Adolescent Idiopathic Scoliosis

Abstract

Adolescent idiopathic scoliosis (AIS) is a common spinal disorder that primarily affects adolescents during their growth spurt. It is characterized by a lateral rotation curvature of the spine, typically in an “S” or “C” shape. The exact cause of this condition is still unknown, but it is believed to be influenced by a combination of genetic and environmental factors. Symptoms of adolescent idiopathic scoliosis may vary depending on the severity of the curvature, ranging from mild back pain to noticeable changes in posture. Early detection and intervention are essential to prevent further progression of the curve and to minimize potential complications. Treatment options include observation, bracing, and in severe cases, surgery. Regular monitoring and follow-up care are crucial in managing this condition and ensuring the overall well-being of affected individuals.

1. Introduction

Scoliosis, a condition characterized by lateral curves in the vertebral column, affects spinal alignment in all three dimensions [1]. The term “scoliosis” originates from the ancient Greek word “skolios,” meaning curved or crooked, and was first defined by Galen in the 2nd century AD [2]. There are various types of scoliosis categorized by factors like age of onset, cause, severity, and curvature type. Each type has distinct characteristics, including the rate of curve progression and the pattern of three-dimensional (3D) deformity [3]. The two main groups of scoliosis are idiopathic (unknown cause) and non-idiopathic. Idiopathic scoliosis is diagnosed when non-idiopathic causes are ruled out. Congenital scoliosis, on the other hand, is caused by vertebral malformations like hemivertebrae, unilateral web, or block vertebrae [4]. While not always noticeable at birth, it typically develops during adolescence. Both genetic and environmental factors can contribute to these malformations [5, 6, 7]. Scoliosis that is classified as neuromuscular is a result of weakened muscles that provide support for the spine. This type of scoliosis is commonly observed in individuals with conditions such as cerebral palsy, spinal muscular atrophy, spina bifida, muscular dystrophies, or spinal cord injuries [8]. On the other hand, mesenchymal scoliosis is caused by the weakening of passive stabilizers of the spine. This form of scoliosis is often present in individuals with conditions such as Marfan syndrome (Figure 1), [9] mucopolysaccharidosis, osteogenesis imperfecta, inflammatory diseases, or complications arising after surgery.

Figure 1.

Male 15 years old with triple curve scoliosis in Mar Fan Syndrome [9].

Infantile scoliosis, affecting children aged 0–3 years, has a prevalence rate of 1%. The recommendation for infants to be placed in the prone position during the 1980s resulted in a significant decrease in the number of cases [10, 11]. Unlike adolescent idiopathic scoliosis (AIS), more than half of the cases of infantile scoliosis regress over time [12]. When the rib-vertebrae angle (RVA) exhibits a difference of more than 20 degrees, it indicates a negative prognosis and a rapid advancement of the condition. Juvenile scoliosis, which typically manifests between the ages of 4 and 10, accounts for approximately 10–15% of all cases of idiopathic scoliosis in children. Failure to address this condition can result in severe complications related to the heart and lungs (Figure 2) [13]. It is worth noting that curvatures measuring 30 degrees or greater tend to worsen over time, leading to the necessity of surgical intervention in 95% of affected patients. Adolescent scoliosis, which typically arises in individuals aged 11–18 years, is a common form of scoliosis found in teenagers [14].

Figure 2.

Male 8 years old with lumbar juvenile scoliosis pelvic tile more than 1.5 degree and Cobb angel 10.3.

2. Etiology

Several studies suggest that genetic factors play a crucial role in the etiology of AIS. Familial aggregation and twin studies have provided evidence of heritability, indicating that there is a genetic predisposition to AIS [15, 16]. Genome-wide association studies (GWAS) have identified potential candidate genes associated with AIS, such as LBX1, GPR126, and PAX1 [17]. Polymorphisms in estrogen receptor genes have been linked to the risk of developing AIS, implying that hormonal imbalances could also be implicated in its etiology [18]. Despite these findings, the specific mechanisms by which these genetic factors contribute to the development of AIS are still not fully understood. Apart from genetic factors, non-genetic factors may also play a significant role in AIS etiology. Biomechanical factors, such as asymmetrical loading of the spine, abnormal spinal growth patterns, and imbalances in muscle tension, have been proposed as potential triggers of AIS [19]. These factors can lead to mechanical forces that disrupt the normal growth and development of the spine during adolescence, contributing to the onset of scoliosis. Additionally, neurologic abnormalities, including abnormal proprioception and impaired neuromuscular control, have been suggested to play a role in AIS etiology. Changes in the central nervous system’s ability to control posture and muscular activation may result in abnormalities in spinal alignment and development [20, 21, 22]. Hormonal imbalances during adolescence have been implicated in the etiology of AIS. Estrogens, particularly 17β-estradiol, have been shown to influence bone growth and remodeling [23, 24]. Experimental studies have suggested that estrogen deficiency or altered estrogen signaling may disrupt the balance between bone formation and resorption, leading to structural abnormalities in the spine [23, 25]. However, the exact role of hormones in AIS etiology is still under investigation, and further research is required to establish a clear causative relationship.

3. Epidemiology

The frequency of AIS is approximately 1–3%. Prearrange female and the right-side curves. To be considered scoliosis, the degree of coronal plane’s curvature must be more than 10°. For patients with curvatures that are greater than 40 degrees, the frequency is approximately 0.1% [26].

4. History

A comprehensive history and physical examination are necessary. Detailed developmental history to exclude other causes of scoliosis. Also, attention must be paid to questions pertaining to skeletal development, including the age of menarche. In a gross description, most adolescents with idiopathic scoliosis that present with no pain at the back will not have a dramatic reaction to the curvature. Many will participate in activities that are both physical and mental, including athletes, cheerleaders, and otherwise healthy children [27, 28, 29].

5. Physical examination

5.1 Assessment of shoulder tilt

Shoulder tilt can be assessed looking at the patient posteriorly as well as anteriorly. If one shoulder is higher than the other, it should be noted: larger space from arm to the side of the body when comparing both sides (Figure 3).

Figure 3.

Shoulder and pelvis tilts with waist creases.

5.2 Assessment of pelvic tilt

The presence of asymmetry of waist crease, truncal shift, and pelvic tilt should also be assessed by direct visualization. One hip higher than the other; head not centered over pelvis uneven waist creases.

5.3 Assessment of angle of trunk rotation

A scoliometer is used to assess the angle of trunk rotation for the thoracic as well as the lumbar prominence while the patient is in a forward bending position in “Adam’s forward test.” (Figure 4).

Figure 4.

Adam’s forward test.

5.4 Presence of any cutaneous abnormalities

The presence of cutaneous abnormalities, such as hairy spots or “café au lait” spots, can be a presence of non-idiopathic types of scoliosis and should be kept in mind [30].

5.5 Indicators of maturity

Development of secondary sexual characteristics is a rough indication of skeletal maturity and should be kept in mind.

5.6 Gait assessment

It is important for indicating any leg length discrepancies or ataxia, which may be an indication of spinal cord disorders.

6. Radiological assessment

The formal evaluation that is proper includes X-ray imaging. Patients require a permanent coronal X-ray, a sagittal X-ray, a left and right bend X-ray. The Risser classification is typically derived from the iliac crest on a coronal X-ray view. Consensus is that a computed tomography (CT) scan and a magnetic resonance imaging (MRI) of the typical AIS patient are not necessary.

6.1 Essential radiographs

Radiologic analysis includes standing, long view of the spine, including the pelvis, to assess the Cobb angle (measured between the superior surface of the proximal and inferior surface of the distal end vertebrae tilted maximally into curvature) (Figures 5 and 6).

Figure 5.

Long view of the spine, including the pelvis.

Figure 6.

Cobb angle (measured between the superior surface of the proximal and inferior surface of the distal end vertebrae tilted maximally into curvature).

6.2 Flexibility views

Left and right bending view with the patient positioned supine (Figures 7 and 8) are obtained to determine the structural nature of the curve. Disc space neutralization defined as opening of the disc space across both sides on bending radiographs helps decide the distal extent of the fusion. These techniques are useful during surgical planning.

Figure 7.

Right bending view to measure the proximal thoracic and thoracolumbar/lumbar curves.

Figure 8.

Left bending view to measure main thoracic curve.

6.3 Lateral view

Cobb angles are measured in a more uniform fashion in the following way:

1. T2–T5

2. T5–T12

3. T10–L2

4. L1–S1

In the case of a severe kyphotic deformity, an additional measurement of maximal kyphosis can be used. The superior end-plate is used for the proximal end vertebra, while the inferior end-plate is used for the distal end vertebra to measure out the area of maximal kyphosis (Figures 9 and 10).

Figure 9.

Measure the maximal kyphosis case of scoliosis with severe kyphosis.

Figure 10.

Radiographic marker of CSVL; SV; NV; Risser Sign.

6.4 Skeletal maturity

The Risser Sign is a physical indicator used in orthopedics to measure the maturity of the pelvic bones in adolescents. To measure skeletal development, one can utilize the Risser sign, which only requires an X-ray of the pelvis. The X-ray reveals the ossification of the iliac apophysis as it advances from the crest toward the spine. The Risser sign is categorized into five different stages, with stage 1 indicating 25% ossification and occurring during early puberty. Once a person reaches Risser stage 5, their bones are fully ossified, and they are deemed to be skeletally mature.

The Sanders Maturity Scale is a tool utilized to measure the maturity of an individual or group. A child’s bone maturity can be evaluated by an X-ray of the fingers and wrist on the left hand, using what is known as the Sanders score. This score uses a scale of 1–8, with 1 signifying slow growth during early adolescence and 8 representing complete skeletal maturity. Recent studies have shown that the Sanders Maturity Scale is a more dependable metric for measuring skeletal maturity in patients with adolescent idiopathic scoliosis, particularly during the curve acceleration phase, as opposed to the Risser classification.

7. Diagnosis

The diagnosis of AIS remains a diagnosis of exclusion, and other probable causes of scoliosis, such as spinal infections and neoplasms, neuromuscular and syndromic diseases, and congenital anomalies of the spine or neural axis, should be excluded.

7.1 Staging

The Lenke System of AIS Classification is most effective at categorizing stages. The objective of this classification scheme is to create a common method of naming and describing curves. The overall goal at this advanced level is also to favor the protocol for operative treatment [31].

7.1.1 Lenke classification

The Lenke classification for AIS has gained popularity and consists of three steps:

1. curve type (1–6)

2. lumbar mixed spine modifier (A, B, C)

3. sagittal thoracic modifier (−, N, +)

7.1.1.1 Identification of primary curve (Type 1–6)

1. Measure regional curves

   • proximal thoracic (PT)

   • main thoracic (MT)

   • thoracolumbar/lumbar (TL/L)

7.1.1.2 Identify major curve (biggest curve)

• always either MT (Type 1–4) or.MT/L (Type 4*,5,6)

7.1.1.3 Determine if minor curve is structural or not

• definition of structural

• >25° in coronal plane on standing anteroposterior (AP) and do not bend out to <25° on bending views.

• OR > 20° in sagittal plane.

Structural (major) – has the largest Cobb angle and is always structural. In Type 4, it can be either MT or FL/L depending on which Cobb is larger, if is the largest curve, then by default assign major curve to MT (Table 1) [32].

Type	Curve	Proximal thoracic	Main thoracic	Thoracolumbar/lumbar
1	Main thoracic	Not structural	Structural	Not structural
2	Double thoracic	Structural	Structural	Not structural
3	Double major	Not structural	Structural	Structural
4	Triple major	Structural	Structural	Structural
5	Thoracolumbar/lumbar	Not structural	Not structural	Structural
6	Thoracolumbar/lumbar-main thoracic	Structural	Structural	Structural

Table 1.

Description of Lenke classification.

7.1.1.4 Assignment of Lumbar modifiers (A, B, C)

• Identify apical lumbar vertebrae (ALV)

• is the inferior lumbar body that falls outside of the curve

• Draw central sacral vertical line (CSVL) and see where it sits in relationship to pedicles of ALV (Table 2 and Figure 11) [32].

Modifiers
Lumbar spine modifier	CSVL to lumbar apex	Thoracic sagittal profile
A	CSVL between pedicles	− (below normal)	<10°
B	CSVL touches apical bodies	N (normal)	10°–40°
C	CSVL completely medial	+ (above normal)	>40°

Table 2.

Lumbar modifier of Lenke classification.

A if CSVL passes between pedicles of apical lumbar vertebrae (ALV).

B modifier if CSVL touches the pedicle of apical lumbar vertebrae (ALV).

C modifier if CSVL does not touch apical lumbar vertebrae (ALV) apex of lumbar curve falls completely off the midline depicting a curve with complete apical translation off the CSVL.

Figure 11.

Lumbar modifier Lenke Classification.

7.1.1.5 Assignment of sagittal thoracic modifier (−, N, +)

Measure sagittal Cobb from T5 to T12:

1. hypokyphotic (−) if <10°

2. normal if 10–40°

3. hyperkyphotic (+) if >40°

7.1.2 The three-dimensional classification system of scoliosis

The system for classifying scoliosis is based on its three-dimensional (3D) features. It was developed in 2001 by Dr. Lenke and colleagues at the University of Iowa (UI). The system is based on the following factors:

• The location of the curves in the coronal plane (front view)

• The location of the curves in the sagittal plane (side view)

• The flexibility of the curves

• The amount of rotation of the vertebrae

It is a more comprehensive system than previous systems, as it considers the 3D features of the curves. This allows surgeons to better plan treatment and predict the outcome of surgery.

Table 3 summarizes the different types of scoliosis in the Three-Dimensional Classification System:

Type	Location of curves in coronal plane	Location of curves in sagittal plane	Flexibility of curves	Amount of rotation of vertebrae
Lenke 1	Single thoracic curve	Thoracic kyphosis	Flexible	Variable
Lenke 2	Double thoracic curves	Thoracic kyphosis	Flexible	Variable
Lenke 3	Thoracolumbar curve	Thoracic kyphosis or lordosis	Flexible or stiff	Variable
Lenke 4	Lumbar curve	Lumbar lordosis	Flexible or stiff	Variable
Lenke 5	Double major curves	Thoracic kyphosis or lordosis	Flexible or stiff	Variable
Lenke 6	Triple major curves	Thoracic kyphosis or lordosis	Flexible or stiff	Variable
Lenke 7	C curve	Variable	Variable	Variable
Lenke 8	Nonstructural curve	Variable	Variable	Variable
Lenke 9	Unclassified curve	Variable	Variable	Variable

Table 3.

Description of three-dimensional classification system of scoliosis.

The Three-Dimensional Classification System of scoliosis is a valuable tool for surgeons and other healthcare professionals who treat scoliosis. It provides a more comprehensive understanding of the deformity and helps to guide treatment decisions.

8. Treatment

The approach to treating AIS is contingent upon the severity of the curvature and factors such as the patient’s age and growth status. In general, AIS curves advance in two distinct manners: first, during the rapid growth phase of the patient, and second, into adulthood if the trends are substantial. As scoliosis curves intensify during periods of growth, the potential for growth is evaluated by considering the patient’s age, the onset of menstruation, and radiographic measurements. Typically, girls experience maturation around the age of 14, while boys reach maturity around the age of 16. Girls undergo rapid growth primarily during their initial menstrual cycle, which is then followed by a deceleration in growth. However, they will continue to grow for a period of 18 to 24 months after their first period. A widely employed method for evaluating the skeletal maturity of children, specifically the amount of growth remaining in the pelvis and spine, is the Risser system of grading (Figure 8). This system utilizes a scale ranging from 0 to 5 to determine the degree of skeletal maturation in a child. Patients classified as Risser 0 and 1 are still experiencing growth, whereas those categorized as Risser 4 and 5 have reached a point where growth has ceased. The three primary treatment options available include observation, bracing, and surgery (Table 4).

Treatment	Description	Advantages	Disadvantages
0bservation	The patient is monitored regularly with X-rays to see if the curve progresses.	No side effects	Curve may progress.
Bracing	A brace is worn to help correct the curve.	Curve may be corrected or stabilized.	Brace can be uncomfortable and may not be effective for all patients.
Surgery	The spine is fused to straighten it.	Curve is corrected.	Surgery is invasive and has risks.

Table 4.

Treatment options of AIS.

8.1 Observation

It is the most conservative approach to treatment. It’s typically recommended for patients with curves of 10–25 degrees who are evaluated by means of serial X-rays. This is typically accomplished at 3, 6, or 12 monthly intervals [33].

8.2 Bracing

Those with a degree of curve greater than 25 but less than 40–45 are considered candidates for bracing. The Bracing in Adolescent Idiopathic Scoliosis Trial (BrAIST) was a National Institutes of Health (NIH)-funded experimental research trial that demonstrated the efficacy of bracing in the adolescent population. Despite the common usage of braces, these uncomfortable devices have a low rate of compliance, and their overall success is still debatable. Concerns have been expressed regarding every form of brace for dealing with scoliosis (Figure 12) [34, 35].

Figure 12.

Male 12 years old case of thoracolumbar AIS treated by physiotherapy and bracing for 9 months where A after 3: B after 6 and C after 9 months of treatment.

8.3 Surgery

When it comes to the treatment of scoliosis, surgery is considered the most drastic and intrusive option. Typically, it is advised for individuals with curves that exceed 45 degrees or those that are advancing rapidly [36, 37, 38]. Vertebral body tethering (VBT) is a non-fusion, compression-based, growth preserving alternative to posterior spinal fusion (PSF) based on the concept of “growth modulation” to prevent possible functional complications secondary to fusion while correcting scoliotic deformity. The surgical procedure. The goal of the procedure is to provide tension to the convexity of the thoracolumbar curve and thereby slow down the ipsilateral paraspinal musculature growth [39, 40]. When it comes to treating Type 1 curves, experts recommend fusing the structural main thoracic curve. The UIV, or upper instrumented vertebra, typically falls between T3 and T5, while the LIV, or lowest instrumented vertebra, will vary depending on the location of both the stable and neutral vertebrae. The selection of the UIV considers shoulder balance as well as the presence of proximal thoracic kyphosis. It is important to avoid ending the construct at a region of kyphosis. For instance, if dealing with a right main thoracic curve and level shoulders, T3 would be the UIV of choice; however, T4 or T5 would be selected if the right shoulder was higher. The choice of LIV depends on the lumbar adjuster and CSVL. For lumbar adjusters A and B, the LIV can be selected as the heaviest lumbar vertebra that intersects the CSVL and is rotationally neutral. The LIV is usually located between the terminal and stabilizing vertebrae of the main thoracic curve. While not commonly observed in type 1 curves, T2 can be chosen as the upper instrumented vertebra (UIV) if the left shoulder is elevated higher than the right. Intraoperatively, the selection of the UIV may vary depending on the amount of main thoracic (MT) correction planned. The greater the correction planned, the likelier it is to fuse at a higher point in the proximal thoracic (PT) region to prevent the elevation of the opposite shoulder. The selection of the UIV can therefore be a dynamic process that is adjusted according to the amount of correction needed.

The determination of the most suitable treatment for a specific patient is a collaborative effort involving a healthcare team consisting of a physician, a physical therapist, and an expert in scoliosis braces. Factors, such as the patient’s age, growth status, severity of the curve, and other relevant considerations, are considered to provide a personalized recommendation [41].

9. Prevention

Early detection and intervention play a crucial role in managing AIS effectively. Regular screenings in schools and healthcare settings can help identify the condition early, allowing for timely intervention and preventing the progression of the curve. If left untreated, AIS can lead to various complications, such as chronic pain, respiratory problems, and psychological distress, due to body image concerns. Early initiation of treatment can significantly improve the long-term outcomes and quality of life for individuals with AIS.

Conflict of interest

The authors declare no conflict of interest.

Declaration of figures’ authenticity

All figures submitted have been created by the authors who confirm that the images are original with no duplication and have not been previously published in whole or in part.

List of abbreviations

RVA	rib-vertebra angle
GWAS	genome-wide association studies
PA View	posterior–anterior view
NV	neutral vertebra
SV	stable vertebra
CSVL	central sacrum vertical line
PTC	proximal thoracic curve
MTC	main thoracic curve
TLC	thoracolumbar curve
LC	lumbar curve
SRS	Scoliosis Research Society
ALV	apical lumbar vertebra
UI	University of Iowa
BrAIST	The Bracing in Adolescent Idiopathic Scoliosis Trial