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(ii) Scoliosis in children and teenagers
MINI-SYMPOSIUM: SPINAL DEFORMITY
(ii) Scoliosis in children and teenagers
(lateral) plane. Consideration of time, the fourth dimension, requires the surgeon to judge the possible therapeutic effect or potential damaging effects of growth on the spinal deformity. At birth, the spine has a gentle C-shaped curve throughout its length in the sagittal plane and is straight in the coronal plane. The normal cervical lordosis develops as the child gains head control and begins crawling; the lumbar lordosis begins to appear at the time of walking. There are subtle changes in the sagittal profile throughout growth until the normal adult pattern is achieved. The sagittal profile is never fixed, and will continue to change as the spine ages, becoming more kyphotic with advancing years. The net effect of the normal spinal sagittal profile is to position the head and thoracic cage over the centre of the pelvis. It is the relative positioning of head, shoulders, thorax and pelvis that gives the normal body surface contour. Normal shape is much harder to define than a simple Cobb angle. It is accepted that symmetry is important, but beyond that questions of ‘normal’ or ‘attractive’ become very subjective.
Nigel W Gummerson Peter A Millner
Abstract Scoliosis is a three-dimensional deformity of the spine whose cardinal feature is a curve in the coronal plane with a Cobb angle that exceeds 10 . In the growing spine and the degenerative spine scoliosis will evolve over time; the fourth dimension. This article discusses the possible causes of scoliosis in the paediatric population. The aim is to provide the reader with a basic understanding of spinal growth, the natural history of scoliotic spinal deformity and outline the options for treatment.
Keywords congenital abnormalities; scoliosis; spine
Clinical assessment of scoliosis The clinical assessment of patients presenting with scoliosis and the subsequent radiological investigation is described in another article in this mini-symposium.
Introduction Scoliosis is a common and relatively slowly evolving condition. With the exception of some neuromuscular conditions, young patients with scoliosis are usually active and mobile. Scoliosis in children tends to present as a cosmetic problem, whereas scoliosis in adults more often presents with pain and neurological symptoms. Deformity of the axial skeleton may have a bearing on other musculoskeletal problems in the upper or lower limb and vice versa. Patients with spinal deformity will often present to non-spinal orthopaedic surgeons with other joint problems (particularly shoulder and hip problems). These observations mandate that all orthopaedic surgeons should have a basic understanding of scoliotic spinal deformity. Surgical trainees should also be aware that paediatric patients and their parents are usually very happy to appear at higher surgical examinations!
Causes of scoliosis Scoliosis may be structural or non-structural. A non-structural curve will usually have no rotational element, being a pure coronal plane deformity. A non-structural scoliosis may be due to: Pelvic tilt secondary to leg length inequality Pain or irritation Hysterical scoliosis. The key feature of non-structural scoliosis is that the curve will spontaneously straighten when the underlying cause is corrected or removed. In the case of pelvic tilt scoliosis, the curve will disappear when the pelvis is leveled and this can be achieved by sitting the patient or by equalizing any leg-length-discrepancy with blocks. This may be done prior to radiographic examination. Pain-induced or irritant scoliosis is seen with disc prolapse and other painful conditions, such as osteoid osteoma, typically triggering muscle spasm (Figure 1). The scoliosis will resolve when the underlying pathology is treated. Hysterical scoliosis is very, very rare and should only be diagnosed once all other possible diagnoses have been eliminated. Structural scoliosis may be classified according to the underlying aetiology. The aetiology may be reasonably obvious, as it is in congenital (15%) or neuromuscular (10%) cases. Trauma, tumour and infection are also possible causes, but are not frequently encountered. In most cases there is no detectable underlying cause (idiopathic). This is the most common aetiology, with 70% of all cases of paediatric scoliosis being of the idiopathic type. A long list of rare conditions, including hereditary and mesenchymal abnormalities such as neurofibromatosis, Marfan’s syndrome, EhlerseDanlos syndrome etc. make up the remainder; a detailed discussion of these rare conditions is outside the scope of this article.
The normal spinal profile The spine is a three-dimensional structure and spinal deformities can only be fully described in these three dimensions. Scoliosis is defined as a deformity primarily in the coronal or frontal plane (a Cobb angle of >10 seen on an AP or PA erect spine radiograph). The plain radiograph is a repeatable investigation and much of what is known regarding the natural history of scoliosis comes from serial measurement of the Cobb angle. This is merely a two-dimensional assessment of the deformity, but it still has its uses. However, in order to fully understand the spinal deformity, one must consider the axial (transverse) plane and the sagittal
Nigel W Gummerson MA FRCS(Tr&Orth) Consultant Orthopaedic Spinal Surgeon, Leeds General Infirmary, Great George Street, Leeds, UK. Peter A Millner BSc FRCSOrth Consultant Orthopaedic Spinal Surgeon, Leeds General Infirmary, Great George Street, Leeds, UK.
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The paraxial mesoderm is a condensation around the neural tube and notochord. This paraxial mesoderm segments to form paired somites (42e44 in humans, up to 500 in some snakes). This occurs in a time-dependent manner from cranial to caudal and is under the control of the hairy gene. The expression of hairy is seen to cycle over a 90-min period in the chick embryo, acting like a molecular clock. Other fantastically named genes, such as notch and lunatic fringe are also involved! Under the influence of signalling molecules from either the notochord or the neural tube, the somite will differentiate into sclerotome and dermomyotome. The dermomyotome goes on to form the dermis of the back and the muscles of the back and limbs. The cells of the sclerotome migrate ventrally and dorsally around the notochord and neural tube and give rise to the vertebrae and ribs. The somites will then go through a process of re-segmentation (week 5e6). Each somite forms the inferior half and posterior elements of the superior vertebra, the intervertebral disc and the superior half of the vertebral body below. A fissure arises in each somite (von Ebner’s fissure), which will form the intervertebral disc. Notochord remnants within the discs become the nucleus pulposus. Notochord within the vertebral body degenerates. Chondrofication (appearance of three paired centres of chondrofication) begins at week 6. Ossification centres appear at week 8, beginning at the thoracolumbar junction and progressing rostrally and caudally. It is the process of somite formation and re-segmentation that may be disrupted, leading to congenital vertebral anomalies. Bilateral failures of formation or segmentation may have no structural consequences. A shift of ventral fusion between the two sides (hemimetameric shift) may lead to balanced hemivertebrae, separated by a normal level, again with little structural consequence. It is the asymmetric anomalies that will affect spinal growth leading to progressive spinal deformity (Figure 2). The commonest congenital deformity is congenital scoliosis. Congenital kyphosis or lordosis may also occur dependent on the 3D configuration of the anomaly. It is common for other developmental anomalies to cluster with congenital spinal anomalies. Neural axis anomalies such as Chiari malformation, diastematomyelia, syringomyelia and tethered cord occur in around 40% of patients with congenital scoliosis. Renal anomalies are seen in 30% of patients and cardiac anomalies in 20%. These associated anomalies reflect the timing of the development of these organ systems, their common embryonic origin and the underlying genetic and intercellular signalling pathways, which control their development. In general, congenital scoliosis is not a hereditary problem. The majority of patients do not have affected relatives. There are a few families with multiple affected members. In these cases the parents are more likely to be closely related.
Figure 1 (a) Painful scoliosis. (b) Bone scan of the same patient showing intense uptake. The underlying pathology is osteoid osteoma.
Congenital scoliosis A brief history of spinal development The fertilized egg (zygote) divides to produce a ball of cells: the morula. A cavity forms within this ball, now called the blastocyst (the cavity is the blastocoele). A group of cells at one side of the blastocoele forms the inner cell mass. The inner cell mass (embryoblast) will go on to form the bilaminar embryo by week two of gestation. The amniotic cavity forms dorsal to this bilaminar disc and the yolk sac forms ventrally. By week three, the primitive knot (also known as Hensen’s node in bird embryogenesis) and the primitive streak form. Gastrulation occurs, with an ingress of cells (derived from primitive ectoderm) through the primitive streak, to form a three-layer embryo with ectoderm, mesoderm and endoderm. Bone Morphogenic Proteins and Fibroblast-derived Growth Factors are important signalling molecules during this process. Ectoderm will go on to form the nervous system and epidermis. The endoderm will form the epithelium of GI tract and associated organs, the respiratory system and the urinary bladder. The mesoderm (middle layer) goes on to form bones, muscles, dermis, haemopoietic tissue, spleen, the renal system, the reproductive system and much of the circulatory system. During gastrulation the notochord forms from mesoderm. The notochord induces changes in the overlying cells of the ectoderm, causing them to form the neural plate, which then develop into the neural tube. The mesodermal cells cluster into lateral mesoderm, intermediate mesoderm and paraxial mesoderm. The lateral mesoderm forms the limbs and the intermediate mesoderm differentiates into the kidneys.
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Spinal growth in congenital scoliosis Neonates are approximately 50 cm long at birth. In the first year, the length increases by 25 cm and then by 12.5 cm in the second year. A 2-year-old child is therefore approximately 87.5 cm tall. Children then grow at around 6 cm per year until the pubertal growth spurt, which peaks at approximately10 cm per year at the age of 11e12 years for girls and approximately11 cm per year at the age of 13e15 years for boys.
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a
b
c
d
e
f
group of complex anomalies that defy description. This classification comes from the work of Winter, Moe & Eilers1 and McMaster & Ohtsuka,2 which was based largely on plain radiographs. Kawakami et al. have suggested an update to this system, analyzing the 3D CT appearances of the deformity.3 CT will reveal additional abnormalities in 50% of patients, over and above those seen on the plain films. A 3D CT analysis allows for a better understanding of the relative (3D) position of the abnormalities, as well as providing more information regarding fusions between levels and the anatomy of the posterior elements around the abnormality. Consideration of any associated rib anomalies is an important aspect of congenital scoliosis. Multiple rib fusions may be seen in JarchoeLevin syndrome (spondylothoracic dysostosis). This condition causes marked a reduction in thoracic growth and results in early death from thoracic insufficiency syndrome. A lesser form, spondylocostal dysostosis, causes less severe rib problems and has no appreciable effect on life expectancy. Isolated rib abnormalities may be seen in cases that do not have these syndromes, reflecting the common embryonic origin of the rib and vertebral body from the sclerotome of the somite. Nonsyndromic rib anomalies are most commonly seen with unsegmented bars. Specific examples of congenital vertebral anomalies are considered below as we discuss what is known regarding the natural history (Figure 3). Natural history Our knowledge of the natural history comes from the work of Winter et al.1 and McMaster et al.2 Around 50% of all cases of congenital scoliosis will progress by a significant degree, 25% do not progress and the remainder progress only slightly or not at all. The most benign form of congenital spinal anomaly is a block vertebra. This is the result of bilateral failure of segmentation. Block vertebrae do not cause progressive curves, but may cause shortening of the trunk when multiple block vertebrae are present. An incarcerated or non-segmented hemivertebra has very little potential for progression. A wedged vertebra will cause only 1e2 progression per year. A single semisegmented or fully segmented vertebra will progress at 1e3.5 per year, worse at the thoracolumbar junction. Multiple hemivertebrae will progress more rapidly.
Figure 2 Defects of formation and segmentation in congenital scoliosis. (a) Semisegmented hemivertebra. (b) Unsegmented hemivertebra. (c) Hemimetameric shift, with balanced hemivertebrae. (d) Fully segmented hemivertebra. (e) Multiple hemivertebrae. (f ) Unilateral bar.
If a deformity progresses with growth, then the most significant period of progression will be during the first 2 years of life, with a second at-risk period during the pubertal growth spurt. Classification The classification of congenital scoliosis is largely descriptive (Table 1). Congenital anomalies are divided in to defects of segmentation, defects of formation, mixed defects and a small
Descriptive classification of congenital scoliosis Defects of segmentation Defects of formation
Bilateral Unilateral Partial unilateral Complete unilateral
Block vertebra Unsegmented bar Wedge vertebra Hemivertebra
Mixed anomalies
Incarcerated Unsegmented Semisegmented Fully segmented
Unsegmented bar with contralateral hemivertebra
Unclassifiable anomalies Table 1
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Figure 3 (a) Complex congenital scoliosis. Demonstrates: segmented hemivertebra at L3 bony diastematomelia at L1 multiple semisegmented hemivertebrae on the right side in the thoracic spine abnormalities right 3rd and 4th ribs. (b) MRI scan showing split cord and bony diastematomelia. (c) CT scan showing diastematomelia at L1.
Treatment There is a choice between continued observation and surgery in congenital scoliosis. Neither bracing nor physiotherapy can alter the natural history of these curves. Surgery is indicated for progressive curves. The potential for progression can be determined by a thorough work up with CT and MRI. Associated conditions should be actively sought and the possibility of an
An unsegmented bar will cause progression of between 2 and 9 per year. Again this is worse at the thoracolumbar junction. The most troublesome combination is the mixed defect of unsegmented bar with a contralateral, fully segmented hemivertebra. The thoracolumbar junction is the problematic location for this abnormality, where it may progress at more than 10 per year, necessitating early (prophylactic) surgical treatment when detected.
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underlying syndrome considered prior to surgery. A formal assessment of pulmonary function before intervention, as a baseline, will guide treatment and prognosis. The surgical options range from hemiepiphysiodoesis (short segment anterior growth arrest over the convexity of the curve) to more complex osteotomies such as resection of a hemivertebra or vertebral column resection. The choice of treatment will depend on the nature of the abnormality and the age at presentation. Techniques such as hemiepiphysiodoesis rely on significant growth potential in the concavity and are of little use in the older patient. There is little to be gained by waiting ‘to preserve growth’ with a progressive deformity. Combined anterior and posterior fusion is often indicated in these cases. ‘Normal’ levels should be preserved where possible, but the whole curve may need to be instrumented to restore normal spinal balance. Each congenital curve pattern must be assessed on its own merits but, as a general rule, early surgical treatment should be considered for curves with more than one hemivertebra, a unilateral bar or a mixed defect, as these are the curves which tend to progress.
a description of a small and heterogeneous group. This term is of little value for the purposes of treatment, prognosis or research.
Early onset idiopathic scoliosis (EOIS) Classification and natural history EOIS is rare (1% in the USA, w5% in Europe). It is typically a left-sided curve, which develops after birth, but is not present at birth. It is more common in boys (M:F ¼ 3:2). EOIS is strongly associated with other conditions such as talipes equinovarus, developmental dysplasia of the hips, torticollis and inguinal herniae. The classification of EOIS is descriptive, with useful discriminating features being the curve size, the ribvertebral-angle difference (RVAD) and the appearance of the rib heads. In true EOIS, 90% of cases will resolve spontaneously. Interestingly and inexplicably, girls with a right sided-curve have a much poorer prognosis than those with left-sided curves. Progressive EOIS is associated with increased mortality and a consequent reduction in life expectancy. It is likely that the historical descriptions of this group of patients included many who had an underlying cause for their scoliosis. 22% of patients with presumed EOIS with curves less than 20 have an underlying neural axis anomaly (i.e. they were not truly idiopathic). In one series, eight out of 10 patients with a neural axis anomaly required neurosurgical intervention. For prognostic purposes it is useful to differentiate curves according to the RVAD (rib-vertebral-angle difference). This measurement was defined by Mehta4 and is the difference between the right and left sides in the magnitude of the angle measured from the long axis of the rib and a line drawn perpendicular to end plate of the vertebra at the apex of the curve (Figure 4). Mehta showed that if this difference in the angles was less than 20 , then there was an 85e90% chance that the curve would resolve spontaneously. She went on to describe a second feature: the phase of the rib head on the convex side at the apex. A ‘phase 1’ rib head does not overlap the vertebral body and is associated with resolution in 84e98% of cases. A ‘phase 2’ rib head does overlap the vertebral body and is associated with progression in 84e97% of cases. Double curves are more likely to progress than single curves.
Neuromuscular scoliosis The clinical presentation and treatment of patients with neuromuscular scoliosis is described in another article in this minisymposium.
Idiopathic scoliosis Idiopathic scoliosis is a structural curve in the absence of any other underlying problem (such as a congenital anomaly, neuromuscular disorder, connective tissue disease etc.). By definition, the deformity is self-generating and the underlying cause is yet to be established, although there are many theories with regard to aetiology and some of these will be explored later in this article. It is possible that ‘idiopathic scoliosis’ describes a heterogeneous group of patients who have curves with a variety of underlying causes. As yet, we do not have evidence to support this theory. Idiopathic scoliosis has been subdivided by a number of authors. James described three groups: infantile, juvenile and adolescent. Dickson proposed a strong case for division into two groups: early and late onset, with the cut-off being the age of 5 years. The logic behind this comes from an analysis of thoracic and lung development and the consequence of spinal deformity on this development. It is well recognized that the patients who present with progressive infantile curves will develop life-shortening respiratory complications, whilst adolescent scoliosis has little effect on physical well-being or life expectancy. The difference between the two groups relates to the timing of respiratory development. Alveolar numbers and thoracic volume increase most rapidly during the first 5e8 years of life (full alveolar number by age 8, 30% of adult thoracic volume by age 5). Curves that appear early will have the most deleterious effect on both lung volume and alveolar numbers; curves appearing after the age of 5 will have less of an effect. It is argued that the juvenile group represents a mixture of late presenting infantile cases and early presenting adolescent type cases. Therefore, the description of a juvenile group is in fact
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Figure 4 Measurement of the RVAD. The rib vertebral angle is the difference between angle A and B.
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Aetiology It has been suggested that EOIS is the result of intrauterine moulding; the counter to this suggestion is the fact that EOIS is rarely seen at birth. Others argue that it is the result of ‘body moulding’ from the positioning of the child. If the infant lies in the lateral decubitus position a curve will develop; this is supported by the observation of plagiocephaly in this group.
curves do not present clinically. The data on small curves originates from school screening programs.5 School screening programs have largely been abandoned, as there is no reliable treatment that we can offer to children with small curves that would alter the natural history of the curve. The development of a late onset curve is an insidious process. It is unsurprising that small curves go unnoticed by parents, who rarely see their teenage children undressed.
Treatment Most spinal surgeons agree that serial casting is a reasonable non-operative treatment option for progressive EOIS. Rigid braces are of little use, due to the rapid growth rate of the child, but serial plaster casts such as those popularized by Cotrel and used to good effect by Mehta (elongation de-rotation flexion, or EDF casts) can be moulded to control a small, progressive curve. Large curves (greater than approximately 50 Cobb angle) are best treated surgically. The dilemma is that early spinal fusion will prevent thoracic growth and this in turn will lead to thoracic insufficiency syndrome, respiratory failure and reduced life expectancy. Therefore the goal of surgical treatment is to control the curve, whilst maintaining growth. Many techniques have been tried. Our favoured technique is a dual rod growing system. Here, the curve is instrumented proximally and distally (usually two levels at each end), but the centre of the curve is left undisturbed. Rods are used on each side to connect the proximal and distal instrumentation. The rods have to be lengthened every four to 6 months to allow growth and clearly this necessitates repeated surgical procedures. Complications such as wound infection or rod breakage will be encountered in all of these cases eventually, due to repeated extension of instrumentation through the same scar. A rod with an intrinsic magnetic motor that allows telescoping has recently entered clinical use and offers the possibility of repeated lengthening using an external magnet in the outpatient clinic, obviating the need for repeated surgery. Another possible solution is to selectively inhibit growth on the curve convexity. This technique is still somewhat experimental and not widely adopted although it has been used in both EOIS and late-onset idiopathic scoliosis (LOIS). Memory metal (Nitinol) staples are used on the convexity of the spine to arrest or slow growth in much the same way as staples across the physis are used to correct deformity around the knee. Memory metal staples undergo a change in shape at a sharply defined temperature, being inserted ‘open’ and closing when they reach body temperature. The problems with this technique relate to the staples themselves and the application of the staples. Nitinol is difficult to make and work with and contains nickel, which is a potential carcinogen. It is difficult to be sure of the optimum position for a staple around the physis (which is a circular structure); misplaced staples will induce sagittal plane deformity.
Classification We have yet to find the ideal classification6,7 system for LOIS. Currently, the most widely used classification is that of Lenke et al., published in 2001. Lenke and the Harms Study Group have provided us with a useful tool, which allows reproducible description of LOIS curves, can guide treatment and facilitates research. The Lenke classification is based on static erect and supine bending radiographs. There are three component; curve pattern, lumbar modifier and sagittal thoracic modifier (Figure 5). Three structural curves are identified. Thoracic curves have an apex at T2 to the T11/12 disk, thoracolumbar curves have an apex at T12 to L1 and lumbar curves have their apex at L1-L2 disk to L4. A curve which bends down to less than 25 does not meet the structural criteria in this classification unless it is the main curve or has more than 20 of local kyphosis. Identifying the structural curves gives six groups (see figure). The next step is to examine the position of the lumbar pedicles relative to the central sacral vertical line (CSVL) to give the lumbar modifier. If the pedicles of the most displaced lumbar vertebra fall either side of the CSVL the modifier is A. If both pedicles lie to one side of the CSVL the modifier is C. If a pedicle falls on the line or there is uncertainty, the modifier is B. The lumbar modifier gives a measure lumbar coronal plane deformity. The final measure is the degree of kyphosis from T5-T12, normal (in this classification) is 10e40 . This classification is two-dimensional and addresses both the sagittal and the coronal plane. Work continues to find a truly 3D classification. These classification systems do not address the problems of which the patients complain e their cosmesis. Aetiology Idiopathic e arising spontaneously or from an obscure or unknown cause. There are many theories regarding the aetiology of LOIS, but much remains unknown. Endocrine, neurological, muscular and skeletal causes have all been postulated. It is more common in tall and slim (exomorphic) females. The deformity is lordosis with scoliosis, or lordo-scoliosis. The rotation of the curve as the spine deforms may give the appearance of kyphosis on the standard lateral radiograph, but a derotated view will give a more accurate assessment. It is thought that excess anterior spinal growth relative to posterior growth reduces the stability of the thoracic kyphosis, which then buckles to produce a scoliosis.8
Late-onset idiopathic scoliosis (LOIS) Late-onset idiopathic scoliosis is a relatively common condition. Small curves are more common than large curves. The prevalence of curves greater than 10 is 2%; for curves greater than 30 , the prevalence is 0.2e0.3%. Overall, only 6 in 10 000 children will require treatment for LOIS. The gender ratio approaches 1:1 for curves of 10 although for curves greater than 20 , the male/female ratio is 1:5. Small
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Natural history The main driver of progression in late onset curves is remaining growth. Indicators of remaining growth correlate with curve progression:
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Figure 5 The Lenke classification of late-onset idiopathic scoliosis. (Illustration Copyright by AOSpine International, Switzerland).
In the long term, LOIS patients have a normal life expectancy.9,10 The incidence of back pain is no higher than the general population, but when painful episodes do occur they may be a little more severe and last a little longer than the average. Unexplained back pain in this group should prompt a search for other possible causes, especially pathologies that cause painful scoliosis, such as osteoid osteoma or spondylolysis. There is an increased awareness of body image in this group, and there is certainly a psychological effect of the deformity. Girls with LOIS have a higher incidence of eating disorders and a lower BMI (body mass-index). LOIS does not cause significant cardiopulmonary compromise unless the curve is very large. A curve size of 80e90 is often quoted as a threshold for such compromise, although in truth some degree of measurable pulmonary dysfunction may be seen across all curve sizes. In contrast, severe pulmonary dysfunction is much more common in EOIS. The important distinction is where pulmonary dysfunction becomes clinically significant. Patients with a curve of more than 50 may have symptoms of exertional dyspnoea. There is little evidence that LOIS causes any significant problems in pregnancy of childbirth. There may be difficulties in siting an epidural in women who have had previous long posterior fusions. There is long term data to suggest that all curves progress a little, even after skeletal maturity. This progression is approximately 0.5 per year on average. Progression is more rapid in
Risk of progression (>5 ) C C C C C C
Age <10 Age >15 Pre-menarche Post-menarche Risser grade 0 Risser grade 3e4
88% 29% 53% 11% 68% 18%
The Risser grade is the degree of fusion of the iliac apophysis as seen on an AP radiograph. At grade 0 the apophysis has yet to appear. At grade 5 it is fully fused. Grades 1e4 represent progressive fusion of the apophysis to the iliac blade from lateral to medial. Menarche is a useful indicator of growth. Girls grow rapidly for 18 months before and 18 months after menarche. Formal assessment of bone age using a radiograph including the left hand and wrist is also useful. Even with significant remaining growth, small curves are unlikely to progress. Data for curves of 5e19 shows that 22% progress if the child is Risser grade 0e1, and only 1.6% progress if the child is Risser grade 2e4. Note that a curve of 5 is below the current accepted threshold for a diagnosis of scoliosis.
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Figure 6 (a) and (b) Pre and postoperative PA radiographs of a Lenke 1A-late-onset idiopathic curve.
larger curves (>50 ). This data comes from a study where the patients were Risser grade 4e5 at entry and one could argue that they were not truly skeletally mature; it should be noted that the spine continues to grow for a couple of years after growth of the long bones has ceased. A number of LOIS patients will represent to spinal surgeons as adults with progression and degeneration in the curve, with symptoms of pain and possibly nerve root compression.
years with curves less than 25 . The test costs US$3000 and the full scientific methodology behind the test has yet to be fully disclosed. Treatment Many areas of possible treatment in LOIS remain controversial and are still hotly debated at scientific meetings. Physiotherapy can be helpful for those children who develop back pain and in those who have significant coronal imbalance. There is no good evidence that physiotherapy can alter the underlying curve. Spinal bracing is still a common treatment in the USA. A spinal brace has to be worn for the majority of the time for there to be any measurable effect. There is evidence that the brace changes the spinal shape while the brace is worn, but no good evidence that the brace alters the long-term natural history of the curve being treated. There is a strong argument, which suggests that the brace may improve the coronal plane deformity at the expense of the sagittal plane.11 However, bracing comes with other problems, particularly with compliance; the braces are rigid and restricting and can be unsightly. Dynamic (elasticated) braces have been developed, and are still being evaluated.
Natural history e genetic studies There is a genetic component to LOIS. Patients with LOIS will have a first degree relative with the condition in 8e20% of cases. The search for the genes responsible continues. It is likely that scoliosis is the result a complex interaction between multiple genes. A couple of candidate genes have been identified. A genetic test (ScoliScoreÔ) is currently being marketed. This aims to stratify the risk of progression for patients with small curves. If a patient is stratified to a low risk group, monitoring of the curve may be less frequent. If a patient is in a high-risk group, then the decision to treat the curve surgically may be made earlier, when the curve is smaller and surgery is technically easier. The test is only suitable for Caucasian patients aged 9e13
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Figure 7 (a) and (b) Pre and postoperative PA radiographs of a Lenke 3CN late-onset idiopathic curve.
Surgery can change the underlying spinal shape and the cosmetic appearance (Figures 6 and 7).12e15 A curve of less than 40 is unlikely to require surgical treatment on the grounds of dyscosmesis. The aims of scoliosis surgery are to prevent progression and leave a stable and well-balanced spine with the maximum safe cosmetic correction, preserving as many motion segments as possible. Cosmetic correction equates to level shoulders, centralization of the trunk with balanced waist creases and correction of spinal axial rotation to reduce the rib or loin prominence. There is a decision to be made regarding the approach taken and which levels to fuse.16 The majority of scoliosis surgery is done via a posterior approach. Anterior surgery may be indicated for larger, stiffer curves and is usually combined with posterior fixation. Thoracotomy in scoliosis results in a statistically significant decrease in lung function (10%).17 The clinical significance of this is unclear. To identify fusion levels, the simple rule followed in the majority of cases is to identify the end vertebrae i.e. the vertebrae with endplates that are most tilted from the horizontal plane and fuse all structural curves from upper end-vertebra to lower end
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vertebra. The highest level should be chosen to ensure that the shoulders become or remain level and there should be a normal sagittal profile at the junction from fused to unfused. The lowest level should be selected based on the neutral and stable vertebra on the standing film, as well as examining the correction achieved across the disc spaces on the bending films. Choices regarding the precise levels of fusion will be determined by the choice of approach and the philosophy of correction. Scoliosis surgery is a major undertaking and carries significant risks. Spinal cord function is monitored during the procedure, most commonly using somatosensory evoked potentials (SSEPs) using posterior tibial nerve stimulation at the ankle and detection of evoked potentials by scalp electrodes or an epidural electrode placed in the upper thoracic or lower cervical level. In recent years the monitoring standard has developed to include motor evoked potentials (MEPs) in conjunction with SSEPs. As the motor and sensory pathways travel in different spinal tracts, multimodal monitoring gives much more information regarding spinal cord function and is believed to increase the safety profile for scoliosis surgery. EMG monitoring is more frequently being used in conjunction with SSEPs (the motor and
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6 Stirling AJ, Howel D, Millner PA, Sadiq S, Sharples D, Dickson RA. Late-onset idiopathic scoliosis in children six to fourteen years old. A cross-sectional prevalence study. J Bone Jt Surg Am Sep 1996; 78: 1330e6. 7 Millner PA, Dickson RA. Idiopathic scoliosis: biomechanics and biology. Eur Spine J 1996; 5: 362e73. 8 Weinstein S. Natural history. Spine 1999; 24: 2592. 9 Weinstein SL, Ponseti IV. Curve progression in idiopathic scoliosis. J Bone Jt Surg Am 1983 Apr; 65: 447e55. 10 Dickson RA, Weinstein SL. Bracing (and screening) e yes or no? J Bone Jt Surg Br 1999 Mar; 81: 193e8. 11 Hibbs RA. A report of fifty-nine cases of scoliosis treated by the fusion operation. J Bone Jt Surg 1924; 6: 3. 12 Harrington PR. Treatment of scoliosis: correction and internal fixation by spine instrumentation. J Bone Jt Surg 1962; 44-A: 591e610. 13 Dickson RA, Archer I. Surgical treatment of late-onset idiopathic thoracic scoliosis. The leeds procedure. J Bone Jt Surg Br 1987; 69: 709. 14 Lenke LG, Kuklo TR, Ondra S, Polly Jr DW. Rationale behind the current state-of-the-art treatment of scoliosis (in the pedicle screw era). Spine 2008; 33: 1051e4. 15 Gummerson NW, Millner PA. Spinal fusion for scoliosis, clinical decision-making and choice of approach and devices. Skeletal Radiol 2010 Oct; 39: 939e42. 16 Kim YJ, Lenke LG, Bridwell KH, Cheh G, Sides B, Whorton J. Prospective pulmonary function comparison of anterior spinal fusion in adolescent idiopathic scoliosis: thoracotomy versus thoracoabdominal approach. Spine 2008; 33: 1055e60. 17 Winter RB, Lonstein JE, Denis F. How much correction is enough? Spine 2007; 32: 2641e3.
sensory pathways travel in different spinal tracts and monitoring both gives more information regarding cord function). Neural complications occur in 1:150 cases (e.g. dural tear and nerve root injury). Spinal cord injury occurs in approximately 1:325 cases. In the two recent large reported series of complications, all cord injuries recovered. Patients should be counselled pre-operatively regarding the degree of correction that surgery can deliver. It is unlikely that that the correction will normalize all measurable parameters. In some cases it is better to leave small balanced curves, than attempt 100% correction. The important factor is overall cosmesis and this is the hardest outcome to measure! Conclusion Late-onset idiopathic scoliosis is the most commonly seen scoliotic deformity in the paediatric population. The clinician should keep an open mind to alternative diagnoses, even in the ‘typical’ late-onset idiopathic scoliosis patient. A
REFERENCES 1 Winter RB, Moe JH, Eilers VE. Congenital scoliosis a study of 234 patients treated and untreated part I: natural history. J. Bone Jt Surg Am Jan 1968; 50: 1e15. 2 McMaster MJ, Ohtsuka K. The natural history of congenital scoliosis. A study of two hundred and fifty-one patients. J Bone Jt Surg Am 1982 Oct; 64: 1128e47. 3 Mehta MH. The rib-vertebra angle in the early diagnosis between resolving and progressive infantile scoliosis. J Bone Jt Surg Br May 1972; 54: 230e43. 4 King HA, Moe JH, Bradford DS, Winter RB. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Jt Surg Am Dec 1983; 65: 1302e13. 5 Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Jt Surg Am 2001; 83-A: 1169e81.
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Acknowledgement The authors would like to thank Dr James Rankine, who provided a number of radiographic images for use in this article.
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(ii) Scoliosis in children and teenagers
(lateral) plane. Consideration of time, the fourth dimension, requires the surgeon to judge the possible therapeutic effect or potential damaging effects of growth on the spinal deformity. At birth, the spine has a gentle C-shaped curve throughout its length in the sagittal plane and is straight in the coronal plane. The normal cervical lordosis develops as the child gains head control and begins crawling; the lumbar lordosis begins to appear at the time of walking. There are subtle changes in the sagittal profile throughout growth until the normal adult pattern is achieved. The sagittal profile is never fixed, and will continue to change as the spine ages, becoming more kyphotic with advancing years. The net effect of the normal spinal sagittal profile is to position the head and thoracic cage over the centre of the pelvis. It is the relative positioning of head, shoulders, thorax and pelvis that gives the normal body surface contour. Normal shape is much harder to define than a simple Cobb angle. It is accepted that symmetry is important, but beyond that questions of ‘normal’ or ‘attractive’ become very subjective.
Nigel W Gummerson Peter A Millner
Abstract Scoliosis is a three-dimensional deformity of the spine whose cardinal feature is a curve in the coronal plane with a Cobb angle that exceeds 10 . In the growing spine and the degenerative spine scoliosis will evolve over time; the fourth dimension. This article discusses the possible causes of scoliosis in the paediatric population. The aim is to provide the reader with a basic understanding of spinal growth, the natural history of scoliotic spinal deformity and outline the options for treatment.
Keywords congenital abnormalities; scoliosis; spine
Clinical assessment of scoliosis The clinical assessment of patients presenting with scoliosis and the subsequent radiological investigation is described in another article in this mini-symposium.
Introduction Scoliosis is a common and relatively slowly evolving condition. With the exception of some neuromuscular conditions, young patients with scoliosis are usually active and mobile. Scoliosis in children tends to present as a cosmetic problem, whereas scoliosis in adults more often presents with pain and neurological symptoms. Deformity of the axial skeleton may have a bearing on other musculoskeletal problems in the upper or lower limb and vice versa. Patients with spinal deformity will often present to non-spinal orthopaedic surgeons with other joint problems (particularly shoulder and hip problems). These observations mandate that all orthopaedic surgeons should have a basic understanding of scoliotic spinal deformity. Surgical trainees should also be aware that paediatric patients and their parents are usually very happy to appear at higher surgical examinations!
Causes of scoliosis Scoliosis may be structural or non-structural. A non-structural curve will usually have no rotational element, being a pure coronal plane deformity. A non-structural scoliosis may be due to: Pelvic tilt secondary to leg length inequality Pain or irritation Hysterical scoliosis. The key feature of non-structural scoliosis is that the curve will spontaneously straighten when the underlying cause is corrected or removed. In the case of pelvic tilt scoliosis, the curve will disappear when the pelvis is leveled and this can be achieved by sitting the patient or by equalizing any leg-length-discrepancy with blocks. This may be done prior to radiographic examination. Pain-induced or irritant scoliosis is seen with disc prolapse and other painful conditions, such as osteoid osteoma, typically triggering muscle spasm (Figure 1). The scoliosis will resolve when the underlying pathology is treated. Hysterical scoliosis is very, very rare and should only be diagnosed once all other possible diagnoses have been eliminated. Structural scoliosis may be classified according to the underlying aetiology. The aetiology may be reasonably obvious, as it is in congenital (15%) or neuromuscular (10%) cases. Trauma, tumour and infection are also possible causes, but are not frequently encountered. In most cases there is no detectable underlying cause (idiopathic). This is the most common aetiology, with 70% of all cases of paediatric scoliosis being of the idiopathic type. A long list of rare conditions, including hereditary and mesenchymal abnormalities such as neurofibromatosis, Marfan’s syndrome, EhlerseDanlos syndrome etc. make up the remainder; a detailed discussion of these rare conditions is outside the scope of this article.
The normal spinal profile The spine is a three-dimensional structure and spinal deformities can only be fully described in these three dimensions. Scoliosis is defined as a deformity primarily in the coronal or frontal plane (a Cobb angle of >10 seen on an AP or PA erect spine radiograph). The plain radiograph is a repeatable investigation and much of what is known regarding the natural history of scoliosis comes from serial measurement of the Cobb angle. This is merely a two-dimensional assessment of the deformity, but it still has its uses. However, in order to fully understand the spinal deformity, one must consider the axial (transverse) plane and the sagittal
Nigel W Gummerson MA FRCS(Tr&Orth) Consultant Orthopaedic Spinal Surgeon, Leeds General Infirmary, Great George Street, Leeds, UK. Peter A Millner BSc FRCSOrth Consultant Orthopaedic Spinal Surgeon, Leeds General Infirmary, Great George Street, Leeds, UK.
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The paraxial mesoderm is a condensation around the neural tube and notochord. This paraxial mesoderm segments to form paired somites (42e44 in humans, up to 500 in some snakes). This occurs in a time-dependent manner from cranial to caudal and is under the control of the hairy gene. The expression of hairy is seen to cycle over a 90-min period in the chick embryo, acting like a molecular clock. Other fantastically named genes, such as notch and lunatic fringe are also involved! Under the influence of signalling molecules from either the notochord or the neural tube, the somite will differentiate into sclerotome and dermomyotome. The dermomyotome goes on to form the dermis of the back and the muscles of the back and limbs. The cells of the sclerotome migrate ventrally and dorsally around the notochord and neural tube and give rise to the vertebrae and ribs. The somites will then go through a process of re-segmentation (week 5e6). Each somite forms the inferior half and posterior elements of the superior vertebra, the intervertebral disc and the superior half of the vertebral body below. A fissure arises in each somite (von Ebner’s fissure), which will form the intervertebral disc. Notochord remnants within the discs become the nucleus pulposus. Notochord within the vertebral body degenerates. Chondrofication (appearance of three paired centres of chondrofication) begins at week 6. Ossification centres appear at week 8, beginning at the thoracolumbar junction and progressing rostrally and caudally. It is the process of somite formation and re-segmentation that may be disrupted, leading to congenital vertebral anomalies. Bilateral failures of formation or segmentation may have no structural consequences. A shift of ventral fusion between the two sides (hemimetameric shift) may lead to balanced hemivertebrae, separated by a normal level, again with little structural consequence. It is the asymmetric anomalies that will affect spinal growth leading to progressive spinal deformity (Figure 2). The commonest congenital deformity is congenital scoliosis. Congenital kyphosis or lordosis may also occur dependent on the 3D configuration of the anomaly. It is common for other developmental anomalies to cluster with congenital spinal anomalies. Neural axis anomalies such as Chiari malformation, diastematomyelia, syringomyelia and tethered cord occur in around 40% of patients with congenital scoliosis. Renal anomalies are seen in 30% of patients and cardiac anomalies in 20%. These associated anomalies reflect the timing of the development of these organ systems, their common embryonic origin and the underlying genetic and intercellular signalling pathways, which control their development. In general, congenital scoliosis is not a hereditary problem. The majority of patients do not have affected relatives. There are a few families with multiple affected members. In these cases the parents are more likely to be closely related.
Figure 1 (a) Painful scoliosis. (b) Bone scan of the same patient showing intense uptake. The underlying pathology is osteoid osteoma.
Congenital scoliosis A brief history of spinal development The fertilized egg (zygote) divides to produce a ball of cells: the morula. A cavity forms within this ball, now called the blastocyst (the cavity is the blastocoele). A group of cells at one side of the blastocoele forms the inner cell mass. The inner cell mass (embryoblast) will go on to form the bilaminar embryo by week two of gestation. The amniotic cavity forms dorsal to this bilaminar disc and the yolk sac forms ventrally. By week three, the primitive knot (also known as Hensen’s node in bird embryogenesis) and the primitive streak form. Gastrulation occurs, with an ingress of cells (derived from primitive ectoderm) through the primitive streak, to form a three-layer embryo with ectoderm, mesoderm and endoderm. Bone Morphogenic Proteins and Fibroblast-derived Growth Factors are important signalling molecules during this process. Ectoderm will go on to form the nervous system and epidermis. The endoderm will form the epithelium of GI tract and associated organs, the respiratory system and the urinary bladder. The mesoderm (middle layer) goes on to form bones, muscles, dermis, haemopoietic tissue, spleen, the renal system, the reproductive system and much of the circulatory system. During gastrulation the notochord forms from mesoderm. The notochord induces changes in the overlying cells of the ectoderm, causing them to form the neural plate, which then develop into the neural tube. The mesodermal cells cluster into lateral mesoderm, intermediate mesoderm and paraxial mesoderm. The lateral mesoderm forms the limbs and the intermediate mesoderm differentiates into the kidneys.
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Spinal growth in congenital scoliosis Neonates are approximately 50 cm long at birth. In the first year, the length increases by 25 cm and then by 12.5 cm in the second year. A 2-year-old child is therefore approximately 87.5 cm tall. Children then grow at around 6 cm per year until the pubertal growth spurt, which peaks at approximately10 cm per year at the age of 11e12 years for girls and approximately11 cm per year at the age of 13e15 years for boys.
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a
b
c
d
e
f
group of complex anomalies that defy description. This classification comes from the work of Winter, Moe & Eilers1 and McMaster & Ohtsuka,2 which was based largely on plain radiographs. Kawakami et al. have suggested an update to this system, analyzing the 3D CT appearances of the deformity.3 CT will reveal additional abnormalities in 50% of patients, over and above those seen on the plain films. A 3D CT analysis allows for a better understanding of the relative (3D) position of the abnormalities, as well as providing more information regarding fusions between levels and the anatomy of the posterior elements around the abnormality. Consideration of any associated rib anomalies is an important aspect of congenital scoliosis. Multiple rib fusions may be seen in JarchoeLevin syndrome (spondylothoracic dysostosis). This condition causes marked a reduction in thoracic growth and results in early death from thoracic insufficiency syndrome. A lesser form, spondylocostal dysostosis, causes less severe rib problems and has no appreciable effect on life expectancy. Isolated rib abnormalities may be seen in cases that do not have these syndromes, reflecting the common embryonic origin of the rib and vertebral body from the sclerotome of the somite. Nonsyndromic rib anomalies are most commonly seen with unsegmented bars. Specific examples of congenital vertebral anomalies are considered below as we discuss what is known regarding the natural history (Figure 3). Natural history Our knowledge of the natural history comes from the work of Winter et al.1 and McMaster et al.2 Around 50% of all cases of congenital scoliosis will progress by a significant degree, 25% do not progress and the remainder progress only slightly or not at all. The most benign form of congenital spinal anomaly is a block vertebra. This is the result of bilateral failure of segmentation. Block vertebrae do not cause progressive curves, but may cause shortening of the trunk when multiple block vertebrae are present. An incarcerated or non-segmented hemivertebra has very little potential for progression. A wedged vertebra will cause only 1e2 progression per year. A single semisegmented or fully segmented vertebra will progress at 1e3.5 per year, worse at the thoracolumbar junction. Multiple hemivertebrae will progress more rapidly.
Figure 2 Defects of formation and segmentation in congenital scoliosis. (a) Semisegmented hemivertebra. (b) Unsegmented hemivertebra. (c) Hemimetameric shift, with balanced hemivertebrae. (d) Fully segmented hemivertebra. (e) Multiple hemivertebrae. (f ) Unilateral bar.
If a deformity progresses with growth, then the most significant period of progression will be during the first 2 years of life, with a second at-risk period during the pubertal growth spurt. Classification The classification of congenital scoliosis is largely descriptive (Table 1). Congenital anomalies are divided in to defects of segmentation, defects of formation, mixed defects and a small
Descriptive classification of congenital scoliosis Defects of segmentation Defects of formation
Bilateral Unilateral Partial unilateral Complete unilateral
Block vertebra Unsegmented bar Wedge vertebra Hemivertebra
Mixed anomalies
Incarcerated Unsegmented Semisegmented Fully segmented
Unsegmented bar with contralateral hemivertebra
Unclassifiable anomalies Table 1
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Figure 3 (a) Complex congenital scoliosis. Demonstrates: segmented hemivertebra at L3 bony diastematomelia at L1 multiple semisegmented hemivertebrae on the right side in the thoracic spine abnormalities right 3rd and 4th ribs. (b) MRI scan showing split cord and bony diastematomelia. (c) CT scan showing diastematomelia at L1.
Treatment There is a choice between continued observation and surgery in congenital scoliosis. Neither bracing nor physiotherapy can alter the natural history of these curves. Surgery is indicated for progressive curves. The potential for progression can be determined by a thorough work up with CT and MRI. Associated conditions should be actively sought and the possibility of an
An unsegmented bar will cause progression of between 2 and 9 per year. Again this is worse at the thoracolumbar junction. The most troublesome combination is the mixed defect of unsegmented bar with a contralateral, fully segmented hemivertebra. The thoracolumbar junction is the problematic location for this abnormality, where it may progress at more than 10 per year, necessitating early (prophylactic) surgical treatment when detected.
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underlying syndrome considered prior to surgery. A formal assessment of pulmonary function before intervention, as a baseline, will guide treatment and prognosis. The surgical options range from hemiepiphysiodoesis (short segment anterior growth arrest over the convexity of the curve) to more complex osteotomies such as resection of a hemivertebra or vertebral column resection. The choice of treatment will depend on the nature of the abnormality and the age at presentation. Techniques such as hemiepiphysiodoesis rely on significant growth potential in the concavity and are of little use in the older patient. There is little to be gained by waiting ‘to preserve growth’ with a progressive deformity. Combined anterior and posterior fusion is often indicated in these cases. ‘Normal’ levels should be preserved where possible, but the whole curve may need to be instrumented to restore normal spinal balance. Each congenital curve pattern must be assessed on its own merits but, as a general rule, early surgical treatment should be considered for curves with more than one hemivertebra, a unilateral bar or a mixed defect, as these are the curves which tend to progress.
a description of a small and heterogeneous group. This term is of little value for the purposes of treatment, prognosis or research.
Early onset idiopathic scoliosis (EOIS) Classification and natural history EOIS is rare (1% in the USA, w5% in Europe). It is typically a left-sided curve, which develops after birth, but is not present at birth. It is more common in boys (M:F ¼ 3:2). EOIS is strongly associated with other conditions such as talipes equinovarus, developmental dysplasia of the hips, torticollis and inguinal herniae. The classification of EOIS is descriptive, with useful discriminating features being the curve size, the ribvertebral-angle difference (RVAD) and the appearance of the rib heads. In true EOIS, 90% of cases will resolve spontaneously. Interestingly and inexplicably, girls with a right sided-curve have a much poorer prognosis than those with left-sided curves. Progressive EOIS is associated with increased mortality and a consequent reduction in life expectancy. It is likely that the historical descriptions of this group of patients included many who had an underlying cause for their scoliosis. 22% of patients with presumed EOIS with curves less than 20 have an underlying neural axis anomaly (i.e. they were not truly idiopathic). In one series, eight out of 10 patients with a neural axis anomaly required neurosurgical intervention. For prognostic purposes it is useful to differentiate curves according to the RVAD (rib-vertebral-angle difference). This measurement was defined by Mehta4 and is the difference between the right and left sides in the magnitude of the angle measured from the long axis of the rib and a line drawn perpendicular to end plate of the vertebra at the apex of the curve (Figure 4). Mehta showed that if this difference in the angles was less than 20 , then there was an 85e90% chance that the curve would resolve spontaneously. She went on to describe a second feature: the phase of the rib head on the convex side at the apex. A ‘phase 1’ rib head does not overlap the vertebral body and is associated with resolution in 84e98% of cases. A ‘phase 2’ rib head does overlap the vertebral body and is associated with progression in 84e97% of cases. Double curves are more likely to progress than single curves.
Neuromuscular scoliosis The clinical presentation and treatment of patients with neuromuscular scoliosis is described in another article in this minisymposium.
Idiopathic scoliosis Idiopathic scoliosis is a structural curve in the absence of any other underlying problem (such as a congenital anomaly, neuromuscular disorder, connective tissue disease etc.). By definition, the deformity is self-generating and the underlying cause is yet to be established, although there are many theories with regard to aetiology and some of these will be explored later in this article. It is possible that ‘idiopathic scoliosis’ describes a heterogeneous group of patients who have curves with a variety of underlying causes. As yet, we do not have evidence to support this theory. Idiopathic scoliosis has been subdivided by a number of authors. James described three groups: infantile, juvenile and adolescent. Dickson proposed a strong case for division into two groups: early and late onset, with the cut-off being the age of 5 years. The logic behind this comes from an analysis of thoracic and lung development and the consequence of spinal deformity on this development. It is well recognized that the patients who present with progressive infantile curves will develop life-shortening respiratory complications, whilst adolescent scoliosis has little effect on physical well-being or life expectancy. The difference between the two groups relates to the timing of respiratory development. Alveolar numbers and thoracic volume increase most rapidly during the first 5e8 years of life (full alveolar number by age 8, 30% of adult thoracic volume by age 5). Curves that appear early will have the most deleterious effect on both lung volume and alveolar numbers; curves appearing after the age of 5 will have less of an effect. It is argued that the juvenile group represents a mixture of late presenting infantile cases and early presenting adolescent type cases. Therefore, the description of a juvenile group is in fact
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Figure 4 Measurement of the RVAD. The rib vertebral angle is the difference between angle A and B.
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Aetiology It has been suggested that EOIS is the result of intrauterine moulding; the counter to this suggestion is the fact that EOIS is rarely seen at birth. Others argue that it is the result of ‘body moulding’ from the positioning of the child. If the infant lies in the lateral decubitus position a curve will develop; this is supported by the observation of plagiocephaly in this group.
curves do not present clinically. The data on small curves originates from school screening programs.5 School screening programs have largely been abandoned, as there is no reliable treatment that we can offer to children with small curves that would alter the natural history of the curve. The development of a late onset curve is an insidious process. It is unsurprising that small curves go unnoticed by parents, who rarely see their teenage children undressed.
Treatment Most spinal surgeons agree that serial casting is a reasonable non-operative treatment option for progressive EOIS. Rigid braces are of little use, due to the rapid growth rate of the child, but serial plaster casts such as those popularized by Cotrel and used to good effect by Mehta (elongation de-rotation flexion, or EDF casts) can be moulded to control a small, progressive curve. Large curves (greater than approximately 50 Cobb angle) are best treated surgically. The dilemma is that early spinal fusion will prevent thoracic growth and this in turn will lead to thoracic insufficiency syndrome, respiratory failure and reduced life expectancy. Therefore the goal of surgical treatment is to control the curve, whilst maintaining growth. Many techniques have been tried. Our favoured technique is a dual rod growing system. Here, the curve is instrumented proximally and distally (usually two levels at each end), but the centre of the curve is left undisturbed. Rods are used on each side to connect the proximal and distal instrumentation. The rods have to be lengthened every four to 6 months to allow growth and clearly this necessitates repeated surgical procedures. Complications such as wound infection or rod breakage will be encountered in all of these cases eventually, due to repeated extension of instrumentation through the same scar. A rod with an intrinsic magnetic motor that allows telescoping has recently entered clinical use and offers the possibility of repeated lengthening using an external magnet in the outpatient clinic, obviating the need for repeated surgery. Another possible solution is to selectively inhibit growth on the curve convexity. This technique is still somewhat experimental and not widely adopted although it has been used in both EOIS and late-onset idiopathic scoliosis (LOIS). Memory metal (Nitinol) staples are used on the convexity of the spine to arrest or slow growth in much the same way as staples across the physis are used to correct deformity around the knee. Memory metal staples undergo a change in shape at a sharply defined temperature, being inserted ‘open’ and closing when they reach body temperature. The problems with this technique relate to the staples themselves and the application of the staples. Nitinol is difficult to make and work with and contains nickel, which is a potential carcinogen. It is difficult to be sure of the optimum position for a staple around the physis (which is a circular structure); misplaced staples will induce sagittal plane deformity.
Classification We have yet to find the ideal classification6,7 system for LOIS. Currently, the most widely used classification is that of Lenke et al., published in 2001. Lenke and the Harms Study Group have provided us with a useful tool, which allows reproducible description of LOIS curves, can guide treatment and facilitates research. The Lenke classification is based on static erect and supine bending radiographs. There are three component; curve pattern, lumbar modifier and sagittal thoracic modifier (Figure 5). Three structural curves are identified. Thoracic curves have an apex at T2 to the T11/12 disk, thoracolumbar curves have an apex at T12 to L1 and lumbar curves have their apex at L1-L2 disk to L4. A curve which bends down to less than 25 does not meet the structural criteria in this classification unless it is the main curve or has more than 20 of local kyphosis. Identifying the structural curves gives six groups (see figure). The next step is to examine the position of the lumbar pedicles relative to the central sacral vertical line (CSVL) to give the lumbar modifier. If the pedicles of the most displaced lumbar vertebra fall either side of the CSVL the modifier is A. If both pedicles lie to one side of the CSVL the modifier is C. If a pedicle falls on the line or there is uncertainty, the modifier is B. The lumbar modifier gives a measure lumbar coronal plane deformity. The final measure is the degree of kyphosis from T5-T12, normal (in this classification) is 10e40 . This classification is two-dimensional and addresses both the sagittal and the coronal plane. Work continues to find a truly 3D classification. These classification systems do not address the problems of which the patients complain e their cosmesis. Aetiology Idiopathic e arising spontaneously or from an obscure or unknown cause. There are many theories regarding the aetiology of LOIS, but much remains unknown. Endocrine, neurological, muscular and skeletal causes have all been postulated. It is more common in tall and slim (exomorphic) females. The deformity is lordosis with scoliosis, or lordo-scoliosis. The rotation of the curve as the spine deforms may give the appearance of kyphosis on the standard lateral radiograph, but a derotated view will give a more accurate assessment. It is thought that excess anterior spinal growth relative to posterior growth reduces the stability of the thoracic kyphosis, which then buckles to produce a scoliosis.8
Late-onset idiopathic scoliosis (LOIS) Late-onset idiopathic scoliosis is a relatively common condition. Small curves are more common than large curves. The prevalence of curves greater than 10 is 2%; for curves greater than 30 , the prevalence is 0.2e0.3%. Overall, only 6 in 10 000 children will require treatment for LOIS. The gender ratio approaches 1:1 for curves of 10 although for curves greater than 20 , the male/female ratio is 1:5. Small
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Natural history The main driver of progression in late onset curves is remaining growth. Indicators of remaining growth correlate with curve progression:
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Figure 5 The Lenke classification of late-onset idiopathic scoliosis. (Illustration Copyright by AOSpine International, Switzerland).
In the long term, LOIS patients have a normal life expectancy.9,10 The incidence of back pain is no higher than the general population, but when painful episodes do occur they may be a little more severe and last a little longer than the average. Unexplained back pain in this group should prompt a search for other possible causes, especially pathologies that cause painful scoliosis, such as osteoid osteoma or spondylolysis. There is an increased awareness of body image in this group, and there is certainly a psychological effect of the deformity. Girls with LOIS have a higher incidence of eating disorders and a lower BMI (body mass-index). LOIS does not cause significant cardiopulmonary compromise unless the curve is very large. A curve size of 80e90 is often quoted as a threshold for such compromise, although in truth some degree of measurable pulmonary dysfunction may be seen across all curve sizes. In contrast, severe pulmonary dysfunction is much more common in EOIS. The important distinction is where pulmonary dysfunction becomes clinically significant. Patients with a curve of more than 50 may have symptoms of exertional dyspnoea. There is little evidence that LOIS causes any significant problems in pregnancy of childbirth. There may be difficulties in siting an epidural in women who have had previous long posterior fusions. There is long term data to suggest that all curves progress a little, even after skeletal maturity. This progression is approximately 0.5 per year on average. Progression is more rapid in
Risk of progression (>5 ) C C C C C C
Age <10 Age >15 Pre-menarche Post-menarche Risser grade 0 Risser grade 3e4
88% 29% 53% 11% 68% 18%
The Risser grade is the degree of fusion of the iliac apophysis as seen on an AP radiograph. At grade 0 the apophysis has yet to appear. At grade 5 it is fully fused. Grades 1e4 represent progressive fusion of the apophysis to the iliac blade from lateral to medial. Menarche is a useful indicator of growth. Girls grow rapidly for 18 months before and 18 months after menarche. Formal assessment of bone age using a radiograph including the left hand and wrist is also useful. Even with significant remaining growth, small curves are unlikely to progress. Data for curves of 5e19 shows that 22% progress if the child is Risser grade 0e1, and only 1.6% progress if the child is Risser grade 2e4. Note that a curve of 5 is below the current accepted threshold for a diagnosis of scoliosis.
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Figure 6 (a) and (b) Pre and postoperative PA radiographs of a Lenke 1A-late-onset idiopathic curve.
larger curves (>50 ). This data comes from a study where the patients were Risser grade 4e5 at entry and one could argue that they were not truly skeletally mature; it should be noted that the spine continues to grow for a couple of years after growth of the long bones has ceased. A number of LOIS patients will represent to spinal surgeons as adults with progression and degeneration in the curve, with symptoms of pain and possibly nerve root compression.
years with curves less than 25 . The test costs US$3000 and the full scientific methodology behind the test has yet to be fully disclosed. Treatment Many areas of possible treatment in LOIS remain controversial and are still hotly debated at scientific meetings. Physiotherapy can be helpful for those children who develop back pain and in those who have significant coronal imbalance. There is no good evidence that physiotherapy can alter the underlying curve. Spinal bracing is still a common treatment in the USA. A spinal brace has to be worn for the majority of the time for there to be any measurable effect. There is evidence that the brace changes the spinal shape while the brace is worn, but no good evidence that the brace alters the long-term natural history of the curve being treated. There is a strong argument, which suggests that the brace may improve the coronal plane deformity at the expense of the sagittal plane.11 However, bracing comes with other problems, particularly with compliance; the braces are rigid and restricting and can be unsightly. Dynamic (elasticated) braces have been developed, and are still being evaluated.
Natural history e genetic studies There is a genetic component to LOIS. Patients with LOIS will have a first degree relative with the condition in 8e20% of cases. The search for the genes responsible continues. It is likely that scoliosis is the result a complex interaction between multiple genes. A couple of candidate genes have been identified. A genetic test (ScoliScoreÔ) is currently being marketed. This aims to stratify the risk of progression for patients with small curves. If a patient is stratified to a low risk group, monitoring of the curve may be less frequent. If a patient is in a high-risk group, then the decision to treat the curve surgically may be made earlier, when the curve is smaller and surgery is technically easier. The test is only suitable for Caucasian patients aged 9e13
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Figure 7 (a) and (b) Pre and postoperative PA radiographs of a Lenke 3CN late-onset idiopathic curve.
Surgery can change the underlying spinal shape and the cosmetic appearance (Figures 6 and 7).12e15 A curve of less than 40 is unlikely to require surgical treatment on the grounds of dyscosmesis. The aims of scoliosis surgery are to prevent progression and leave a stable and well-balanced spine with the maximum safe cosmetic correction, preserving as many motion segments as possible. Cosmetic correction equates to level shoulders, centralization of the trunk with balanced waist creases and correction of spinal axial rotation to reduce the rib or loin prominence. There is a decision to be made regarding the approach taken and which levels to fuse.16 The majority of scoliosis surgery is done via a posterior approach. Anterior surgery may be indicated for larger, stiffer curves and is usually combined with posterior fixation. Thoracotomy in scoliosis results in a statistically significant decrease in lung function (10%).17 The clinical significance of this is unclear. To identify fusion levels, the simple rule followed in the majority of cases is to identify the end vertebrae i.e. the vertebrae with endplates that are most tilted from the horizontal plane and fuse all structural curves from upper end-vertebra to lower end
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vertebra. The highest level should be chosen to ensure that the shoulders become or remain level and there should be a normal sagittal profile at the junction from fused to unfused. The lowest level should be selected based on the neutral and stable vertebra on the standing film, as well as examining the correction achieved across the disc spaces on the bending films. Choices regarding the precise levels of fusion will be determined by the choice of approach and the philosophy of correction. Scoliosis surgery is a major undertaking and carries significant risks. Spinal cord function is monitored during the procedure, most commonly using somatosensory evoked potentials (SSEPs) using posterior tibial nerve stimulation at the ankle and detection of evoked potentials by scalp electrodes or an epidural electrode placed in the upper thoracic or lower cervical level. In recent years the monitoring standard has developed to include motor evoked potentials (MEPs) in conjunction with SSEPs. As the motor and sensory pathways travel in different spinal tracts, multimodal monitoring gives much more information regarding spinal cord function and is believed to increase the safety profile for scoliosis surgery. EMG monitoring is more frequently being used in conjunction with SSEPs (the motor and
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6 Stirling AJ, Howel D, Millner PA, Sadiq S, Sharples D, Dickson RA. Late-onset idiopathic scoliosis in children six to fourteen years old. A cross-sectional prevalence study. J Bone Jt Surg Am Sep 1996; 78: 1330e6. 7 Millner PA, Dickson RA. Idiopathic scoliosis: biomechanics and biology. Eur Spine J 1996; 5: 362e73. 8 Weinstein S. Natural history. Spine 1999; 24: 2592. 9 Weinstein SL, Ponseti IV. Curve progression in idiopathic scoliosis. J Bone Jt Surg Am 1983 Apr; 65: 447e55. 10 Dickson RA, Weinstein SL. Bracing (and screening) e yes or no? J Bone Jt Surg Br 1999 Mar; 81: 193e8. 11 Hibbs RA. A report of fifty-nine cases of scoliosis treated by the fusion operation. J Bone Jt Surg 1924; 6: 3. 12 Harrington PR. Treatment of scoliosis: correction and internal fixation by spine instrumentation. J Bone Jt Surg 1962; 44-A: 591e610. 13 Dickson RA, Archer I. Surgical treatment of late-onset idiopathic thoracic scoliosis. The leeds procedure. J Bone Jt Surg Br 1987; 69: 709. 14 Lenke LG, Kuklo TR, Ondra S, Polly Jr DW. Rationale behind the current state-of-the-art treatment of scoliosis (in the pedicle screw era). Spine 2008; 33: 1051e4. 15 Gummerson NW, Millner PA. Spinal fusion for scoliosis, clinical decision-making and choice of approach and devices. Skeletal Radiol 2010 Oct; 39: 939e42. 16 Kim YJ, Lenke LG, Bridwell KH, Cheh G, Sides B, Whorton J. Prospective pulmonary function comparison of anterior spinal fusion in adolescent idiopathic scoliosis: thoracotomy versus thoracoabdominal approach. Spine 2008; 33: 1055e60. 17 Winter RB, Lonstein JE, Denis F. How much correction is enough? Spine 2007; 32: 2641e3.
sensory pathways travel in different spinal tracts and monitoring both gives more information regarding cord function). Neural complications occur in 1:150 cases (e.g. dural tear and nerve root injury). Spinal cord injury occurs in approximately 1:325 cases. In the two recent large reported series of complications, all cord injuries recovered. Patients should be counselled pre-operatively regarding the degree of correction that surgery can deliver. It is unlikely that that the correction will normalize all measurable parameters. In some cases it is better to leave small balanced curves, than attempt 100% correction. The important factor is overall cosmesis and this is the hardest outcome to measure! Conclusion Late-onset idiopathic scoliosis is the most commonly seen scoliotic deformity in the paediatric population. The clinician should keep an open mind to alternative diagnoses, even in the ‘typical’ late-onset idiopathic scoliosis patient. A
REFERENCES 1 Winter RB, Moe JH, Eilers VE. Congenital scoliosis a study of 234 patients treated and untreated part I: natural history. J. Bone Jt Surg Am Jan 1968; 50: 1e15. 2 McMaster MJ, Ohtsuka K. The natural history of congenital scoliosis. A study of two hundred and fifty-one patients. J Bone Jt Surg Am 1982 Oct; 64: 1128e47. 3 Mehta MH. The rib-vertebra angle in the early diagnosis between resolving and progressive infantile scoliosis. J Bone Jt Surg Br May 1972; 54: 230e43. 4 King HA, Moe JH, Bradford DS, Winter RB. The selection of fusion levels in thoracic idiopathic scoliosis. J Bone Jt Surg Am Dec 1983; 65: 1302e13. 5 Lenke LG, Betz RR, Harms J, et al. Adolescent idiopathic scoliosis: a new classification to determine extent of spinal arthrodesis. J Bone Jt Surg Am 2001; 83-A: 1169e81.
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Acknowledgement The authors would like to thank Dr James Rankine, who provided a number of radiographic images for use in this article.
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