Introduction
Idiopathic scoliosis is the most common type of spinal deformity confronting orthopedic surgeons.1 Its onset can be rather insidious, its progression relentless, and its end results deadly. Proper recognition and treatment of idiopathic scoliosis help to optimize patient outcomes. Once the disease is recognized, effective ways exist to treat it.2
Recent studies
Asher et al performed a retrospective study to determine implant/fusion survivorship without reoperation and the risk factors influencing such survival in 207 patients. 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 2 implant variables: transverse connector design and the lower instrumented vertebra anchors used.3
Luhman et al reviewed the prevalence of and indications for reoperations in 1057 spinal fusions for idiopathic scoliosis. Of the 1057 fusions, 41 (3.9%) required reoperation: 11 anterior, 25 posterior, and 5 circumferential. In addition, 47 other procedures were needed: 20 revision spinal fusions (for pseudarthroses, uninstrumented curve progression, or junctional kyphosis); 16 because of infections (5 acute, 11 chronic); 7 for implant removal because of pain and/or prominence (4 complete, 3 partial); 2 (4%) revisions for loosened implants; and 2 elective thoracoplasties.4
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. They evaluated the patients for vital capacity (VC) and peak flow (PF) before surgery and after surgery at 1, 3, 6, 12, and 24 months. They found that scoliosis approaches that penetrated the chest wall resulted 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.5
For excellent patient education resources, visit eMedicine's Bone Health Center and Back, Ribs, Neck, and Head Center. Also, see eMedicine's patient education article Scoliosis.
History of the Procedure
Scoliosis is an ancient disease that remains incompletely understood despite a collective medical experience that approaches 4000 years. This 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 BC) 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.6 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 BC) stated, "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."7 The postural and muscular theory of scoliosis thus stated has persisted for thousands of years and remains firmly embraced by some.
Hippocratic scoliosis treatment methods focused primarily on spinal manipulation and traction.8 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 it was largely performed by charlatans to impress the public.9
Ambroise Pare has been described as the "most celebrated surgeon of the Renaissance."10 Pare 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. Pare'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 Ambroise Pare espoused the postural theory of scoliosis.
Nicholas Andry was a French pediatrician who hated the brutal barber surgeons of his day.11 . 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 (paedia) to create the name still used for the broad musculoskeletal field, 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.9 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.12 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 they performed their exercises. Similar elaborate efforts to treat scoliosis still exist in the physical therapy outpatient setting.13 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.7
An important event of the 1800s was the advent of surgical treatment of scoliosis by the French orthopedic surgeon Jules Guerin. He was very enthusiastic about subcutaneous tenotomy and myotomy and first reported their use in his patients with scoliosis in 1839. When he later published the results of treatment of 1,349 patients with this technique, tremendous controversy was ignited.7 Guerin's harshest critic was Joseph Malgaigne, who described Guerin's work as "some orthopedic illusion."7 This led to one of the most famous orthopedic lawsuits in history: Guerin versus Malgaigne. This defamation trial ended 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.9 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 is 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.14 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, as follows:
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 bedrest 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.15 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.15 It would be another 20 years before Paul Harrington would introduce the spinal instrumentation system that would further refine scoliosis surgery.16 Although Harrington's original concept was instrumentation without fusion, persons such as John Moe would convince him of the value of spinal fusion in concert with Harrington rods.17
Further refinement in surgical technique and instrumentation has led to the greater than 50% correction and single-digit pseudarthrosis rates to which contemporary orthopedists have become accustomed.
Problem
Scoliosis represents a disturbance of an otherwise well-organized 25-member intercalated series of spinal segments. It is, at times, grossly oversimplified as mere lateral deviation of the spine, when in reality, it is a complex 3-dimensional deformity.18,19 In fact, some have used the term rotoscoliosis to help emphasize this very point. Two-dimensional 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.
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.20 Robert Winter teaches that idiopathic scoliosis is a hypokyphotic disease.21,22 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 this occurs relatively rarely.
J.I.P. James is credited with classifying idiopathic scoliosis according to the age of the patient at the time of diagnosis.23 Using his classification system, children diagnosed when they are younger than 3 years have infantile idiopathic scoliosis. Children diagnosed when they are aged 3-10 years have juvenile idiopathic scoliosis, and those 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 almost 70% of these patients went on to require surgery.24 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.25 This is discussed in greater detail later in this article.
Frequency
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 based on what particular definition of scoliosis is used and what patient population is being studied. Several important studies are included below.
Stirling and his coauthors 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 of 15,799 patients).26 The prevalence of scoliosis was highest (1.2%) in patients aged 12-14 years.26 Data such as these have helped reiterate the idea that the focus of screening efforts should be on children in this age group. When smaller Cobb angle measurements have been accepted (eg, 6° or greater), a significantly higher scoliotic rate may be identified, such as the 4.5% rate reported by Rogala et al.27 Other studies using the 10° definition of scoliosis have placed the overall prevalence in the 1.9-3.0% range.28
Scoliosis has been suggested to develop more frequently in children born to mothers who are aged 27 years or older.29 One might hypothesize 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. They also suggested that efforts to screen for boys with scoliosis should be performed a little later than similar screenings for girls.30
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 and his colleagues from Denver studied the level of platelet calmodulin in 27 patients with adolescent idiopathic scoliosis.31 Using indirect measurement methods, these researchers had conducted previous work indicating that increased levels of platelet calmodulin were associated with increasingly severe idiopathic scoliosis. Using a direct measurement technique, they showed that patients with a progressive curve (>10° progression) had statistically higher platelet calmodulin levels (3.83 ng/mcg vs 0.60 ng/mcg, P <.01).31 If these data are reproduced in larger studies, they hold the potential to allow clinicians to identify patients at higher risk of curve progression.
An elastic fiber system defect (abnormal fibrillin metabolism) has been offered as one potential etiologic explanation for idiopathic scoliosis.32 Such abnormal connective tissue has not been found universally in patients with idiopathic scoliosis. No clear cause-and-effect relationship 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.33 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.34
David Aronsson has conducted a series of experiments that have explored this mechanical modulation of growth. Using two different animal models (rats and calves), he showed that the force exerted by external ring fixators were quite capable of producing vertebral segment wedging akin to that seen in human idiopathic scoliosis.35,36 Correlation of his 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 a greater amount of thoracic wedging coming from the vertebral bodies.37 The asymmetric mechanical forces have also been associated with elevated synthetic activity in the convex side of scoliotic curves.38
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.39,40,41 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 rather strongly suggested by several avenues of research. An X-linked inheritance pattern (with variable penetrance and heterogeneity) has been suggested by several authors.42 Studies of twins with scoliosis have 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
Pathophysiology
Much has been written regarding the potential influence of melatonin on the development of idiopathic scoliosis.46,47 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 and his coauthors studied pinealectomized chickens to which they administered therapeutic doses of melatonin.48 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 might be present in patients who have idiopathic scoliosis.49,50 Such central nervous system dysfunction was hypothesized to be manifested as decreased vibratory sensation. McInnes and her fellow researchers later pointed out that the vibration device used in earlier studies (a Bio-Thesiometer) did not demonstrate sufficient reliability characteristics to allow valid conclusions.51 This line of research might be attractive to those who feel that a postural disturbance is the root cause of scoliosis.
Presentation
The vast majority of patients initially present due to perceived deformity. This may be patient or family perception of asymmetry about the shoulders, waist, or rib cage. A primary care physician or school-screening nurse may perceive similar findings. Adams forward-bending test (in conjunction with the use of a scoliometer) has been found to be an effective screening tool.
Highlights of the patient's history include information relative to other family members with spinal deformity, assessment of physiologic maturity (eg, menarche), and presence or absence of pain.
Traditionally, scoliosis has been described as a nonpainful condition, and aggressive workup has been recommended for patients in whom this rule is violated.52 Ramirez and his coworkers from the Texas Scottish Rite Hospital studied more than 2400 patients with scoliosis and found that a full 23% (560 of 2442 patients) had back pain at the time of presentation.53 An underlying pathologic condition was identified in 9% (48 of 560) of the patients with back pain, including mainly spondylolysis and spondylolisthesis but also intraspinal tumor in one instance. Thus, it would seem that pain is not associated with scoliosis as rarely as previously thought.
Physical examination should include a baseline assessment of posture and body contour. Shoulder unleveling and protruding scapulae are common. In the most common curve pattern (right thoracic), the right shoulder is consistently rotated forward and the medial border of the right scapula protrudes posteriorly. Assessment of lower (and often upper) extremity reflexes should be performed. Abdominal reflex patterns should also be assessed. The presence or absence of hamstring tightness should be investigated, and screening should be performed for ataxia and/or poor balance or proprioception (ie, Romberg test). One or two different methods of measuring leg length will prove valuable, as a significant percentage of patients presenting with scoliosis have several centimeters of limb-length discrepancy.
Indications
An extensive yet incomplete understanding of the natural history of idiopathic scoliosis remains a reality. Thus, more than a modicum of uncertainty remains associated with selection of recommended treatments for idiopathic scoliosis. The main treatment options for idiopathic scoliosis may be summarized as "the 3 O's": (1) observation, (2) orthosis, and (3) operative intervention. When to choose each of these treatments is a complicated matter.
The risk of curve progression varies based on the idiopathic scoliosis group in which a patient belongs (ie, infantile, juvenile, adolescent).
Infantile idiopathic scoliosis
Although defined by a seemingly arbitrary age limit (<3 y at the time of diagnosis), infantile idiopathic scoliosis demonstrates marked differences that distinguish it from the other 2 categories of idiopathic scoliosis. Infantile idiopathic scoliosis is the only type of idiopathic scoliosis whose most common curve pattern is left thoracic. Infantile idiopathic scoliosis is the only type of scoliosis that is more common in boys. It is more common in European patients or those of immediate European descent. In the past, infantile idiopathic scoliosis may have constituted up to 41% of all idiopathic scoliosis cases in parts of Europe, but the rate would appear to be closer to 4%. This is still dramatically higher than the estimated 0.5% rate in North America.54
Infantile idiopathic scoliosis is also the only type of idiopathic scoliosis with any significant reputation for spontaneous resolution. Reported spontaneous resolution rates range from 20-92%.23,55 Ceballos et al studied 113 Spanish patients with infantile idiopathic scoliosis. They found a 92% rate of associated plagiocephaly and an almost 25% rate of congenital hip dysplasia.56 These same researchers found that nearly 74% of their patients' curves were of the resolving variety (mainly left thoracic curves) and the other 26% were progressive curves (mainly double primary type curves).56
Prediction of curve progression in infantile idiopathic scoliosis has been tied to assessment of the rib vertebral angle difference (RVAD) originally described by Mehta in 1972.57 As described by Mehta, this measurement is carried out at the apical vertebra of the curve. In instances in which the curves resolved spontaneously, the RVAD was less than 20° in about 80% of cases, and in those instances in which the curves were progressive, the RVAD exceeded 20° in about 80% of cases.57 Other authors have confirmed the prognostic value of the RVAD, as well as its reliable application.56,58
Nonoperative treatment of progressive infantile idiopathic scoliosis predominates and may involve the use of conventional thoracolumbosacral orthosis (TLSO)–type braces, Milwaukee-type braces, and even intermittent Risser casting. Some have questioned the value of bracing in infantile idiopathic scoliosis and have stated, "a curve that resolves in a brace would probably have resolved without treatment."54
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 such surgical intervention as long as possible to optimize spinal growth, but relentless curve progression should not be accepted or tolerated while awaiting some arbitrary chronologic age. Although intuitively attractive, convex spinal epiphysiodesis (which has been shown to be quite effective in the management of congenital scoliosis) has not been shown to be as reliable in the setting of infantile idiopathic scoliosis.59 Addition of some type of posterior instrumentation may improve the results of epiphysiodesis.60
A treatment outline for infantile idiopathic scoliosis may be as follows:
- Curves less than 25° with an RVAD less than 20° are preferentially observed and monitored with spinal radiographs at regular intervals.
- Curves exceeding these parameters are typically braced, with some consideration given to the value of intermittent Risser casting.
- Surgery is considered for curves not adequately controlled with nonoperative measures.
Juvenile idiopathic scoliosis
Juvenile idiopathic scoliosis most closely mimics the epidemiology and demographics of the adolescent version of the disease. It is more common in females, and its most common curve pattern is a right thoracic curve.24 In fact, due to its demographic similarities, high rate of progression, and need for surgery, juvenile idiopathic scoliosis might be considered to be a malignant subtype of adolescent idiopathic scoliosis. Robinson and McMaster studied 109 patients with juvenile idiopathic scoliosis in Scotland and found that 95% (104 of 109 patients) demonstrated curve progression and 64% (70 of 109 patients) progressed to require a spinal fusion.24 This spinal fusion rate is similar to that reported by J.I.P. James 15 years earlier.61
A study from Washington University found a 50% rate of neural axis abnormalities in young children (<10 y) with idiopathic scoliosis.62 These findings included Chiari type I malformations and dural ectasia. At least one case report also exists in which a spinal intraosseous arteriovenous malformation was found in association with juvenile scoliosis.63
One potential treatment algorithm for juvenile idiopathic scoliosis is as follows:
- Observation for curves less than 25° with follow-up radiographs at regular intervals
- Bracing for curves that range from 25-40° and at least consideration of bracing (based on curve flexibility) for curves from 40-50°
- Bracing for smaller curves that demonstrate rapid progression to the 20-25° range
- Surgical intervention for inflexible curves that exceed 40° or virtually any curve that exceeds 50°.
Bracing and casting may be used outside the above-mentioned parameters in an effort to help control a large curve in a young child for whom the surgeon is attempting to optimize spinal growth. Similar recommendations exist regarding the value of MRI in juvenile idiopathic scoliosis due to a significant rate of neural axis abnormalities.62
Adolescent idiopathic scoliosis
Adolescent idiopathic scoliosis is the most common type of idiopathic scoliosis and the most common type of scoliosis overall. Progressive curvature may be predicted by a combination of physiologic and skeletal maturity factors and curve magnitude. Small curves in more mature patients have a substantially lower risk of progression (about 2%) than larger curves in more immature patients, in whom the risk is much higher (risk may approach or exceed 70%).
Treatment recommendations for adolescent idiopathic scoliosis are driven almost totally by curve magnitude (the only caveat being that brace treatment is thought to be effective only in patients who are still growing). It is thus somewhat ironic to note that stated recommendations urge observation for curves less than 30°, bracing of curves that reach the 30-40° range, and consideration of surgery for curves that exceed 40°. This amounts to a 10° window between observation and major spinal surgery. It is even more ironic to note that 10° is a commonly discussed margin of error for measuring such scoliotic curves. Additional patient factors may also influence some orthopedic surgeons to brace patients with curves measuring less than 30° or in excess of 40°. For instance, a rapidly progressive curve in a 12-year-old child that suddenly goes from 16-26° may easily prompt bracing.
When it comes to surgical considerations, patients with adolescent idiopathic scoliosis may be functionally subdivided into those patients in whom significant anterior spinal growth is a concern and those in whom it is not. This amounts to a quantification of risk of development of the complication known as crankshaft phenomenon.64 This can have a major impact on the surgical treatment plan in that a child at significant risk for crankshaft phenomenon will require an anterior spinal fusion procedure.
Much effort has been devoted to predicting which patients may suffer from this continued anterior spinal growth that results in progressive angulation and rotation of the spine.64,65,66,67,68 . In fact, a hierarchy of risk can be constructed in which progressively more precise estimates can be made. In this hierarchy, the presence of a radiographic Risser sign and reaching menarche are somewhat predictive but less so than closure of the triradiate cartilage, and reaching one's peak height velocity is perhaps the most powerful predictor of being at rather low risk for the crankshaft phenomenon.
Relevant 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. Scoliosis surgery is usually still performed via a posterior approach to the spine; thus, significant discussion of posterior anatomy is provided. A growing appreciation and need for anterior surgical procedures for scoliosis also demands additional discussion of retroperitoneal anatomy and intrathoracic anatomy, especially as it relates to video-assisted thoracoscopic surgery (VATS).
Developmental anatomy
Significant growth, development, and differentiation occur as a single-celled zygote progresses to become an approximately 100 trillion–celled adult human. Identifiable spine development has begun by the third week of gestation. First, the neural tube forms. Later, paired somites appear (at 4.5 weeks' gestation) and spinal nerves are present by the sixth gestational week. A discernible cartilage model of the spine is present by the seventh week of gestation. 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. Alain Dimeglio has shown that the majority of spinal canal diameter (about 90%) has been achieved by age 5 years.69 By age 10 years, approximately 80% of sitting height has also been achieved.70 During adolescence, radiographic evidence of ossification of the growth cartilage of the vertebral bodies occurs. Prior to this, these completely cartilaginous growth plates remained nestled between their respective vertebral bodies and intervertebral disks.
Posterior anatomy
The major superficial muscles of the back are not often directly visualized during posterior surgical approaches for scoliosis, but they must not be forgotten. These muscles include the trapezius, rhomboid major, rhomboid minor, and latissimus dorsi. Using an animal model, Kawaguchi et al showed that significant posterior muscle injury can be induced by the pressure exerted by surgical retractors.71 This certainly makes a case for intermittent removal and replacement of such retractors during the course of posterior spinal surgery.
The route for exposure of the posterior spinal elements passes through the cartilaginous apophyses of the spinous processes. These structures, often referred to as the cartilaginous caps, are systematically split in the midline to allow sequential subperiosteal dissection of the spinous processes, laminae, facet joints, and transverse processes. The laminae of the thoracic vertebrae spread out from the midline like wings and flow upwards (cranially) in the direction of the transverse processes. The facet joints of the thoracic spine are shingled in a coronal plane such that the inferior facet that contributes to each joint is located posteriorly and the superior facet is located anteriorly. The thickness of the interior and superior facets of the thoracic spine range from about 3-5 mm.72 The thoracic facet joints are located a mere 7-11 mm from the midline of the posterior spine.72
Progressing from the thoracic to the lumbar spine, important differences are noted. The V-shaped laminae of the thoracic spine give way to the butterfly-shaped laminae of the lumbar spine. This orientation change is important for the surgeon to remember when exposing these bony elements. The facet joints of the thoracic spine, which are oriented in more of a coronal plane, transition into the more sagittally oriented facet joints of the lumbar spine. The transverse processes of the thoracic spine, which seem to flow directly up and away from the laminae, change significantly in the lumbar spine such that they are no longer in close proximity to the laminae and are located anterior and inferior to the lumbar facet joints.
The ribs are also obviously absent in the lumbar vertebrae. What some consider a rib remnant does persist and is referred to as a mamillary body or mamillary process. It is most pronounced near the thoracolumbar junction but may be identified on nearly all of the lumbar segments. In the sagittal plane, one must also appreciate that the normal gentle kyphosis of the thoracic spine reaches its apex at about the T7 through T9 region. Below this, a rather definite transition to lumbar lordosis occurs, with an apex around the L3 level. Thoracic kyphosis typically ranges from 20-40° (Cobb measurements usually taken from the top of T3 to the bottom of T12). Some authors have stated that up to 50° of thoracic kyphosis should be considered normal.73 Normal lumbar lordosis is considered by some to range from 35-55° (Cobb measurements usually taken from the top of L1 to the top of L5).
Anterior anatomy
Anterior scoliosis surgery involves 3 main strategies, as follows:
- Anterior lumbar or thoracolumbar surgery through a retroperitoneal approach that may or may not involve a diaphragmatic incision
- Anterior thoracic surgery via traditional open thoracotomy
- Anterior thoracic surgery via VATS
Various factors relative to skeletal maturity, curve location, and curve flexibility help determine which (if any) of these anterior surgeries may be appropriate.
The most common reason to use the retroperitoneal approach is for an instrumented anterior thoracolumbar spinal fusion. The most common curve pattern in that particular type of scoliosis is an apex left curve pattern, and as such, the patient is usually positioned lying on the right side. This position is advantageous in that it provides the best access to the scoliotic spine and it also places the thick-walled aorta closer to the surgical field (as opposed to the thin-walled inferior vena cava). After superficial muscle dissection, the surgeon approach proceeds through the bed of the rib that corresponds with the highest vertebrae in which instrumentation is planned. This is often either the ninth or tenth rib, with the rib itself being harvested for later use as a bone graft.
Careful dissection is then performed to mobilize the peritoneum (with its contents) in an anterior direction; it is peeled off of the undersurface of the diaphragm. Posterior division of the diaphragm (leaving about a 2-cm cuff for repair) helps to avoid damage to the phrenic nerve. Diaphragmatic division begins with splitting of the costal cartilage and proceeds in a posterior direction with intermittently placed tagging sutures to aid in closure.
The remainder of the retroperitoneal approach to the thoracolumbar spine requires careful superior retraction of the lung, anterior retraction of the peritoneum (with associated aorta and ureter), and posterior retraction of the iliopsoas musculature. Careful identification and division of the segmental vessels (overlying the vertebral bodies) is carried out with either electrocautery or ligatures. Small sympathetic nerve branches in this same area are sacrificed during this stage of the exposure. This results in at least a transient period in which the left foot (for a left-sided approach) will be both pinker and warmer than the contralateral foot. At times, this may result in nursing personnel notifying the surgeon that the contralateral foot is pale and cold, but in reality, the foot ipsilateral to the exposure has changed.
Open thoracotomy might be performed either for anterior thoracic spine release followed by posterior fusion or for anterior thoracic spine fusion with instrumentation. The most common curve pattern to address with this approach would be a right thoracic curve, and as such, the patient would be positioned with the right side upward.
A similar rib selection and resection technique may be used if desired. From the interior of the chest, the intercostalis musculature (located between each of the ribs) can be seen. Identification of the azygous vein (anteriorly oriented along the vertebral bodies) is necessary. Further medial (ie, central) and running parallel to the azygous vein is the thoracic duct. Several portions of the sympathetic chain may be sacrificed as the segmental vessels overlying the thoracic vertebral bodies are divided and mobilized anteriorly and posteriorly. Blood flow changes similar to those noted in the retroperitoneal approach may be noted in the right foot (for a right thoracotomy).
In addition to this, thoracic surgical dissection carries with it the possibility of sacrificing branches to the greater splanchnic nerve, which would theoretically decrease visceral referred pain that one might feel from an inflamed gallbladder or similar condition.
Thoracoscopic appreciation of the anatomy of the thoracic spine is becoming more common as endoscopic anterior release and fusion is rapidly moving from being considered an innovation to standard practice. Just as arthroscopic knee surgeons enjoyed an expansion in visualized anatomy compared to that visible with knee arthrotomies, the endoscopic spine surgeon benefits from much greater intrathoracic latitude. Most VATS also involve the right thoracic cavity, and this discussion focusses on that particular side.
Proper rib counting and visualization of the superior intercostal vein (formed by the confluence of the second, third, and fourth intercostal veins) as it empties into the azygous vein are necessary steps to orient the surgeon. Beyond this, one also notes the mounds and valleys of the thoracic spine, with the mounds being the disks and the valleys being the vertebral bodies with the segmental vessels that overly them.74
The same anatomy outlined in the thoracotomy discussion still clearly applies, but further endoscopic fine points are needed. Specifically, the thoracic spine may be considered to be composed of 3 separate fields with important anatomic nuances.75 The upper field may be considered to be T2-T5, the middle field may be considered to be T6-T9, and the lower field may be considered to be T10-L1.75 The upper field is dominated by the superior intercostal vein, and it is characterized by the fact that the rib heads tend to completely span their respective disk spaces and articulate with 2 vertebral bodies. This results in a rib such as the third rib coming directly into the region of the T2-T3 disk space such that it will articulate with both the T2 and T3 vertebral bodies. In the middle field, the rib head once again comes directly in toward the disk space, but now, it rather firmly attaches itself only to the disk space proper.
In the lower field, the rib head articulates directly with its corresponding vertebral body. Thus, in the lower field, the 11th rib is traced to its corresponding vertebral body and then moves directly cephalad to reach the T10-11 disk or directly caudad to reach the T11-12 disk. Once the vertebral bodies have been exposed in a skeletally immature patient, the growth cartilage of the vertebral endplate can be visualized. It has an odd tendency to appear green in color (a quirk of endoscopic optics) and is colloquially referred to as a Wolf line in honor or Randall K. Wolf.
Contraindications
Few, if any, absolute contraindications exist regarding scoliosis care, just as few, if any, absolute indications for intervention exist. Accepted contraindications for bracing include skeletal maturity and excessive curve magnitude. Thoracic lordosis and certain curve patterns such as double thoracic curves also have been offered as at least relative contraindications to bracing.
The main contraindication to posterior scoliosis surgery would be medical instability and inability to survive surgery. Anterior scoliosis surgery would also be contraindicated in these patients, as well as in those with a precarious pulmonary status.
More on Idiopathic Scoliosis |
 Overview: Idiopathic Scoliosis |
| Workup: Idiopathic Scoliosis |
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Further Reading
Related eMedicine topics
Adolescent Idiopathic Scoliosis
Infantile Scoliosis
Juvenile Idiopathic Scoliosis
Neuromuscular Scoliosis
Scoliosis, Idiopathic (Radiology)
Clinical guidelines
Screening for idiopathic scoliosis in adolescents: recommendation statement. U.S. Preventive Services Task Force (USPSTF). Screening for idiopathic scoliosis in adolescents: recommendation statement. Rockville (MD): Agency for Healthcare Research and Quality (AHRQ); 2004 Jun. 4 p. [4 references]
Clinical trials
Surgical Outcomes Using Variable Rod Diameters in the Treatment of Idiopathic Scoliosis
Risk Factors for Psychiatric Disorders Associated With Adolescent Idiopathic Scoliosis
Keywords
adolescent idiopathic scoliosis, adolescent scoliosis, early onset idiopathic scoliosis, early onset scoliosis, idiopathic scoliosis, infantile idiopathic scoliosis, infantile scoliosis, juvenile idiopathic scoliosis, juvenile scoliosis, kyphoscoliosis, late onset scoliosis, late onset idiopathic scoliosis, lumbar scoliosis, neuromuscular scoliosis, rotoscoliosis, spinal deformity, thoracic scoliosis, thoracolumbar scoliosis
