Behandlung der kongenitalen Skoliose mit dem Vertical-expandable-prosthetic-titanium-rib-Implantat

Children with congenital thoracic scoliosis associated with fused ribs and unilateral unsegmented bars adjacent to convex hemivertebrae will invariably have curve progression without treatment. It is assumed that the unilateral unsegmented bars do not grow and therefore early spinal fusion has been performed in the past with consecutive short thoracic spines and loss of lung volume. A new surgical technique is based on an indirect deformity correction and enlargement of the thorax via a longitudinal implant, the vertical expandable prosthetic titanium rib (VEPTR).The length of the thoracic spine after VEPTR implantation was analyzed in 21 children with an average follow-up of 4.2 years. Eighteen children did not have any prior surgery while three had already undergone spinal fusion. Using a 3-D analysis of computed tomography, a significant growth of the concave (7.9 mm/7.1% increase per year) and convex (8.3 mm/6.4%) side of the thoracic spine was found with no significant difference between sides. Unilateral unsegmented bars showed significant growth as well.Contrary to common knowledge, we were able to demonstrate the growth of the concave side of the thoracic spine and of the unilateral unsegmented bars after expansion thoracoplasty and VEPTR implantation.     

The vertical expandable prosthetic titanium rib implant for the treatment of thoracic insufficiency syndrome associated with congenital and neuromuscular scoliosis in young children

Expansion thoracoplasty and vertical expandable prosthetic titanium rib (VEPTR; Synthes Spine Co., West Chester, Pennsylvania, USA) implantation is a new method for the treatment of thoracic insufficiency syndrome and congenital spinal deformity in children. The longitudinal rib implant expands the thorax and indirectly corrects spinal deformity, thus allowing spinal, thoracic and probably lung growth. VEPTR has been used since 1989 in San Antonio, USA, and was introduced to Europe in 2002. This paper describes the preliminary experience with the European patients. Fifteen children with progressive scoliosis had a VEPTR implantation at a mean age of 6 years (11 months to 12 years). Nine children had thoracic insufficiency syndrome due to unilateral unsegmented bars (n = 4), absent ribs (n = 1), hemivertebrae (n = 2) or bilateral fused ribs (n = 2). Six children had severe thoracolumbar scoliosis and pelvic obliquity due to neuromuscular scoliosis. After VEPTR implantation, families and patients reported improvement of the thoracic insufficiency syndrome and better sitting abilities in the neuromuscular patients, as well as radical cosmetic improvement. There were three complications (skin breakage, lumbar hook displacement, rib fracture) after performing fifteen primary VEPTR implantations and 13 expansion surgeries in eight patients. Our experience suggests that expansion thoracoplasty and VEPTR implantation is a safe and efficient method for the treatment of thoracic insufficiency syndrome in young children with severe scoliosis.     

The effect of opening wedge thoracostomy on thoracic insufficiency syndrome associated with fused ribs and congenital scoliosis

BACKGROUND: Thoracic insufficiency syndrome is the inability of the thorax to support normal respiration or lung growth and is seen in patients who have severe congenital scoliosis with fused ribs. Traditional spinal surgery does not directly address this syndrome. METHODS: Twenty-seven patients with congenital scoliosis associated with fused ribs of the concave hemithorax had an opening wedge thoracostomy with primary longitudinal lengthening with use of a chest-wall distractor known as a vertical, expandable prosthetic titanium rib. Repeat lengthenings of the prosthesis were performed at intervals of four to six months. Radiographs were analyzed with respect to correction of the spinal deformity, as indicated by a change in the Cobb angle, and lateral deviation of the spine, as indicated by the interpedicular line ratio. Spinal growth was assessed by measuring the change in the length of the spine. Correction of the thoracic deformity and thoracic growth were assessed on the basis of the increase in the height of the concave hemithorax compared with the height of the convex hemithorax (the space available for the lung), the increase in the thoracic spinal height, and the increase in the thoracic depth and width. The thoracic deformity in the transverse plane was measured with computed tomography, and the scans were analyzed for spinal rotation, thoracic rotation, and the posterior hemithoracic symmetry ratio. Clinically, the patients were assessed on the basis of the relative heights of the shoulders and of head and thorax compensation. Pulmonary status was evaluated on the basis of the respiratory rate, capillary blood gas levels, and pulmonary function studies. RESULTS: The mean age at the time of the surgery was 3.2 years (range, 0.6 to 12.5 years), and the mean duration of follow-up was 5.7 years. All patients had progressive congenital scoliosis, with a mean increase of 15 degrees /yr before the operation. The scoliosis decreased from a mean of 74 degrees preoperatively to a mean of 49 degrees at the time of the last follow-up. Both the mean interpedicular line ratio and the space available for the lung ratio improved significantly. The height of the thoracic spine increased by a mean of 0.71 cm/yr. At the time of the last follow-up, the mean percentage of the predicted normal vital capacity was 58% for patients younger than two years of age at the time of the surgery, 44% for those older than two years of age (p < 0.001), and 36% for those older than two years of age who had had prior spine surgery. In a group of patients who had sequential testing, all increases in the volume of vital capacity were significant (p < 0.0001), but the changes in the percentages of the predicted normal vital capacity were not. There was a total of fifty-two complications in twenty-two patients, with the most common being asymptomatic proximal migration of the device through the ribs in seven patients. CONCLUSIONS: Opening wedge thoracostomy with use of a chest-wall distractor directly treats segmental hypoplasia of the hemithorax resulting from fused ribs associated with congenital scoliosis. The operation addresses thoracic insufficiency syndrome by lengthening and expanding the constricted hemithorax and allowing growth of the thoracic spine and the rib cage. The procedure corrects most components of chest-wall deformity and indirectly corrects congenital scoliosis, without the need for spine fusion. The technique requires special training and should be performed by a multispecialty team.     

Kongenitale Fehlbildungen an der Wirbelsäule

Congenital anomalies of the spine usually originate in (toxic) disturbances during pregnancy. There are occasional hereditary types. These are characterized by the presence of multiple anomalies. Congenital scolioses are often associated with other anomalies like spinal dysraphy (20-30%) and fusion of the ribs. Furthermore heart defects, Sprengel's deformity, cleft palates, hemimelias, clubfeet or congenital vertical talus are frequently associated with congenital scoliosis. We classify in failures of formation, segmentation and combined types. The type of malformation determines the prognosis. One hemivertebra is associated with a risk of progression of 0-2 degrees/year, 2 ipsilateral hemivertebra with 2-3 degrees/year, a unilateral unsegmented bar with 5 degrees/year and a combination of a unilateral unsegmented bar with a contralateral hemivertebra with approximately 10 degrees/year. Conservative treatment is usually ineffective. The indication for operative treatment should be made before the deformity becomes unacceptable, as a correction is difficult and dangerous. The following operations can be carried out: Anterior and/or posterior fusion with or without instrumentation, epiphyseodesis, (hemi)vertebrectomies (with anterior and/or posterior approach), distraction with a halo, osteotomies, separation of the fused ribs and gradual distraction (Campbell's expansion thoracoplasty). The operations carry significant risks and the indication to the various treatment modalities is difficult. Operations should be made under monitoring of sensory and motor evoked potentials. From 498 patients with congenital anomalies of the spine in our observation we have operated on 143. Hemivertebrectomies were the most frequent interventions (56).     

Rib cage surgery for the treatment of scoliosis: a biomechanical study of correction mechanisms.

Rib shortening or lengthening are surgical options that are used to address the cosmetic rib cage deformity in scoliosis, but can also alter the equilibrium of forces acting on the spine, thus possibly counteracting in a mechanical way the scoliotic process and correcting the spinal deformities. Although rib surgeries have been successful in animal models, they have not gained wide clinical acceptance for mechanical correction of scoliosis due to the lack of understanding of the complex mechanisms of action involved during and after the operation. The objective of this study was to assess the biomechanical action of different surgical approaches on the rib cage for the treatment of scoliosis using a patient-specific finite element model of the spine and rib cage. Several unilateral and bilateral rib shortening/lengthening procedures were tested at different locations on the ribs (convex/concave side of the thoracic curvature; at the costo-transverse/costo-chondral joint; 20 and 40 mm adjustments). A biomechanical analysis was performed to assess the resulting geometry and load patterns in ribs, costo-vertebral articulations and vertebrae. Only slight immediate geometric variations were obtained. However, concave side rib shortening and convex side rib lengthening induced important loads on vertebral endplates that may lead to possible scoliotic spine correction depending on the remaining growth potential. Convex side rib shortening and concave side rib lengthening produced mostly cosmetic rib cage correction, but generated inappropriate loads on the vertebral endplates that could aggravate vertebral wedging. This study supports the concept of using concave side rib shortening or convex side rib lengthening as useful means to induce correction of the spinal scoliotic deformity during growth, though the effects of growth modulation from induced loads must be addressed in more detail to prove the usefulness of rib shortening/lengthening techniques.     

Operative Strategies for Thoracic Insufficiency Syndrome by Vertical Expandable Prosthetic Titanium Rib Expansion Thoracoplasty

VEPTR expansion thoracoplasty can control exotic scoliosis in patients with congenital scoliosis and fused ribs with improvement in the coronal plane of the 3-dimensional thoracic deformity and stabilization of the transverse plane three-dimensional deformity of the thorax. Vital capacities at short-term follow-up are acceptable, especially in those patients who were younger than age 2 years at time of their initial surgery with no history of prior spinal surgery. Additional VEPTR expansion thoracoplasties have been developed for treatment of thoracic insufficiency syndrome associated with other volume depletion deformities of the thorax and will be the subject of later reports.     

Patterns and progression in congenital scoliosis

Sixty cases of congenital scoliosis over a 13-year period were studied. The female:male ratio was 1.4:1. The deformity usually presented itself first either at 2 or 8-13 years of age. A positive family history was present in five cases, and parental consanguinity was observed in 40% of patients. Five patterns of deformity were recognized. Hemivertebra was the most common type, and unilateral unsegmented bar with contralateral hemivertebra was the most severe and most progressive pattern of deformity. Thoracic curves were more prevalent while larger curves were more commonly seen in the thoracolumbar area. The curves measured >40 degrees in 70% of the patients who had reached maturity. The curve progression index was 9 degrees for unilateral unsegmented bar with contralateral hemivertebra, and 6 degrees without contralateral hemivertebra. This index was 1.5 degrees for hemivertebra and complex type of deformity, and 0.5 degrees for block vertebra. Unbalanced fully segmented hemivertebra was next after the two types of unsegmented bars in terms of potential for progression. Presence of fused ribs on concave side of lower thoracic curves increased the rate of curve progression. Spinal dysraphism, diagnosed in 20% of cases, was the most commonly associated anomaly.     

Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction

BACKGROUND: Several studies have provided data on the vertebral morphology of normal spines, but there is a paucity of data on the vertebral morphology in patients with idiopathic scoliosis. METHODS: The morphology of the pedicles and bodies of 307 vertebrae as well as the distance between the pedicles and the dural sac (the epidural space) in twenty-six patients with right-sided thoracic idiopathic scoliosis were analyzed with use of magnetic resonance imaging and multiplanar reconstruction. RESULTS: A distinct vertebral asymmetry was found at the apical region of the thoracic curves, with significantly thinner pedicles on the concave side than on the convex side (p < 0.05). The degree of intravertebral deformity diminished farther away from the apex, with vertebral symmetry restored at the neutral level. In the thoracic spine, the transverse endosteal width of the apical pedicles measured between 2.3 mm and 3.2 mm on the concave side and between 3.9 mm and 4.4 mm on the convex side (p < 0.05). In the lumbar spine, the pedicle width measured between 4.6 mm at the cephalad part of the curve and 7.9 mm at the caudad part of the curve. The chord length and the pedicle length gradually increased from 34 mm and 18 mm, respectively, at the fourth thoracic vertebra to 51 mm and 25 mm, respectively, at the third lumbar vertebra. The transverse pedicle angle measured 15 in the cephalad aspect of the thoracic spine, decreased to 7 at the twelfth thoracic vertebra, and increased again to 16 at the fourth lumbar vertebra. The width of the epidural space was <1 mm at the thoracic apical vertebral levels and averaged 1 mm at the lumbar apical vertebral levels on the concave side, whereas it was between 3 mm and 5 mm on the convex side (p < 0.05). CONCLUSION: Idiopathic scoliosis is associated with distinctive intravertebral deformity, with smaller pedicles on the concave side and a shift of the dural sac toward the concavity.     

The characteristics of thoracic insufficiency syndrome associated with fused ribs and congenital scoliosis

1. Thoracic insufficiency syndrome is the inability of the thorax to support normal respiration or lung growth. 2. The rare condition of fused ribs and congenital scoliosis may result in a three-dimensional thoracic deformity with adverse effects on thoracic growth and function with development of thoracic insufficiency syndrome. 3. The normal thorax is defined by two characteristics: normal, stable volume and the ability to change that volume. Volume depends on the width and depth of the rib cage, and the thoracic spine provides height. The ability to change volume, termed thoracic function, is provided by the diaphragm and the secondary muscles of respiration. 4. On radiographs, the loss of the vertical height of the lung of the concave, restricted hemithorax is defined by the percentage of space available for the lung. 5. Spine rotation causes a windswept thorax, with both restriction of the volume of the convex hemithorax and restriction of the motion of the involved ribs. 6. Constrictive three-dimensional deformity of the thorax may cause extrinsic, restrictive lung disease. 7. Progressive thoracic insufficiency syndrome is diagnosed on the basis of clinical signs of respiratory insufficiency, loss of chest wall mobility as demonstrated by the thumb excursion test, worsening indices of three-dimensional thoracic deformity on radiographs and computed tomography scans, or a relative decline in percent predicted vital capacity due to thoracic "failure to thrive," as demonstrated by pulmonary function tests. 8. Treatment of progressive thoracic insufficiency syndrome should provide an acute increase in the thoracic volume with stabilization of any flail chest-wall defects and maintain these improvements as the patient grows, without the need for spine fusion.     

Treatment of congenital thoracic scoliosis with associated rib fusions using VEPTR expansion thoracostomy: a surgical technique

European Spine Journal - Untreated growing patients with congenital scoliosis and fused ribs will develop finally thoracic insufficiency syndrome. The technique of expansion thoracoplasty with...     

Surgical treatment of severe congenital scoliosis with unilateral unsegmented bar by concave costovertebral joint release and both-ends wedge osteotomy via posterior approach

Introduction  

Congenital scoliosis with unilateral unsegmented bar has remained a surgical challenge. If it is treated with a traditional release of the convex side and an apical wedge osteotomy, there is a risk of bony bridge fracture on the concave side and spine translation during correction maneuvers, which may then result in spinal cord injuries. The authors developed a technique that consists of a concave-side costovertebral joint release followed by both-ends wedge osteotomy via a posterior-only approach. In this article, we describe the technique in detail, and present the results of ten patients treated with this technique.     

Pedicle morphology of the thoracic spine in preadolescent idiopathic scoliosis: magnetic resonance supported analysis

Although several studies have been reported on the adult vertebral pedicle morphology, little is known about immature thoracic pedicles in patients with idiopathic scoliosis. A total of 310 pedicles (155 vertebrae) from T1 to T12 in 10–14 years age group were analyzed with the use of magnetic resonance imaging and digital measurement program in 13 patients with right-sided thoracic idiopathic scoliosis. Each pedicle was measured in the axial and sagittal planes including transverse and sagittal pedicle width and angles, chord length, interpedicular distance and epidural space width on convex and concave sides of the curve. The smallest transverse pedicle widths were in the periapical region and the largest were in the caudal region. No statistically significant difference in transverse pedicle widths was detected between the convex and concave sides. The transverse pedicle angle measured 15.56° at T1 and decreased to 6.32° at T12. Chord length increased gradually from the cephalad part of the thoracic spine to the caudad part as the shortest length was seen at T1 convex level with a mean of 30.45 mm and the largest length was seen at T12 concave level with a mean of 41.73 mm. The width of epidural space on the concave side was significantly smaller than that on the convex side in most levels of the curve. Based on the anatomic measurements, it may be reasonable to consider thoracic pedicle screws in preadolescent idiopathic scoliosis.     

Growth modification in the treatment of scoliosis

Structural deformities, of which scoliosis is a notable example, imply a skeletal length discrepancy which may involve all three dimensions. Once the deformity is established, secondary mechanisms come into action. Physiological treatment concerns modifying spinal growth and the convex side can be retarded, the concave side stimulated, the neurocentral physis arrested to correct rotation, and the forces acting along the ribs can be altered. Thus stapling, epiphysiodesis, posterior fusion, combined convex side epiphysiodesis, and convex side posterior fusion, convex side tether, costodesis, and concave side rib head excision have all been tried. Of these, combined anterior and posterior fusion of the convexity is the most effective, particularly for congenital hemivertebrae without rotation.     

Lung function asymmetry in children with congenital and infantile scoliosis

BACKGROUND CONTEXT: Progressive scoliosis alters lung function by reducing chest wall compliance and excursion and rotating intrathoracic contents, producing an increasingly asymmetric lung size. The effect of this distortion on regional lung perfusion and ventilation has not been described in children with congenital and infantile forms of scoliosis. The severity of scoliosis is often described by the Cobb angle of the spine, but the relationship between Cobb angle and lung function asymmetry between concave and convex lungs has not been described in this group of children. PURPOSE: To describe the frequency of asymmetric lung perfusion and ventilation among children with congenital or infantile thoracic scoliosis before surgical treatment and the relationship between Cobb angle and asymmetry of lung function. STUDY DESIGN/SETTING: Prospective comparison of lung perfusion scans and spine film findings in children evaluated in two pediatric spine referral clinics for expansion thoracoplasty and vertical expandable prosthetic titanium rib (VEPTR) implantation. PATIENT SAMPLE: Thirty-nine children, aged 1 year 8 months to 15 years 6 months, with congenital or infantile forms of scoliosis who are clinically stable outpatients and have neither primary pulmonary disease nor neuromuscular weakness. OUTCOME MEASURES: 1) Cobb angle measurements from weightbearing spine films and 2) right and left contributions to total lung perfusion and total lung ventilation compared with normal values. METHODS: Lung perfusion scans using technetium-labeled albumin macroaggregates were performed in all children; 15 of the children also underwent ventilation lung scans using aerosolized technecium-labeled diethylenetriaminepentaacetic acid (DTPA). The degree of asymmetry between right and left lung function from the normal right-to-left lung distribution was correlated with the Cobb angle of the spine. Ventilation and perfusion asymmetry between right and left lungs was also compared. RESULTS: Sixteen of the 25 children with congenital scoliosis had fused ribs; 13 additional children had infantile scoliosis. Cobb angles ranged from 30 degrees to 112 degrees in the group (median=71 degrees ), with the concave lung being the left lung in 61% of cases. Lung function relations between the right and left lungs were abnormal (>5% deviation from the normal 55% right [R]/45% left [L]) in 21 (54%) patients. Right-left contributions to lung perfusion ranged from 86% R/14% L to 26% R/74% L among the 39 children. Lung function in the concave lung was reduced below the normal proportion in only 20 children (51%). Lung function asymmetry, measured as the deviation from the normal contributions of the right and left lungs, did not correlate with Cobb angle values (r=.14, p=.4). Ventilation asymmetry and perfusion asymmetry were concordant and correlated closely (r=.93, p<.0001). CONCLUSIONS: Asymmetric ventilation and perfusion between the right and left lungs occurs in more than half of the children with severe congenital and infantile thoracic scoliosis. However, the severity of lung function asymmetry does not relate to Cobb angle measurements. Asymmetry in lung function is influenced by deformity of the chest wall in multiple dimensions, and cannot be ascertained by chest radiographs alone.     

Congenital anomalies of the ribs and chest wall associated with congenital deformities of the spine

BACKGROUND: Congenital anomalies of the ribs and chest wall as well as Sprengel deformity of the shoulder are often associated with congenital deformities of the spine. It has been suggested that rib anomalies may adversely affect the progression of the spinal deformity. METHODS: We conducted a retrospective study of the medical records and spine radiographs of 620 consecutive patients with congenital deformities of the spine; 497 patients (80%) had scoliosis; eighty-eight patients (14%), kyphoscoliosis; and thirty-five patients (6%), kyphosis. The rib anomalies were classified into simple and complex, and the presence of a Sprengel deformity of the shoulder was recorded. The rate of scoliosis deterioration without treatment before the age of eleven years, as well as the patient age and curve size at the time of surgery, was compared for different types of vertebral abnormalities in patients with and without rib anomalies. RESULTS: A total of 119 patients (19.2%) had rib anomalies, which were most commonly associated with congenital scoliosis (111 patients; 93%) and were much less frequently associated with congenital kyphoscoliosis or kyphosis (eight patients). The rib anomalies were simple in ninety-five patients and complex in twenty-four. Eighty-five patients (71%) with rib abnormalities had a scoliosis due to a unilateral failure of vertebral segmentation, and seven patients had mixed or unclassifiable vertebral anomalies. In contrast, only sixteen of 203 patients with a scoliosis due to a hemivertebra alone had rib anomalies. The rib anomalies were most frequently associated with a thoracic or thoracolumbar scoliosis (102 patients; 92%) and occurred on the concavity in eighty-two patients (74%), the convexity in twenty-two patients (20%), and were bilateral in seven patients. The Sprengel deformity occurred in forty-five patients and most frequently in association with a thoracic scoliosis due to a unilateral failure of vertebral segmentation (twenty-seven patients). No significant difference was detected in the rate of curve progression without treatment in patients with and without rib anomalies. The only exception was the mean age at the time of surgery, which was higher for patients with a unilateral unsegmented bar without rib anomalies (p = 0.005). In addition, no significant difference was found with regard to any tethering effect due to the site of the rib fusions on the concavity of the scoliosis, i.e., whether they were in close approximation to the spine or were more lateral (p > 0.05). CONCLUSIONS: Congenital rib anomalies occur most commonly on the concavity of a thoracic or thoracolumbar congenital scoliosis that is due to a unilateral failure of vertebral segmentation, and they do not appear to have an adverse effect on curve size or rate of progression.     

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.     

An analysis of the effect of the Zielke operation on the rib cage of S-shaped curves in idiopathic scoliosis

This report evaluates the rib cage in 16 patients with S-shaped idiopathic scoliosis having the Zielke operation and followed-up for an average period of 30 months. Methods used include Cobb angle and a segmental evaluation (T7-T12) of each of convex and concave rib-vertebra angles (RVAs), rib-vertebra angle differences (RVADs), vertebral rotation, tilt and displacement. Preoperatively, the apical convex ribs droop more than the concave ribs, but the most striking difference is an asymmetry of RVAs, with increasing droop of the concave RVAs from T7-T12. The effect of the Zielke operation (on the lower curve) is: (a) to correct the Cobb angle, vertebral tilt, and displacement of the upper (thoracic) curve; (b) to derotate the spine; (c) to elevate the mobile concave ribs; (d) to have little or no effect on the stiff apical convex ribs; and (e) to increase the droop of the mobile lower convex ribs. During follow-up, six of the upper (thoracic) curves progressed. The apical RVAD and apical convex RVA are not prognostic. The concave RVAs maintain their position while convex RVAs elevate relative to the concave ribs.     

Segmental vessel ligation in patients undergoing surgery for anterior spinal deformity

Segmental vessel ligation during anterior spinal surgery has been associated with paraplegia. However, the incidence and risk factors for this devastating complication are debated. We reviewed 346 consecutive paediatric and adolescent patients ranging in age from three to 18 years who underwent surgery for anterior spinal deformity through a thoracic or thoracoabdominal approach, during which 2651 segmental vessels were ligated. There were 173 patients with idiopathic scoliosis, 80 with congenital scoliosis or kyphosis, 43 with neuromuscular and 31 with syndromic scoliosis, 12 with a scoliosis associated with intraspinal abnormalities, and seven with a kyphosis. There was only one neurological complication, which occurred in a patient with a 127 degrees congenital thoracic scoliosis due to a unilateral unsegmented bar with contralateral hemivertebrae at the same level associated with a thoracic diastematomyelia and tethered cord. This patient was operated upon early in the series, when intra-operative spinal cord monitoring was not available. Intra-operative spinal cord monitoring with the use of somatosensory evoked potentials alone or with motor evoked potentials was performed in 331 patients. This showed no evidence of signal change after ligation of the segmental vessels. In our experience, unilateral segmental vessel ligation carries no risk of neurological damage to the spinal cord unless performed in patients with complex congenital spinal deformities occurring primarily in the thoracic spine and associated with intraspinal anomalies at the same level, where the vascular supply to the cord may be abnormal.     

The length and ash weight of the ribs of normal and scoliotic persons

The length and ash weight of ribs were studied in cadaveric specimens from 10 women and eight men with normal spines and from 15 women with scoliosis, six of them with idiopathic right convex thoracic curves. In each case, three rib pairs were removed, those from the scoliotic women corresponding to the apex and the suprajacent and subjacent vertebrae, and those from the normal male and female subjects usually being the 7th-9th. Between the female and the male control groups, there was a significant difference in rib length asymmetry, expressed as the mean of the left minus right difference for the three rib pairs for each person. The difference in ash weight was not significant. There was a significant mean difference in rib length asymmetry between the six patients with right convex thoracic idiopathic scoliosis (concave minus convex rib) and the group of normal females (left minus right rib). Ash weight displayed no significant differences. In five of the six patients with right convex thoracic scoliosis the left ribs of the three examined pairs were on average longer than the right ribs, but the difference was not significant.     

Muscle fiber types in thoracic erector spinae muscles. Fiber types in idiopathic and other forms of scoliosis

Histochemical studies of the thoracic part of the erector spinae muscles in scoliosis have shown a consistently higher proportion of Type 1 fibers on the convex side. The fiber distribution of the multifidus and semispinalis muscles was studied in adolescent idiopathic scoliosis (AIS). Compared with sex- and age-matched controls, a "normal" percentage of Type 1 fibers was found on the convex right side and significantly smaller percentage of Type 1 fibers on the concave side. Boys with AIS showed the same pattern as girls. In two patients with double major curves, the same pattern could be seen on the convexity of both curves. Patients with congenital scoliosis or scoliosis with early onset showed a different pattern with a "normal" percentage of Type 1 fibers on the concave side but a significantly greater percentage of Type 1 fibers on the convex side. In AIS, the deviation in the fiber distribution may constitute a primary factor in the pathogenesis of scoliosis. In congenital scoliosis the differences in fiber distribution between the convex and concave sides are considered secondary in the pathogenesis of the spinal curvature.