Idiopathic Scoliosis

Idiopathic Scoliosis

Peter O. Newton

Dennis R. Wenger

Burt Yaszay


Idiopathic scoliosis defines a potentially severe musculoskeletal disorder of unknown etiology that occurs most commonly in adolescents. In its milder forms, the scoliosis may produce only a change in the shape of the trunk, but when severe can be markedly disfiguring and ultimately lead to cardiopulmonary compromise (Fig. 17-1). The goal of this chapter is to present the key elements in diagnosis, natural history, and treatment of both early-onset and adolescent idiopathic scoliosis (AIS).

The etiology of typical scoliosis is not yet known, and therefore the term idiopathic remains appropriate. Scoliosis can also be classified based on associated conditions because it occurs in many neuromuscular disorders (cerebral palsy, muscular dystrophy, and others) as well as in association with generalized diseases and syndromes (neurofibromatosis, Marfan syndrome, bone dysplasia). Congenital scoliosis, caused by a failure in vertebral formation or segmentation, causes a more mechanically understandable type of scoliosis.

The etiology of a scoliotic deformity (idiopathic, neuromuscular, syndrome-related, congenital) largely dictates its natural history, including the risk for and rate of curve progression. Additionally, the age at onset has a significant effect on the natural history, since spinal growth will typically result in progression of the scoliosis. Although scoliosis includes both sagittal plane and transverse plane rotation malalignment of the spinal column, the deformity is most readily recognized on the coronal plane. A better understanding of the three-dimensional nature of scoliosis has led to many recent advances in its treatment.


The normal spine is straight in the frontal plane, but has sagittal plane contours including thoracic kyphosis averaging 30 to 35 degrees (range: 10 to 50 degrees, T5-T12) and lumbar lordosis averaging 50 to 60 degrees (range: 35 to 80 degrees, T12-S1) (1, 2 and 3). The scoliotic spine deviates from midline in the frontal plane and rotates maximally at the apex of the curve (4, 5). It is this vertebral rotation at the apex of the curve, through the attached ribs that produces the typical posterior chest wall prominence (Adams sign) that allows early diagnosis (6, 7) (Fig. 17-2). The axial plane rotation can also produce anterior chest wall deformity that can be manifested as breast asymmetry, with the right breast less prominent in most patients with the typical right thoracic curve (8).

In the past, it was thought that the lateral curvature of scoliosis was also kyphotic (increased roundback). It is now understood that most thoracic idiopathic scoliosis is associated with a decrease in normal thoracic kyphosis (9, 10). Dickson et al. (11, 12) have added to Somerville’s postulate (13) that an early evolution to lordosis in the normally kyphotic thoracic spine leads to a rotational buckling of the spinal column (Fig. 17-3). The apical thoracic lordosis is more easily seen on three-dimensional reconstructions by viewing the spine with a true lateral projection of the apical vertebra. Standard lateral radiographs overestimated the apical region kyphosis by an average of 10 degrees (14). In some case, there may be an increase in kyphosis that should raise suspicion for a nonidiopathic cause of the curvature (syringomyelia, Chiari malformation). For unknown reasons, most progressive idiopathic thoracic scoliosis in adolescents is convex to the right side (15).

The global deformity of the spine includes local deformity in both discs and vertebrae. Wedging develops in both structures, and changes in vertebral body shape are thought to follow the Hueter-Volkmann principles of bone growth (16),
that is, reduced growth in regions of excessive compression as might occur in the concavity of a scoliotic spine. This causes asymmetric growth and/or remodeling (according to Wolff’s law) of the vertebral bodies, pedicles, laminae, and facet joints, as well as of the transverse and spinous processes (Fig. 17-4). The vertebral body is noted to deform in a clockwise direction, while the spinous process deforms in a compensatory counterclockwise direction as seen on computerized tomography (CT) scan (17). Reduced concave growth accentuates the deformity, increases the compressive forces, and perpetuates the process (18).

FIGURE 17-1. A: This 16-year-old girl with severe scoliosis refused early treatment and had severe progression. Her clinical examination demonstrated marked trunk and rib deformity, and she had reduced pulmonary function. B: The PA radiograph demonstrates a right thoracic curvature of 125 degrees. With proper diagnosis and early treatment, deformity such as this should be completely avoidable in AIS.


Despite the substantial research that has been performed, the etiology for AIS remains unknown. Many theories have been proposed including genetic factors; disorders of bone, muscle, and disc; growth abnormalities; and factors related to the central nervous system.

Genetic Factors.

Several studies have demonstrated an increased incidence of scoliosis in the family members of affected individuals, thereby suggesting the existence of a genetic component to the etiology of scoliosis (19, 20, 21 and 22). Risenborough and Wynne-Davies (23) found scoliosis in 11.1% of first-degree relatives of 207 patients with idiopathic scoliosis. Examination of scoliosis in twins has further supported this with monozygotic (identical) twins demonstrating a higher concordance rate when compared to dizygotic twin (24, 25 and 26). Genetic studies of families in which multiple family members are affected have suggested several sites within the genome that appear to be linked to scoliosis (27, 28); however, the exact genes remain unknown. An evaluation of the family pedigrees of 131 patients with AIS found 127 with connections to other scoliosis patients. The authors concluded that there is at least one or two major genes responsible for AIS (29). Some specific candidate genes have been ruled out (type I and II collagen, fibrillin, and elastin), while other hormonerelated genes appear promising (30, 31 and 32). Currently, genetic
tests are being evaluated to assess for risk of a patient with a mild curve progressing to a severe curve.

FIGURE 17-2. A three-dimensional reconstruction of the scoliotic spine and trunk demonstrates the three-plane deformity of the spine and attached ribs. The torsional deformity is maximal at the apex of the curvature. (Courtesy of St. Justine Hospital, Montreal, Quebec, Canada.)

Tissue Deficiencies.

Considering that scoliosis affects patients with known musculoskeletal diseases, some believe that the primary pathology involves specific structural tissues of the spine (bone, muscle, ligament, and/or disc). For example, fibrous dysplasia (bone-collagen abnormality) resulting in dysplastic, misshapen vertebrae (33), muscle disorders such as Duchenne muscular dystrophy leading to a collapsing scoliosis, and soft tissue-collagen disorders such as Marfan syndrome are all associated with the development of scoliosis. It seems plausible that subtle deficiencies in any of the tissues of the spine could result in a predilection for collapse of the spine and idiopathic scoliosis progression (34). Some studies (35, 36 and 37) have found that girls with scoliosis had a lower bone mineral density when compared to matched controls suggesting that AIS may be related to osteopenia (35, 38). Recent studies, however, have suggested that this relative decrease bone mineral density was more strongly related to the patient’s body mass index (BMI) than the scoliosis (39). Therefore, the rationale for how osteopenia relates to the pathogenesis of scoliosis remains undefined.

Vertebral Growth Abnormality Theories.

Considering that the development of scoliosis and its progression are
temporally related to the time of rapid adolescent growth has led many to believe that the etiology is related to abnormalities in spinal growth (40, 41). Initially, differential growth rates between the right and the left sides of the spine were thought to generate an asymmetry that would be accentuated with asymmetric biomechanical loading and the Hueter-Volkmann effect (42, 43, 44 and 45). Others have postulated that the etiology of scoliosis relates to a relative overgrowth of the anterior spinal column compared to the posterior column resulting in a relative thoracic lordosis (11, 12, 43, 46, 47, 48 and 49). If the condition is severe enough, the spine rotates laterally to maintain global sagittal balance, effectively shortening by rotation or buckling (50) the “extra” anterior column length. This theory accounts for all three planes of deformity. In addition, computer-generated finite element modeling of anterior spinal overgrowth has been able to replicate the typical three-dimensional deformity of scoliosis (51). Studies of the growth mechanism of the anterior and posterior aspects of the vertebral elements suggest a different mechanism of growth in each (endochondral growth anteriorly and intramembranous growth posteriorly) (52).

FIGURE 17-3. A: This PA radiograph demonstrates the appearance of a double thoracic scoliosis curve pattern. B: The lateral radiograph demonstrates the relatively straight sagittal profile of the thoracic spine with loss of normal thoracic kyphosis. This is a common feature of AIS. C: The clinical appearance of this patient demonstrates a prominent scapula. However, this is not caused by kyphosis but by the rotational deformity of the ribs, which secondarily makes the right scapula more prominent. Additionally, a left upper thoracic trapezial fullness can be appreciated in this patient, caused by the left upper thoracic curvature.

Several studies suggest that adolescents with scoliosis are taller than their peers (53, 54, 55, 56 and 57). Increased levels of growth hormones (58, 59) and characteristic body morphometry (thin, increased arm span, physically less developed appearance) (60, 61 and 62) also appear to be related to the development of scoliosis. Hormones are known to be involved in pubertal changes, and their roles in scoliosis development have been widely studied (58, 63, 64). Although the relation between scoliosis progression and skeletal growth is well recognized, the proposed alterations in the regulation of growth that could be responsible for scoliosis are not yet defined.

Central Nervous System Theories.

Disorders of the brain, spinal cord, and nerves may result in scoliosis. The role of the central nervous system in idiopathic scoliosis has been studied in detail (65, 66, 67, 68, 69, 70 and 71). Goldberg et al. noted greater asymmetry of the cerebral cortices in patients with scoliosis (67). Also, abnormalities in equilibrium and vestibular function have been noted in patients with scoliosis (70, 72, 73, 74, 75 and 76); however, it is difficult to be sure whether these findings are primary or secondary (77). A recent study, however, has suggested that idiopathic
scoliosis is not related to brain function (78). Syringomyelia is associated with an increased incidence of scoliosis (79, 80 and 81), possibly due to direct pressure on the sensory or motor tracts of the spinal cord. Alternatively, there may be no relation to the dilation of the central canal, but instead brain-stem irritation from an associated Chiari malformation or enlargement of the fourth ventricle of the brain could be the cause.

FIGURE 17-4. This anterior view of a human scoliotic specimen demonstrates the substantial wedging of the apical vertebra. These changes in shape of the vertebra are thought to be a result of altered growth, according to the Hueter-Volkmann law. This appears to be a component of the progression seen in idiopathic scoliosis during rapid phases of growth. (Courtesy of Stefan Parent, MD.)

It has also been postulated that melatonin and the pineal gland may be related to scoliosis. This theory is based on research involving pinealectomy in chickens. The procedure was found to result in a high incidence of severe scoliosis in the birds (82, 83 and 84). Results of subsequent studies of primate and human melatonin levels have been conflicting and inconclusive. Machida et al. (85) found a lower-than-normal melatonin concentration in the serum of patients with progressive scoliosis compared to the serum of those with stable curves. In contrast, others have found no difference in either urine or serum melatonin levels between patients with scoliosis and age-matched controls or pinealectomized nonhuman primates (86, 87, 88 and 89). Confounding these studies is a recent report of melatonin signaling dysfunction in osteoblasts from patients with scoliosis (90). Currently, there is no confirmation that melatonin deficiency in humans is associated with scoliosis, as is seen in chickens.

In summary, the etiology of scoliosis remains unknown. As Stagnara (91) has noted, one should not be surprised that a minor disturbance in the structure, support system, or growth of the spine could lead to scoliosis, particularly in a complex structure whose “normal” state has multiple curves in the sagittal plane. There are likely several causes of idiopathic scoliosis, and active research continues in an attempt to find a unifying theory as to its development. The most promising clues seem to be coming from the advanced genome-wide studies that are underway.


In North America, a screening examination either in a school or at a routine primary care visit often leads to referral to a specialist. Many of these patients, therefore, have no symptoms
and are completely unaware of their potential spinal deformity. Evaluating a patient with scoliosis requires the physician to assess the patient for all conditions (Table 17-1) that are associated with scoliosis. While most adolescents presenting with scoliosis will be diagnosed as idiopathic, a careful history and physical examination are required in order to be certain no other causes exist that may affect their management.

TABLE 17-1 SRSs Diagnoses by Which Scoliosis Can Be Classified


Fiber-type disproportion



Congenital hypotonia



Myotonia dystrophica

Spondyloepiphyseal dysplasia



Diastrophic dwarfism





Failure of formation



Wedge vertebra





Upper motor neuron

Failure of segmentation


Cerebral palsy

Unilateral bar

Rheumatoid disease

Spinocerebellar degeneration

Bilateral (fusion)


Friedreich disease



Charcot-Marie-Tooth disease

Associated with neural tissue defect

Juvenile osteoporosis

Roussy-Levy disease


Osteogenesis imperfecta



Related to lumbosacral area

Spinal cord tumor

Spinal dysraphism


Spinal cord trauma






Lower motor neuron






Other viral myelitides

Marfan syndrome





Spinal muscular atrophy

Ehlers-Danlos syndrome


Werdig-Hoffmann disease



Kugelberg-Welander disease



Myelomeningocoele (paralytic)

Fracture or dislocation (nonparalytic)

Secondary to short leg

Dysautonomia (Riley-Day syndrome)


Due to muscle spasm





Soft-tissue contractures



Muscular dystrophy


Duchenne (pseudohypertrophic)




Physical Examination.

Physical examination of a patient with scoliosis includes evaluation of trunk shape, trunk balance, the neurologic system, limb length, skin markings, and skeletal abnormalities. Assessment of pubertal development includes assessment of the stages of breast development and the presence of axillary/pubic hair (Tanner stages). This can be done discreetly without fully undressing the patient. Girls can be asked to wear a two-piece swimsuit for the physical examination (the instruction regarding this can be given at the time of fixing the appointment). This reduces the patient’s anxiety and apprehension, yet allows assessment of breast and overall development.

With the patient standing, the back and the trunk are inspected for asymmetry of shoulder height, scapular position, and shape of the waist viewed from both front and rear. Potential pelvic tilt (an indicator of limb-length difference) is determined by palpating the iliac crests and the posterior inferior iliac spines bilaterally in the standing patient with both hips and knees fully extended. Lateral translation of the head can be measured in centimeters of deviation from the gluteal cleft by dropping a plumb line from C7. Deviation of the chest cage (trunk shift) should also be assessed because patients can have full head compensation (return of the head and neck back to midline) yet have marked lateralization of the trunk (Fig. 17-7).

Forward Bend Test.

The forward bend test, first described by Adams in Britain (109), has the patient bend forward at the waist with the knees straight and the palms together. This examination should be performed from behind (to assess lumbar and midthoracic rotation) and from the front (to assess upper thoracic rotation), as well as from the side (to assess kyphosis). Any asymmetry of the upper thoracic, midthoracic, thoracolumbar, and lumbar regions should be quantitated with a scoliometer (110) [to determine the angle of trunk rotation (ATR)] or by measuring the height of the prominence in centimeters (Fig. 17-8). This prominence reflects the rotational deformity of the spine associated with scoliosis (111, 112). Although there is not always an exact correlation, in general an ATR of 5 to 7 degrees is associated with a radiographic Cobb angle measurement of 15 to 20 degrees. [This is only an approximate guideline-occasionally patients may have little trunk rotation and yet have significant radiographic scoliosis, and vice versa (113).]

An inability to bend directly forward at the waist or a decreased range during forward/side bending may be caused by pain, lumbar muscle spasm, and/or hamstring tightness; any of these should suggest underlying pathology. These findings plus abnormalities in straight-leg-raise testing suggest irritation of the lumbar roots caused by spondylolysis, disc herniation, infection, neoplasm, or other factors.

Neurologic Examination.

The neurologic examination should evaluate balance, motor strength in the major muscle groups of all four extremities, and sensation. Watching the patient’s gait, toe-and-heel walk, tandem walk, deep squat, and single-leg hop allows rapid assessment of balance and motor strength. The presence of a cavus deformity of the feet, especially if it is unilateral, suggests an abnormality of the neurologic system/spinal cord. Testing for reflexes should include deep tendon reflexes of the upper and lower extremities as well as the Babinksi test for long tract signs. Abdominal reflexes are obtained by lightly stroking the abdominal wall with a blunt instrument (end of reflex hammer) adjacent to the umbilicus with the patient supine and relaxed. The expected brisk and symmetrical unilateral contraction of the abdominal musculature pulling the umbilicus toward the side being stroked indicates normalcy. When the reflex is persistently abnormal (reflex absent on one side and present on the other), intraspinal disorders, particularly syringomyelia, should be considered. The lower cranial nerves and the upper extremity examination should not be ignored because cervical-level pathology (particularly syringomyelia) presents here (81, 114).

FIGURE 17-7. Careful examination of the back is required in order to identify the physical features of scoliosis. These include asymmetry of the scapulae, shift of the trunk, and asymmetry of the waistline, as well as asymmetry in the level of the shoulders.

Further Assessment, Limb Length.

Additional components of a comprehensive scoliosis examination include inspection of the skin (both on the back and elsewhere) for
cutaneous evidence of an associated disease. Café-au-lait spots and/or axillary freckles suggest possible neurofibromatosis, whereas dimpling or a hairy patch in the lumbosacral area may suggest an underlying spinal dysraphism. Excessive laxity of skin or joints may be related to a connective tissue disorder such as Marfan syndrome or Ehlers-Danlos syndrome.

FIGURE 17-8. A: A 28-degree right thoracic scoliosis as seen on the PA radiograph. B: The Adams forward bend test demonstrated an 11-degree scoliometer measurement, indicating a corresponding measure for the ATR associated with this scoliosis. The forward bend test remains one of the most reliable means of detecting early scoliosis, other than a radiograph. Scoliometer measurements >7 degrees generally warrant a screening PA radiograph.

Limb length should also be measured in the supine position if pelvic tilt is noted during the standing examination. A spinal curvature that results from a limb-length difference is usually compensatory and serves to rebalance the trunk over the pelvis. A short right leg results in a compensatory right lumbar curve. There is no rotational deformity of the spine with these curves, and in the lumbar region the prominence noted on the forward bend test is on the concave side of the curve (the long leg makes the iliac crest and the lumbar spine more prominent on that side). This is the opposite of what is seen in true lumbar scoliosis, where the rotational prominence noted on the bending test is found on the side of the curve convexity. The presence of the bending test rotational prominence on the “wrong” side in a lumbar curve is almost always diagnostic of spinal asymmetry caused by limb-length discrepancy rather than true scoliosis. The prominence disappears if the pelvis is leveled with an appropriately sized block underneath the short leg.

Radiographic Assessment.

The ideal screening radiographs for scoliosis are upright (standing) posteroanterior (PA) and lateral projections of the entire spine exposed on a single cassette. The radiograph must be taken with the patient standing because diagnostic and treatment standards developed over
the years are based on films in the upright posture. In very young patients, or in those with severe neuromuscular involvement, radiographs taken in the sitting or even supine position may be the only ones possible. The magnitude of the curve is greater when the patient is upright (compared to supine), and this is of particular importance in infantile and congenital curves when radiographs are taken before and after walking age. “Curve progression” may mistakenly be noted with the first upright-position radiograph as compared to prior supine views, when in fact one has simply documented that gravity causes a curve to be more severe. The sagittal balance varies with the method of arm positioning (the arms must be flexed for the spine to be clearly visualized). With the arms held straight forward, the trunk shifts posteriorly, and therefore the best position for viewing relaxed standing is with the arms flexed as little as possible to clear the spine (115). A lateral view of the lumbosacral junction is often performed in lumbar scoliosis to assess for spondylolysis/spondylolisthesis as a possible cause (Fig. 17-9).

Radiographic techniques that are used for minimizing radiation exposure of sensitive tissue (e.g., breast, thyroid, ovaries, and bone marrow) include taking only the required number of x-rays, utilizing rare earth radiographic enhancing screens with fast film, and a posterior-to-anterior exposure (116, 117 and 118). The lifetime risk for developing breast or thyroid cancer has been suggested to increase by 1% to 2% in patients who are exposed to multiple x-rays during the course of treatment of scoliosis; however, these data relate to the 1960s and 1970s, before new radiation-reducing techniques became available. The greatest reduction in breast and thyroid exposure is associated with the PA exposure [compared to the anteroposterior (AP)]; this reduces breast/thyroid exposure three- to sevenfold (118). AP projection can shield the breasts; this is, however, not recommended because this projection increases thyroid exposure (shielding the thyroid obstructs the view of the upper spine). A new x-ray detection system that requires roughly one-eighth the radiation has been developed by Charpak, which has the potential to substantially reduce radiation for this population (116, 117). Doctors counsel their patients by assuring them that during the radiographic procedure, the exposure to the x-rays required to treat the disorder correctly will be minimal and that the benefit of undergoing the procedure outweighs the risk of not knowing the type and severity of the scoliosis.

When surgical treatment is being considered, lateralbend radiographs (to assess curve flexibility) are required. Radiographs of side bending allow one to determine the degree of curve flexibility, and to decide what levels to include in the instrumented and fused segments. Controversy remains regarding the best method of obtaining AP films of side bending. Supine-position side-bending views (patient maximally bent to the right and left) are standard at many institutions, whereas others believe that a standing-position bend film is a better indicator, particularly in the lumbar spine. Lateral bending over a bolster provides somewhat greater correction and has been proposed as a more accurate predictor of the correction obtainable with the more powerful modern surgical instrumentation methods (87, 119) (Fig. 17-10). In curves >60 to 70 degrees, longitudinal traction films may also be helpful in evaluating curve flexibility (120, 121). There is no universal standard for how to obtain radiographs of bending. Additionally, there is little agreement on how to make use of the information gained. Flexible minor curves may be spared arthrodesis in many cases, and this flexibility information has been utilized (yet not necessarily standardized) in surgical decision making. More severe cases of scoliosis, that is, curves that do not straighten to <50 to 60 degrees, have been suggested as benefiting from an anterior release procedure prior to posterior instrumentation.

The Stagnara oblique view, taken perpendicular to the rib prominence rather than in the PA direction, provides a more accurate picture of large curves that have a large rotational component. From this angle, the true magnitude of the scoliosis can be measured more accurately (14, 122). Similarly, an oblique lateral may show the true sagittal alignment at the apex.

Reading Scoliosis Films.

Assessment of the standing PA film begins by looking for soft-tissue abnormalities, congenital bony abnormalities (wedge vertebrae, etc.), and then by assessing curvature (coronal plane deviation). Bone assessment includes looking for wedged or hemivertebrae (Fig. 17-11) and bar formation bridging a disc space as well as midline irregularities such as spina bifida or a bony spike suggesting diastematomyelia. The pedicles should be inspected in order to verify that they are present bilaterally and that the interpedicular distance is not abnormally increased, which would suggest an intraspinal mass (123, 124). Absent pedicles or vertebral body lucency are associated with lytic processes, such as tumor or infection. If a curve is noted, the symmetry and the levelness of the pelvis are analyzed. A limb-length discrepancy can be estimated by determining height differences between iliac wing and hip joint, assuming the patient had hips and knees fully extended when the film was exposed.

Curve measurement using the Cobb method (125) allows quantification of the curve. A protractor or digital software tool allows for accurate measurements. The caudal and cranial end vertebrae to be measured are the vertebrae that are the most tilted, with the degree of tilt between these two vertebrae defining the Cobb angle (in a normal spine this angle is 0 degrees). One should outline the superior end plate of the cranial end vertebra and the inferior end plate of the caudal end vertebra. If measuring by hand, construct a perpendicular to each of these lines and then measure the angle at which the lines cross. When more than one curve exists, a Cobb angle measurement should be made for each curve (Fig. 17-12). The wide variation of inter- and intraobserver error (approximately 5 degrees for any curve measurement) should be understood by the surgeon and the anxious parents (and patient) (126). Therefore, a 6-degree difference is accepted by most surgeons as the criterion for determining curve progression in idiopathic scoliosis.

FIGURE 17-9. A: This 10-year-old girl presented with symptoms of increasing trunk decompensation, as well as low back pain and posterior thigh discomfort. She has an obvious trunk shift to the left, suggesting scoliosis. The PA rather than the AP view is preferred because there is reduced radiation exposure. B: The standing-position PA radiograph confirms a 43-degree left lumbar scoliosis. C: Standing-position lateral view focused at the L5-S1 level demonstrates severe spondylolisthesis. Most of this patient’s lumbar deformity is related to an asymmetric forward slipping of L5 on S1, with rotational deformity translated to the lumbar spine above. Following correction of her spondylolisthesis with fusion from L4 to the sacrum, her scoliosis reduced to <15 degrees.

FIGURE 17-10. A: This standing-position preoperative PA radiograph demonstrates right thoracic scoliosis with moderate left lumbar scoliosis. B: The flexibility of the left upper thoracic and left lumbar curves was assessed via the left-side-bending radiograph. C: The flexibility of the right thoracic curve was evaluated using the bolster side-bending technique. D: The bolster side-bending film is taken with the trunk laterally flexed on a bolster positioned under the ribs that correspond to the apex of the deformity.

Vertebral rotation, maximal at the apex of a curve, is demonstrated on radiographic film by asymmetry of the pedicles and a shift of the spinous processes toward the concavity. Two methods are available for quantifying this rotation, one suggested by Nash and Moe (127) and the other by Perdriolle (128). Vertebral rotation is not routinely measured clinically, however, and both methods have substantial inaccuracies, which limit their usefulness (129).

Skeletal maturity should be assessed radiographically in order to estimate remaining spinal growth, an important predictor of risk for curve progression. The most widely used method in patients with scoliosis, although probably the least reliable, is that of Risser (130), who noted that the iliac crest apophysis ossifies in a predictable fashion from lateral to medial, and that its fusion to the body of the ilium mirrors the fusion of the vertebral ring apophysis, signifying completion of spinal growth. The lateral-to-medial ossification of the iliac crest apophysis occurs over a period of 18 to 24 months, finally capping the entire iliac wing. Risser classified the extent of apophyseal ossification in stages, ranging from Risser 0, indicating absence of ossification in the apophysis, to Risser V, indicating fusion of the fully ossified apophysis to the ilium (spinal growth complete) (131). Risser I through IV are assigned to the intermediate levels of maturity as seen in Figure 17-13.

Risser originally described this finding on AP radiographs, which place the iliac apophysis close on the x-ray film. This is in contrast to the common current practice of PA projections and may explain some of the difficulties in reading this sign
(132). Despite the common reporting of the Risser sign as a measure of maturity, the appearance of the iliac apophysis generally occurs after the most important period of rapid growth (97, 99). Little and Sussman (133) have suggested that the Risser sign is no more accurate at predicting scoliosis progression than chronologic age.

FIGURE 17-11. A: This adolescent patient presented with spinal deformity. The standing-position PA radiograph demonstrates an obvious left thoracolumbar deformity. On careful examination, an abnormality at the lumbosacral junction is suggested. B: A cone-down radiograph of the lumbosacral junction demonstrates a clear hemivertebra. This congenital malformation is the primary deformity, and the thoracolumbar deformity above is a compensatory curve. It is certainly important to recognize this because treatment of the thoracolumbar curve would lead to marked decompensation to the left.

The status of the triradiate cartilage of the acetabulum also provides a landmark for assessing growth potential. The triradiate growth cartilage usually closes before the iliac apophysis appears (Risser 0), at about the time of maximal spinal growth (134, 135) (Fig. 17-14). Skeletal age can also be measured using the Greulich and Pyle atlas (136) to compare hand radiographs against illustrated standards, although these readings become less accurate (large standard deviations) in the juvenile age group. Some authors have recommended using the maturation of the olecranon to determine skeletal age (137). Sanders has recently reported on the “digital skeletal age,” which provides information about growth potential particularly useful during the Risser 0 phase (138). This system uses the progressive development of the epiphysis of the metacarpal and phalanges to determine skeletal age.

Specialized Imaging Studies.

Most idiopathic scoliosis cases do not require imaging beyond plain radiography. Specialized imaging methods that can be used to evaluate cases with unusual features include MRI, CT, and bone scintigraphy, each with specific indications and advantages.

MRI has almost completely replaced myelography in the study of the neural elements in spine disorders. An exception is the patient who has had prior placement of stainless steel implants (making MRI visualization nearly impossible) and who continues to have symptoms or develops new ones that have to be studied.

MRI study of the spine is indicated for all patients with idiopathic scoliosis in the infant and juvenile age groups (92, 93, 139, 140) and also for those with congenital bony anomalies if surgical correction is planned (141, 142). Left thoracic curves have been shown to have an increased association with spinal cord anomalies and may be an indication for MRI study (140, 143). It has also been suggested that all male patients should have a screening MRI, although no studies exist to substantiate this. Indications are not clear for routine MRI prior to corrective surgery in patients with typical idiopathic scoliosis (for whom clinical neurologic examination has shown normal results) (144). Several prospective studies have been completed (145, 146 and 147) of routine MRI screening for preoperative assessment (spine and brain) of all patients with idiopathic scoliosis. There is no evidence that an MRI is helpful in an otherwise normal adolescent with scoliosis. Clearly, however, patients with an abnormality in the neurologic examination (140) or with cutaneous findings (suggestive of dysraphism or neurofibromatosis) should have an MRI study of the spine and/or brain. Additionally, Ouellet et al. (148) have suggested that a hyperkyphotic sagittal alignment of the thoracic spine should raise suspicion of a syringomyelia and trigger an MRI study. Severe angular and rotational deformities may be difficult to analyze with an MRI because the spinal canal deviates into and out of the planar cuts of the sagittal and coronal images. CT myelography that produces a dye column may be better for revealing stenosis or an intraspinal filling defect in extremely severe cases of scoliosis.

FIGURE 17-12. A: Measurement of the Cobb angle. The end vertebrae of each curve must be selected before any measurement can be made. The end vertebrae of the curve are those which are most tilted from the horizontal. B: The endplates of the superior and inferior end vertebrae of the thoracic curve are marked on this figure. Perpendicular lines are constructed. C: The angle between the two lines is measured with a protractor and defined as the Cobb angle measure of the scoliosis. D: This method is used for quantifying the magnitude of scoliosis at each of the three regions: upper thoracic, main thoracic, and lumbar.

FIGURE 17-13. Risser sign. The iliac apophysis ossifies in a predictable manner beginning laterally and progressing medially. The capping of the iliac wing is correlated with slowing and completion of spinal growth, generally occurring over a period of 18 to 24 months.

The workup of patients with substantial back pain with no obvious cause may require a bone scan and/or MRI to evaluate for possible tumor, infection, or spondylolysis. The bone scan is an excellent screening test for studying the patient with scoliosis who is experiencing pain. The test allows one to screen for conditions ranging from osteoid osteoma to hydronephrosis. A single-photon emission computed tomography type of bone scan (computerized tomographic enhancement) is very useful in identifying spondylolysis and its varying presentations (unilateral, bilateral, cold scan, hot scan, etc.). If an area of increased activity is noted on the bone scan, additional imaging (either MR or CT) may be required. An MRI may also be used as a screening tool for patients who are in pain, although cortical lesions (spondylolysis) may be harder to identify, and benign osteoid osteomas have been overinterpreted as malignancies. A screening MRI should include the entire length from the brain stem/posterior fossa to the sacrum. Individual MRI sequences for the brain, cervical, thoracic, and lumbar regions are not required. A limited number of images, primarily in the sagittal and coronal planes, are sufficient to identify a tumor, Chiari malformation, syringomyelia, or tethered cord. All aspects of the evaluation of a patient with scoliosis (history, physical examination, imaging studies) should be focused first on identifying possible nonidiopathic causes of the deformity, and only secondarily on characterizing the specific features of the curve. If one assumes an idiopathic etiology, an underlying spinal cord abnormality or associated syndrome will be very difficult to identify. One cannot recognize what one does not look for.

FIGURE 17-14. The triradiate cartilage of the acetabulum is seen here (arrow). The closure of this growth cartilage signifies completion of the most rapid phase of adolescent growth. However, at least 2 years of growth may be remaining following closure of the triradiate cartilage.


Idiopathic scoliosis makes up the largest subset of patients with spinal deformity and, because its etiology is unknown, this diagnosis is one of exclusion made only after a careful evaluation has ruled out other causes of scoliosis. The natural history of nonidiopathic scoliosis along with the appropriate choice of treatment (and associated risks of treatment) may deviate substantially from that of idiopathic scoliosis. The history,
examination, and imaging studies should be focused both on evaluating the severity of the deformity and on identifying its cause. Clinical features and treatment of idiopathic scoliosis also vary according to the age group to which the patient belongs (infantile, juvenile, adolescent). These are summarized in the subsequent text.

TABLE 17-2 Prevalence of Scoliosis

(% of patients with curves of this magnitude)


No. of patients

>5 degrees

>10 degrees

>20 degrees

>30 degrees

Stirling et al. (155 )




Bruszewski and






Kamza (149 )

Rogala et al. (153 )




Shands and Eisberg






(154 )

Kane and Moe (151 )



Huang (112 )





Morais et al. (156 )




Soucacos et al. (99 )





Prevalence of Idiopathic Scoliosis.

The prevalence of idiopathic scoliosis (with a curve of >10 degrees) in the childhood and adolescent population has been reported as ranging from 0.5 to 3 per 100 (149, 150, 151, 152, 153, 154 and 155). The reported prevalence of larger curves (>30 degrees) ranges from 1.5 to 3 per 1000 (156, 157). Therefore, small-to-moderate curves are the more common ones, and severe (life-threatening) curves are rare (Table 17-2).

The percentage of cases seen in each age group demonstrates a strong predominance of adolescent scoliosis, with a series from Boston showing 0.5% infantile, 10.5% juvenile, and 89% adolescent incidence (23). The natural history for each group varies substantially.

Although classically idiopathic scoliosis has been divided into three groups according to the age of onset (infantile, juvenile, adolescent), there is a movement to simplify this to “earlyonset scoliosis” (before age 10 years) and “late-onset scoliosis” (typical adolescent scoliosis) (155). Dickson and Weinstein (158) and Weinstein et al. (159) believe that only early-onset scoliosis has the potential for evolution into severe thoracic deformity with cardiac and pulmonary compromise.

Infantile Idiopathic Scoliosis.

Infantile idiopathic scoliosis (IIS) cases have been more commonly reported from Britain than North America (23, 160, 161). More recent reports, however, suggest a decrease in the frequency of infantile cases, more closely paralleling the North American experience (162).

IIS presents as a left thoracic curve in approximately 90% of cases, with a male:female ratio of 3:2 (160, 161, 163, 164). The curvature is often accompanied by plagiocephaly, hip dysplasia, congenital heart disease, and mental retardation (21, 165). The series from Britain suggests that the vast majority (up to 90%) of these curves are self-limiting and resolve spontaneously (164); however, the few that are progressive can be difficult to manage, often resulting in lasting deformity and pulmonary impairment (166).

Prediction of Progression in Infantile Curves.

Risk factors that predict a high likelihood for curve progression have been identified by Mehta (167) who, in a study of 135 patients with IIS, determined certain radiographic prognostic parameters: (a) rib vertebral angle difference (RVAD) and (b) phase of the rib head. The difference in the obliquity between the two ribs attaching to the apical vertebra (right versus left) is known as the RVAD. The RVAD is the most commonly utilized measure and is determined at the apical vertebra on an AP radiograph. The ribs in the concavity of progressive infantile scoliosis are relatively horizontal, whereas those on the convex side are more vertically aligned (Fig. 17-15). Eighty-three percent of Mehta’s reported cases resolved when the RVAD was
<20 degrees, compared to 84% progressing when the RVAD was >20 degrees (167, 168).

FIGURE 17-15. In IIS, the RVAD helps in predicting curve progression. The RVAD is constructed by first determining the angle of the right and left ribs at the apical vertebral level of the deformity. The slope of the ribs relative to the transverse plane is measured for each rib. The difference in the angle between the right and left sides is the RVAD. A difference of more than 20 degrees suggests a high likelihood of a progressive form of IIS, according to Mehta.

Juvenile Idiopathic Scoliosis.

Juvenile idiopathic scoliosis (JIS), defined as scoliosis with an onset at the ages of 4 to 10 years, accounts for approximately 8% to 16% of childhood idiopathic scoliosis (25, 169, 170), and in many respects represents a transitional group between the infantile and adolescent groups. Curves with onset in this age group are often progressive, with potential for severe trunk deformity and eventual cardiac and pulmonary compromise. Many patients who present in adolescence (previously undiagnosed and untreated) with severe thoracic curves requiring immediate surgery had the onset of their curves in the juvenile age period, making the differentiation between juvenile and adolescent grouping problematic.

In JIS, boys seem to be affected earlier than girls (171, 172). In a series of 109 patients evaluated by Robinson and McMaster, the boys presented at a mean age of 5 years 8 months compared to a mean age of 7 years 2 months for the girls. The ratio of girls to boys was 1:1.6 for those younger than 6 years and 2.7:1 for those older than 6 years at presentation. Additionally, there were equal numbers of right- and left-side curves in the younger group (<6 years) with a preponderance of right-side curves (3.9:1) in the patients older than 6 years (171). When curves reach 30 degrees, they are nearly always progressive if left untreated (172). The rate of progression is 1 to 3 degrees per year before the age of 10 years, and this increases sharply to 4.5 to 11 degrees per year after that age (171). This is particularly true of thoracic curves that, despite treatment with braces, require arthrodesis in more than 90% of the patients (169, 171). The surgical treatment of JIS is similar to that for AIS; however, anterior growth ablation (fusion) in addition to posterior instrumentation and fusion is more commonly indicated to prevent “crankshaft” rotational growth following posterior fusion (see subsequent text). In very young patients, instrumentation involving a system that can be periodically lengthened is sometimes used (instrumentation without fusion or fusion only at proximal and distal hook sites).

FIGURE 17-16. During the adolescent growth spurt, the rate of increase in height rises from approximately 6cm per year to as much as 10 cm per year. The age at peak height velocity or the time of most rapid growth occurs before the onset of menses or appearance of the Risser sign. It is during this phase of growth that scoliosis progression is most likely. (From Little DG, Song KM, Katz D, et al. Relationship of peak height velocity to other maturity indicators in idiopathic scoliosis in girls. J Bone Joint Surg Am 2000;82:685-693, with permission.)

Adolescent Idiopathic Scoliosis.

Patients with this most common category of scoliosis theoretically develop a curve after the age of 10 years, corresponding to the rapid growth phase of adolescence. Again, the separation of adolescent and juvenile curves is somewhat arbitrary because an 11-year-old girl who presents with a 70-degree scoliosis almost certainly had the onset of scoliosis in the juvenile age period. As noted previously, the data indicate that the prevalence of curves of 10 degrees or greater ranges between 0.5% and 3%. These data have been collected from a variety of sources including screening chest x-rays and school-screening programs. Roughly 2% of adolescents have a scoliosis of 10 degrees or greater, but only 5% of these cases experience progression of the curve to >30 degrees. The ratio of boys to girls is equal among patients with minor curves, but girls predominate as the curve magnitude increases, with the ratio reaching 1:8 among those requiring treatment (170).

Risk Factors for Progression.

Knowledge of which curves will likely worsen and which will not is critical in deciding which patients need treatment. The parameters that are significant in assessing the risk for scoliosis progression include gender, remaining skeletal growth, curve location, and curve magnitude. Scoliosis progression is most rapid during peak skeletal growth (early infancy and adolescence). The peak growth velocity of adolescence averages 8 to 10 cm of overall height gain per year (40, 135), with half of this growth coming from the trunk (spine) (25) (Fig. 17-16). Several determinants are useful in predicting the remaining growth. The age of the patient is one such obvious determinant. However, substantial variations in skeletal growth are seen among patients of the same chronologic age; therefore, bone age is a more consistent indicator (173). Menarchal status helps determine the growth spurt in girls (the onset of menses generally follows approximately
12 months after the most rapid stage of skeletal growth). (For additional information on growth, see Chapter 2.)

The Risser sign, which is associated with the inaccuracies noted in the preceding text, has been used for assessing the risk for curve progression. When the Risser sign is 1 or less the risk for progression is up to 60% to 70%, whereas if the patient is Risser 3 the risk is reduced to <10% (4, 174).

Unfortunately, many of the readily identifiable markers of maturity (menarcheal status, Risser sign) are quite variable and appear just after the adolescent growth spurt. If there is no accurate record of prior growth performance, it is impossible to tell whether a premenarcheal, Risser 0 patient is approaching, in the midst of, or past the time of most rapid growth and consequent risk for scoliosis progression. Closure of the triradiate cartilage of the acetabulum as well as capping of the digital epiphysis has been identified as radiographic signs that more closely approximate the time of peak growth velocity (137, 143).

The curve pattern has also been identified as an important variable for predicting the probability of progression. Curves with an apex above T12 are more likely to progress than isolated lumbar curves (174). Curve magnitude at initial diagnosis also appears to be a factor associated with progression (41, 175) (Fig. 17-17). In a series of skeletally immature patients (Risser 0 or 1), curve progression occurred in 22% of cases with a curve at initial diagnosis of 5 to 19 degrees, compared with 68% incidence of curve progression when the initial curve was 20 to 29 degrees (40). The rate of curve progression increased to 90% when the initial curve was 30 to 59 degrees (159, 176).

Natural History in Adulthood.

The long-term effects of idiopathic scoliosis in adults should be understood when considering treatment in childhood and adolescence. The risk of curve progression is greatest during the rapid phases of growth as discussed in the preceding text; however, not all curves stabilize after growth stops. In the long-term studies performed at the University of Iowa, more than two-thirds of the patients experienced curve progression even after skeletal maturity. Thoracic curves of <30 degrees tended not to progress, with the most marked progression occurring in curves between 50 to 75 degrees at the completion of growth (continuing to progress at a rate of approximately 1 degree per year). Lumbar curves generally progressed if they were >30 degrees at skeletal maturity (177, 178). Several studies provide insights into what the future holds for affected individuals. Early studies of patients with untreated scoliosis whose cases were followed for up to 50 years reported a mortality rate twice that expected in the general population, with cardiopulmonary problems being cited as the most common cause of death (179, 180). Disability and back pain were common among the patients (180, 181). Unfortunately, the etiology of the scoliosis in these studies was mixed (idiopathic, congenital, neuromuscular), and the severity of the scoliosis was not known in the cases of many of the patients, making correlations to those with idiopathic scoliosis impossible.

FIGURE 17-17. The incidence of scoliosis curve progression is greatest for younger ages and for larger curves. (From Lonstein JE, Carlson JM. The prediction of curve progression in untreated idiopathic scoliosis during growth. J Bone Joint Surg Am 1984;66:1061-1071, with permission.)

In more recent studies, in which only patients with AIS were included, the increased mortality rate reported previously has not been confirmed (159, 182). Mortality from cor pulmonale and right heart failure was seen only in severe thoracic curves (>90 to 100 degrees) (183, 184).

Pulmonary function becomes limited as thoracic scoliosis becomes more severe (>70 degrees) (159, 182, 185, 186 and 187). The incidence of mild-to-moderate impairment in forced vital capacity and forced expiratory volume in 1 second (FEV1) increases with curve magnitude (183, 188) (Fig. 17-18). The associated deformity of the chest cavity causes restrictive lung disease.
Thoracic lordosis also decreases lung volume and increases the deleterious effects of scoliosis on pulmonary function (183).

FIGURE 17-18. Pulmonary function as it relates to thoracic curve severity. As can be seen, a greater thoracic Cobb magnitude is associated with a greater risk of moderate-to-severe pulmonary impairment. (From Newton PO, et al. Results of preoperative pulmonary function testing of adolescents with idiopathic scoliosis. J Bone Joint Surg Am 2005;87:1937-1946, with permission.)

Estimates regarding the frequency of back pain and associated disability in adults with scoliosis vary, but most studies have demonstrated slightly higher rates of back pain compared to control groups (182, 184, 189, 190). The 1476 patients with AIS surveyed in Montreal had more frequent and more severe back pain than did 1755 control subjects (184). Disability rates have been higher in some series (180, 184) and similar in others (182). After 50-year follow-up, 65% of patients with late-onset idiopathic scoliosis reported chronic back pain compared with 35% of the controls (159).

The social impact of scoliosis varies with the individual and with the cultural setting. Nowadays, many patients are seriously concerned about the appearance of their backs and seek medical treatment to correct their deformities (188). Some studies report that the rate of marriage is lower among women with scoliosis; this implies a psychosocial impact of the deformity (179, 180). Many modern parents are unwilling to accept significant deformity of any type in their child, whether it is dental, dermatologic, or orthopaedic, particularly if there is a reasonable and safe way to correct the condition. However, as safe as scoliosis surgery has become, it carries with it finite risks and lasting consequences, most notably loss of spinal motion within the treated segments. Balancing these risks against current and/or future deformity challenges the decision-making skills of the treating surgeon.


School-screening programs have been instituted in many countries to detect scoliosis at an early stage. The goal is to detect childhood scoliosis early enough to allow brace treatment rather than in its late stages when surgical correction and fusion would be needed (191, 192 and 193). Screening programs for any disease are indicated if effective early treatment methods exist, and if the disorder is frequent enough to justify the cost. Although screening programs for scoliosis are widespread in North America, the variable sensitivity and specificity of the screening exam and the questioned efficacy of brace treatment have caused some to suggest that school screening is not justified (158, 192, 194, 195 and 196). Despite these concerns, scoliosis screening is commonly performed on school children between the fifth and the sixth grades (age 10 to 12 years) (110). The Adams forward bend test is employed in combination with scoliometer (110) measurement of the maximum ATR (Fig. 17-8). A referral and a radiograph are recommended when the ATR is >7 degrees (25, 170). The 7-degree ATR standard detects nearly all curves >30 degrees, but leads to a large number of patient referrals (2 to 3 per 100 children screened) (110, 111) for radiographs in adolescents who have only spinal asymmetry (Cobb angle <10 degrees) or mild scoliosis (Cobb angle <25 degrees) not needing treatment. Overall, in school-screening programs, the incidence of curves of Cobb angle >10 degrees is approximately 3%, and of curves >25 degrees, about 0.3%.

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Jul 21, 2016 | Posted by in ORTHOPEDIC | Comments Off on Idiopathic Scoliosis

Full access? Get Clinical Tree

Get Clinical Tree app for offline access