decompensation after Cotrel-Dubousset (C-D) instrumentation in the King type II curve pattern has become a recognized complication secondary to progression of the unfused lumbar curve. Twenty-three patients with type II curves who underwent selective thoracic fusion according to the guidelines established by King et al. were reviewed. Mean follow-up was 19.5 months. Lumbar curves >45° associated with a low flexibility index were significantly more likely to develop postoperative progression of the uninstrumented lumbar curve with resultant spinal decompensation, suggesting that in these curves the King criteria for selective thoracic fusion may not be appropriate.
7520468
Frontal Plane and Sagittal Plane Balance following Cotrel-Dubousset Instrumentation for Idiopathic Scoliosis
Postoperative decompensation has been reported following Cotrel-Dubousset instrumentation for right thoracic idiopathic scoliosis. The authors examined balance in the frontal and sagittal planes in 53 patients to determine optimal levels for fusion. King et al Type II curves, particularly larger ones, shifted to the left when the thoracic curve was fused to the stable vertebra or just below. Most Type III curves balanced well regardless of the levels fused. One-third of all patients developed mild radiographic junctional kyphosis at the lower level instrumented, more commonly when instrumentation ended at or above T12. The authors recommend fusing one segment short of the stable vertebra in most Type II curves. Large Type II curves need both curves fused for optimal balance. Type III curves can be fused short of the stable vertebra.
45263425
Decompensation After Cotrel‐Dubousset Instrumentation of Idiopathic Scoliosis
Spinal decompensation after corrective surgery for scoliosis appears to be a significant problem after Cotrel-Dubousset instrumentation (CDI). CDI produces torsional changes in the instrumented and uninstrumented spine that could result in spinal imbalance. Preoperative and postoperative three-dimensional analysis including computed tomography (CT) scans to measure vertebral rotation and segmental rotation were performed to evaluate the importance of torsional changes. Moe/King Type II deformities had a substantially greater risk of imbalance. Deformities instrumented over fewer spinal segments were less likely to decompensate. Specifically, instrumentation excluding the mobile transition segment, determined by maximum segmental rotation and segmental Cobb angle, was likely to decompensate. Derotation and deformity correction excessive in relation to preoperative side bending flexibility and segmental rotation frequently resulted in imbalance. Spinal imbalance after CDI can be reduced by avoiding overcorrection and inclusion of mobile transition segments.
24078742
Interobserver Reliability and Intraobserver Reproducibility of the System of King et al. for the Classification of Adolescent Idiopathic Scoliosis*
The classification of adolescent idiopathic scoliosis with use of the system of King et al. has become widely accepted since its introduction. The purpose of the present study was to establish the interobserver reliability and intraobserver reproducibility of this classification system. The preoperative radiographs of sixty-three patients who were managed operatively for adolescent idiopathic scoliosis were classified by five observers with the system of King et al. Interobserver reliability was assessed by comparison of the classification of the curves among the observers, and intraobserver reproducibility was evaluated by comparison of the classifications of each set of radiographs by each observer on two occasions three weeks apart. The median interobserver reliability kappa coefficient for the classification system of King et al. was 0.44 (range, 0.28 to 0.50), and the median intraobserver reproducibility kappa coefficient was 0.64 (range, 0.44 to 0.72). According to the definition of Landis and Koch, the classification system of King et al. is substantially reproducible but is only moderately reliable. However, according to the stricter definition of Svanholm et al., its reproducibility is only fair and its reliability is poor.
24296465
Intraobserver and Interobserver Reliability of the Classification of Thoracic Adolescent Idiopathic Scoliosis*†
The system described by King et al. is the standard method for the classification of thoracic adolescent idiopathic scoliosis. Although it is widely used and referenced, its reliability and reproducibility among scoliosis surgeons are unknown. We used a scoliosis case-presentation format to examine the interobserver and intraobserver reliability of the classification of thoracic adolescent idiopathic scoliosis with the system of King et al. Eight active, current members of the Scoliosis Research Society reviewed twenty-seven full-length radiographs that had been made before operative correction of the scoliotic deformity. On the basis of these images, which included posteroanterior and lateral radiographs made with the patient standing as well as right and left forced-side-bending radiographs made with the patient supine, the reviewers assigned a type to each curve according to the classification system of King et al. Kappa coefficients were used to test statistical reliability. The mean interobserver reliability of the classification was only 64 per cent (range, 54 to 77 per cent) when the responses of seven of the reviewers were compared with those of one of the originators of the classification. The mean kappa coefficient was 0.49 (range, 0.27 to 0.73), which indicates poor reliability. When each reviewer's responses were compared with those of the other reviewers, the reliability was similarly poor (interobserver reliability, 55 per cent [range, 33 to 81 per cent] and mean kappa coefficient, 0.40 [range, 0.21 to 0.63]). Intraobserver reliability was evaluated in a trial in which five reviewers in a group setting were shown the same radiographs in a different order at two different viewings. Comparison of the results at the two viewings revealed a mean intraobserver reliability of 69 per cent (range, 56 to 85 per cent) and a mean kappa coefficient of 0.62 (range, 0.34 to 0.95), which indicates fair reliability. The current method of classification of adolescent idiopathic scoliosis does not appear to have sufficient intraobserver or interobserver reliability among scoliosis surgeons to portray curve types accurately. Thus, it may not help to guide treatment with use of modern spinal fixation methods.
40044141
Adolescent Idiopathic Scoliosis: A New Classification to Determine Extent of Spinal Arthrodesis
Background: The lack of a reliable, universally acceptable system for classification of adolescent idiopathic scoliosis has made comparisons between various types of operative treatment an impossible task. Furthermore, long‐term outcomes cannot be determined because of the great variations in the description of study groups. Methods: We developed a new classification system with three components: curve type (1 through 6), a lumbar spine modifier (A, B, or C), and a sagittal thoracic modifier (-, N, or +). The six curve types have specific characteristics, on coronal and sagittal radiographs, that differentiate structural and nonstructural curves in the proximal thoracic, main thoracic, and thoracolumbar/lumbar regions. The lumbar spine modifier is based on the relationship of the center sacral vertical line to the apex of the lumbar curve, and the sagittal thoracic modifier is based on the sagittal curve measurement from the fifth to the twelfth thoracic level. A minus sign represents a curve of less than +10°, N represents a curve of 10° to 40°, and a plus sign represents a curve of more than +40°.Five surgeons, members of the Scoliosis Research Society who had developed the new system and who had previously tested the reliability of the King classification on radiographs of twenty‐seven patients, measured the same radiographs (standing coronal and lateral as well as supine side-bending views) to test the reliability of the new classification. A randomly chosen independent group of seven surgeons, also members of the Scoliosis Research Society, tested the reliability and validity of the classification as well. Results: The interobserver and intraobserver kappa values for the curve type were, respectively, 0.92 and 0.83 for the five developers of the system and 0.740 and 0.893 for the independent group of seven scoliosis surgeons. In the independent group, the mean interobserver and intraobserver kappa values were 0.800 and 0.840 for the lumbar modifier and 0.938 and 0.970 for the sagittal thoracic modifier. These kappa values were all in the good-to-excellent range (>0.75), except for the interobserver reliability of the independent group for the curve type (kappa = 0.74), which fell just below this level. Conclusions: This new two-dimensional classification of adolescent idiopathic scoliosis, as tested by two groups of surgeons, was shown to be much more reliable than the King system. Additional studies are necessary to determine the versatility, reliability, and accuracy of the classification for defining the vertebrae to be included in an arthrodesis.
11430332
NEW UNIVERSAL INSTRUMENTATION IN SPINAL SURGERY
A new instrumentation for posterior spinal surgery consists of metallic rods carved with diamond-shaped asperities on which vertebral hooks or screws can be screwed in any position, level, or degree of rotation. The rods are interlocked by means of devices for transverse traction (DTTs), rectangular constructs with multiple vertebral grips, the stability of which allows suppression of any postoperative external support. Initially designed to treat scoliosis, this instrumentation design allows mobilization of the vertebrae located at the apex of the curve and obtains a three-dimensional correction. Correction of the areas of the most important structural deformation can also be obtained at the level of the end vertebrae, without any need to resort to an important distraction force. The technique varies according to the various types of curvatures. Approximately 250 patients were operated upon from 1983 to 1985. In idiopathic scoliotic curvatures, the mean percentage of correction was 66%. An important improvement of the associated sagittal deformations and of the apical derotation was observed in flexible curves. In paralytic curves, particularly with a pelvic obliquity, the percentage of correction of the frontal deformation is 77%. All of the spine patients were ambulatory in the first postoperative week, without any external support, and returned to their school or family activities. In 43 patients with follow-up periods longer than two years, there were no technical errors in 38. The final angular loss of correction was less than 2 degrees in the error-free group.
24805086
Coronal and Sagittal Balance in Surgically Treated Adolescent Idiopathic Scoliosis With the King II Curve Pattern: A Review of 67 Consecutive Cases Having Selective Thoracic Arthrodesis
Study Design. A retrospective study by an independent observer of a consecutive series of 67 cases of adolescent idiopathic scoliosis presenting with a King II curve pattern. Objectives. To demonstrate the validity of a selective thoracic fusion as a treatment of King II curves with special attention to immediate postoperative and long‐term trunk balance in the coronal and sagittal planes. Summary of the Background Data. The literature has been fairly controversial in terms of the recommended treatment of King II curve patterns in adolescent idiopathic scoliosis. The main confusion appears to be whether the thoracic curve alone or both curves should be instrumented and fused. Methods. Sixty‐seven patients were identified as having had a selective posterior thoracic spine fusion with instrumentation between 1961 and 1994. None of these cases had a fusion of the lumbar spine. Preoperative radiographs were analyzed for determination of the appropriate fusion level using the criteria of the stable and neutral vertebra. Follow‐up radiographs were evaluated for balance in the coronal and sagittal planes using the central sacral line on posteroanterior radiograph and the C7 sacral promontory line on lateral film. Results. At 2‐year or greater follow‐up, the unfused lumbar curve remained equal to or less than the corrected thoracic curve in 63 patients (94%). No patient required extension of fusion. Frontal plane balance analysis showed that 47 of the 67 patients had the T1 plumb line within 2 cm of the midline for an average decompensation of 8.7 mm. In no patient was the loss of balance greater than 3.8 cm. Sagittal plane balance analysis showed that only one patient had inferior junctional kyphosis greater than 10°. This did not require extension of fusion. There were no cases of superior junctional kyphosis. Conclusions. The concept of selective thoracic fusion in the King II curve pattern appears to be valid. These findings suggest that arthrodesis of the lumbar spine can be avoided when this pattern is properly diagnosed and appropriately treated. Proper identification of the stable and neutral vertebra and of the appropriate level of fusion are important to achieve good postoperative balance. Successful preservation of lumbar motion segments is important to long‐term satisfactory outcome in adolescent idiopathic scoliosis.
46573184
Lumbar Pedicle Screws Versus Hooks: Results in Double Major Curves in Adolescent Idiopathic Scoliosis
Study Design. A retrospective assessment of the effectiveness of lumbar pedicle screws versus laminar hooks in lumbar curve correction with double major curves in adolescent idiopathic scoliosis. Objective. To determine if pedicle screw fixation of the lumbar spine has any advantage compared with multiple laminar hook instrumentation in the treatment of double major curves in adolescent idiopathic scoliosis. Summary of Background Data. Although hooks have been used most commonly, pedicle screws may offer advantages in correction and maintenance of reduction of the lumbar curve in adolescent idiopathic scoliosis. Methods. A consecutive series of 39 patients with double major curves underwent thoracic and lumbar instrumentation by a single surgeon. Lumbar pedicle screws and hooks were used in 20 patients (Group S) and in 19 patients only lumbar hooks were used (Group H). Thoracic Cotrel-Dubousset instrumentation with hooks was the same in both groups. Preoperative age, gender, bracing, and Cobb angles were similar in both groups. Preoperative, 1-month postoperative, and latest follow-up standing posteroanterior and lateral spine radiographs were blinded to the surgeon and lumbar instrumentation covered to hide its identity. Measurements included Cobb angles, preoperative flexibility, lumbar and thoracic apical vertebral deviation, and reduction of lateral tilt and lateral displacement of the first free lumbar vertebra below the instrumentation. Percent correction, maintenance of correction at follow-up, and total levels fused were calculated. Results. The mean follow-up was 3.5 years (range, 2-8 years), which was similar for Groups H and S. Pedicle screws appear to offer some advantage in lumbar curve correction, maintenance of correction, and correction of the uninstrumented spine below the fusion when compared with the use of hooks alone. Horizontalization of the first free lumbar vertebra below the instrumentation (percent correction of tilt: 62% screws vs. 11% hooks; P = 0.0003), residual tilt (8° screws vs. 17° hooks; P = 0.004), and loss of horizontalization at follow-up (5% screws vs. 26% hooks) were dramatically better for the group using screws. Lumbar curve correction (72% screws vs. 60% hooks; P = 0.026), loss of lumbar curve correction (5% screws vs. 13% hooks), and correction of lateral apical vertebral deviation (2.2-cm screws vs. 1.5-cm hooks or 63% vs. 31%; P = 0.013) were better when screws were used. There was no significant difference in loss of correction of the thoracic curves (35% vs. 37%) or any difference in loss of correction of lateral displacement of the thoracic apical vertebra (12% vs. 14%). There was no difference in total levels fused, operative blood loss, operative time, or ultimate patient outcome. No patients in either group had spinal imbalance at latest follow-up. There were no complications related to pedicle screw placement. Two cases of transient postoperative superior mesenteric artery syndrome (duodenal obstruction by the superior mesenteric artery) in the pedicle screw group are attributed to acute correction of the lumbar scoliosis and thoracolumbar kyphosis with resultant lordosis at the thoracolumbar junction. Conclusions. Lumbar pedicle screws may offer greater lumbar curve correction, better maintenance of correction, and greater correction of the uninstrumented spine below double major curves. No complications were associated with the placement of pedicle screws.
25986765
Results of Spinal Instrumentation of Adolescent Idiopathic Scoliosis by King Type
The purpose of this study is to datermine the usefulness of the King classification in predicting decompensation in adolescent idiopathic scoliosis, Fifty-one patients were reviewed with a mean follow-up of 25 months. Five patients had Type 1 adolescent idiopathic scoiiosis: four were treated with Zielke/Cotrel-Dubousset Instrumentation or Zielke instrumentation alone. Correction was greater than 51% in these cases and there was no decompensation. Twenty-three patients had Type II scollosis. Nineteen of whom were treated with Cotrel-Dubousset instrumentation; 3 with Zielke and Cotrel-Dubousset instrumentation, and 1 with Zielke. The best correction occurred with anterior/posterior instrumentation. Decompensation occurred in 9 patients, all of whom were treated with Cotrel-Dubousset instrumentation atone. Fourtean patients had Type III scoliosis. All were treated with Cotrel-Dubousset instrumentation with correction of 65%. Decompensation occurred In 4 patients, all of whom were fused to or beyond the stable vertebra. Four patients had Type IV scoliosis; all were fused short of the stable vertebra with Cotrel-Dubousset instrumentation, resulting in correction of 52% and no decompensation. Five patients had Type V instrumentation; four were treated with Cotrel-Dubousset instrumentation and 1 with Zielke. There was no relationship between level of fusion and decompensation. Based on this study, the authors contend that the King classilication is a valuable tool in the selection of type of instrumentation and fusion level.
28963962
Sagittal plane analysis in idiopathic scoliosis patients treated with Cotrel-Dubousset instrumentation.
One hundred sixty patients with idiopathic scoliosis underwent preoperative and postoperative sagittal plane analysis of the thoracic spine, thoracolumbar junction, and lumbar spine. The data suggest that mild to moderate improvements in thoracic hypokyphosis are possible. When crossing the thoracolumbar junction, reversal of rod bend and reversal of hooks on the derotation rod appears to provide the most physiologic sagittal contour. Cotrel-Dubousset instrumentation to the mid and distal lumbar spine can preserve and, at times, enhance lumbar lordosis.
37489668
Fusion Levels and Hook Patterns in Thoracic Scoliosis with Cotrel‐Dubousset Instrumentation
This study reports the results of treatment of adolescents with King Types 2, 3, and 4 idiopathic curves using Cotrel-Dubousset instrumentation. Imbalance was seen in Types 2 and 4 curves when distraction direction hook patterns crossing the thoracolumbar junction were employed. Imbalance was not seen when a modified hook pattern employing compressing forces across the thoracolumbar junction was employed. No imbalance was observed in Type 3 curves using the basic right thoracic curve hook pattern. In Type 4 curves, a second modified hook pattern is required to obtain improved correction and balance. The mechanism of production of imbalance is explained by a three dimensional analysis of the deformity and of the forces generated by the Cotrel-Dubousset system.