► [Abnormal spinal curvature in the coronal plane (scoliosis); abnormal, posteriorly convex spinal curvature in the sagittal plane (kyphosis, or gibbus)]
Abnormal curvatures of the spine are common in human pathology, occurring as primary disorders, as part of the malformation spectrum of syndromic and nonsyndromic conditions, or secondary to focal or diffuse vertebral defects, either congenital or acquired in origin.
The most common cause of spinal malalignment is idiopathic scoliosis, a designation used for scoliosis developing in the absence of any primary vertebral abnormality or known disorder directly affecting the spine (Fig. 3.55). Idiopathic scoliosis is not present at birth and usually becomes manifest during childhood. On the basis of the patient's age at the time of presentation, idiopathic scoliosis is divided into three types: infantile (detection before 4 years), juvenile (detection between 4 and 10 years), and adolescent type (detection after 10 years of age and before skeletal maturity is reached). It has been estimated that the frequency of idiopathic scoliosis is about 2-3% for scoliosis equal to or greater than 10° and about 0.5% for scoliosis more than 20° (Kane 1977; Renshaw 1988).Among adolescents, scoliosis is more common and progressive in girls than in boys. Progression of the spinal curve mostly depends upon the severity of the scoliosis, ranging from 5% to 80% in some series (Lonstein and Carlson 1984; Perdriolle and Vidal 1985). Based on the presence of skull depression at the same side of the body as the convexity of the curve, the etiology of infantile scoliosis has been related to molding effects initiated and maintained by prolonged recumbency of babies in an obliquely supine position in their cribs (Wynne-Davies 1975; Ponseti et al. 1976). However, the cause of idiopathic scoliosis remains unknown. Familial occurrence has been well documented (one third of first-degree relatives of patients with idiopathic scoliosis have spinal curvatures of 10° or more) (Ozonoff 1995), and in the offspring of parents with idiopathic scoliosis the risk of being affected is increased by a factor of 50. There is evidence for a dominant, X-linked inheritance pattern with incomplete pene-trance and variable expressivity (Cowell et al. 1972). Most specialists tentatively assume a multifactorial inheritance, with a genetic tendency to the deformity that is triggered in different individuals by different external factors. A familial autosomal dominant form
of scoliosis has been mapped to chromosome 17 (Salehi et al. 2000).
Scoliosis occurring in association with neuromuscular disorders can be due either to asymmetrical innervation or to unbalanced muscular control (Hensinger and MacEwen 1976). The list of conditions leading to neuromuscular scoliosis includes cerebral palsy (especially spastic quadriplegia) (Thometz and Simon 1988),syringomelia (Batnitzky et al. 1976), traumatic paraplegia (Hackney 1990), spinal muscular atrophy (Riccick et al. 1982), Friedreich's ataxia (Labelle et al. 1986), familial dysautono-mia (Hayek et al. 2000), and muscular dystrophy (Daher et al. 1985; Wilkins and Gibson 1976). The typical curvature in patients with neuromuscular scoliosis extends in the shape of a long letter 'C' from the upper thoracic region to the distal lumbar spine. Often, the pelvis is tilted and the hips may be dislocated (Kozonoff 1995).
Scoliosis also occurs in association with inherited connective tissue disorders with (Marfan syndrome, osteogenesis imperfecta) or without (Ehlers-Danlos syndrome) primary involvement of the skeleton. In Marfan syndrome (OMIM 154700) scoliosis occurs in about half the patients, with a radiographic pattern similar to that of idiopathic scoliosis (right-sided convexity of the curve in the thoracic spine). However, the scoliosis in Marfan syndrome has an earlier onset, is progressive, and affects both sexes equally. Posterior scalloping of the vertebral bodies due to dural ectasia, an increased incidence of Scheuermann disease, increased thoracic kyphosis, focal widening of the central canal in the sacral region, sacral meningocele, widening of the interpediculate distance, and atlanto-axial subluxation are additional spinal findings in patients with Marfan syndrome (Ozonoff 1995; Sponseller et al. 1995). Kyphoscoliosis, often of severe degree, occurs in about 40% of patients with osteogenesis imperfecta. It begins at an early age (under 5 years) and tends to progress at the same rate before and after puberty. Ligamentous laxity, osteoporosis, and vertebral compression fractures are likely to act in concert in the development of scoliosis in osteogenesis imperfecta (Norimatsu et al. 1982). The vertebral bodies are markedly flat and can have either a biconcave or a wedge-shaped configuration (Yong-Hing and MacEwen 1982; Falvo et al. 1974). Kyphoscoliosis at the thoracolumbar junction is also common in Ehlers-Danlos syndrome, being present even at birth in some cases, and is attributed to the ligamentous laxity typical of the condition. In later life kyphosis is accompanied by anterior wedging of the vertebral bodies and can be associated with posterior scalloping, spondylolysis, and spondylolisthesis (Beighton and Thomas 1969; Lewkonia and Pope 1985). In idiopathic juvenile osteoporosis (OMIM 259750) progressive kyphos-coliosis is related to osseous weakening. In neurofibromatosis type 1 (OMIM 162200) scoliosis can be due to focal damage to the vertebral spine or to the inherent defect of the osseous tissues. Therefore, either an abrupt spinal curvature with deformed vertebrae (enlarged foramina, erosion of the transverse processes) or an S-shaped curve resembling that of idiopathic scoliosis can be seen (Calvert et al. 1989; Funasaki et al. 1994).
Congenital scoliosis is the designation for the type of scoliosis caused by congenital vertebral defects, such as hemivertebrae, unilateral block vertebrae, pediculate bars, and neural arch fusions. These defects are directly responsible for the imbalance in the architecture of the spine (McMaster and Ohtsuka 1982; Nasca et al. 1975). The thoracolumbar spine is the region most commonly affected. Unilateral un-segmented bars cause spinal deviation by restricting the linear growth of the spine on one side while the uninvolved side continues to grow. Hemivertebrae, particularly if supernumerary, act as an enlarging
wedge that enhances the potential growth of the spine on the convexity of the curve. Progression of the scoliotic curve occurs in the majority of patients and is more severe in the presence of a unilateral bar on one side associated with a hemivertebra on the contralateral side. The presence of fused ribs on the concave side of lower thoracic curves increases the rate of curve progression (Shahcheraghi and Hobbi 1999). Possible associated anomalies include spinal dysraphism (Fig. 3.56) and Klippel-Feil syndrome (Theiss et al. 1997). When fusion involves the neural elements, the tethering effect exerted posteriorly leads to the development of congenital lordosis. Fusion of the posterior portions of the ribs also occurs in some cases. Congenital lordosis is uncommon, and it is usually limited to the thoracic spine. Respiratory problems are frequent and are related to the restrictive thoracic dysplasia. Congenital kyphosis, which is much more frequent than congenital lordosis, is caused in most cases by the presence of a dorsal hemivertebra (Williams et al. 1982). Less commonly, this defect of spinal alignment is due to segmentation failure of the anterior portion of two contiguous vertebral bodies (Remes et al. 2000). The thoracolumbar spine is typically affected. Congenital kyphosis may be associated with Klippel-Feil anomaly, genitourinary abnormalities, and myelomeningocele. With abrupt angulation of the spine the hypoplastic vertebra can be displaced backward, with secondary encroachment on the thecal sac and spinal cord (Beals 1969). Congenital kyphosis and scoliosis can coexist (congenital kyphoscoliosis). Careful monitoring of patients with congenital kyphosis and/or scoliosis for evidence of progression of the spinal curvature is advised. Associated anomalies of the ribs and the genitourinary tract, including unilateral renal agenesis, horseshoe kidneys, renal duplication, and renal ectopia, are common (Lorenzo et al. 1983).
Scoliosis and/or kyphosis also occur in several bone dysplasias and malformation syndromes, in association with focal or generalized vertebral abnormalities. Larsen syndrome (OMIM 150250,245600), a condition characterized by multiple congenital joint dislocations,exhibits abnormal spinal curvature with vertebral malformations, including errors in segmentation, spina bifida, and vertebral flattening. These changes are especially prominent in the cervical spine, where either kyphosis of extreme degree or hyperlordosis may be seen. Varying degrees of scoliosis and lordosis are common in the thora-columbar spine. Progressive, severe thoracolumbar kyphoscoliosis, frequently developing after infancy, cervical kyphosis, irregular deformities of the vertebral bodies, and narrowing of the interpediculate distance in the lumbar spine are prominent features of diastrophic dysplasia (OMIM 22600) (Fig. 3.57). Kyphosis of the cervical spine is also a feature in campomelic dysplasia (OMIM 114290, 211990) (Fig. 3.58). In metatropic dwarfism (OMIM 250600) the vertebrae are flat and underdeveloped in early infancy, with lack of ossification of the posterior elements and diamond-shaped vertebral bodies; later in life, universal platyspondyly develops, almost invariably associated with kyphoscoliosis. The vertebrae are flat and broad and anteriorly wedged, especially at the apex of the kyphotic curve, with central and dorsal hump-like buildup of the end-plates. This feature clearly distinguishes the spinal changes of metatropic dwarfism from those of Kniest dysplasia (OMIM 156550), which are otherwise similar in early life. Additional distinctive features in anatomical areas other than the spine are found at the level of the thorax, which is short and broad in Kniest dysplasia and narrow in metatropic dwarfism, and that of the metaphyses of long bones, which are round in Kniest dysplasia and angulated in metatropic dwarfism (Vitko et al. 1972). Although spinal changes in spon-dylometaphyseal dysplasia, Kozlowski type (OMIM
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