3.11 Congenital scoliosis and kyphosis

Congenital scoliosis and kyphosis are deformities of the spine in the coronal and sagittal planes caused by failures of formation or segmentation of the spine, or combinations of both. They are due to a combination of genetic and environmental factors (e.g. alcohol). The notochord appears to be a key structure in pathogenesis. The Pax-1 gene is required for the formation of the ventral parts of the vertebrae during primary segmentation and border formation between structures of the vertebral column. Reduced or impaired Pax-1 gene expression may lead to failure of segmentation (i.e. border formation) and subsequent vertebral fusions. Vertebral malformation is usually apparent on radiographs or on prenatal ultrasound examination. They are frequently related to other mesodermal and ectodermal anomalies, which often arise from the same segments. Cardiac anomalies are commonly associated with congenital scoliosis, which is often first identified from radiographs taken to manage the cardiac problem. At least 20% of cases of congenital scoliosis have anomalies within the vertebral canal, including syrinx formation, and a divided spinal cord. When this occurs, a diastematomyelia may be found. This is a sagittal fibrous or bony band dividing the vertebral canal, dural sheath, or spinal cord.

The body axis is established during gastrulation. Cells migrate through the primitive streak and the three layers of the embryonic disc are generated. At about 16 days, some cells pass through the anterior tip of the streak (called Hensen’s node) to give rise to the notochord. The overlying ectoderm becomes the neural plate, later the neural tube. The paraxial mesoderm differentiates into 42–44 small epithelial spheres with central lumina (somites) in a craniocaudal sequence (Figures 3.11.1A and 3.11.2A). The first five (occipital) somites appear in stage 9 (about 20 days). The dorsolateral parts of the somites retain their epithelial arrangement to form dermatomes and myotomes (giving rise to smooth muscle of the dermis and striated trunk musculature respectively). The ventromedial sclerotomes migrate toward the midline to surround the notochord and form the perichordal zone (Figure 3.11.1B).

The lateral part of each sclerotome shows a division to loose cranial and dense caudal halves in stage 13 (about 28 days) (Figure 3.11.2B). The loose cranial halves contain the spinal nerves, dorsal roots, ganglia, and the intersegmental vessels, while the dense caudal halves give rise to the lateral processes (ribs and transverse processes) and neural arches of the vertebrae.

At stage 14 (about 32 days), the perichordal zone also shows zones of high and low cell density axially (Figure 3.11.2C). The zone of high cell density contributes to the formation of intervertebral discs, whereas the low-density areas develop into the centra of the vertebrae. Two somites contribute to each vertebral body on both sides. The only deviation from this rule is the five occipital somites forming basiocciput, which becomes the clivus.

Chondrification of the vertebral column begins at 6 post-ovulatory weeks in the vertebral bodies and progresses dorsally and ventrally to the neural arches and rib anlagen.

The first signs of ossification are detectable at about 9 weeks and at birth there are three ossification centres for each vertebra, one for the vertebral body and one for each neural arch. Bony union between these primary ossification centres begins during early childhood. At puberty, secondary ossification centres (apophyses) appear at the tips of spinous processes and vertebral endplates. Atypical vertebrae (atlas, axis, and sacrum) show special patterns of ossification. The notochord expands in the area of discs forming the nucleus pulposus. The notochordal cells disappear by about 10 years. Axial position and vertebral phenotype along the embryonic axis is an early event controlled by the combinatorial expression of Hox genes.

Common vertebral congenital anomalies are spina bifida, hemivertebrae, wedge vertebrae and fusions. Scoliosis involves deviation and rotation of vertebral bodies and congenital scoliosis may be caused by hemivertebrae and wedge vertebrae and by vertebral bars. Hemivertebrae have an absence of one chondrification centre or possibly lateral deviation of the notochord. A vertebral bar is a localized failure of segmentation. Posterolaterally it will result in progressive combination of lordosis and scoliosis. Anteriorly it will cause progressive kyphosis. Butterfly vertebrae (sagittal cleft vertebrae) are perhaps due to an inadequate amount of sclerotome cells around the notochord or failure of fusion of bilateral chondrification centres. The spectrum of spina bifida ranges from myeloschisis to spina bifida occulta and is due to variably severe defects in neural tube closure. Normally, neurulation is completed by the end of the fourth week. Klippel–Feil sequence and fusion anomalies are a failure of primary segmentation.

Classification is an aid to both prognosis and treatment. The McMaster classification is widely acknowledged and based on untreated outcome. Like all classifications, it is idealized and there will always be patterns that do not fit neatly into the scheme. The McMaster system does not encompass the similar defects seen in congenital kyphosis, nor the developmental anomalies of the posterior elements which may be mistaken for idiopathic scoliosis.

The main types are summarized in Table 3.11.1 and illustrated in Figure 3.11.3. The expected degree of progression for the various types is shown in Figure 3.11.4.

Prenatal ultrasound and postnatal radiographs are the main method of diagnosis. Spinal deformity may be visible from birth. In the absence of significant deformity, congenital anomalies may come to light at any age. It is important to pay particular attention to the spine of a child with lower-limb asymmetries or foot deformities. Congenital vertebral anomalies may be associated with myelodysplasia and lumbosacral agenesis. They are also seen in the VATER (vertebral–anal–cardiac–tracheo–(o)esophageal–renal) syndrome, the Freeman–Sheldon syndrome, and Larsen’s syndrome.

The majority of malformations occur in the thoracic spine or thoracolumbar junction. Those involving failure of segmentation in the cervical spine are usually known as the Klippel–Feil syndrome (Figure 3.11.5). Affected individuals have a short neck, a low posterior hairline, and limited neck movement. The malformations are associated with a wide variety of anomalies including facial asymmetry, cleft palate, ptosis, facial nerve palsy, deafness, torticollis, webbing of the neck, thoracic scoliosis (both congenital and ‘idiopathic’ patterns), Sprengel’s shoulder, a variety of cardiac anomalies, respiratory problems due to chest deformity, and abnormalities of central control. Up to 20% demonstrate mirror movements of the hands (synkinesia), which may be due to spinal cord anomalies; voluntary movement of one hand is associated with involuntary movement of the other. Thirty per cent of affected individuals have genitourinary tract anomalies. A hemivertebra at the lumbosacral junction causes a particularly severe deformity and requires early surgical treatment. Vertebral anomalies at the cervicothoracic junction usually cannot be corrected surgically, and require early fusion in situ. Occasionally there are anomalies separated by apparently normal vertebrae. Curves may develop above and below congenital anomalies, as well as the more usual pattern with the anomaly at the apex of the curve. Neurological deficit is very unusual in scoliosis, unless there is spinal cord anomaly or diastematomyelia. It is common in congenital kyphosis.

This may occur through failure of formation, failure of segmentation, and rotatory dislocation of the spine. Failure of formation may occur, very rarely with, or without dislocation of the vertebral canal. A dorsal hemivertebra will cause a kyphosis. This will be more severe if the vertebral body does not form at all. These are dangerous deformities, and usually progress and may cause spinal cord compression. This produces an insidious myelopathy, which may not be recognized until the deficit is profound. If left untreated, these deformities eventually cause a complete paraplegia. Therefore they require early surgery. An unusual, but particularly dangerous, pattern is when a congenital scoliosis is combined with a kyphotic element and dislocation of the canal. This requires fusion in situ at diagnosis.

McMaster and Singh have published a series of 112 patients with congenital kyphosis. They distinguished 68 patients with type I kyphosis (failure of anterior formation of a vertebral body), 24 with type II (failure of anterior segmentation), and 12 with type III (mixed type). Eight were unclassifiable (Type IV). These anomalies can occur at any level in the spine, but 66% of all types had an apex between T10 and L1. All progressed during adolescence, but certain patterns were particularly dangerous.

Infantile idiopathic scoliosis is diagnosed in the absence of recognized congenital malformations. Congenital scoliosis is seen in some rare syndromes such as spondylothoracic dysplasia (Jacko–Levin syndrome), the VATER association, Goldenhar syndrome, Russell–Silver syndrome, Williams syndrome, and rarely in common syndromes such as Down syndrome. Freeman–Sheldon syndrome and Larsen’s syndrome may also have congenital spinal deformities.

Cases may present throughout life, although the majority of severe cases will present in the first 2 years of life. Prenatal ultrasound identifies an increasing proportion of cases.

Cases are often spotted by the parents, and a low threshold for requesting spinal radiography is needed when there is clinical suspicion of spinal deformity. A common reason for referral to a spine surgeon is diagnosis from a chest radiograph taken during investigation of cardiac anomalies found at routine postnatal examination.

There may be anomalies of posterior elements that are undiagnosed. They may be found incidentally during surgery of ‘idiopathic’ scoliosis and risk surgical damage to the cord.

There is a high incidence of associated anomalies in children with congenital scoliosis, since this is a defect of development of both the mesoderm and the ectoderm. These include spinal, cardiac, and urogenital anomalies. Rib anomalies are commonly associated with the vertebral anomalies.

Intraspinal anomalies include neurenteric and epidermoid cysts, lipofibromas, teratoma, absent or duplicated nerve roots, filum terminale thickening or tethering, bone or fibrous spurs (diastematomyelia), and diplomyelia. These are best identified by magnetic resonance imaging (MRI), which is an essential preoperative investigation.

Skin dimples, naevi, and hairy patches over the spine should be treated with suspicion. Masses due to lipomata or meningoceles, or the scars of closed meningoceles are also an indication for radiography. There is a probable relationship between spinal dysraphism and congenital scoliosis.

Any baby presenting with lower-limb anomalies or leg-length discrepancies should have the spine examined clinically, and probably radiologically. If a congenital scoliosis has been diagnosed, look for asymmetries of the legs and feet, and foot anomalies such as club-foot, vertical talus, cavus foot, etc. Neurological examination should include looking for wasting of muscles and reflex alteration or asymmetry. Unexplained trophic changes in the skin of the foot may be manifestations of spinal cord dysfunction.

Approximately 10% of patients with congenital scoliosis have cardiac anomalies which range from minor to severe.

Renal tract anomalies are seen in 25–40% of cases. These may be identified by ultrasound or contrast radiography. Some are identified from spinal MRI scans. Less commonly there may be uterine or vaginal anomalies.

Prognosis depends mainly on the degree of growth-plate asymmetry and growth potential. If a child has a significant curvature by the age of 10 years, there is likely to be a large curve by skeletal maturity. Associated anomalies of the neurological system, cerebral palsy, and other syndromes may also influence prognosis. Cardiac anomalies themselves may not influence curvature of the spine, but the thoracotomies needed to treat them can be detrimental to the spine. If a wide laminectomy is needed to treat intracanal lesions, kyphosis may develop in the presence of a neurological deficit. Generally, children with congenital scoliosis are shorter than average.

Prognosis is important in this condition and given in Figure 3.11.6.

Plain radiography is essential for evaluating and monitoring the progress of the curve. Once the child can sit or stand, an erect whole-spine radiograph is best. In younger children, radiographs every 6 months are necessary to monitor the curve. Measurement of the Cobb angle is not very accurate (within 5 degrees at best), so that significant small changes may be missed. Close attention to the behaviour of the more aggressive patterns is essential, with regular and regularized radiographs. Older children can be monitored with surface topography where it is available. Plain radiography can usually be used to evaluate the bony anatomy and pedicle widening, and to identify ossified diastematomyelia.

MRI scanning of the spine, including the craniocervical junction, is essential in all patients with congenital scoliosis. If surgery is not contemplated, this investigation can wait until the child is old enough to cooperate with the investigation without a general anaesthetic. The object is to identify spinal anomalies. If any are found, the patient should be sent for advice from a neurosurgeon. Controversy exists on the advisability of surgical resection of spurs, dividing the filum of tethered cords, and drainage of cysts. Generally the threshold for surgery is lower where there is an actual or progressive neurological deficit.

In general, bracing does not have much to offer patients with congenital scoliosis. It can be used to buy time when surgery is threatened in a small child. However a ‘wait and see’ policy is usually ill advised.

Surgery should be attempted sooner rather than later, particularly in the malignant patterns and in hemivertebrae at the lumbosacral junction.

The simplest procedure is a posterior fusion in situ. Clearly, the earlier this is done, the smaller will be the curve and consequent deformity. Posterior fusion is usually appropriate for the cervicothoracic junction because the risk of obtaining anterior access at these levels is unjustified. Elsewhere in the spine this is usually combined with an anterior fusion. The posterior procedure alone does not prevent continuing anterior growth and the ‘crankshaft phenomenon’. However, it is the safest option in the presence of spinal cord anomalies. This type of surgery may prevent progression, but does nothing for present cosmesis except that the brace can be removed once the fusion is established.

It is sometimes possible to correct mobile curves associated with a congenital malformation with modern instrumentation systems. It is important that congenital anomalies of the spinal cord are identified preoperatively, as correction of the curve may cause paraplegia.

A convex growth arrest involves a combined anterior and posterior ablation of growth plates. Normally rib graft is available from the anterior approach.

The best result is an improvement in the curve. Otherwise there should be stabilization of the curve. If the curve progresses, then instrumentation and an extended fusion is needed.

This is an option where there is a block vertebra or where a previous fusion in situ has been performed.

This is the procedure of choice for treating an isolated hemivertebra, particularly at the lumbosacral junction.

This technique depends on expanding the thoracic cavity unilaterally or bilaterally. Serial lengthening is needed, followed by definitive fusion.

This is outside the scope of this book. Neurosurgical advice is essential.