Idiopathic Scoliosis

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CHAPTER 23 Idiopathic Scoliosis

Fernando E. Silva, MD, Ronald A. Lehman, Jr., MD, Lawrence G. Lenke, MD

Idiopathic scoliosis is the most common cause of spinal deformity; 80% of all scoliosis cases are due to idiopathic scoliosis. Before arriving at the diagnosis of idiopathic scoliosis in a patient, other causes, such as congenital, neuromuscular (developmental or acquired), functional, inflammatory or infectious, pathologic, and intraspinal, have to be discounted. Ponseti and Friedman ¹ first described early-onset scoliosis in 1950. Dickson² expounded further on that concept and proposed that idiopathic scoliosis be divided into early (0 to 5 years old) and late onset (>5 years old), based on spinal growth velocity noted in these two age groups. Presently, idiopathic scoliosis is divided into three categories based on chronologic age: infantile (birth to 2 years + 11 months), juvenile (3 years to 9 years + 11 months), and adolescent (10 years to 17 years + 11 months).³ The radiographic diagnosis necessitates measuring the coronal plane angle, using the Cobb method, as equal to or greater than 10 degrees. Patients with curves less than 10 degrees are considered to have spinal asymmetry.^4,⁵

Epidemiology

Infantile and juvenile scoliosis are less prevalent than adolescent idiopathic scoliosis. Infantile idiopathic scoliosis is more common in Europe, constituting less than 1% of idiopathic scoliosis cases in the United States, and tends to comprise left-sided thoracic curves, typically occurring in boys. More recent reviews suggest that there might be a decline in its incidence.⁶ Juvenile cases are typically diagnosed at age 7 years in girls and 5 years in boys and account for about 10% to 20% of idiopathic scoliosis cases.³ In contrast to infantile idiopathic scoliosis, juvenile cases tend to occur predominantly in girls and tend to comprise right-sided curves. Between the ages of 3 and 6 years, there seems to be a similar distribution between boys and girls, however, again becoming predominant in girls after age 6 years.

Adolescent idiopathic scoliosis is more prevalent than other types of idiopathic scoliosis. Among adolescents, the prevalence of 10-degree curves is less than 3%, with about 5% of curves showing progression of greater than 30 degrees.⁴ This prevalence decreases as a function of curve magnitude, however, to about 0.3% to 0.5% and 0.1% in curves measuring 20 degrees and 40 degrees.⁷ The prevalence of curves greater than 10 degrees is higher among girls, with a 4 : 1 ratio of girls to boys.⁸

Etiology

Infantile scoliosis occurs roughly in 1 of 10,000 births. Possible causes are thought to occur from intrauterine molding or postnatal pressure on the spinal column from supine positioning while sleeping. Other etiologic factors that have been considered in idiopathic scoliosis include dysfunction in proprioception to maldevelopment in central pattern generators in the spinal cord ⁹^–¹¹ and connective tissue, hormonal, and muscle structural changes.¹² More recent reports in the literature strongly suggest a genetic link. The growth spurt noted among adolescents seems to play a role in progression, as a critical buckling load is reached on the existing curve as the spine grows. In a review of the literature, Kouwenhoven and Castelein¹³ concluded many factors may play a role in the initiation and progression of adolescent idiopathic scoliosis at a certain age. The literature suggests, however, that in the observed deformation of the spine, genetics and the unique mechanics of the fully erect posture, which is exclusive to humans, play an important role.

The genetics of idiopathic scoliosis seem to be similar in all idiopathic groups. The incidence rate is 11% among first-degree relatives, 2.4% among second-degree relatives, and 1.4% among third-degree relatives.¹⁴ Concordance among monozygotic and dizygotic twins has been reported to range from 73% to 92% and 36% to 63%.^15,¹⁶ In 2007, Anderson and colleagues¹⁷ published a population-based study taken from the Danish Twin Registry in which 46,418 twins were registered. From the 34,944 respondents, the concordance rate for monozygotic twins was 13% versus 0% for dizygotic twins. In 2007, Gao and colleagues¹⁸ published a report providing evidence of linkage and association with 8q12 loci. Through further investigation, they discovered the first gene (CHD7) associated with a susceptibility to idiopathic scoliosis. In 2008, Kulkarni and colleagues¹⁹ mapped a developmentally critical CHD gene to 15q26.1 and when taken together with CHD7, this suggested a possible role for CHD2 in the embryonic development of the spine. More recently in 2009, Gurnett and colleagues²⁰ published a report of a single multigenerational family in which adolescent idiopathic scoliosis and pectus excavatum segregated as an autosomal dominant condition. Through linkage analysis, the investigators identified a genetic locus for the two conditions on chromosome 18q. Although genetic mapping for idiopathic scoliosis is still in its infancy, great strides are being made to help clinicians better understand the etiology and prevalence of this condition.

Natural History

About 90% of infantile curves show spontaneous resolution, especially among infants who are younger than 1 year when idiopathic scoliosis is diagnosed.^6,²¹ The curves that typically progress are double curves with a thoracic component. Insight into the curves that can progress can be obtained from the rib-vertebral angle difference (RVAD) and “phase of the rib head.”²² In terms of phase of the rib head, if the head and neck of the convex rib of the vertebral body at the apex of the curve does not overlap the vertebral body, it is termed phase I; if it does overlap, it is termed phase II. In terms of the latter, curves with RVAD greater than 20 degrees or phase II angles are very likely to progress. Phase II angles are almost certain to progress; RVAD calculation is unnecessary when a curve is noted to be phase II type. Juvenile curves less than 25 degrees also can spontaneously resolve. These curves tend to progress, however, if they are discovered before age 6 years and idiopathic scoliosis is diagnosed or if they are greater than 30 degrees. About 70% of juvenile curve types tend to progress. The RVAD has not proved to be useful as a predictor of curve progression.

Many factors are considered in the natural history of adolescent idiopathic scoliosis. Growth potential, skeletal maturity, curve magnitude, and curve location are important considerations when assessing progression of adolescent idiopathic scoliosis. Although family history, gender, and rotation do not seem to have an effect on progression, growth potential seems to have a significant effect. Peak height growth seems to correlate best with, and is a better predictor of, progression than skeletal maturity. In terms of biomechanics, this likely is secondary to attaining vertebral column height, which leads to a critical buckling load and greater bending moments with eventual curve progression. In girls, peak height growth seems to occur 6 to 12 months before the onset of menarche. In boys, peak height growth seems to correlate with the closure of triradiate cartilages. Larger or double curves tend to progress more than single curves. Additionally, curves can progress after skeletal maturity; thoracic curves greater than 50 degrees and thoracolumbar/lumbar curves greater than 30 degrees can progress on average 1 degree per year.^23,²⁴

Evaluation

History and Physical Examination

A complete history and physical examination is completed, and any family history of scoliosis is noted. With infantile and juvenile cases in particular, a thorough prenatal and birth and developmental history is obtained. In adolescent cases, growth spurt history, if any at the time of presentation, is noted. This information is imperative in determining peak growth velocity and its implications on curve progression. Symptoms of pain or weakness and how the patient perceives his or her appearance relative to the deformity are especially important with adolescent idiopathic scoliosis.²⁵ Age at onset of menarche and voice changes in boys are noted as well because they are likely predictors of growth potential and possible curve progression.

During the examination, height, weight, and age (years plus months since last birthday) are recorded. The head is examined with special attention to torticollis and plagiocephaly because the latter has been associated with higher incidence in infantile scoliosis. Possible conditions and anomalies that might be present are buccal and palatal anomalies; café au lait spots; and midline dimples or hair patches or both over the lumbodorsal spine, which can be important clinical clues that an intraspinal pathologic process might be present. Limb laxity is also checked, and genetic counseling and testing is requested when laxity is present.

Trunk shift is evaluated with the patient standing and the hips and knees fully extended. The relationship of the patient’s head to the pelvis is also noted in evaluating the overall coronal and sagittal balance. Any shoulder, breast, or pelvic asymmetry is noted.²⁶ Curve rotation is assessed by performing an Adams forward-bend test and is quantified with a scoliometer. This assessment is modified in infants by laying the patient on the examiner’s knee. This test also helps assess the rigidity of the curve, which is an important factor in terms of prognostication. Leg-length discrepancy and pelvic obliquity are evaluated. Alternatively, a sitting forward test can be performed. The latter maneuver can also help rule out plagiocephaly and developmental hip dysplasia, especially in infants. When leg-length discrepancy is the likely cause of the deformity, a shoe lift is used to reevaluate the patient to determine if the curve corrects.

A thorough neurologic examination is performed. The neurologic examination includes all cranial nerves; motor strength; reflexes (including abdominal reflexes), often associated with Chiari malformations; sensory modalities; and gait.²⁷ Finally, other possible causes of scoliosis, such as congenital, neuromuscular, and syndromic types, must be ruled out. Infection, neoplasms, and spondylolisthesis also must be discounted.

Radiographic Evaluation

Posteroanterior and lateral 36- × 14-inch long cassette views including bending films—with appropriately placed bolsters—for further curve classification and planning bracing or surgical intervention are obtained, and the Cobb angles are measured.⁵ Curves greater than 20 degrees in infants and children, neurologic symptoms in all patients with idiopathic scoliosis, and left-sided, sharp angular or irregular curve patterns require further investigation, including screening total spine magnetic resonance imaging (MRI).^28,²⁹ When anomalies of the nervous system are present on MRI, a neurosurgical consultation is indicated.

Classification Systems

There is no formal curve classification system for infantile or juvenile scoliosis. The first treatment-based adolescent idiopathic scoliosis classification was developed in 1983 by King and colleagues.³⁰ They reported on a series of 405 patients with adolescent idiopathic scoliosis, developing a uniplanar system based on thoracic curves and analyzing only the coronal plane. This system allowed for surgical planning and helped in assessing whether or not a King II curve could be selectively fused.³¹ Interobserver and intraobserver reliability of this traditional thoracic classification system is fair at best, however.^32,³³ Additionally, coronal decompensation has been reported after selective fusions.

Lenke and colleagues ³⁴ developed a comprehensive, practical two-dimensional classification system in 2001, which included the sagittal plane as well (Fig. 23–1). The Lenke curve classification includes not only thoracic curves, but also thoracolumbar/lumbar curve patterns. Additionally, this classification allows the surgeon to assess curves in coronal and sagittal planes, and it has been proven reliable in terms of interobserver and intraobserver reliability.^32,³³ Its definition of the structural characteristics of a proximal thoracic curve has been deemed reliable, leading to shorter proximal fusions when this curve pattern is nonstructural.³⁵ The Lenke classification allows a stricter structural curve evaluation, permitting a more objective analysis of when a given curve would tolerate a selective fusion leading to a balanced outcome.^36,³⁷ The latter is clinically significant because one of the most important principles in preventing postoperative decompensation is proper identification of curve patterns, including curves that tolerate selective fusion.^31,³⁸ This three-tiered classification combines a curve type (1 through 6) and coronal lumbar and sagittal thoracic modifiers to produce a triad comprehensive curve classification (e.g., 1A−).

FIGURE 23–1 Lenke adolescent idiopathic scoliosis (AIS) classification system.

More recently, the addition of a lower end vertebra (LEV) modifier has been proposed for the Lenke classification. The LEV of the lowest structural curve was found to be a highly reliable vertebral landmark, and comparison of the LEV with a selected lowest instrumented vertebra (LIV) is an important consideration in the overall evaluation of the surgical treatment of adolescent idiopathic scoliosis.³⁹ A more detailed postoperative assessment of the distal fusion length is theoretically allowed by comparing the LIV with the LEV. Such a modifier aids in a more thorough evaluation of the Lenke curve classification (e.g., 5CN-L3 when L3 is the LEV of the curve being classified).

Three-Dimensional Classification

Although the Lenke classification system has criteria in the coronal and the sagittal planes that have an impact classification, it still has shortcomings because scoliosis is a known three-dimensional deformity, and the axial or transverse plane is not a component of this system. A task force of the Scoliosis Research Society has been charged with developing a clinically useful three-dimensional analysis and ultimate classification of scoliosis.⁴⁰ The key factor in this assessment would be the plane and maximal curvature, which is the three-dimensional deformity that occurs as the spine translates and rotates out of the normal sagittal profile in scoliosis deformities. It is expected that in the next decade much more information will be provided so that three-dimensional analysis and classification will become a standard for all practitioners.

Nonoperative Treatment Options and Indications

Three fundamental treatment options exist for idiopathic scoliosis: observation, bracing and casting, and surgery. These treatment modalities are based on the natural history of idiopathic scoliosis or the potential or probability of curve progression.^4,⁴¹ Many modalities have been proposed to slow or halt curve progression, such as electrical stimulation and physical therapy; however, none of these modalities have been scientifically proven to be a viable alternative in the treatment of scoliosis.^42,⁴³

Observation

Most infantile curves are left-sided; these curves have been known to resolve spontaneously up to 90% of the time, but they can progress.⁴¹ Deciphering which curves will progress can be guided by the RVAD and the relationship of the apical rib head to the vertebral body (i.e., phase I or II).²² Typically, curves less than 20 degrees are expectantly followed every 6 to 8 months. Infants with curves less than 25 degrees and RVAD less than 20 degrees and children with curves less than 25 degrees should be followed clinically and radiographically every 6 months. Treatment is instituted for curves greater than 25 degrees. Treatment is also started for a progression of 5 degrees or greater in two consecutive visits or 10 degrees or greater in one follow-up visit. Juvenile curves more often require operative intervention, however.

Bracing and Casting

Bracing ⁴⁴ is the nonoperative treatment of choice in small but progressive scoliosis in growing children and teens. In about 75% of cases, bracing can control the curve and avoid progression, rendering the curve small enough so that the risk of progression after growth is unlikely.⁴² In a younger child, whose growth potential remains a significant issue, bracing allows for continued growth until the patient requires eventual operative treatment because of curve progression. With infantile cases, molded casting followed by bracing used to be the mainstay in nonoperative management. Bracing and casting of these patients comes with potential consequences, however, that include pulmonary restriction, which can have future ramifications.^45,⁴⁶ Sanders and colleagues⁴⁷ found serial casting to be beneficial in the treatment of infantile scoliosis. They reported that curves less than 60 degrees often fully corrected in infants if casting was started before age 20 months.

Adolescents with curves less than 20 degrees at presentation are observed and followed at 4-month and 6-month intervals. For curves between 20 degrees and 30 degrees, bracing is started if a curve progresses 5 degrees or more in two consecutive visits or 10 degrees or more in one visit.

Bracing is usually started the first office visit when the patient is skeletally immature (Risser ≤2) and presents with a 25- to 40-degree curve. Several brace options exist, and deciding which brace to use depends on the apex of the curve and physician preference. Curves with an apex above T6 would likely require the use of a Milwaukee (cervicothoracolumbosacral orthosis) brace.⁴⁸ Conversely, curves with apices at T7 or below and above L2 do well in a Boston underarm thoracolumbosacral orthosis brace, and these braces are more socially acceptable because of the lack of a cervical extension. The Charleston bending brace is an option if the child is noncompliant to brace-wear. This brace is typically worn at night, and some studies have shown its efficacy.^49,⁵⁰ The efficacy of a brace seems to depend on the length of time the brace is worn.⁵¹ When bracing is initiated and pad placement is deemed appropriate, patient follow-up occurs every 4 to 6 months, with in-brace radiographic evaluation and appropriate fitting adjustments made when necessary.

Modifications to the standard thoracolumbosacral orthosis include variations of the Chêneau brace (Jacques Chêneau, Münster, Germany) and the SpineCor dynamic brace (SpineCorporation, Chesterfield, UK). The Chêneau 2000 orthosis allows for a greater amount of initial correction by using a hypercorrected mold and pads, which provide derotational forces.⁵² This brace is the first that uses the theory of expansion to allow for active correction by respiratory movements.⁵³ The SpineCor⁵⁴ and TrIAC (Boston Brace International, Avon, MA) are nonrigid braces. They work by using straps, which correspond to a specific correcting movement depending on the curve pattern, producing a progressive positional change, dynamic curve correction, and appropriate muscle balance.

Operative Intervention

Operative intervention is usually recommended for patients whose curves progress despite nonoperative management.⁵⁴ In infants, operative intervention is controversial; it is occasionally performed in infants with curves greater than 45 degrees or thoracolumbar/lumbar curves greater than 40 degrees. Children are typically more prone to curve progression and are more likely to require operative intervention. Other patients who are likely to benefit from operative intervention are skeletally immature patients with adolescent idiopathic scoliosis with a greater than 40- to 45-degree curve and mature patients with curves greater than 50 degrees.^23,⁵⁵

Surgical Techniques

Currently, anterior-only, posterior-only, and circumferential procedures are the mainstay of surgical treatment options.⁵⁷ The prevalence of anterior-only and circumferential procedures has declined with a concomitant increase in posterior-only procedures. Surgeons have become aware more recently that early intervention with a definitive anteroposterior fusion for progressive infantile and juvenile curves leads to loss of trunk height development, which can lead to chest wall and lung underdevelopment.^58,⁵⁹ This problem has promoted innovative techniques to try to control progressive curves surgically without definitive fusion, which include epiphysiodesis,^60,⁶¹ growing rod placement (Figs. 23-2 and 23-3),⁶² intervertebral stapling (Fig. 23–4),⁸⁶ spinal tethering (Fig. 23–5),⁶⁶ and the vertical expandable prosthetic titanium rib⁶⁷; the last-mentioned is used more in progressive early-onset scoliosis in which rib and chest wall deformities can be quite severe.⁶⁴

FIGURE 23–2 A and B, A girl age 2 years + 1 month who presented with 77-degree left thoracic infantile idiopathic scoliosis. C and D, She was treated with a posterior single hook growing rod with only partial correction of her deformity and increasing sagittal kyphosis. E and F, Ultimately, she underwent posterior spinal fusion ending up with overall acceptable coronal and sagittal balance 5 years after fusion.

FIGURE 23–3 A and B, A girl age 2 years + 9 months who presented with severe infantile-onset idiopathic scoliosis. Her left thoracic curve measured 122 degrees. C and D, She was placed in halo-gravity traction, and underwent a short apical anterior release and fusion and was prepared for a growing rod construct. E and F, She had a dual rod, pedicle screw growing rod construct placed, and at 5 years + 6 months after initiation of growing rod construct, she continues to be lengthened with overall good coronal and sagittal balance and acceptable lung fields produced via this treatment. G and H, Clinical photographs of preoperative and latest lengthening show maintenance of trunk alignment and growth.

FIGURE 23–4 A and B, A boy age 7 years + 9 months who presented with progressive juvenile-onset right thoracic idiopathic scoliosis. His main thoracic curve measured 60 degrees and was progressive despite bracing. C and D, He had anterior thoracic stapling performed with slow progression of deformity with growth. E and F, A posterior dual screw-rod growing construct was placed, and 5 years after insertion, his deformity correction has been maintained to 18 degrees of the main thoracic curve with good sagittal profile. G-I, Clinical photographs before surgery, status post stapling, and 5 years status post growing rod construct show improvement of truncal deformation.

FIGURE 23–5 A and B, A girl age 8 years + 8 months who presented with progressive left thoracic scoliosis. She had a positive family history of scoliosis with her mother requiring scoliosis fusion as a child. Her left thoracic curve progressed to 25 degrees with normal sagittal profile. C and D, She was treated with a single left thoracic mobile tether, with slow progressive correction of her deformity to 6 degrees with a normal sagittal profile 4 years after treatment. She had only one surgery and did not wear a brace postoperatively.

Many surgeons today still prefer to perform an anterior approach in younger patients when there is risk of crankshaft development and especially for thoracolumbar and lumbar major curves (Lenke type 5). With the introduction of pedicle screws, a posterior approach has shown numerous benefits over an anterior procedure, such as better maintenance of the obtained correction, providing more powerful corrective forces, three-column control, and obviating the need for anterior releases and thoracoplasties.⁶⁸^–⁷⁴ In addition, a posterior approach avoids the negative consequences of chest cage disruption and pulmonary compromise that can result from an open anterior approach (Fig. 23–6).⁷⁵^–⁷⁷ In addition, the thoracic aorta is at risk if an anteriorly placed screw penetrates the vertebral cortex on the opposite side.^78,⁷⁹

FIGURE 23–6 A-D, A girl age 12 years + 8 months with severe right thoracic adolescent idiopathic scoliosis deformity. Her curve progressed to 110 degrees bending to 66 degrees with overall 44 degrees of thoracic kyphosis—a 4A+ classification. E and F, She underwent open anterior release and primary posterior hook construct from T2-L3. At 6 years postoperatively, adequate coronal and sagittal alignment and balance is shown. G and H, Preoperative and postoperative clinical photographs show improved truncal correction with right thoracotomy, posterior midline and iliac crest scars visible.

According to Tis and colleagues,⁸⁰ with advances in anterior instrumentation, surgeons theoretically should see a reduction in the rate of rod breakage, pseudarthrosis, and sagittal decompensation and improved correction rates. These authors concluded that open anterior spinal fusion surgery is a safe method for the treatment of thoracic adolescent idiopathic scoliosis. At 5-year follow-up, they reported good coronal and sagittal correction of the main thoracic and compensatory thoracolumbar/lumbar curves, but they also reported that pulmonary function was mildly decreased as with any procedure in which a thoracotomy is performed. Tis and colleagues⁸⁰ also concluded that in skeletally immature patients, an open anterior spinal fusion can increase kyphosis; however, newer techniques used in their series seemed to limit progressive kyphosis, which has been noted in previously published reports.

Adolescent curves can typically be surgically treated via an anterior or posterior approach (or both) with instrumentation and fusion.⁷⁷ Anterior fusion levels typically extend from end-to-end vertebrae, as measured with the Cobb technique. Short fusions above and below the apex, depending on whether the apex is a disc or a vertebra, have been advocated for flexible thoracolumbar curves.⁸¹ In this technique, if the apex is a vertebral body, the discs above and below the apex are included in the fusion. If the apex is a disc, the two discs above and below the apex are included in the fusion. Brodner⁸² predicted fusion levels based on the supine-pull (“stretch”) films, ensuring a thorough release is performed to obtain a “bone-on-bone” fusion. Anterior structural grafts have been used to counter the kyphogenesis associated with anterior instrumentation.⁷⁷

Thoracoscopic procedures have been shown to provide advantages over open anterior thoracotomy procedures.⁸¹ Kishan and colleagues⁸⁵ showed that anterior thoracoscopy had fewer adverse affects on pulmonary function. Sucato and colleagues⁸⁶ found that adding a thoracoscopic release performed in the prone position to a posterior instrumentation and fusion offered the advantages of minimally invasive surgery and did not require repositioning to perform the posterior procedure. In addition, when double-lung ventilation is used, acute pulmonary complications are significantly reduced. A steep learning curve is required, however, and these techniques have diminished in popularity owing to the proliferation of pedicle screw constructs.

Determining proximal and distal fusion levels is paramount in preventing decompensation because choosing the incorrect levels is the main reason for postoperative decompensation.^26,⁸⁷ Adding-on is another phenomenon that can result if a fusion is stopped “short.” Suk and colleagues⁸⁸ reported 5-year results of 203 patients in which they found that adding-on occurred in 17 patients who were fused on average two levels short of the neutral vertebra.

Distal fusion levels are based on the understanding and determination of the end, neutral, and stable vertebrae of the distal structural curve that is to be included in the fusion.⁸⁹ Current correction techniques employing pedicular fixation and derotation maneuvers allow for preservation of distal fusion levels, however. When fusing to a vertebra cephalad to the stable vertebra, the intended LIV must touch the central sacral vertical line (CSVL), not have a significant rotation (Nash-Moe grade ≤1.5), and the disc below this proximal vertebra must be parallel or closed on the convexity. In placing thoracic screws, it is essential to follow sequential steps at every screw placement.^68,⁶⁹ With small pedicles, time should be taken to expand the pedicle to accommodate a screw.⁹⁰ Although the authors advocate the use of pedicle screws whenever possible, when employing hook and rod segmental instrumentation, it is imperative to reverse hook orientation where the discs are reversed in orientation to maintain coronal and sagittal balance.⁹¹ Based on the lumbar modifier, attention must also be paid to the degree of tilt left on the LIV when carrying out selective fusions.

A rough estimate of the degree of tilt to be left on the LIV is equal to the remaining tilt on a preoperative supine film, with judicious use of intraoperative radiographs. This tilt can be assessed on intraoperative full-length radiographs ⁹²; this is imperative in allowing accommodation of the structural component of the lumbar curves, especially with selective fusions.³⁷ The lower endplate of the LIV should be horizontal for type A lumbar modifier curves, a mild tilt should be left on type B curves, and an appropriate degree of tilt should be left on the LIV for type C curves. Clinical assessment of the deformity cannot be overemphasized because it plays as important a role as the radiographic findings when deciding whether to perform a selective fusion.

Selective Fusions

A selective fusion is performed when one or more curves present are not included in the fusion. Strictly speaking, the term selective fusion is reserved for untreated minor thoracic or lumbar curves that cross the midline. Situations arise when one considers fusing nonstructural, secondary curves for the sake of cosmesis or spinal balance or both.

The Lenke classification system allows a more objective way to decide when to perform selective fusions in patients with adolescent idiopathic scoliosis, especially with type C curve patterns.^37,⁸⁸ The Lenke system has stricter criteria that define the structural characteristics of individual curves, leading to an objective analysis when choosing which curves can be selectively fused without ensuing clinical imbalance.³³ Radiographic parameters aid in objective analysis of the structural nature of each curve relative to the other, such that if parameters match, both curves usually require surgical attention.^54,⁹³ Relative Cobb angle measurements and apical vertebral rotation and apical vertebral translation ratios of the thoracic and thoracolumbar/lumbar curves are important in such analysis and decision processes.^38,³⁹

Skeletal immaturity and clinical appearance are additional important factors.^31,^33,⁸⁷ The magnitude of the rib and lumbar prominences is important during the clinical analysis and decision making for selective fusion (e.g., is the patient willing to accept a moderate lumbar hump when contemplating a selective thoracic fusion and vice versa). One cannot overlook the thoracolumbar sagittal profile because this can lead to curve misclassification and incorrect operative management. As previously noted, based on the lumbar modifier, attention must be paid to the degree of tilt left on the LIV when carrying out selective thoracic fusions, allowing accommodation of the structural lumbar curve (Fig. 23–7).

FIGURE 23–7 A-D, A girl age 15 years + 9 months with progressive right thoracic decompensatory left lumbar scoliosis. Her main thoracic curve progressed to 53 degrees, and her nonstructural lumbar curve of 40 degrees side bended to 16 degrees. She had a normal sagittal profile—a 1CN classification. E and F, She underwent posterior selective thoracic fusion with a hook-rod, Wisconsin wire construct. At 6 years postoperatively, she has near-perfect spinal balance with matched 33-degree thoracic, 32-degree lumbar coronal plane deformities and normal sagittal profile. G and H, Preoperative and postoperative clinical photographs show improved coronal truncal alignment and balance.

Selective anterior fusions of major thoracolumbar/lumbar curves associated with minor and partially structural thoracic curves in Lenke 5C and 6C curves can occasionally be considered, provided that the thoracic curve is less than 50 degrees, the thoracic curve bends out to 20 degrees or less, the thoracolumbar/lumbar-to-thoracic Cobb ratio is 1.25 or greater, and the triradiate cartilages are closed.³⁶ Additionally, such selective fusions should not be undertaken when shoulder depression ipsilateral to the thoracolumbar/lumbar curve exists, the patient is highly skeletally immature, or a clinically unacceptable rib hump is present. To prevent decompensation, if the lumbar curve bends out less than the thoracic curve, the lumbar curve should not be overcorrected because the thoracic curve likely would not compensate to achieve postoperative balance.⁸⁷ One study showed an average spontaneous correction of 14 degrees or 36% improvement of the thoracic curve when selective thoracic fusion was performed.³⁷

Adjuncts to Correction

Direct Vertebral Rotation

In the past, curves greater than 75 degrees, curves with less than 50 degrees of correction, and curves needing a thoracoplasty have required anterior releases. With the use of modern techniques of multisegmental pedicle screw fixation and the addition of DVR techniques, safe and effective procedures demonstrating greater coronal and sagittal realignment along with acceptable cosmesis without the need for an anterior procedure have been reported.⁹⁴^–⁹⁶ In the thoracic region, the DVR helps derotate the spine and significantly decreases the rib prominence (Fig. 23–8). Care must be taken to use stiffer rods, prebent in the sagittal profile to prevent inducing hypokyphosis in the thoracic spine. It also helps to obtain better three-dimensional correction in the thoracolumbar/lumbar component of Lenke double major curves and to minimize the LIV tilt/horizontal angle.⁹⁴

FIGURE 23–8 A-D, A girl age 12 years + 6 months with a severe progressive right thoracic scoliosis. Her curve progressed to 159 degrees bending to only 135 degrees. E-G, She underwent posterior single-level vertebrectomy and pedicle screw construct with marked correction of her coronal plane deformity at 5 years postoperatively. H and I, Preoperative and postoperative clinical photographs show her posterior midline scar.

A DVR is performed if screw placement is adequate, if the thoracic spine is not overly lordotic or kyphotic, and when there is a clinically significant thoracic or lumbar prominence. The DVR technique necessitates accurate placement of pedicle screws at the apex of the deformity and the two levels at the proximal and distal extent of the fusion. When the thoracic spine has a (+) sagittal modifier, according to the Lenke classification, a DVR maneuver is not performed because such degrees of kyphosis place considerable strain on the proximal screws. In these patients, the coronal and sagittal deformity is addressed simultaneously by “convex rod” instrumentation first.

Osteotomies

Several osteotomy choices are available to correct sagittal, coronal, and multiplanar deformities associated with previously fused or more severe idiopathic scoliosis curves, including Ponté osteotomy (or Smith-Petersen osteotomy), pedicle subtraction osteotomy, and vertebral column resection. A Smith-Petersen osteotomy is classically described when performing an osteotomy through a fusion mass, whereas the authors describe here an osteotomy of this type in an unfused spine as a Ponté osteotomy, which was the original description of a posteriorly based chevron osteotomy through previously unfused anatomy.

Sagittal imbalance can generally be divided into two types.⁹⁷ In type I, the patient is in global positive balance owing to compensating for loss of segmental lordosis or kyphosis. In type II, loss of segmental lordosis or kyphosis is not compensated, leading to global imbalance. When scoliosis is associated with type I, multiple Ponté osteotomies can be performed at the site of maximal loss of segmental kyphosis. Mobility of the anterior column is required. In revision cases, these can be done asymmetrically with the widest portion of the osteotomy at the convexity or at the site of a previous fusion mass. The surgeon must pay attention when performing these osteotomies because the patient can be pitched into the concavity, possibly creating global coronal imbalance.⁹⁸ Type II sagittal imbalance is best managed by the use of pedicle subtraction osteotomy because longer lever arms and greater degrees of correction are often warranted, especially with sharp angular deformities. Anterior column mobility is not required, however, because one pivots the correction anterior to the osteotomy site.

Similar to sagittal imbalance, coronal imbalance can be classified as type A or B. In type A, the shoulders and pelvis are tilted in the opposite direction, whereas in type B, they tilt in the same direction.⁹⁷ Typically, single-plane deformities—type A—can be addressed with a single pedicle subtraction osteotomy; additionally, multiple or asymmetrical pedicle subtraction osteotomies can be used when dealing with stiff or kyphoscoliotic cases. Simple trigonometric calculations at the vertebral body where the osteotomy is going to be performed permit precise determination of the angle of bony resection required for global balance.⁹⁹ Type B deformities likely require vertebral column resections.

Vertebral column resections can be performed via a combined anterior and posterior approach (i.e., circumferentially) or from a posterior-only approach (Fig. 23–9).¹⁰⁰ Compromised pulmonary function lends consideration, however, to performing a posterior-only approach. The surgeon must balance the potential pulmonary compromise of the patient with the understanding that the extracavitary approach (i.e., posterior-only) requires a higher level of surgical understanding and is technically more demanding.^101,¹⁰² As with all things, adherence to safety is the most important principle, and if the surgeon is uncomfortable with a particular approach or technique, a referral should be made. This correction modality is appropriate in the setting of congenital cases, multiplanar or kyphoscoliotic stiff curves, curves previously fused circumferentially, and cases of global imbalance. In the last-mentioned situation, attention must be paid to the shoulders and pelvic tilt direction.

FIGURE 23–9 A-D, A girl age 11 years + 9 months with progressive right thoracic compensatory left lumbar scoliosis. Her main thoracic curve progressed to 70 degrees, and her compensatory 46-degree curve side bended to 16 degrees—a 1CN classification. E and F, She underwent selective thoracic fusion with a pedicle screw construct with nicely matched 14-degree thoracic and 13-degree lumbar scoliotic curves at 1 year postoperatively with adequate sagittal balance. G-J, Preoperative and postoperative clinical photographs show improved truncal correction.

Minimally Invasive Techniques

Minimally invasive spine surgery is a popular concept that uses imaging, retraction, and implant technologies to help surgeons locate the exact area on which they are to operate. This type of procedure is done through incisions of less than 1 inch long; damage to surrounding muscles and other tissues is avoided, which rapidly increases the healing and reduces recovery time. It also uses technology to perform the surgery more efficiently. One example is a video-assisted thoracoscopic procedure. According to Newton and colleagues,⁸¹ this procedure can be used for an anterior thoracic release or to achieve deformity correction via rod-screw constructs. Because of the small incisions made and the muscle-splitting technique used, a reduction in chest wall disruption and subsequent lung volume decrease, as is the case with an open thoracotomy approach, was noted. This procedure offers comparable curve correction and a faster return to presurgical function.⁸⁴^–⁸⁶

With advances in instrumentation as mentioned previously and the enhanced ability to perform a direct vertebral derotation with posterior pedicle screw constructs, the use of video-assisted thoracoscopic instrumentation procedures has declined substantially. The decision between an anterior and a posterior approach is based purely on surgeon preference at this point.

Postoperative Care

Patients are observed in the intensive care unit overnight. Sitting and standing with assistance is permitted, and physical therapy is started on the 1st postoperative day for patients undergoing a posterior-only procedure. When stable, patients are transferred to the regular floor. As bowel function returns and patients are able to tolerate clear fluids, routine intravenous narcotics are replaced with oral narcotics as needed. Typically, no postoperative bracing is used. When patients are ambulatory, the urinary catheter is removed. On postoperative day 3, the drains are discontinued along with prophylactic antibiotics. After discharge, usually postoperative day 4 or 5, patients resume showering at approximately 2 weeks postoperatively.

Complications

Complications can occur during any of the treatment stages—preoperative, intraoperative, or postoperative.¹⁰³ During the preoperative period, inappropriate curve classification and inadequate surgical planning can lead to inappropriate surgical decisions. It is essential to ensure that when performing a selective fusion, appropriate structural curve criteria are met.⁸⁷ Choosing inappropriate fusion levels can also be included in the category of preoperative complications, which is discussed later.

Intraoperative complications most commonly result from technical errors, including instrumentation misplacement. Hooks that do not hug the lamina or misplaced pedicle screws can lead to devastating complications including spinal cord deficit. Overcorrection of curves and, conversely, inadequate releases, leading to an unbalanced spine, account for other types of intraoperative complications. Inappropriate decortication, inadequate bone graft material, and the use of bulky crosslinks can result in a higher rate of pseudarthrosis.

Intraoperative neurophysiologic monitoring with somatosensory evoked potentials and motor evoked potentials helps alert the surgeon to any impending intraoperative spinal cord neurologic deficit.¹⁰⁴ These deficits typically occur from spinal cord distraction, from overcorrection, from vascular compromise, or, rarely, directly from instrumentation. If the somatosensory evoked potentials and motor evoked potentials decline past warning criteria, the surgeon should implement a course of action that includes ensuring that the irrigation being used is of adequate temperature, keeping adequate mean arterial blood pressure elevated at a minimum greater than 80 to 90 mm Hg, and reversing instrumentation or spinal correction to the prewarning criteria state. Appropriate-dosed steroid boluses are also considered in accordance with the National Acute Spinal Cord Injury Study (NASCIS) III protocol if motor evoked potentials do not return to baseline within a reasonable time. A wake-up test should also be performed to assess true upper and lower neurologic function. In addition to adhering to the proven sequential technique of free hand screw placement, pedicle screw stimulation provides an added safety measure.^68,⁶⁹ Judicious use of intraoperative imaging can also be employed, especially with significant deformities.

Postoperative complications can arise from delayed consequences of technical errors, neurovascular compromise, medical comorbidities, and wound infections. Although perioperative antibiotics are commonly used, when wound infections do occur, they generally are treated aggressively with wound irrigation and débridement. Instrumentation well seated on the spine is always left in place; however, the decision to remove or maintain the bone graft is defined by the individual case and surgeon preference. In addition, removal of instrumentation can lead to loss of curve correction and decompensation.¹⁰⁵ Additionally, at final closure, heat-stable, powder antibiotics can be placed inside the wound (deep and superficial to the fascia), and long-term parenteral antibiotics are provided based on the results of intraoperative wound cultures and sensitivities. With delayed or late infections, the instrumentation is initially removed and later replaced because the deformity can progress as the fusion mass is subject to repeated bending forces.^105,¹⁰⁶ Also, the fusion mass is inspected further, and any pseudarthrosis noted is repaired at the reinstrumentation stage.