Idiopathic Scoliosis

Updated: Jan 03, 2023
  • Author: Charles T Mehlman, DO, MPH; Chief Editor: Jeffrey A Goldstein, MD  more...
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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. [6, 7] 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. [8] 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. [9] 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. [10] This is discussed in greater detail later in this article.

That scoliosis remains incompletely understood despite a collective medical experience that approaches 4000 years is a sad commentary on the learning curve of medical practitioners. Nevertheless, the history of the recognition and treatment of scoliosis is rich with important lessons for the modern practitioner.

Ancient Hindu religious literature (circa 3500-1800 BCE) describes the treatment of spinal deformity rather clearly. The story is told of a woman who was "deformed in three places" and how Lord Krishna straightened her back. [11] This was accomplished by pressing down on her feet and pulling up on her chin. The orthopedic trappings of the story are unmistakable, including excellent immediate posttreatment results and no long-term follow-up.

Hippocrates (circa 400 BCE) stated that "there are many varieties of curvature of the spine even in persons who are in good health; for it takes place from natural conformation and from habit." He also stated that "lateral curvatures also occur, the proximate cause of which is the attitudes in which these patients lie." [12] The postural and muscular theory of scoliosis thus stated has persisted for thousands of years and remains firmly embraced by some.

Hippocrates' methods of scoliosis treatment focused primarily on spinal manipulation and traction. [13] He used an elaborate traction table called the scamnum. Medical practitioners used slight variations of the Hippocratic scamnum well into the 1500s. Another treatment approach that Hippocrates discussed involved attempting to diminish spinal deformity with a method called succussion. This involved strapping the patient (often upside down) to a ladder, which was then hoisted into the air and dropped from a height. Hippocrates thought that this method was occasionally useful but was largely performed by charlatans to impress the public. [14]

Ambroise Paré, the "most celebrated surgeon of the Renaissance," [15] is recognized as the first physician to treat scoliosis with a brace. He also recognized that once a patient with scoliosis had reached maturity, bracing was not useful. Paré's orthosis consisted of a metal corset (fashioned in a village smithy setting) with many holes in it to help diminish its significant weight. The record also makes it quite clear that Paré espoused the postural theory of scoliosis.

Nicholas Andry was a French pediatrician who hated the brutal barber surgeons of his day. [16] At the age of 83 (a year before his death) he wrote a short book entitled Orthopaedia. Thus, in 1741 this name combined the root words for "straight" (orthos) and "child" (pais) to create the name still used for the broad musculoskeletal field of orthopedics.

Andry believed that scoliosis was caused by asymmetric muscle tightness and, thus, helped foster the French belief in "convulsive muscular contraction" as the cause of spinal deformity. [14] Andry stated, "It is well worth while to remark that the crookedness of the spine does not always proceed from a fault of the spine itself, but is sometimes owing to muscles of the forepart of the body being too short, whereby the spine is rendered crooked, just in the same manner as a bow is made more crooked by tying its cord tighter." [17] Andry used rest, suspension, postural approaches, and padded corsets in his treatment of scoliosis.

Jacques Mathieu Delpech was a successful and skilled surgeon, yet he focused a great deal of his attention on nonsurgical approaches to orthopedic problems. The highlight of this focus was his orthopedic institute at Montpellier, in the south of France. This facility included elaborate gardens, a heated winter gymnasium, and an outdoor gymnasium for the treatment of various musculoskeletal problems.

For the treatment of scoliosis, Delpech devised graded exercises for strengthening muscles of the trunk in the belief that the deformity was due to a weak axial musculature. This belief was almost certainly due to the influence of Andry. Delpech also used stretching and traction techniques but did not believe in braces. His patients usually stayed for 1 or 2 years at the institute, and they would wear uniforms while performing their exercises. Similar elaborate efforts to treat scoliosis still exist in the physical therapy outpatient setting. [18] Delpech's life and that of his institute came to an abrupt end in 1832 when a disgruntled patient shot him to death as he was riding back to Montpellier in an open carriage. [12]

The 1800s saw the advent of surgical treatment of scoliosis by the French orthopedic surgeon Jules Guérin, who was enthusiastic about subcutaneous tenotomy and myotomy and first reported their use in his scoliosis patients in 1839. When he later published the results of treatment of 1349 patients with this technique, tremendous controversy was ignited. [12] Guérin's harshest critic was Joseph Malgaigne, who described Guérin's work as "some orthopedic illusion." [12] This led to one of the most famous orthopedic lawsuits in history: Guérin vs Malgaigne. This defamation trial was decided in Malgaigne's favor and helped to establish an important precedent for open criticism of scientific papers.

Another important tool in the treatment of scoliosis was the plaster body jacket (ie, body cast). The American orthopedic surgeon Lewis Sayre popularized its use in the mid-1800s. Sayre's technique involved a large tripod that allowed the patient to be suspended while the corrective plaster cast was applied. Sayre was said to be "a brusque, forceful and therefore controversial personality" but also "an eloquent speaker" who toured internationally demonstrating his casting techniques. [14] He also used a "jury mast" extension from some of his casts in order to provide constant head traction—a clear predecessor to halo traction.

The early 1900s saw what was arguably the most important advance in scoliosis treatment in more than 3000 years: posterior spinal fusion. Russell Hibbs first performed his "fusion operation" for tuberculous spinal deformity in 1911, but by 1914 he also was applying his technique to patients with scoliosis. [19] The Hibbs approach focused on achieving maximum deformity correction via a variety of plaster jackets before surgery. Hibbs's 1924 description of his own technique is eloquent:

The dissection is carried farther and farther forward upon each vertebra in turn, until the spinous processes, the posterior surfaces of the laminae, and the base of the transverse processes are bared...[and] with a bone gouge, a substantial piece of bone is elevated from the adjacent edges of each lamina, of half its thickness and of half its width. The free end of the piece from above is turned down to make contact with the lamina below, and the free end of the piece from the lamina below is turned up to make contact with the lamina above...Each spinous process is then partially divided with bone forceps and broken down, forcing the tip to come into contact with the bare bone of the vertebra below.

In the postoperative period, Hibbs typically allowed 2 weeks of bed rest for wound healing, followed by a final traction plaster jacket. The patient would continue to be confined to bed while wearing the corrective cast for another 6 weeks. Following this, the patient would wear a removable brace during the day for an additional 6-12 months. It was clear to Hibbs that with his technique, he could at least partially correct and, more important than this, prevent progression of the curves he was treating.

By 1941, such spinal fusion operations for idiopathic scoliosis were common enough that Shands (of the Alfred I duPont Institute) and his fellow researchers could assess more than 400 cases. [20] Hibbs-type fusion procedures were performed in all cases, but most surgeons (60%) used supplemental bone graft (often from the tibia). An approximately 25% final curve correction was achieved, and an overall 28% pseudarthrosis rate was noted. [20]

Some two decades later, Paul Harrington introduced the spinal instrumentation system that would further refine scoliosis surgery. [21] Although Harrington's original concept was instrumentation without fusion, persons such as John Moe convinced him of the value of spinal fusion in concert with Harrington rods. [22] Early instrumentation techniques relied on hooks and wires, but in 1959, H H Boucher published his technique for using pedicle screws in the lumbar spine. [23] Later, S I Suk described the use of pedicle screws in the thoracic spine and continued to publish on the improved results of this method over wires and hooks, to the point where it has now largely replaced the older methods. [24]

For patient education resources, see the Bone Health Center and Back, Ribs, Neck, and Head Center, as well as Scoliosis.



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. [25, 26] 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.



Much has been written regarding the potential influence of melatonin on the development of idiopathic scoliosis. [27, 28] 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. [29] 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. [30, 31] 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. [32] This line of research might be attractive to those who feel that a postural disturbance is the root cause of scoliosis.



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. [33] 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). [33] 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) has been offered as one potential etiologic explanation for idiopathic scoliosis. [34] 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. [35] 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. [36]

Aronsson et al conducted a series of experiments exploring this mechanical modulation of growth. Using two different animal models (rats and calves), thye showed that the force exerted by external ring fixators was capable of producing vertebral segment wedging akin to that seen in human idiopathic scoliosis. [37, 38] Correlation of this laboratory information with the clinical setting has drawn 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. [39] The asymmetric mechanical forces have also been associated with elevated synthetic activity in the convex side of scoliotic curves. [40]

Bylski-Austrow and Wall led a group of Cincinnati Children's Hospital researchers who further analyzed the mechanical modulation of spinal growth. Using a porcine model, they successfully induced growth changes by means of an endoscopically implanted spinal staple. [41]  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 the disease referred to as 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. [42] Studies of twins with scoliosis pointed in a similar direction. [43, 44]  More than 90% of monozygotic twins and more than 60% of dizygotic twins demonstrate concordance regarding their idiopathic scoliosis. [43] Some evidence has also directed attention to portions of chromosomes 6, 10, and 18 as possible scoliosis-related loci. [45]



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). [46] The prevalence of scoliosis was highest (1.2%) in patients aged 12-14 years. [46] 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. [47] Other studies using the 10° definition of scoliosis have placed the overall prevalence in the 1.9-3.0% range. [48]

Henderson et al suggested that scoliosis may develop more frequently in children born to mothers who are aged 27 years or older. [49] 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 only articles written on idiopathic scoliosis in males is that by Karol et al, from the Texas Scottish Rite Hospital. 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. [50]



Clinical outcomes following treatment of idiopathic scoliosis are strongly linked to curve magnitude. [51] Unrealistic presurgical expectations have been shown to correlate with a decreased likelihood of postoperative satisfaction. [52] 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. [53]

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. 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. [54, 55]

A subset of the cohort (700-1500 patients) was analyzed further with respect to low back pain. [56, 57] 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). [56] 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." [57]

Asher et al performed a retrospective study to determine implant/fusion survivorship without reoperation and the risk factors influencing such survival. 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. [58]

Luhman et al reviewed the prevalence of and indications for reoperations in patients undergoing spinal fusion for idiopathic scoliosis. 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. [59]

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. 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). [60]

After a 10-year follow-up, the data from another study noted that 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. 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. [61]

Regarding possible prognostication related to curve progression, Wei-Jun et al suggest that body weight in adolescent males may be an important parameter. 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. [62]

The use of 3D computer modeling combined with machine learning demonstrates promise for reasonably predicting curve progression. [63]   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.