Practice Essentials
Scoliosis (abnormal curvature of the spine) represents a disturbance of an otherwise well-organized 25-member intercalated series of spinal segments. It is sometimes grossly oversimplified as mere lateral deviation of the spine, when in reality it is a complex three-dimensional (3D) deformity. [1, 2] In fact, some have used the term rotoscoliosis to help emphasize this very point. Two-dimensional (2D) imaging systems (plain radiographs) remain somewhat limiting, and scoliosis is commonly defined as greater than 10° of lateral deviation of the spine from its central axis.
Idiopathic scoliosis is the most common type of spinal deformity confronting orthopedic surgeons. [3] Its onset can be rather insidious, its progression relentless, and its end results deadly. Proper recognition and treatment of idiopathic scoliosis help optimize patient outcomes. Once the disease is recognized, effective ways exist to treat it. [4]
In the past, terminology such as kyphoscoliosis was inappropriately used to describe certain patients with idiopathic scoliosis. Idiopathic scoliosis has a strong tendency to flatten the normal kyphosis of the thoracic spine. [5] Winter taught that idiopathic scoliosis is a hypokyphotic disease. In most cases, diagnoses of kyphoscoliosis were clinical misinterpretations of the rib hump associated with an otherwise hypokyphotic thoracic spine. Idiopathic scoliosis may present as a true kyphoscoliosis, but such a presentation is relatively rare.
James is credited with classifying idiopathic scoliosis according to the age of the patient at the time of diagnosis. In his classification system, children diagnosed when they are younger than 3 years have infantile idiopathic scoliosis, those diagnosed when they are aged 3-10 years have juvenile idiopathic scoliosis, and those diagnosed when they are older than 10 years have adolescent idiopathic scoliosis.
These age distinctions, though seemingly arbitrary, have prognostic significance. For instance, Robinson and McMaster reviewed 109 patients with juvenile idiopathic scoliosis and found that nearly 90% of curves progressed and that almost 70% of these patients went on to require surgery. [6] These rates are much higher than the rates associated with other categories of idiopathic scoliosis. The real challenge is to predict which curves will progress significantly and which ones will not. [7, 8] This is discussed in greater detail later in this article.
The vast majority of patients with idiopathic scoliosis initially present because of a perceived deformity. Highlights of the history include obtaining information relative to other family members with spinal deformity, performing an assessment of physiologic maturity (eg, menarche), and ascertaining the presence or absence of pain. Physical examination should include a baseline assessment of posture and body contour. A basic neurologic evaluation should be performed. A limb-length discrepancy, if present, is a valuable finding. (See Presentation.)
Laboratory workup for patients with scoliosis consists primarily of preoperative testing. Radiography is the primary diagnostic imaging modality. Adolescent idiopathic scoliosis is commonly categorized according to the Lenke classification system, which includes the following three main components: curve type (1, 2, 3, 4, 5, or 6), a lumbar spine modifier (A, B, or C), and a sagittal thoracic modifier (–, N, or +). Routine use of magnetic resonance imaging (MRI) to evaluate all patients with adolescent idiopathic scoliosis is not recommended, but MRI can be warranted in the setting of a rapidly progressing curve, associated kyphosis, or other atypical features. (See Workup.)
Nonoperative management consists of either simple observation or orthosis use; treatments such as electrical muscle stimulation, usual physical therapy, spinal manipulation, and nutritional therapies, have not been shown to be effective for managing the spinal deformity associated with idiopathic scoliosis. If surgical treatment becomes necessary, anterior release and fusion followed by posterior spinal fusion with instrumentation is considered to be the functional treatment. Every effort should be made to delay surgical intervention as long as possible, but relentless curve progression should not be accepted or tolerated while some arbitrary chronologic age is awaited. (See Treatment.)
Anatomy
The anatomy relevant to idiopathic scoliosis is that of the thoracic and lumbar spine. Key points regarding developmental anatomy of the spine are outlined below. The anatomy specifically relevant to anterior and posterior surgical approaches to the spine is discussed further elsewhere (see Treatment, Surgical Therapy).
Developmental anatomy
Significant growth, development, and differentiation occur as a single-cell zygote progresses to become an approximately 100 trillion–cell adult human. Identifiable spine development has begun by week 3 of gestation. First, the neural tube forms. Later, paired somites appear (at 4.5 weeks' gestation), and spinal nerves are present by gestational week 6. A discernible cartilage model of the spine is present by gestational week 7.
The bone and cartilage of the spine are mesodermal derivatives, as are significant portions of the cardiovascular and urogenital systems. This explains the frequent coexistence of congenital spine anomalies with congenital cardiac and kidney defects. Thus, gestational weeks 3-7 are very important in the development of all of these major body systems.
Postnatal spinal growth also must be understood and appreciated. Dimeglio showed that the majority of spinal-canal diameter (about 90%) has been achieved by age 5 years; by age 10 years, approximately 80% of sitting height has also been achieved. [9, 10] During adolescence, radiographic evidence of ossification of the growth cartilage of the vertebral bodies occurs. Before this, these completely cartilaginous growth plates remained nestled between their respective vertebral bodies and intervertebral disks.
Pathophysiology
Much has been written regarding the potential influence of melatonin on the development of idiopathic scoliosis. [11, 12] This has largely originated from studies in which the pineal gland was removed in chickens and scoliosis developed. These same studies suggested that the melatonin deficiency following pinealectomy might be the underlying reason for the development of scoliosis.
Bagnall et al studied pinealectomized chickens to which they administered therapeutic doses of melatonin. [13] They were unable to demonstrate any ability of the melatonin to prevent the development of scoliosis. It is fair to say that no final answer is yet available.
Some authors have suggested that a posterior-column lesion within the central nervous system (CNS) might be present in patients who have idiopathic scoliosis. [14, 15] Such CNS dysfunction was hypothesized to be manifested as decreased vibratory sensation.
McInnes et al later pointed out that the vibration device used in earlier studies (a Bio-Thesiometer) did not demonstrate sufficient reliability characteristics to allow valid conclusions. [16] This line of research might be attractive to those who feel that a postural disturbance is the root cause of scoliosis.
Etiology
The precise etiology of idiopathic scoliosis remains unknown, but several intriguing research avenues exist.
A primary muscle disorder has been postulated as a possible etiology of idiopathic scoliosis. The contractile proteins of platelets resemble those of skeletal muscle, and calmodulin is an important mediator of calcium-induced contractility. Kindsfater et al studied the level of platelet calmodulin in 27 patients with adolescent idiopathic scoliosis. [17] Using a direct measurement technique, they showed that patients with a progressive curve (>10° progression) had statistically higher platelet calmodulin levels (3.83 ng/μg vs 0.60 ng/μg). [17] If these data are reproduced in larger studies, they hold the potential to allow clinicians to identify patients at higher risk for curve progression.
An elastic fiber system defect (abnormal fibrillin metabolism) was offered as one potential etiologic explanation for idiopathic scoliosis. [18] Such abnormal connective tissue has not been found universally in patients with idiopathic scoliosis. No clear cause-and-effect relation has been established. Further research in this area is clearly warranted.
Disorganized skeletal growth, probably with its root cause at a gene locus or group of loci, has been discussed as a possible etiologic explanation for idiopathic scoliosis. This theory is simply that a rather localized primary growth dysplasia leads to a cascading Hueter-Volkmann effect on a much larger portion of the spine. [19] The Hueter-Volkmann principle states that compressive forces tend to stunt skeletal growth and that distractive forces tend to accelerate skeletal growth. A possible, yet unproven, association with such a growth disturbance is the osteopenia that has been identified in patients with idiopathic scoliosis. [20]
Aronsson et al conducted a series of experiments exploring this mechanical modulation of growth. [21, 22] Using two different animal models (rats and calves), they showed that the force exerted by external ring fixators was capable of producing vertebral segment wedging akin to that seen in human idiopathic scoliosis. Correlation of this laboratory information with the clinical setting drew attention to the fact that wedging occurs both from the vertebral bodies themselves and from the disk spaces, with more thoracic wedging coming from the vertebral bodies. [23] The asymmetric mechanical forces have also been associated with elevated synthetic activity in the convex side of scoliotic curves. [24]
Bylski-Austrow and Wall led a group of Cincinnati Children's Hospital researchers who further analyzed the mechanical modulation of spinal growth. [25] Using a porcine model, they successfully induced growth changes by means of an endoscopically implanted spinal staple. Within the context of 8 weeks' follow-up, they were able to create 35-40° of scoliotic curvature in growing pigs. Histologic analysis of vertebral specimens revealed increased paraphyseal density and disorganized chondrocyte development in the region of the staple blades.
Genetic roots of idiopathic scoliosis have been strongly suggested by several avenues of research. An X-linked inheritance pattern (with variable penetrance and heterogeneity) was suggested by several authors. [26] Studies of twins with scoliosis pointed in a similar direction. [27, 28] More than 90% of monozygotic twins and more than 60% of dizygotic twins demonstrate concordance regarding their idiopathic scoliosis. [27] Some evidence has also directed attention to portions of chromosomes 6, 10, and 18 as possible scoliosis-related loci. [29]
Epidemiology
Scoliosis is almost always discussed in terms of its prevalence (ie, the total number of existing cases within a defined population at risk). Rates may vary quite significantly according to what particular definition of scoliosis is used and what patient population is being studied. Several important studies are included below.
Stirling et al studied almost 16,000 patients aged 6-14 years in England and found the point prevalence of idiopathic scoliosis (Cobb angle >10°) to be 0.5% (76/15,799). [30] The prevalence of scoliosis was highest (1.2%) in patients aged 12-14 years. [30] Data such as these have helped reinforce the idea that the focus of screening efforts should be on children in this age group. When smaller Cobb angle measurements (eg, ≥6°) have been accepted, a significantly higher scoliotic rate may be identified, such as the 4.5% rate reported by Rogala et al. [31] Other studies using the 10° definition of scoliosis have placed the overall prevalence in the 1.9-3.0% range. [32]
Henderson et al suggested that scoliosis may develop more frequently in children born to mothers who are aged 27 years or older. [33] It could be hypothesized that gene fragility might be involved (eg, higher rate of infants with Down syndrome born to older mothers). The precise explanation as to why this might be the case has not been elucidated. In addition to this, no other authors have duplicated these results.
As mentioned previously, most patients with idiopathic scoliosis are female, and the vast majority of research has focused on females. One of the relatively few articles written on idiopathic scoliosis in males is that by Karol et al, from the Texas Scottish Rite Hospital. [34] These authors showed that boys with scoliosis are at risk for curve progression for a longer period than girls are. They also suggested that efforts to screen for boys with scoliosis should be performed a little later than similar screenings for girls.
Prognosis
Clinical outcomes following treatment of idiopathic scoliosis are strongly linked to curve magnitude. [35] Unrealistic presurgical expectations have been shown to correlate with a decreased likelihood of postoperative satisfaction. [36] More long-term follow-up studies of surgically treated patients with scoliosis are becoming available. This section outlines some of these data.
One study reported that conservative treatment may result in decreased self-concept in adolescent patients with mild-to-moderate scoliosis, particularly in patients with Cobb angles of 40-50°. Comparatively, the study reported that surgically treating these patients resulted in a significant increase in self-concept. [37]
A large cohort (nearly 2000 subjects) of patients with idiopathic scoliosis in Montreal, Canada, referred to as the St Justine Cohort Study, was monitored for 10-20 years. [38, 39] These patients were compared to a population-based control group drawn from the general Quebec population. Compared to the general population and regardless of whether their scoliosis was treated surgically or nonsurgically, patients with scoliosis were found to have a higher self-reported rate of arthritis and poorer perceptions of their overall health, body image, and ability to participate in vigorous activities.
A subset of the cohort (700-1500 patients) was analyzed further with respect to low back pain. [40, 41] The researchers found a higher overall rate of significant back pain reported within the last year (75% of patients with scoliosis vs 56% of control subjects). [40] Patients with scoliosis who were treated surgically also reported a high rate (73%) of back pain within the last year, but it did not correlate with the distal extent of the spinal fusion. The St Justine authors went on to state that their study "does not provide any evidence that extending the level of fusion down even as far as L4 will increase the prevalence of back pain in adulthood." [41]
Asher et al performed a retrospective study to determine implant/fusion survivorship without reoperation and the risk factors influencing such survival. [42] Of the 207 patients followed, 19 (9.2%) required reoperation, with 16 of those being for indications related to posterior spine instrumentation. Survival of the implant/fusion without reoperation for spine instrumentation-related indications was 96% at 5 years, 91.6% at 10 years, 87.1% at 15 years, and 73.7% at 16 years. The need for reoperation was significantly influenced by two implant variables: transverse connector design and the lower instrumented vertebra anchors used.
Luhman et al reviewed the prevalence of and indications for reoperations in patients undergoing spinal fusion for idiopathic scoliosis. [43] Of the 1057 fusions, 41 (3.9%) required reoperation: 11 anterior, 25 posterior, and five circumferential. In addition, 47 other procedures were needed: 20 revision spinal fusions (for pseudarthroses, uninstrumented curve progression, or junctional kyphosis); 16 because of infections (five acute, 11 chronic); seven for implant removal because of pain and/or prominence (four complete, three partial); two (4%) revisions for loosened implants; and two elective thoracoplasties.
Yaszay et al measured the effects of different surgical approaches for adolescent idiopathic scoliosis on pulmonary function over a 2-year period in 61 patients. [44] Patients were evaluated for vital capacity (VC) and peak flow (PF) before surgery and after surgery at 1, 3, 6, 12, and 24 months. Scoliosis approaches that penetrated the chest wall were found to result in a significant decline in postoperative pulmonary function. Return of pulmonary function did not occur until 3 months after posterior fusion with thoracoplasty; until 3 months after open anterior fusion; and until 1 year after video-assisted thoracoscopic surgery (VATS).
After a 10-year follow-up, according to the data from another study, patients who experienced intraoperative chest wall violation during their spinal fusion demonstrated a significant decrease in percent-predicted forced VC and forced expiratory volume in 1 second (FEV1) values. [45] However, those who underwent posterior-only procedures showed significant improvements in forced VC and FEV1 absolute values without any change in percent-predicted values; no changes were noted in percent-predicted values at 5 and 10 years in either group. These results suggest that procedures sparing the chest wall may result in better long-term pulmonary function.
Regarding possible prognostication related to curve progression, Wei-Jun et al suggest that body weight in adolescent males may be an important parameter. [46] Abnormal pubertal growth was noted in idiopathic scoliosis patients compared with healthy controls, with longitudinal growth being similar but body weight being significantly lower in the male adolescent scoliosis subjects.
The use of 3D computer modeling combined with machine learning demonstrates promise for reasonably predicting curve progression. [47] However, the 3D classification system and machine learning techniques are not yet widely available. Therefore, these techniques are still under study and are not standard practice at present.
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Mild juvenile scoliosis.
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Anteroposterior (AP) radiograph shows mild adolescent scoliosis.
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Lateral view of mild adolescent scoliosis.
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Moderate scoliosis.
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54-degree Lenke 1A curve.
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12-month-old male with 55-degree curve.
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EDF (Mehta cast) for infantile idiopathic scoliosis.
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Infantile idiopathic scoliosis after several months of EDF cast treatment.
