A three-dimensional radiographic comparison of Cotrel-Dubousset and Colorado instrumentations for the correction of idiopathic scoliosis

STUDY DESIGN: A prospective clinical study comparing two instrumentation systems for the correction of idiopathic scoliosis. OBJECTIVES: To measure the short-term three-dimensional changes in the shape of the spine after corrective surgery and compare the Cotrel-Dubousset instrumentation to the more recent Colorado instrumentation to determine whether one system provides better three-dimensional correction. SUMMARY OF BACKGROUND DATA: Adequate three-dimensional correction of scoliotic deformities has been reported with the Cortrel-Dubousset instrumentation system. During the past decade, a new generation of more versatile and user-friendly spinal implants has appeared, but there are no reports available to indicate whether similar or better correction can be obtained with these newer systems. METHODS: The three-dimensional geometry of the thoracic and lumbar spine was documented in the standing position using a three-dimensional reconstruction technique based on multiplanar radiography in 67 adolescents with idiopathic scoliosis undergoing correction by a posterior approach. Changes in spinal shape were measured 3 days before and 1 month after the surgery in 31 patients with Cotrel-Dubousset instrumentation and 36 patients with Colorado instrumentation. RESULTS: In both groups, adequate three-dimensional correction of the scoliotic deformities was documented for thoracic and lumbar curves, with significant changes in the frontal plane, in the plane of maximum curvature, and in its orientation. When comparing both groups, better correction was obtained in the frontal plane with the Colorado instrumentation (65% vs. 48% with Cotrel-Dubousset), a finding that may be explained by the significantly greater proportion of pedicle screws used in this group. CONCLUSION: Both instrumentation techniques achieve an effective and comparable three-dimensional correction of the scoliotic deformities.     

Role of conservative treatment of cervical spine injuries

This is a clinical radiographic study, spanning over three decades, analyzing the three-dimensional (3-D) changes in spine geometry after corrective surgery for adolescent idiopathic scoliosis (AIS) using four generations of instrumentation systems. The objective of this study was to retrospectively evaluate the evolution of spinal instrumentation over time by measuring the 3-D changes of spinal shape before and after surgical correction of subjects with AIS using Harrington/Harrington-Luque (H/HL) instrumentation, original and recent generations of Cotrel-Dubousset Instrumentation (CDI) with rod rotation maneuvers, as well as third generation systems using thoracic pedicle screws and direct vertebral derotation (DVD) manoeuver in order to determine if the claims for improved 3-D correction from generation to next generation could be substantiated. The 3-D shape of the thoracic and lumbar spine was recorded from a pair of standing radiographs using a novel 3-D reconstruction technique from uncalibrated radiographs in 128 adolescents with AIS undergoing surgery by a posterior approach. Changes in coronal Cobb angles, kyphosis, lordosis, as well as in a series of 3-D parameters computed from the spine reconstructions before and after surgery were used to compare the four groups. Results demonstrate statistically significant differences (P = 0.05) between generations with regards to the correction of the coronal Cobb angle, and different loss of physiological lordosis. More importantly, significant differences in the 3-D correction of the spine based on the orientation of the planes of maximal curvature were observed (20/−6% H/HL vs. 39/39% CDI vs. 42/18% DVD for the thoracic/lumbar regions, respectively), confirming that recent CDI and third generation instrumentations coupled with DVD can bring the deformity significantly closer to the sagittal plane. An increased correction in apical vertebra axial rotation was observed with the DVD manoeuver (74%), while fewer notable differences were found between DVD and recent CDI systems in terms of 3-D correction. This is the first quantitative study to clearly demonstrate that the rod derotation and DVD maneuvers can significantly improve 3-D correction of scoliotic deformities, thereby supporting the transition towards these more elaborate and costly instrumentation technologies in terms of 3-D assessment.     

Long-term three-dimensional changes of the spine after posterior spinal instrumentation and fusion in adolescent idiopathic scoliosis

This is a prospective study comparing the short- and long-term three-dimensional (3D) changes in shape, length and balance of the spine after spinal instrumentation and fusion in a group of adolescents with idiopathic scoliosis. The objective of the study was to evaluate the stability over time of the postoperative changes of the spine after instrumentation with multi rod, hook and screw instrumentation systems. Thirty adolescents (average age: 14.5 ± 1.6 years) undergoing surgery by a posterior approach had computerized 3D reconstructions of the spine done at an average of 3 days preoperatively (stage I), and 2 months (stage II) and 2,5 years (stage III) after surgery, using a digital multi-planar radiographic technique. Stages I, II and III were compared using various geometrical parameters of spinal length, curve severity, and orientation. Significant improvement of curve magnitude between stages I and II was documented in the frontal plane for thoracic and lumbar curves, as well as in the orientation of the plane of maximum deformity, which was significantly shifted towards the sagittal plane in thoracic curves. However, there was a significant loss of this correction between stages II and III. Slight changes were noted in apical vertebral rotation, in thoracic kyphosis and in lumbar lordosis. Spinal length and height were significantly increased at stage II, but at long-term follow-up spinal length continued to increase while spinal height remained similar. These results indicate that although a significant 3D correction can be obtained after posterior instrumentation and fusion, a significant loss of correction and an increase in spinal length occur in the years following surgery, suggesting that a crankshaft phenomenon may be an important factor altering the long-term 3D correction after posterior instrumentation of the spine for idiopathic scoliosis. Received: 3 March 1998 Revised: 22 August 1998 Accepted: 15 September 1998     

Biomechanics of scoliosis]

Scoliosis is defined as a three-dimensional deformity of the spine. The most pronounced component of scoliosis is in the frontal plane, comprising the lateral bending of the spine. Rotation of vertebra takes place in the transverse plane. In most cases of idiopathic scoliosis a decrease of thoracic kyphosis in the sagittal plane occurs. A more rare event is the appearance of a junctional kyphosis between the primary and secondary curve. The instrumentation introduced by Harrington dealt mainly with balancing the bending forces in the frontal plane (distraction of the concavity of the curve), along with fusion of the instrumented area. The multisegmental CD instrumentation allowed for the diminution of the lateral curve in the frontal plane, while at the same time "forcing" an increase of thoracic kyphosis in single curves, and restoration of physiological sagittal curves (thoracic kyphosis lumbar lordosis) in double curve scoliosis. The CD method achieved this good by a 90 degrees rotation of the rod towards the concavity of the curve, "changing" the lateral curve into kyphotic curve. In the AO USS (Universal Spine System) correction is achieved by pulling the hooks towards the rod. The procedure ends with the linking of two rods with transverse connectors forming this way a stable framework. The degree of correction achieved with this method is based on the biomechanic inter relation between the spine and the instrumentation system (application of distraction forces, compensatory forces and translocation of the instrumented segment). Post-op decompensation of the spine is usually the result of incorrect hook fixation, inadequate application of forces (distraction and compression) and use of a standard hook pattern for thoracic curves (type III) in other types of scoliosis.     

Segmental pedicle screw instrumentation in idiopathic thoracolumbar and lumbar scoliosis

The role of posterior correction and fusion in thoracolumbar and lumbar scoliosis as well as pedicle screw instrumentation in scoliosis surgery are matters of debate. Our hypothesis was that in lumbar and thoracolumbar scoliosis, segmental pedicle screw instrumentation is safe and enables a good frontal and sagittal plane correction with a fusion length comparable to anterior instrumentation. In a prospective clinical trial, 12 consecutive patients with idiopathic thoracolumbar or lumbar scolioses of between 40° and 60° Cobb angle underwent segmental pedicle screw instrumentation. Minimum follow-up was 4 years (range 48– 60 months). Fusion length was defined according to the rules for Zielke instrumentation, normally ranging between the end vertebrae of the major curve. Radiometric analysis included coronal and sagittal plane correction. Additionally, the accuracy of pedicle screw placement was measured by use of postoperative computed tomographic scans. Major curve correction averaged 64.6%, with a loss of correction of 3°. The tilt angle was corrected by 67.0%, the compensatory thoracic curve corrected spontaneously according to the flexibility on the preoperative bending films, and led to a satisfactory frontal balance in all cases. Average fusion length was the same as that of the major curve. Pathological thoracolumbar kyphosis was completely corrected in all but one case. One patient required surgical revision with extension of the fusion to the midthoracic spine due to a painful junctional kyphosis. Eighty-five of 104 screws were graded “within the pedicle”, 10 screws had penetrated laterally, 5 screws bilaterally and 4 screws medially. No neurological complications were noted. In conclusion, despite the limited number of patients, this study shows that segmental pedicle screw instrumentation is a safe and effective procedure in the surgical correction of both frontal and sagittal plane deformity in thoracolumbar and lumbar scoliosis of less than 60°, with a short fusion length, comparable to anterior fusion techniques, and minimal loss of correction. Received: 23 September 1999 Revised: 20 January 2000 Accepted: 26 January 2000     

Optimization method for 3D bracing correction of scoliosis using a finite element model

Scoliosis is a complex three-dimensional deformity of the spine and rib cage frequently treated by brace. Although bracing produces significant correction in the frontal plane, it generally reduces the normal sagittal plane curvatures and has limited effect in the transverse plane. The goal of this study is to develop a new optimization approach using a finite element model of the spine and rib cage in order to find optimal correction patterns. The objective function to be minimized took account of coronal and sagittal offsets from a normal spine at the thoracic and lumbar apices as well as the rib hump. Two different optimization studies were performed using the finite element model, which was personalized to the geometry of 20 different scoliotic patients. The first study took into account only the thoracic deformity, while the second considered both the thoracic and lumbar deformities. The optimization produced an average of 56% and 51% reduction of the objective function respectively in the two studies. Optimal forces were mostly located on the convex side of the curve. This study demonstrates the feasibility of using an optimization approach with a finite element model of the trunk to analyze the biomechanics of bracing, and may be useful in the design of new and more effective braces. Received: 8 May 1999 Revised: 15 December 1999 Accepted: 11 January 2000     

Idiopathic scoliosis in three dimensions: a succession of two-dimensional deformities?

STUDY DESIGN: A geometric analysis of computerized three-dimensional (3-D) reconstructions of the spine of adolescents with idiopathic scoliosis. OBJECTIVES: To analyze and describe the 3-D location of scoliotic curves with respect to the global frontal, sagittal, and transverse planes of each subject. SUMMARY OF BACKGROUND DATA: Clinical two-dimensional (2-D) measurements cannot fully describe the 3-D deformity of a scoliotic spine because they are done in the 2-D frontal or sagittal plane projection of a subject and do not correspond to the actual deformity. METHODS: The spinal deformity from T1 to L5 of 50 adolescents with thoracic idiopathic scoliosis was reconstructed in 3-D using a multiplanar digital radiographic technique allowing the visualization of the vertebral line of the spine in any projection using auto CAD software. The curvature was segmented in three distinct curves for each subject: a high thoracic, a thoracic, and a lumbar. A regional plane passing through the two end-vertebrae and the apical vertebra was defined, and a series of geometric manipulations were performed to realign each regional plane with the global axis system of each subject. RESULTS: A total of 91% of the 147 curves studied were found to be entirely contained within its 2-D regional plane, and all scoliotic curves were found to be oriented in a 3-D location different from the classic frontal, sagittal, and transverse orthogonal planes of each subject. CONCLUSION: In thoracic idiopathic scoliosis the deformity of the spine is 3-D, but the regional deformity of each high thoracic, thoracic, or lumbar curve is almost always 2-D. The orientation in space of each 2-D plane is such that it cannot be seen in its true frontal or sagittal projection using standard frontal or sagittal radiologic views of the subject.     

Preoperative and early postoperative three-dimensional changes of the rib cage after posterior instrumentation in adolescent idiopathic scoliosis

Rib cage deformity is an important component of scoliosis, but few authors have reported the three-dimensional (3-D) effect of surgical procedures with posterior instrumentation systems on the shape of the rib cage. The objective of this prospective clinical study was to measure the short-term 3-D changes in the shape of the rib cage at the apex of the curve after corrective surgery of adolescent idiopathic scoliosis by a posterior approach using a multi rod, hook and screw system. The 3-D shape of the spine and rib cage was modelled pre- and postoperatively using a 3-D reconstruction technique based on multi-planar radiography in a group of 29 adolescents with idiopathic scoliosis. Geometrical indices describing the scoliotic deformity of the rib cage were computed from these models and were compared pre- and postoperatively using Student's t-tests. The frontal spinal curve correction averaged 53% in the frontal plane, while no significant change was noted in the sagittal plane. Significant changes were noted in the shape of the rib cage: rib hump at the apex and at the adjacent lower level were improved (36% and 38%), and small but significant differences were detected in rib frontal orientation in the concavity of the curves at the apex and adjacent lower rib levels. Multi rod, hook and screw instrumentation systems, such as Cotrel-Dubousset instrumentation, are effective in producing significant improvements in the 3-D shape of the rib cage, but these changes are less important than those observed at the spine level.     

Double-segment total vertebrectomy for the surgical treatment of congenital kyphoscoliosis: a case report

BACKGROUND CONTEXT: Congenital kyphosis or kyphoscoliosis is an uncommon deformity that usually is progressive without surgical intervention. In the lately diagnosed or neglected cases of congenital kyphoscoliosis, the patients may come with shoulder-trunk imbalance anomalies, severe deformity in coronal and sagittal plane, rib cage deformities, pelvic tilt, presence of intramedullary anomalies, neurological deficit, and difficulty in walking and cardiopulmonary problems. PURPOSE: To present a technical note related with double-segment total vertebrectomy for the surgical treatment of a patient who had neglected congenital kyphoscoliosis in lumbar spine. STUDY DESIGN: Case report. METHODS: A 19-year-old girl had submitted to our center with complaints of deformity and pain in her back. Her physical examination revealed scoliosis and gibbosity in lumbar region. Her neurological examination was normal. In the radiological examination, X-ray films showed 42 degrees lumbar scoliosis in frontal plane and 35 degrees kyphotic curvature in the sagittal plane. RESULTS: Three-staged (posterior-anterior-posterior) surgery in the same session (same anesthesia) was performed. CONCLUSION: Total or partial vertebrectomy on the apex of the deformity and the adjacent vertebral bodies along with anterior stabilization by means of a cylindrical cage combined in one operative procedure preceded by temporary posterior instrumentation and followed by posterior instrumentation and fusion may be preferred for the treatment of congenital kyphoscoliosis in neglected cases to provide spinal cord decompression.     

Isola spinal instrumentation system for idiopathic scoliosis

Since the definition of three-dimensional components of the scoliotic deformity, there have been important improvements in the surgical treatment of the problem. A derotation maneuver was proposed as a treatment option with CD instrumentation, but the reports of imbalance and decompensation with this system repopularized sublaminar wiring and translation as a corrective maneuver. Isola spinal instrumentation is one of the modern systems that utilizes vertebral translation instead of rod rotation. This study analyzes the results of 24 patients with idiopathic scoliosis who had been followed up for at least 2 years, and were surgically treated with titanium Isola Spinal Instrumentation in the Department of Orthopaedics and Traumatology, Ankara Social Security Hospital. Patients were grouped according to the King-Moe classification. Patients with type III, IV or V curves received only posterior instrumentation while this procedure followed anterior release and discectomy in the same session in patients with type I or II curves. A translation maneuver was utilized in the correction of scoliotic curves using the cantilever technique, either alone or supplemented by sublaminar wiring with Songer multifilament titanium cables. This study aimed to elucidate the effects of this technique in the frontal and sagittal plane curves and the trunk balance. The balance was analyzed clinically and radiologically by measurement of the lateral trunk shift (LT), shift of stable vertebra (SS), and shift of head (SH) in vertebral units (VU). The postoperative correction was significant in the frontal plane for all types of curves (p < 0.05). The postoperative correction was 80.9% +/- 9.5% in type III curves. Overall, the mean Cobb angle of the major curve value in the frontal plane was 66.9 degrees +/- 18.8 degrees, and it was corrected by 62.8% +/- 20.1%. The correction loss of Cobb angles in the frontal plane was 5.4 degrees +/- 5.5 degrees at the last follow-up visit. A normal physiologic thoracic contour (30 degrees - 50 degrees) was achieved in 83.3% of the patients and normal lumbar contour (40 degrees - 60 degrees) in 66.7% of the patients in the sagittal plane. The correction was found to be significant in all balance values (p < 0.05). The postoperative correction in LT values correlated with the correction of the Cobb angle values in the frontal plane. All patients had complete balance (SH: 0 VU and SS: 0 VU) or balanced curves (0 VU < SH, SS < 0.5 VU).Finally, the study concluded that the translation maneuver, especially when used with the cantilever technique, resulted in high correction rates in the frontal plane. Additionally, the technique was also successful in obtaining normal sagittal contours and correcting balance values.     

Deformity planning for sagittal plane corrective osteotomies of the spine in ankylosing spondylitis

Ankylosing spondylitis (AS) may lead to a severe fixed thoracolumbar kyphotic deformity (TLKD) of the spine. In a few patients, the TLKD is so extreme that a corrective osteotomy of the spine may be considered. Several authors have reported the results of patients treated by a lumbar osteotomy, but there is no consensus on the level of the osteotomy and on the exact degree of correction required. This can be explained by the lack of quantification of the sagittal plane deformity, since compensation mechanisms of the lower extremities have to be reckoned with for the assessment of spinal sagittal balance in AS. Therefore, there is a need for a method of deformity planning for sagittal plane corrective osteotomies of the spine in AS. In this study, a biomechanical analysis and a newly developed planning procedure are presented and illustrated with two cases of AS. Sagittal balance of the spine was defined in relation to the physiologic sacral end plate angle using trigonometric terms. Nomograms were constructed to show the relationship between the correction angle, horizontal position of the C7 plumb line and the level of the spinal osteotomy. The surgical results of two patients were retrospectively analyzed with our method. It showed that the effect of a spinal osteotomy on the horizontal position of the C7 plumb line depends on the combination of correction angle and the level of osteotomy. In one patient, the achieved correction of the deformity proved to correct the sagittal spinal balance and the pelvic sacral endplate angle. In the other patient, the achieved correction was not sufficient. It is concluded that adequate deformity planning for sagittal plane corrective osteotomies of the spine in AS is essential for reliable prediction of the effect of a lumbar osteotomy on the correction of the spine. Received: 17 January 2000 Revised: 12 May 2000 Accepted: 22 May 2000     

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.     

Influence of implant rod curvature on sagittal correction of scoliosis deformity

Background contextDeformation of in vivo–implanted rods could alter the scoliosis sagittal correction. To our knowledge, no previous authors have investigated the influence of implanted-rod deformation on the sagittal deformity correction during scoliosis surgery.PurposeTo analyze the changes of the implant rod's angle of curvature during surgery and establish its influence on sagittal correction of scoliosis deformity.Study designA retrospective analysis of the preoperative and postoperative implant rod geometry and angle of curvature was conducted.Patient sampleTwenty adolescent idiopathic scoliosis patients underwent surgery. Average age at the time of operation was 14 years.Outcome measuresThe preoperative and postoperative implant rod angle of curvature expressed in degrees was obtained for each patient.MethodsTwo implant rods were attached to the concave and convex side of the spinal deformity. The preoperative implant rod geometry was measured before surgical implantation. The postoperative implant rod geometry after surgery was measured by computed tomography. The implant rod angle of curvature at the sagittal plane was obtained from the implant rod geometry. The angle of curvature between the implant rod extreme ends was measured before implantation and after surgery. The sagittal curvature between the corresponding spinal levels of healthy adolescents obtained by previous studies was compared with the implant rod angle of curvature to evaluate the sagittal curve correction. The difference between the postoperative implant rod angle of curvature and normal spine sagittal curvature of the corresponding instrumented level was used to evaluate over or under correction of the sagittal deformity.ResultsThe implant rods at the concave side of deformity of all patients were significantly deformed after surgery. The average degree of rod deformation Δθ at the concave and convex sides was 15.8° and 1.6°, respectively. The average preoperative and postoperative implant rod angle of curvature at the concave side was 33.6° and 17.8°, respectively. The average preoperative and postoperative implant rod angle of curvature at the convex side was 25.5° and 23.9°, respectively. A significant relationship was found between the degree of rod deformation and preoperative implant rod angle of curvature (r=0.60, p<.005). The implant rods at the convex side of all patients did not have significant deformation. The results indicate that the postoperative sagittal outcome could be predicted from the initial rod shape.ConclusionsChanges in implant rod angle of curvature may lead to over- or undercorrection of the sagittal curve. Rod deformation at the concave side suggests that corrective forces acting on that side are greater than the convex side.     

Segmental analysis of the sagittal plane alignment of the normal thoracic and lumbar spines and thoracolumbar junction

Recent advances in spinal instrumentation have brought about a new emphasis on the three-dimensional spinal deformity of scoliosis and especially on the restoration of normal sagittal plane contours. Normal alignment in the coronal and transverse planes is easily defined; however, normal sagittal plane alignment is not so simple. This retrospective study was undertaken to increase the understanding of the normal alignment of the spine in the sagittal plane, with a special emphasis on the thoracolumbar junction. Measurements were made from the lateral radiographs of 102 subjects with clinically and radiographically normal spines. Cobb measurements of the thoracic kyphosis (T3-T12), the thoracolumbar junction (T10-T12 and T12-L2), and the lumbar lordosis (L1-L5) were determined. The spices of the thoracic kyphosis and lumbar lordosis also were determined. Using a computerized digitalizing table, the segmental angulation was determined at each level from T1-2 to L5-S1. In conclusion, there is a wide range of normal sagittal alignment of the thoracic and lumbar spines. When using composite measurements of the combined frontal and sagittal plane deformity of scoliosis, this wide range of sagittal variance should be taken into consideration. Using norms established here for segmental alignment, areas of hypokyphosis and hypolordosis commonly seen in scoliosis can be more objectively evaluated. The thoracolumbar junction is for all practical purposes straight; lumbar lordosis usually starts at L1-2 and gradually increases at each level caudally to the sacrum.     

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.     

Partially Overlapping Limited Anterior and Posterior Instrumentation for Adult Thoracolumbar and Lumbar Scoliosis: A Description of Novel Spinal Instrumentation, “The Hybrid Technique”

Progressive and/or painful adult spinal deformity in the thoracolumbar and lumbar spine is sometimes treated surgically by long posterior fusions from the thoracic spine down to the pelvis, especially where there is a major thoracic curve component. Recent advances in anterior spinal instrumentation and spinal surgery technique have demonstrated the improved corrective ability offered by anterior stabilization systems, and the added benefit of limiting the number of vertebral fusion levels required for control of the deformity. The "hybrid technique" is a novel use of anterior instrumentation that applies limited anterior instrumentation down to the low lumbar spine (rods and screws), and partially overlapping short-segment posterior instrumentation to the sacrum (pedicle screws and rods). These constructs avoid posterior thoracic instrumentation and fusions, and avoid extension of posterior instrumentation to the pelvis. In the first 10 patients treated using this technique, thoracolumbar and lumbar major curve correction has averaged 71 and 82% in the immediate postoperative period (n = 7), respectively, and 59 and 68% at 2-year follow-up, respectively. The technique is an appealing and attractive alternative for treatment of thoracolumbar and lumbar scoliosis in the adult population, and avoids the requirement for applying spinal fixation to the thoracic spine and the pelvis.     

Sagittal plane analysis in idiopathic scoliosis patients treated with Cotrel-Dubousset instrumentation

One hundred sixty patients with idiopathic scoliosis treated with Cotrel-Dubousset instrumentation (CDI) 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 appear 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.     

Some aspects of spine biomechanics and their clinical implications in idiopathic scoliosis]

The spine with it's physiological curves is designed to transfer loads to the pelvis and the lower limbs. The complex interplay of forces in the spine can be described by breaking down these forces into their basic components. These forces have a direction and can therefore treated as vectors in three axis, related to the anatomic planes: frontal, sagittal and transverse the static spine forces responsible for a correct posture create tension. Tension is defined as the relation of the vector force to the surface area to which the force is applied. Tension, depending an the direction of the force applied can be normal or tangent. Gravitational force is transferred by the vertebral bodies. Posterior elements of the spine (the lamina, the processes and ligaments) are stabilizing elements. The articular processes bear loads only when lateral bending of the spine. The complex nature of the scoliotic deformity usually leads toa decompensated spine even prior to surgery. Although considerable correction of the curve can be achieved using modern instrumentation systems, the spine can be restored. Lach of decompensation or decompensation of the spine is a major problem among many patients treated surgically with systems based on hooks and rods. Such decompensation in the frontal plane can be a result of correction beyond the compensatory possibilities of the lumbar spine, inadequate placing of hooks and incorrectly applied distraction forces. Overlooking the proximal junctional kyphosis (between the two proximal thoracic curves or overlooking the distal junctional kyphosis (between the lumbar and thoracic curve) can also lead to decompensation of the spine in the sagittal plane.     

Short posterior fusion for patients with thoracolumbar idiopathic scoliosis.

Fifteen percent of all scolioses are idiopathic thoracolumbar and are characterized by significant imbalance in the frontal plane. A large curve of more than 40 degrees creates a trunk shift and under these circumstances an active correction is necessary. It is this imbalance that is the cause of increasing muscular fatigue. Arthritic changes may appear later which also are responsible for pain. The aim of a surgical procedure is to stop the progression of scoliosis, to obtain the reequilibrium of the spine in a frontal and a sagittal plane, and to correct the deformity. During the 1960s Dwyer6 developed his anterior instrumentation mainly for thoracolumbar and lumbar curves. In 1980 Hall developed the concept of a short anterior fusion with overcorrection for patients with thoracolumbar curves. In the present study 10 patients are presented who were operated on for thoracolumbar adolescent idiopathic scoliosis using short posterior fusion instrumented by segmental convex transpedicle screw fixation and concave hook stabilization. With a mean followup of 49 months, the results show that frontal and sagittal balances are restored. In the present study all patients achieved frontal and sagittal balances at the last followup. The angular correction achieved by surgery always is more effective than what is visualized in radiographs of the patient in the bending position obtained before surgery. The correction of the major curve in the frontal plane improved from a mean angle of 47 degrees preoperatively to 14 degrees postoperatively and to 17 degrees at the last followup. In all cases, mobile discs in the lower lumbar area are open. The posterior short fusion has the same power of correction as the anterior fusion with the advantage of an easier surgical approach and a better control of the lordosis. This paper will describe the operative indications, the choices of instrumented levels, and the medium term followup results.     

Perioperative radiographic reconstruction of the scoliotic vertebral column

We have developed a new per-operative three dimensional (3D) reconstruction technique to evaluate the 3D correction of a scoliotic spine induced by surgery using Cotrel-Dubousset instrumentation. A small object with 15 embedded markers was used to calibrate the radiographic system. During surgery, the calibration object was sterilized and fixed to the patient just before the acquisition of two pairs of posterior-anterior and sagittal radiographs; one pair before the rotation maneuver of the rod and one pair after the maneuver. The markers were digitized on each radiograph and their relative 3D positions were measured to establish the relation between the 3D positions of the anatomical structures and their 2D positions on the radiographs. This relation was used to calculate the 3D position of six anatomical landmarks per vertebra (the centers of the superior and inferior vertebral body endplates and the proximal and distal bodies of both pedicles) from the identification of these landmarks on each radiograph. We made a 3D representation of the thoracic and lumbar spine of three patients with idiopathic scoliosis undergoing corrective surgery by the posterior approach. Clinical indices (Cobb angle, axial rotation and the plane of maximum curvature) computed from the 3D reconstruction of the spine obtained before and after the rotation maneuver of the rod were compared to evaluate the 3D correction performed during the surgery. The new proposed approach allows the surgeon to evaluate the per-operative shape of the spine. This approach is simpler, faster and less risky for the patient than the previous method which employed an electromagnetic digitizer to measure the 3D coordinates of anatomical landmarks located on the posterior part of the spine. Furthermore, the 3D representation of the spine visualized from different points of view gives the surgeon an accurate evaluation of the 3D correction during the surgical procedure.