Scoliosis is a rotational deformity of the spine and ribs. While in most cases the cause of scoliosis is unknown (idiopathic scoliosis), in excess of 50 genetic markers have been identified as having a major role in adolescent idiopathic curves. Scoliosis may also result from a variety of congenital, neuromuscular, mesenchymal, and traumatic conditions, and it is commonly associated with neurofibromatosis.
A complicated three-dimensional deformity, scoliosis is characterized by both lateral curvature and vertebral rotation. Although degree of vertebral rotation and lateral curvature do not necessarily proceed in concert, typically, as the curve progresses, the vertebrae and spinous processes in the area of the major curve rotate toward the concavity of the curve (see Plates 1-36 and 1-37). Because the ribs are attached to the vertebral body, the ribs subsequently rotate dorsally on the convexity and volarly on the concave side. The entire thoracic cage can become ovoid, and anterior prominence can become as noticeable as posterior prominence. Most idiopathic curves are noteworthy for relative hypokyphosis of the thoracic spine. Kyphotic curves are more common in congenital and certain neuromuscular conditions. Lordosis (swayback) of the lumbar spine may accompany the scoliotic deformity.
In addition to rotation, scoliosis also causes other pathologic changes in the vertebrae and related structures in the area of the curve. The disc spaces become narrower on the concave side of the curve and wider on the convex side. The vertebrae also may become wedged (i.e., thicker on the convex side). On the concave side of the curve, the pedicles and laminae are frequently shorter and thinner and the vertebral canal is narrower.
The structural changes described are most common in idiopathic forms of scoliosis; the pathologic process may vary somewhat in paralytic and congenital forms. Generally, in the paralytic curve, which is caused by severe muscle imbalance, the ribs assume an almost vertical position on the convex side.
About 85% of patients with scoliosis exhibit an idiopathic (genetic) form. The disease is not primarily a problem of bone and joints but likely a manifestation of genetically mediated neuromuscular imbalance. Significant scoliosis (i.e., curves severe enough to require treatment) occurs up to seven times more often in girls than boys, whereas mild scoliosis affects boys and girls in equal numbers.
About 90% of all idiopathic curves are probably genetic, and thus the two terms are used synonymously. The scoliotic trait may not pass on to every generation (incomplete penetrance) and may cause a severe curve in a parent and a mild curve in a child, or vice versa (variable expressivity). If a person with idiopathic scoliosis has children, about one third of all offspring will have scoliosis; if both parents have genes for scoliosis, even if one parent does not exhibit the disease, the odds that offspring will be afflicted are even greater.
For years, the curve pattern classification system used to evaluate adolescent scoliosis was as described by Moe, Winter, and King the so-called King classification. In recognition of subtleties with newer surgical management of advanced curves not well addressed by this older classification, the Lenke classification system of adolescent idiopathic scoliosis was developed in an effort to provide a comprehensive and interobserver reliable means to categorize curves. Upright posteroanterior and lateral radiographs along with the supine side-bending radiographs are required. The classification system consists of a triad that utilizes a curve type (1 to 6) (see Plate 1-37), a lumbar spine modifier (A, B, C), and a sagittal thoracic modifier (−, N, +). All three regions of the radiographic coronal and sagittal planes the proximal thoracic, main thoracic, and thoracolumbar/lumbar are designated as either the major curve (largest Cobb measurement) or minor curves, with the minor curves separated into structural (rigid correction limited on supine bending films) and nonstructural types (flexible correction on bending film to < 25 degrees). The current recommendations are that the major and structural minor curves be included in the instrumentation and fusion and the nonstructural minor curves be excluded. Overall, this classification system is treatment directed; however, there are other aspects of the deformity that may suggest deviation from the recommendations of the classification system. The goal of this system is to allow organization of curve patterns to provide comparisons of treatment methods in order to provide the best treatment for each scoliosis patient.
|TYPICAL SCOLIOSIS CURVE PATTERNS|
In general, right thoracic curves are the most common. The curve usually extends to and includes T4, T5, or T6 at its upper end and T11, T12, or L1 at its lower limit. Typically, these curves do not correct on side bending. Because of severe vertebral rotation, the ribs on the convex side become badly deformed, resulting in a severe cosmetic defect and serious impairment of cardiopulmonary function when the curve exceeds 60 degrees. Right thoracic curves can develop rapidly and therefore must be treated early.
The right thoracic curve is always a major curve (i.e., the curve is structural and of great significance). There are usually smaller curves in the opposite direction above and below the right thoracic curve. These secondary curves are usually referred to as minor curves. A minor curve usually forms as a compensatory mechanism to help keep the head aligned over the pelvis and may be structural or nonstructural.
The thoracolumbar curve is also a fairly common idiopathic curve pattern. It is longer than the right thoracic curve and may be to either right or left. The upper end of the curve extends to and includes T4, T5, or T6 and the lower end includes L2, L3, or L4, usually with minor upper thoracic and lower lumbar curves. The thoracolumbar curve is usually less cosmetically deforming than the thoracic curve; however, it can cause severe rib and flank distortion due to vertebral rotation.
The double major curve consists of two structural curves of almost equal prominence. Double major curves can be any of the following combinations: right thoracic/left lumbar (most common); right thoracic/left thoracolumbar; left thoracolumbar/right lower lumbar; and right thoracic/left thoracic (double thoracic).
The lumbar major curve is quite common and usually runs from T11 or T12 to L5. In 65% of cases, the curve is to the left. The thoracic spine above the curve usually does not develop a structural compensatory curve and remains flexible. Lumbar major curves are not very deforming but can become quite rigid, leading to severe arthritic pain in later life and during pregnancy.
The extent of deformity varies with the underlying curve pattern, tending to be most severe with the right thoracic and thoracolumbar curves and less severe with balanced double major curves. Severe right thoracic and thoracolumbar curves often produce a marked over- hang of the thorax toward the convexity of the curve and a rib hump, and the torso tilts to the convex side. In contrast, with a balanced double major curve, the shoulders are level over the pelvis, and the rib and lumbar prominences are not too severe. The major deformity with this type of curve is trunk shortening.
Age at Onset
Idiopathic scoliosis is classified into infantile, juvenile, and adolescent types according to peak periods of onset. Infantile idiopathic scoliosis, which occurs between birth and 3 years of age, is usually noticed in the first year of life. Curiously, it is far more common in England, usually occurs in boys, and generally results in a left thoracic curve. The majority of these curves, thought to be a result of molding in the uterus, resolve spontaneously, even if untreated. Some, however, progress to severely rigid structural curves unless treated early and aggressively with serial casting as advocated by Mehta or with bracing.
Juvenile idiopathic scoliosis occurs between the ages of 4 and 10 and is most often detected at or after age 6. Both sexes are affected equally. Most curves in this group are right thoracic curves. Unless early standing and side-bending radiographs are available, it is almost impossible to distinguish cases of late infantile onset from those of early juvenile onset.
Adolescent idiopathic scoliosis is diagnosed when the curve is noticed between 10 years of age and skeletal maturity. Many curves first noticed at this age are probably present before age 10 but are not recognized until the adolescent growth spurt. Although adolescent scoliosis occurs in both boys and girls equally, 70% of cases that progress and need treatment occur in girls. The double major and right thoracic patterns predominate.
Idiopathic curves may or may not progress during growth. The risk of progression may be linked to various factors such as sex, age at onset, delayed maturation, and vertebral anatomy. Usually, the younger the child is when the structural curve develops, the less favorable the prognosis will be. In general, structural curves have a strong tendency to progress rapidly during the adolescent growth spurt, whereas small, nonstructural curves may remain flexible for long periods, never becoming severe. Nevertheless, the worst advice a physician can give a patient with scoliosis is “as soon as you finish growing, your curve will stop.” In a significant number of adults, scoliosis remains progressive, eventually causing pain and disability.
The curve is most likely to progress 1 to 2 degrees a year during adult life; if the curve is greater than 60 degrees at maturity, the curve pattern throws the trunk out of balance or the patient has extremely poor muscle tone. Generally, a curve that is less than 30 degrees at age 25 is unlikely to progress.
Congenital scoliosis is probably the result of some form of trauma to the zygote or embryo in the early embryonic period that causes a vertebral or extravertebral defect. Because many organ systems develop at the same time, children with congenital scoliosis almost always have some urinary tract or cardiac anomaly as well. Children with congenital scoliosis should also be examined for cervical spine anomalies such as Klippel-Feil syndrome (see Plate 1-33) and scapular deformities such as Sprengel deformity.
Congenital curves must be observed carefully. Although most do not progress significantly, some become severe and irreversible. Posterior vertebral defects can be open or closed. The open (dysraphic) defect caused by myelomeningocele can be very severe and is usually associated with partial or complete neurologic deficit with paraplegia and urinary tract problems.
|CONGENITAL SCOLIOSIS: CLOSED VERTEBRAL TYPES (MACEWEN CLASSIFICATION)|
Closed vertebral defects are classified into four types (see Plate 1-38): (1) partial unilateral failure of vertebral formation (wedge vertebra); (2) complete unilateral failure of vertebral formation (hemivertebra); (3) unilateral failure of segmentation (congenital bar); and (4) bilateral failure of segmentation (block vertebra). Other congenital combinations, some of which are extravertebral (e.g., rib fusions), are so mixed and bizarre they defy classification.
In hemivertebral conditions, as the anomalous vertebrae grow they cause the spine to lengthen on the convex side, leading to severe curves. Unilateral bars can also cause severe curvature. The worst possible congenital curve results from hemivertebrae on one side of the spine and several unilateral bars on the opposite side.
The best treatment for a progressive congenital curve is a short, in-situ spinal fusion performed as soon as progression is noted.
Neuropathic forms of neuromuscular scoliosis are caused by a variety of disorders. Muscle imbalance due to poliomyelitis, a lower motor neuron disease, and cerebral palsy, an upper motor neuron disease, may lead to severe, long C-shaped curves that may extend from the lower cervical region to the sacrum. Curves caused by syringomyelia also tend to become quite severe, often necessitating surgery. Because many patients with syringomyelia live well beyond their teenage years, treatment is definitely indicated when progression of the curve is noticed. Occasionally, neurosurgical drainage of the syrinx can help control the curve.
Myopathic forms of neuromuscular scoliosis are caused by both progressive and static disorders. The progressive disorders are exemplified by the muscular dystrophies. These disorders cause muscle imbalance, generally producing long C-shaped curves. Some children with scoliosis due to muscular dystrophy are so weak that their spines appear to collapse when they assume the erect posture. Judicious bracing or surgery may be helpful in some patients, but the prognosis is always guarded.
Other neuromuscular forms may be caused by mixed disorders, such as Friedreich ataxia, in which a muscle imbalance causes muscle weakness plus overpull by the stronger trunk and paraspinal muscles.
MESENCHYMAL AND TRAUMATIC DISORDERS
Congenital mesenchymal disorders leading to scoliosis can occur with various types of dwarfism and in Marfan syndrome. Because patients with Marfan syndrome are usually very tall, their curves can become quite severe. In osteogenesis imperfecta, the extreme brittleness of the bones results in hundreds of microfractures of the spine, eventually producing a scoliotic deformity. Scheuermann disease, if not properly treated, may also lead to a progressive kyphotic deformity in adolescents (see Plate 1-42).
Direct vertebral trauma such as a fracture with wedging or nerve root irritation can cause scoliosis. In some instances, the scoliosis may be secondary to irradiation for cancer treatment that, while saving the child’s life, destroys the growth plates of the vertebral body, resulting in unequal growth and causing spinal deformity.
Physical Examination. As part of the thorough physical examination, the development of secondary sexual characteristics should be noted. Their presence or absence, in addition to a height comparison with siblings and parents, can be significant in predicting future growth patterns. The skin is examined for café-au-lait markings indicative of neurofibromatosis, and the lumbar spine is searched for pigmented areas or patches of hair that can indicate an underlying congenital condition, such as spina bifida or diastematomyelia.
Following the general examination, a more specific examination of the deformity is done, beginning with evaluation of trunk alignment, which is used to gauge balance or displacement of the torso (see Plate 1-39). A tape measure dropped as a plumb line from the occiput can show if the head and trunk are aligned. In patients with a very severe double major curve, however, alignment may remain perfect.
|CLINICAL EVALUATION OF SCOLIOSIS|
The shoulder girdle should be examined for symmetry, and scapular prominence should be noted. The neck-shoulder angle may be distorted by asymmetry of the trapezius muscle caused by cervical or high thoracic curves.
The type of curve is recorded and its flexibility evaluated on side bending and distraction. Lifting the patient gently by the head distracts the curve, allowing the degree of rigidity and flexibility of the spine to be assessed.
Deformities of the thoracic cage are carefully recorded. With the patient bending forward, a scoliometer is used to measure the rib hump (see Plate 1-39). Anterior rib and breast asymmetry should also be noted.
Pelvic obliquity must be carefully assessed. It can be nonstructural, occurring as a result of a habit, or structural, resulting from a lower limb-length discrepancy. Structural pelvic obliquity can also be caused by contractures of muscle groups either above or below the iliac crests.
A brief but thorough neuromuscular examination including evaluation of all reflexes, response to stimuli, and motor capabilities is an important part of the scoliosis workup. In children with congenital conditions, sensory or motor loss can indicate an internal spinal condition, such as diastematomyelia. Decreased vibratory sensation in the limbs is a consistent sign in idiopathic scoliosis, which is due to a brainstem dysfunction; a more extensive neurologic examination is usually not warranted. The findings of the neuromuscular examination should be carefully correlated with the physical examination of the back. Painful scoliosis is uncommon in children, and its presence suggests the possibility of osteoid osteoma, spinal cord tumors, spondylolysis or spondylolisthesis, or infection.
Imaging. A single erect anteroposterior radiograph from the occiput to the iliac crest is sufficient for the initial examination of a new scoliosis patient. A spot lateral view of the lumbosacral spine is indicated if spondylolisthesis or spondylolysis (see Plate 1-44) is suspected. The thyroid, breasts, and gonads should be shielded and radiation exposure kept to a minimum.
Side-bending radiographs are taken to distinguish structural from nonstructural curves. Right side bending allows a right thoracic curve to uncoil, and the radiograph provides evidence of the suppleness of the ligaments and other soft tissue structures. Left side bending uncoils a left lumbar curve. Bending radiographs are typically reserved for preoperative evaluation.
|DETERMINATION OF SKELETAL MATURATION, MEASUREMENT OF CURVATURE, AND MEASUREMENT OF ROTATION|
The curve is measured on the initial radiograph using the Cobb method, which is preferred by the Scoliosis Research Society (see Plate 1-40). The accuracy of the Cobb method relies on determining the upper and lower end-vertebrae of the curve. The end-vertebrae at both the upper and lower limits are those that tilt most severely toward the concavity of the curve. In other words, the superior end-vertebra is the last vertebra whose superior border inclines toward the concavity of the curve to be measured and the inferior end-vertebra is the last one whose inferior border inclines toward the concavity of the curve. Horizontal lines are drawn at the superior border of the superior end-vertebra and the inferior border of the inferior end-vertebra. Perpendicular lines are then drawn from each of the horizontal lines and the intersecting angles measured. (The broken arrows on Plate 1-40 do not converge toward the concavity being measured, indicating that these vertebrae are not end-vertebrae but are in another curve above or below the curve being measured.)
Vertebral rotation is measured most accurately by estimating the amount that the pedicles of the vertebrae have rotated, as seen in the anteroposterior radiograph.
Skeletal maturation must also be determined accurately because scoliosis progression may slow (although it does not always stop) when a patient is fully mature. Girls generally cease growing and mature at about 14 12 years of age; this occurs in boys at age 16 to 17.
Several methods are used to estimate skeletal age. Radiographs of the left hand and wrist are compared with the Radiographic Atlas of Skeletal Development of the Hand and Wrist by Greulich and Pyle. Presence of an open triradiate physis in the acetabulum is an indication of significant skeletal immaturity. Pelvic radiographs can be used to determine the degree of iliac crest secondary ossification center excursion known as the Risser sign. When the iliac crest meets the sacroiliac joint and the physis closes, maturation is nearly complete. Another technique involves examining the superior and inferior growth plates of the thoracic and lumbar vertebrae on high-quality radiographs. If the growth plates are mottled in appearance, the skeletal growth is not complete. Solid union of the growth plates with the vertebral bodies indicates that maturation is complete.
Treatment. A variety of treatment modalities are available.
School Screening. The best treatment for scoliosis is early detection and prompt referral to a center equipped to provide complete scoliosis care. Most curves can be treated without surgery if detected before they become too severe. Scoliosis screening is still being done in schools across the United States and in other countries. A physician, mid-level provider, or school nurse can typically screen scores of children in less than an hour. The screening procedure is simple: the child bends from the waist with the arms hanging freely (see Plate 1-39). This position accentuates even a slight asymmetry in the ribs or lumbar area. School screening should begin in the fifth grade, and boys as well as girls should be examined every 6 to 9 months. If scoliosis or kyphosis is detected in a child, all siblings should be screened.
Exercises. Exercises are mentioned under treatment only to be strongly condemned as a cure for scoliosis. Unfortunately, physicians under the mistaken impression that exercises help to improve or eliminate a curve continue to prescribe an exercise program to many patients, who are then lost to follow-up until their curve becomes more severe. Basically, only two treatments effectively correct scoliosis: spinal bracing and surgery. Braces. With close supervision, a properly constructed, well-fitted brace, such as the Boston, Charleston, or Providence brace, can successfully halt progression of a curve in perhaps 70% of patients, if the patient and family are cooperative. Some curves, however, progress to greater deformity no matter what is done. Unfortunately, there is as yet no way to predict if a curve will respond successfully to bracing.
Low-profile braces have gained broad acceptance among patients and physicians alike. The now “historical” Milwaukee brace, the first brace demonstrated to alter the natural history of a curve, is rarely used in the contemporary management of scoliosis. Patient acceptance is much greater with these braces because they are barely visible under clothing or worn only at night. The inner pad is adjustable to add further pressure on the apex of the curve as the curve improves. The braces can be modified depending on the curve pattern and the presence or absence of kyphosis.
The Boston brace is generally worn over a long undershirt for 16 hours a day. Children can run and play in them relatively freely. Exercises are done daily both in and out of the brace to maintain muscle strength. The Charleston and Providence brace are “bending braces” that exert corrective force on the curve by virtue of a side-bending moment.
Patients using braces are seen every 6 months for brace adjustment. At 4- to 6-month intervals, new radiographs are taken with the patient erect and not wearing the brace. When radiographs show that skeletal maturation is nearly complete, the bracing is discontinued. Some physicians will stop bracing abruptly, whereas others wean from the brace. Neither regimen has demonstrated superiority.
Electrical Stimulation. In years past, electrical stimulation of muscle gained popularity in the treatment of scoliosis. It has been abandoned because it was not proven to alter the natural history of curve progression. In one study, patients who were treated with electrical stimulation actually fared worse than controls.
Surgery. The main indication for scoliosis surgery is relentless curve progression—typically progression of thoracic curves in excess of 45 degrees and progression of thoracolumbar curves to values in excess of 40 degrees. Pain, spinal balance, and general cosmesis are other factors that need to be considered with respect to surgical decision making. Since the first spinal fusion was performed in 1911, many different surgical techniques and types of instrumentation have been developed, each with its own advantages and risks, including neurologic impairment. Regardless of the method and hardware, the goal of surgery is to produce a solid arthrodesis of a balanced spine in the frontal and sagittal planes over a level pelvis.
|BRACES FOR SCOLIOSIS|
Posterior fusion techniques began using Harrington rod instrumentation. In some patients, a compression rod was added and the rods were further attached to the vertebrae with wires passed through holes drilled in the spinous processes. Harrington rods are now primarily of historical interest. The relative lack of restoration of sagittal balance was a major long-term problem.
In the Luque technique, still employed in certain neuromuscular curve types, the spine is straightened with two rods attached to sublaminar wires or cables. The Cotrel-Dubousset method was the first segmental instrumentation that allowed for rotation correction of individual spinal elements and employed two rods coupled together with transverse traction rods and hooks, which effectively derotated the spine.
Current state of the art instrumentation employs primarily pedicle screws that in comparison to hooks or sublaminar wires allow for far greater restoration of sagittal and coronal balance as well as a more rigid construct that typically obviates the need for postoperative bracing.
With the broad acceptance of pedicle screw technology as well as the recognition of its derotational strength, anterior surgery is less common and is typically reserved for exceptionally rigid curves requiring disc space release or curves with absent posterior bony elements.
The technique and approach used should be based primarily on the surgeon’s preference and expertise.