The sagittal curvature of spine in idiopathic scoliosis--its morphological features and the correlation among sagittal and frontal curvatures and rotation of apical vertebra

The change in sagittal curvature especially in thoracic kyphosis of idiopathic scoliosis patients, was analyzed and discussed. Those patients who had scoliotic deformity with typical vertebral rotation only in thoracic spine (ST group), showed significant decrease compared to normal person in thoracic kyphosis, but no difference in lumbar lordosis. Those suffering from scoliotic deformities with typical vertebral rotation in thoracic and lumbar spine showed a significant decrease in thoracic kyphosis and an increase in lumbar lordosis. However those changes in sagittal curvature were not found in FT group patients, who had scoliotic deformity without vertebral rotation. In conclusion, it is not the frontal curvature but the vertebral rotation which influenced the sagittal curvature of spine in patients with idiopathic scoliosis.     

The experimental basis of idiopathic scoliosis

Idiopathic scoliosis is a complex three-dimensional deformity of the spine of which the scoliotic deformity and rotation are entirely secondary to an abnormality of shape in the median sagittal plane. In the thoracic region, there is a lordosis where a kyphosis should exist. In a controlled series of animal experiments using the growing New Zealand white rabbit as the model, idiopathic scoliosis can readily be produced if an asymmetric lordosis is created in the lower thoracic spine. Neither pure lordosis nor pure scoliosis produces the progressive idiopathic deformity. In the experimental animal when the normal thoracic kyphosis is reconstituted before maturity, the idiopathic deformity spontaneously improves. This lays the foundation for a more physiologic approach to treatment.     

Combined idiopathic kyphosis and scoliosis. An analysis of the lateral spinal curvatures associated with Scheuermann's disease

A radiological study of 50 patients with thoracic Scheuermann's disease revealed two types of lateral spinal curvature. A total of 43 lateral curves was present in 35 of the patients. Thirteen were apical at the same level as the Scheuermann's kyphosis and were due to vertebral-body wedging in the coronal plane; these curves had a mean Cobb angle of 15 degrees, occurred with equal prevalence in boys and girls and were directed equally to right and left. Thirty curves occurred in regions of compensatory lordosis (mean 5.6 degrees) situated above or, more commonly, below the Scheuermann's kyphosis. These scolioses had a mean Cobb angle of 16 degrees, were more often convex to the right than to the left and were significantly more prevalent in girls than in boys. The presence of these kyphoses and scolioses in the same spine, separated by only a few vertebrae, emphasises the importance of the sagittal plane in idiopathic spinal deformities and strongly suggests that idiopathic scoliosis and Scheuermann's disease share a common pathological process.     

The sagittal configuration and mobility of the spine in idiopathic scoliosis

The aim of this study is to see how the spinal sagittal configuration and mobility in 127 patients with idiopathic scoliosis are influenced by increasing scoliotic deformity and to determine when this deformity gets clinically significant compared to controls (n = 92). In patients with thoracic curves the degrees of thoracic kyphosis and lumbar lordosis were significantly less than those of the controls. Neither the kyphosis nor the lordosis were correlated to the Cobb angles. Even patients with small curves have straight spines in the sagittal plane; there is no tendency for the kyphosis and lordosis to decrease when the scoliotic deformity increases. This indicates that it is especially individuals with straight spines in the sagittal plane who are prone to develop scoliosis. It is also suggested that the limitation in spinal function for curves with Cobb angles below 50 degrees may be neglected.     

Comparison of the effects of lordosis on the thoracic spine using the Milwaukee and Gschwend brace in scoliosis and kyphosis

64 patients in Milwaukee-Brace and 32 patients in Gschwend-Brace have been assessed for creating lordosis of the thoracic spine. In both types of braces induction of lordosis can be observed although there did not seem to exist a directly proportionate relationship towards the period of treatment. The degree of correction in the thoracic spine depends on the kyphosis at the onset of treatment. In marked kyphosis exceeding 60 degrees or corresponding kyphotic components in scoliosis the Milwaukee-Brace is preferred over against the Gschwend-Brace. In a pure kyphosis with minimal scoliotic curve the Gschwend-Brace remains the treatment of choice.     

Proximal kyphosis after short posterior fusion for thoracolumbar scoliosis

Thoracolumbar idiopathic scoliosis usually is treated by anterior spinal fusion. However, short posterior spinal fusion that includes only the structural curve has been tried in a limited number of patients. The fusion may end cranially in the lower thoracic region and cause an increase in sagittal decompensation at the proximal junction. From July 1989 to July 1998, 14 patients were treated with thoracolumbar idiopathic scoliosis by short posterior spinal fusion. The lateral radiographs were evaluated preoperatively, immediately postoperative, and during followup. The focal kyphotic angle was used to examine the changes in focal sagittal alignment. A 10 degrees progression was defined as the radiographic criterion for the development of junctional kyphosis. Proximal junctional kyphosis occurred in six of the 14 patients, in which one patient needed revision surgery. In all six patients, the average preoperative lumbar lordosis was greater than 35 degrees, and decreased more than 10 degrees during surgery. In the five patients with a focal kyphotic angle larger than 10 degrees, four had proximal junctional kyphosis develop. According to the current findings, short posterior spinal fusion can be done only if the focal kyphotic angle proximal to the fusion is less than 10 degrees, and the lumbar lordosis must be preserved carefully during surgery.     

Harrington-Luque and Cotrel-Dubousset instrumentation for idiopathic thoracic scoliosis. A postoperative comparison using segmental radiologic analysis

This article reports a comparison of the Cotrel-Dubousset (CD) operation with the Harrington-Luque (HL) procedure for the treatment of adolescent idiopathic thoracic scoliosis. Thirty-nine patients were studied preoperatively and postoperatively using segmental radiologic measurements including Cobb angle, end-vertebra angles (EVAs), surgical flexibility index, vertebral rotation, displacement and tilt, convex and concave rib-vertebra angles (RVAs), and kyphosis and lordosis. Cotrel-Dubousset is not significantly different from HL with respect to Cobb angle (%), surgical flexibility index, apical vertebral displacement, apical vertebral rotation, apical rib-vertebra angles, kyphosis, and lordosis. It is significantly better than the HL with respect to the correction of vertebral displacement at T10-11; lower EVA of the thoracic curve; vertebral rotation mainly above the apex; convex RVAs above the apex; and concave RVAs at T10. The surgical correction of vertebral tilt above and below the apex of the thoracic curve is significantly related to the correction of convex and concave RVAs. The view that persistent deformity of ribs is a factor needing surgical correction in some patients with adolescent idiopathic thoracic scoliosis having posterior instrumentation and fusion needs further evaluation.     

Surface stereophotogrammetry of thoracic kyphosis

The thoracic kyphosis angles of 16 normal individuals, 10 patients with Scheuermann's disease and 11 with adolescent idiopathic scoliosis were measured both radiographically and from Integrated Shape Imaging System (ISIS) scans obtained by surface stereophotogrammetry. There was a high correlation between the two measures. The method of kyphosis measurement from ISIS scans was then used for 30 patients with adolescent idiopathic scoliosis who underwent corrective surgery. A significant reduction in thoracic kyphosis was observed postoperatively. In another group of 28 patients managed conservatively by bracing, some hypokyphosis developed after treatment. However, we found no association between hypokyphosis and curve progression.     

Surface stereophotogrammetry of thoracic kyphosis

The thoracic kyphosis angles of 16 normal individuals, 10 patients with Scheuermann's disease and 11 with adolescent idiopathic scoliosis were measured both radiographically and from Integrated Shape Imaging System (ISIS) scans obtained by surface stereophotogrammetry. There was a high correlation between the two measures.

The method of kyphosis measurement from ISIS scans was then used for 30 patients with adolescent idiopathic scoliosis who underwent corrective surgery. A significant reduction in thoracic kyphosis was observed postoperatively. In another group of 28 patients managed conservatively by bracing, some hypokyphosis developed after treatment. However, we found no association between hypokyphosis and curve progression.     

Differences in early sagittal plane alignment between thoracic and lumbar adolescent idiopathic scoliosis

Background contextIt has previously been shown that rotational stability of spinal segments is reduced by posteriorly directed shear loads that are the result of gravity and muscle tone. Posterior shear loads act on those segments of the spine that are posteriorly inclined, as determined by each individual's inherited sagittal spinal profile. Accordingly, it can be inferred that certain sagittal spinal profiles are more prone to develop a rotational deformity that may lead to idiopathic scoliosis; and lumbar scoliosis, on one end of the spectrum, develops from a different sagittal spinal profile than thoracic scoliosis on the other end.PurposeTo examine the role of sagittal spinopelvic alignment in the etiopathogenesis of different types of idiopathic scoliosis.Study design/settingMulticenter retrospective analysis of lateral radiographs of patients with small thoracic and lumbar adolescent idiopathic scoliotic curves.Patients sampleWe included 192 adolescent idiopathic scoliosis patients with either a thoracic (n=128) or lumbar (n=64) structural curve with a Cobb angle of less than 20° were studied. Children with other spinal pathology or with more severe idiopathic scoliosis were excluded, because this disturbs their original sagittal profile. Subjects who underwent scoliosis screening and had a normal spine were included in the control cohort (n=95).Outcome measuresThoracic kyphosis, lumbar lordosis, T9 sagittal offset, C7 and T4 sagittal plumb lines, pelvic incidence, pelvic tilt, and sacral slope, as well as parameters describing orientation in space of each individual vertebra between C7 and L5 and length of the posteriorly inclined segment.MethodsOn standardized lateral radiographs of the spine, a systematic, semi-automatic measurement of the different sagittal spinopelvic parameters was performed for each subject using in-house developed computer software.ResultsEarly thoracic scoliosis showed a significantly different sagittal plane from lumbar scoliosis. Furthermore, both scoliotic curve patterns were different from controls, but in a different sense. Thoracic kyphosis was significantly decreased in thoracic scoliosis compared with both lumbar scoliosis patients and controls. For thoracic scoliosis, a significantly longer posteriorly inclined segment, and steeper posterior inclination of C7–T8 was observed compared with both lumbar scoliosis and controls. In lumbar scoliosis, the posteriorly inclined segment was shorter and located lower in the spine, and T12–L4 was more posteriorly inclined than in the thoracic group. The lumbar scoliosis cohort had a posteriorly inclined segment of the same length as controls, but T12–L2 showed steeper posterior inclination. Lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope, however, were similar for the two scoliotic subgroups as well as the controls.ConclusionsThis study demonstrates that even at an early stage in the condition, the sagittal profile of thoracic adolescent idiopathic scoliosis differs significantly from lumbar scoliosis, and both types of scoliosis differ from controls, but in different aspects. This supports the theory that differences in underlying sagittal profile play a role in the development of different types of idiopathic scoliosis.     

Relationship between thoracic hypokyphosis, lumbar lordosis and sagittal pelvic parameters in adolescent idiopathic scoliosis

Purpose

Sagittal spine and pelvic alignment of adolescent idiopathic scoliosis (AIS) is poorly described in the literature. It generally reports the sagittal alignment with regard to the type of curve and never correlated to the thoracic kyphosis. The objective of this study is to investigate the relationship between thoracic kyphosis, lumbar lordosis and sagittal pelvic parameters in thoracic AIS.

Methods

Spinal and pelvic sagittal parameters were evaluated on lateral radiographs of 86 patients with thoracic AIS; patients were separated into hypokyphosis group (n = 42) and normokyphosis group (n = 44). Results were statistically analyzed. The lumbar lordosis was lower in the hypokyphosis group, due to the low proximal lordosis. The thoracic kyphosis was not correlated with any pelvic parameters but with the proximal lordosis. The pelvic incidence was correlated with sacral slope, pelvic tilt, lumbar lordosis and highly correlated with distal lumbar lordosis in the two groups. There was a significant linear regression between thoracic kyphosis and proximal lordosis and between pelvic incidence and distal lordosis.

Conclusions

We can consider that the proximal part of the lordosis depends on the thoracic kyphosis and the distal part depends on the pelvic incidence. The hypokyphosis in AIS is independent of the pelvic parameters and could be described as a structural parameter, characteristic of the scoliotic deformity.     

Three-dimensional spinal curvature in idiopathic scoliosis

Scoliosis is usually considered as a deformity of the spine in the frontal plane, without reference to curvatures in other planes. In this study, the three-dimensional shape of the spine of 104 patients with untreated idiopathic scoliosis (5-55 degrees Cobb) was studied by means of stereo radiographs to determine relationships between curvature of the spine in the frontal plane view, in the lateral view, and in the intermediate views. There was a weak but statistically significant correlation (r = 0.2) relating greater scoliosis with lesser kyphosis or greater lordosis. In the thoracic region, the sagittal plane spinal curvature was less than that measured in a population without scoliosis (mean difference, 7.72 +/- 9.9 degrees). Seventy-four of 76 scolioses in the upper region of the spine with lateral curvature greater than 5 degrees Cobb were kyphotic. Sixty-four of 84 curves greater than 5 degrees Cobb in the lower region were lordotic. Measuring curvatures in the plane of symmetry of the rotated apical vertebra altered these ratios to 69 of 76 kyphotic in the upper region and 68 of 84 lordotic in the lower region. The plane of maximum curvature of sections of the spine with scoliosis was not related to the plane of symmetry of the rotated apical vertebra, for in kyphotic regions of the spine the rotations of these two planes were in opposite directions. In all cases, the magnitudes of the rotations were quite different, i.e., by a factor of -0.22 for curves in thoracic region and by a factor of 0.24 for curves in the lumbar region. This implies that mechanical measures to correct this spinal deformity or to prevent progression should apply different rotations to the apex from those applied to the curve as a whole and, in opposite senses, in curves in kyphotic regions. There was no evidence of an abnormality of sagittal curvature of a magnitude to implicate it in the etiology or in the treatment.     

Idiopathic scoliosis: biomechanics and biology

For whatever reason, right-left asymmetry has attracted an illogical proportion of research effort. Non-structural scoliosis, for example secondary to a leg length inequality, is indeed a problem of right-left asymmetry, but structural scoliosis is a complex three-dimensional deformity involving all planes. Biomechanical, biological and clinical evidence indicates clearly that the problem is one of front-back asymmetry and not right-left. The importanc of biological factors lies in their ability to bring the spinal column to and beyond its buckling threshold. Thus a taller and more slender spine is more liable to bend and, being stiffer in the sagittal plane, favours movement into other planes. This epitomises the spine of the scoliosis patient who is growing faster with a spinal template similar to other family members allowing idiopathic scoliosis to express itself genetically. It is the opposite condition to idiopathic hyperkyphosis (Scheuermann's disease), but this deformity is rotationally stable, thus remaining in the sagittal plane. The presence of an adjacent area of lordo-scoliosis below the region of hyperkyphosis testifies to the common nature of the pathogenesis of idiopathic scoliosis and Scheuermann's disease. It is the area of compensatory hyperlordosis below the Scheuermann's area that has obligatorily buckled and represents a human model supporting the lordosis theory, as does surgically tethering the back of the young growing human spine, which crankshafts accelerated progression. Similarly the only successful animal model of the formation of idopathic follows creation of a lordotic spinal segment in an otherwise kyphotic spine. For centuries, engineers have recognised that the mechanical behaviour of a column under load is influenced by geometry, as well as by material properties; it is clear that the spinal column also obeys these well-described laws.     

Differential diagnosis of early scoliosis in Scheuermann's disease and idiopathic scoliosis (author's transl)

In order to avoid overtreatment or undertreatment of a beginning scoliosis early differentiation of the clinically unimportant concomitant scoliosis of Scheuermann's disease is essential as against early idiopathic scoliosis, spondyloepiphyseal dysplasia and the fixed round back deformity of adolescents. Scheuermann's scoliosis as opposed to idiopathic scoliosis is characterised by the almost complete lack of vertebral rotation (as with spondyloepiphyseal dysplasia), by a localized unilateral narrowing of the intervertebral space in the a.p. x-ray, as well as by a slight Z- or E-pattern, and a relative shortness of the curves. Simultaneous dorsal kyphosis may be absent. Indispensable is furthermore, the familiarity with the early x-ray signs of Scheuermann's disease in the lateral view as compared with the X-ray of the fixed roundback.     

Scheuermann's kyphosis

Scheuermann's disease is the most common cause of structural kyphosis in adolescents. The kyphotic deformity is frequently attributed to "poor posture," resulting in delayed diagnosis and treatment. Indications for treatment remain somewhat debated, because the true natural history of the disease has not been clearly defined. Brace treatment is almost always successful in patients with kyphosis between 55 degrees and 80 degrees if the diagnosis is made before skeletal maturity. Kyphosis greater than 80 degrees in the thoracic spine or 65 degrees in the thoracolumbar spine is almost never treated successfully without surgery in symptomatic patients. Surgical treatment in adolescents and young adults should be considered if there is documented progression, refractory pain, loss of sagittal balance, or neurologic deficit. The major postoperative complication after surgical treatment is junctional kyphosis proximally or distally, which is usually related to not including all levels of the kyphosis or overcorrection of the deformity (>50%). With proper patient selection, excellent outcomes can be expected with nonoperative or operative treatment in patients with Scheuermann's disease.     

Anterior lengthening in scoliosis occurs only in the disc and is similar in different types of scoliosis

BACKGROUND CONTEXTRelative anterior spinal overgrowth was proposed as a generalized growth disturbance and a potential initiator of adolescent idiopathic scoliosis (AIS). However, anterior lengthening has also been observed in neuromuscular (NM) scoliosis and was shown to be restricted to the apical areas and located in the intervertebral discs, not in the bone. This suggests that relative anterior spinal overgrowth does not rightfully describe anterior lengthening in scoliosis, as it seems not a generalized active growth phenomenon, nor specific to AIS.PURPOSETo determine if compensatory curves in congenital scoliosis exhibit a mechanism of anterior lengthening without changes in the vertebral body, similar to curves in AIS and NM scoliosis.STUDY DESIGN/SETTINGCross-sectional.PATIENT SAMPLECT-scans were included of patients in whom a short segment congenital malformation had led to a long thoracic compensatory curve without bony abnormality. Based on data of other scoliosis types, the calculated required sample size was n=12 to detect equivalence of vertebral bodies as compared with nonscoliotic controls. Out of 143 congenital scoliosis patients, 18 fit the criteria and compared with 30 nonscoliotic controls, 30 AIS and 30 NM scoliosis patients.OUTCOME MEASURESThe anterior-posterior length discrepancy (AP%) of the total curve and for vertebral bodies and intervertebral discs separately.METHODSOf each vertebral body and intervertebral disc in the compensatory curve, the anterior and posterior length was measured on CT-scans in the exact mid-sagittal plane, corrected for deformity in all three planes. The AP% was calculated for the total compensatory curve (Cobb-to-Cobb) and for the vertebral bodies and the intervertebral discs separately. Positive AP% indicated that the anterior side was longer than the posterior side.RESULTSThe total AP% of the compensatory curve in congenital scoliosis showed lordosis (+1.8%) that differed from the kyphosis in nonscoliotic controls (−3.0%; p<.001) and was comparable to the major curve in AIS (+1.2%) and NM scoliosis (+0.5%). This anterior lengthening was not located in the bone; the vertebral body AP% showed kyphosis (−3.2%), similar to nonscoliotic controls (−3.4%) as well as AIS (−2.5%) and NM scoliosis (−4.5%; p=1.000). However, the disc AP% showed lordosis (+24.3%), which sharply contrasts to the kyphotic discs of controls (−1.5%; p<.001), but was similar to AIS (+17.5%) and NM scoliosis (+20.5%).CONCLUSIONSThe current study on compensatory curves in congenital scoliosis confirms that anterior lengthening is part of the three-dimensional deformity in different types of scoliosis and is exclusively located in the intervertebral discs. The bony vertebral bodies maintain their kyphotic shape, which indicates that there is no active anterior bony overgrowth. Anterior lengthening appears to be a passive result of any scoliotic deformity, rather than being related to the specific cause of AIS.     

Surgical treatment of Scheuermann's disease with segmental compression instrumentation

Twenty-one patients with Scheuermann's kyphosis had surgery for progressive kyphotic deformity of 50 degrees or greater. There were six adolescents, with a mean age of 15.6 years (range, 13-17 years) and 15 young adults, with a mean age of 25.4 years (range, 18-40 years). All patients had posterior spine arthrodesis with segmental compression instrumentation. Seven patients with rigid kyphosis had combined anterior and posterior spine arthrodesis. One patient died of superior mesenteric artery syndrome. In the group of 13 patients with posterior arthrodesis only, followup was 4.5 years. The mean preoperative thoracic kyphotic curve of 68.5 degrees improved to 40 degrees at latest review, with an average loss of correction of 5.75 degrees. Junctional kyphosis occurred in two patients with a short arthrodesis: one at the cephalad end and one at the caudal end of the fused kyphotic curve. In the second group of seven patients with combined anterior and posterior arthrodesis, followup was 6 years. The mean preoperative thoracic kyphotic curve of 86.3 degrees improved to 46.4 degrees at latest review, with an average loss of correction of 4.4 degrees. Overall, there was no postoperative neurologic deficit and no pseudarthrosis. Thus, posterior arthrodesis and segmental compression instrumentation seems to be effective for correcting and stabilizing kyphotic deformity in Scheuermann's disease. Despite a long operating time, this technique provided significant correction, avoiding the development of any secondary deformity in most patients. Combined anterior and posterior spine arthrodesis is recommended for rigid, more severe kyphotic deformities.     

Excessive thoracic lordosis and loss of pulmonary function in patients with idiopathic scoliosis.

Idiopathic thoracic lordoscoliosis is more common and more productive of respiratory compromise than is kyphoscoliosis. In some patients with idiopathic scoliosis, thoracic lordosis is the predominant component of the disease. Five such patients, all of whom had idiopathic scoliosis with excessive thoracic lordosis, progressive deformity despite Milwaukee brace treatment, and significant compromise of pulmonary function, are presented. Harrington instrumentation (distraction rod only) and spine fusion improved the deformity and respiratory function. The recommended treatment for this type of idiopathic scoliosis is early recognition and prompt surgical correction. The Milwaukee brace should be avoided. Postoperative management must include early ambulation combined with vigorous breathing exercises.