Etiology and Epidemiology

Scoliosis is a complex, 3-dimensional deformity of the spine, with abnormalities in the coronal, sagittal, and axial planes. The diagnosis is based on a coronal plane curvature of >10 degrees using the Cobb method. Idiopathic scoliosis is a diagnosis of exclusion; other causes must be ruled out (see Table 671-1). The etiology of idiopathic scoliosis remains unknown and is likely multifactorial, involving both genetic and environmental components. Major theories have been based on genetic factors, metabolic dysfunction (melatonin deficiency, calmodulin), neurologic dysfunction (craniocervical, vestibular and oculovestibular), and biomechanical factors (asynchrony in spinal growth, anterior spinal overgrowth, and others). With regard to genetic factors, although several different modes of inheritance have been suggested (autosomal dominant, multifactorial, X-linked), a single locus has yet to be identified. Abnormalities identified in connective tissue, muscle, and bone appear to be secondary. Melatonin and calmodulin might have indirect effects, and subtle abnormalities in vestibular, ocular, and proprioceptive function suggest that abnormal equilibrium might also play a role.

Idiopathic scoliosis is classified according to the age at onset, including infantile (rare, birth to 3 yr), juvenile (3-10 yr), and adolescent (≥11 yr). Adolescent idiopathic scoliosis (AIS) is most common (∼70%). The prevalence of scoliosis (>10 degrees curvature) is ∼2-3%; however, approximately 0.3% have a curve >30 degrees. The incidence is roughly equal in girls and boys for small curves (<10 degrees), but girls have 10 times the risk of developing a curvature >30 degrees.

Clinical Manifestations

Patients usually present with a change in cosmetic appearance noted by family and/or friends or on a screening examination by a school nurse or primary care physician. The patient is evaluated in the standing position, from both the front and the side, to identify any asymmetry in the chest wall, trunk, and/or shoulders. Asymmetry of the posterior chest wall on forward bending (the Adams test) is the earliest abnormality (Fig. 671-1). Rotation of the vertebral bodies toward the convexity results in rotation and prominence of the attached ribs posteriorly. The anterior chest wall may be flattened on the concavity, due to inward rotation of the chest wall and ribs. Associated findings can include elevation of the shoulder, a lateral shift of the trunk, and an apparent leg-length discrepancy. The patient should also be evaluated from the side. The thoracic spine normally has a smooth, rounded kyphosis (20-50 degrees using the Cobb method from T3-T12) that extends down to the thoracolumbar junction, and the lumbar spine is normally lordotic (30-60 degrees using the Cobb method from T12-L5). Children normally have less cervical lordosis and more lumbar lordosis than do adults or adolescents. Typically, idiopathic scoliosis results in a loss of the normal thoracic kyphosis in the region of curvature (relative thoracic lordosis).

Figure 671-1 Structural changes in idiopathic scoliosis. A, As curvature increases, alterations in body configuration develop in both the primary and compensatory curve regions. B, Asymmetry of shoulder height, waistline, and elbow-to-flank distance are common findings. C, Vertebral rotation and associated posterior displacement of the ribs on the convex side of the curve are responsible for the characteristic deformity of the chest wall in scoliosis patients. D, In the school screening examination for scoliosis, the patient bends forward at the waist. Rib asymmetry of even a small degree is obvious

(From Scoles PV: Spinal deformity in childhood and adolescence. In Behrman RE, Vaughn VC III, editors: Nelson textbook of pediatrics, update 5, Philadelphia, 1989, WB Saunders.)

A careful neurologic examination should always be performed. A subset of curves are associated with an underlying neurologic diagnosis, especially in patients who present in the infant and juvenile years (20% have an associated intraspinal abnormality). The index of suspicion is raised in the presence of back pain or neurologic symptoms, café-au-lait spots, a sacral dimple or midline cutaneous abnormalities (hemangioma, hair patch or skin tag), unilateral foot deformity, or an atypical curve pattern. The examiner should always test the superficial abdominal reflex by lightly stroking the skin on both sides of the umbilicus. Normally, the umbilicus should deviate toward the side that was stroked. Asymmetry of the superficial abdominal reflex (or unilateral absence of this reflex) might suggest syringomyelia as an underlying diagnosis.

Screening for scoliosis facilitates earlier diagnosis and treatment, under the assumption that the natural history may be influenced by bracing, and that earlier identification of cases suitable for surgery reduces the complexity and risks of the surgery. Screening may be accomplished during primary care visits or as part of a school screening program. A consensus statement from professional societies (American Academy of Pediatrics, American Academy of Orthopaedic Surgeons, Pediatric Orthopaedic Society of North America, and the Scoliosis Research Society) states that if screening is to be carried out, this should be at 10 and 12 years of age for girls, and once at 13-14 years for boys. The Adams forward-bend test has been used to identify any asymmetry in the thoracic and/or lumbar region, and an inclinometer (scoliometer, Orthopaedic Systems Inc.) is also used to measure the degree of asymmetry. The number of degrees used for referral typically varies from 5 to 7, and the referral rate from these programs varies from 3% to 30%. School screening remains controversial, and less than half of the states in the USA have formal programs. The U.S. Preventive Services Task Force (USPSTF) has recently recommended against school screening in 2004, and further research is required to inform policy.

The natural history of idiopathic scoliosis varies considerably based on the age at diagnosis. Curvatures in excess of 80 degrees can result in restrictive pulmonary disease, and larger curves in excess of 100-120 degrees can result in a reduced life expectancy, due to cor pulmonale and cardiorespiratory failure. Scoliotic curves diagnosed in infancy through childhood are much more likely than adolescent curves to reach this magnitude. In general, adults with untreated AIS are expected to have similar life expectancy and similar functional activities, and no greater risk of cardiopulmonary complications, when compared with age-matched controls. Back pain may be more common, but it does not appear to be more disabling. Thoracolumbar or lumbar curves are more likely to cause pain during adulthood, particularly if there is an associated translational shift of the vertebrae. Dyspnea is common with thoracic curves of >80 degrees. Thoracic curves <30 degrees rarely progress after skeletal maturity, but those >45 or 50 degrees can continue to progress at approximately 1 degree per year through life. The cosmetic aspects of the deformity may be the most significant concern for the majority of patients with untreated AIS.

Radiographic Evaluation

Standing high-quality posteroanterior (PA) and lateral radiographs of the entire spine are recommended at the initial evaluation for patients with clinical findings that suggest a spinal deformity. On the PA radiograph, the degree of curvature is determined by the Cobb method, in which the angle between the superior and inferior end vertebra (tilted into the curve) is measured (Fig. 671-2). A line is drawn across the superior end plate of each end vertebra, and the angle between perpendicular lines erected from each of these is measured. Although the indications for performing MRI are variable, this modality is helpful when an underlying cause for the scoliosis is suspected based on age (infantile, juvenile curves), abnormal findings on the history and physical examination, and atypical radiographic features (curve patterns and/or specific features). Atypical radiographic findings include uncommon curve patterns such as the left thoracic curve, double thoracic curves, high thoracic curves, widening of the spinal canal, and erosive or dysplastic changes in the vertebral body or ribs. On the lateral radiograph, an increase in thoracic kyphosis or an absence of segmental lordosis might suggest the presence of an underlying diagnosis.

Figure 671-2 A-C, Cobb angles measurements.

(From Morrissy, RT, Weinstein, SL: Lovell & Winter’s pediatric orthopaedics, ed 6, Philadelphia, 2006, Lippincott Williams & Wilkins.)

Treatment

Options for treatment include observation, bracing, and surgical treatment. Treatment decisions are based on the natural history of each curvature, which relates to age (degree of skeletal maturity or growth remaining), the magnitude of the curve, and occasionally associated diagnoses and/or medical considerations. A positive family history does not help predict the behavior of an individual curve. Observation is always indicated for curvatures <20 degrees. Curves of larger magnitude may be treated by bracing or surgery. The risk of curve progression depends on the amount of growth remaining, the curve’s magnitude, and gender. More than one parameter must be used when determining the amount of growth remaining, and both clinical (age, annual growth velocity, menarchal status, Tanner stage) and radiographic (Risser sign, skeletal age, maturation of olecranon apophysis) measures are available. Curves are more likely to progress if there is significant growth remaining (premenarchal, Tanner stage I or II, Risser 0 or 1). Premenarchal girls with curves between 20 and 30 degrees have a significantly higher risk of progression than do girls 2 yr after menarche with similar curves. Boys with curvature of the same magnitude appear to have similar risks of progression when judged by other maturation standards; however, the assessment of skeletal maturity in boys is more difficult.

Bracing

The goal of bracing is to prevent progression of the deformity, thereby reducing the need for surgery. The efficacy of bracing in AIS remains controversial, but most centers in North America offer a brace to selected patients with progressive curvatures. In AIS, the typical indications for bracing are a curve >30 degrees, or a curve from 20-25 degrees that has progressed >5 degrees, in a skeletally immature patient (Risser 0,1, or 2). Bracing is thought to be ineffective in curves >45 degrees. An “in brace” correction of 50% in Cobb angle is desirable.

The success of bracing is thought to increase with greater time spent in the brace, and the ideal program includes 23 hours in the brace per day. Protocols vary between 16 and 23 hours per day, recognizing that full compliance is difficult to achieve in the adolescent population. Bracing is commonly used as a temporizing measure for infantile and juvenile scoliosis given the high likelihood of significant progression, and the need to delay more definitive treatment. The success rate is much lower for infantile and juvenile curvatures, but the goal is to delay progression.

There are several options for braces (Fig. 671-3). The Milwaukee brace, employing longitudinal traction from the skull to the pelvis with lateral compression of the chest wall, can be adjusted for growth and thus is a good brace for patients with infantile or juvenile scoliosis. Underarm braces (the Boston or Wilmington braces) are less obvious and so are often preferred by adolescents. The Charleston brace provides a corrective force and is used only at night.

Figure 671-3 Various brace types.

(From Morrissy, RT, Weinstein, SL: Lovell & Winter’s pediatric orthopaedics, ed 6, Philadelphia, 2006, Lippincott Williams & Wilkins.)

Surgery

Surgical treatment is indicated for the majority of patients with infantile or juvenile idiopathic scoliosis and in selected patients with AIS, when other methods of treatment have failed to control the deformity, and when further progression would be expected to result in unacceptable cosmesis and/or physiologic abnormalities. Such deformities are typically treated by a definitive spinal arthrodesis (fusion). The majority of progressive infantile and juvenile curves ultimately require a spinal arthrodesis, and the goal is to delay the definitive procedure until the pulmonary system and thoracic cage have matured and the trunk height has been maximized.

An alternative strategy is required for curvatures that progress despite bracing. In some centers, serial casting under general anesthesia is employed for selected infantile and juvenile curves to gain correction into a “braceable” range, followed by application of a spinal orthosis. The other option for progressive curvatures is a “growing rod” construct. A spinal rod (or 2 rods) is attached to anchors at the top and at the bottom of the curvature, and distraction forces are applied to achieve correction. The rods hold the spine in the corrected position, and they must then be lengthened every 6 months to maintain correction. Many curves have been controlled for years using such a protocol, and definitive fusion is delayed until a more optimal age.

With regard to AIS, surgical treatment is usually indicated for skeletally immature patients with progressive thoracic curves >45 degrees and skeletally mature patients with thoracic curves >50-55 degrees. Lumbar curves are more likely to progress, and surgical stabilization may be offered for curves as low as 35-40 degrees if there is a significant shift of the trunk relative to the pelvis and lower extremities. The goals of surgery are to arrest progression of the deformity, to improve cosmesis, and to minimize the number of vertebral segments that are stabilized. These are achieved through a spinal fusion or arthrodesis, and implants are used to apply mechanical forces to the bony elements to affect correction and to hold the spine in the corrected position until the spine fuses. Postoperative immobilization is usually not required. Options for bone grafting include autograft (iliac crest) or allograft, and in recent years most surgeons have used cancellous allograft with or without enhancers such as demineralized bone matrix.

The most common procedure is an instrumented posterior spinal fusion, and the typical spinal implant construct includes 2 rods anchored to the spine by hooks, wires, and/or screws (Fig. 671-4). In the last few years there has been significant interest in using a construct with pedicle screws at each level. Although correction of the axial deformity (rotation of the rib cage) is more pronounced with this technology, it remains unclear whether patient outcomes are improved. An anterior release and fusion, performed through a thoracotomy or thoracolumbar exposure, is indicated for isolated thoracolumbar and lumbar curves, to improve correctability of stiffer curves, and to prevent curve progression (“crankshaft”) from continued anterior growth of the spine in selected patients with considerable growth remaining. A construct with multiple pedicle screws can allow the surgeon to avoid an anterior approach in many larger or stiffer curves (more powerful correction) and in younger patients (stiff enough to resist anterior spinal growth and prevent crankshaft). Thoracoscopic surgery has also been used to perform an anterior release with or without instrumentation and fusion, but this technique has been used much less often since the advent of thoracic pedicle screws. For idiopathic thoracolumbar and lumbar curves, an anterior fusion with instrumentation (usually screws in the vertebral body connected to 1 or 2 rods) can be done as an alternative to save lumbar motion segments.

Figure 671-4 A, Preoperative standing posteroanterior radiograph of a 14 yr old girl who was skeletally immature and developed a 68-degree right thoracic and a 53-degree left lumbar scoliosis. Her trunk was shifted to the right, and the left shoulder was slightly depressed. B, Based on the risk of future progression, she was treated by an instrumented posterior spinal fusion from T3 to L3, with correction of the right thoracic curve to 20 degrees and the left lumbar curve to 10 degrees. Coronal spinal balance was restored, and shoulder height was maintained.

There has been an interest in developing techniques to tether spinal growth, most commonly by placing metallic staples across each disk space on the convexity of a curvature. The goal is to slow or arrest growth on the convexity while allowing growth to proceed on the concavity, thereby preventing progression and possibly resulting in permanent correction without the need for an arthrodesis. The indications for this technique, and the long-term results, remain to be determined.