Adolescent Idiopathic Scoliosis
Scoliosis is a rotational deformity of the spine in both the coronal and sagittal planes (Figure 1). A diagnosis of idiopathic scoliosis is made when the coronal plane Cobb angle (see Figure 2 ) is >10 degrees on plain film radiographs and there is no underlying spinal cord pathology, neuromuscular disorder, or congenital malformation present. Adolescent idiopathic scoliosis is diagnosed in children between the ages of 10 and 18 years old and represents 80 percent or more of all cases. (Historically, if scoliosis is diagnosed in a patient 4 years of age or younger, it would be designated ‘infantile idiopathic scoliosis’ with the term ‘juvenile idiopathic scoliosis’ referring to patients ages 4-10, but more recently all cases of scoliosis diagnosed before the age of 10 are classified as ‘early onset scoliosis’ [discussed in another chapter.])
Depending on the severity of the curve and age of the patient, scoliosis can be managed with observation, bracing, or surgery. While scoliosis is not generally associated with pain during adolescence, more advanced curves (>40 degrees) can be associated with higher rates of low back pain in adulthood.
Structure and Function
The spine consists of 7 cervical, 12 thoracic, 5 lumbar, and 5-7 sacro-coccygeal vertebrae. Normal alignment is critical to maintain the balance of the axial skeleton between the head and pelvis. This alignment is measured in both the coronal and sagittal plane using a plumb line starting at the base of C7. In neutral coronal balance, the C7 plumb line overlaps the center of the sacrum. When the C7 plumb line is to the left of the sacrum, there is negative coronal balance and when it is to the right there is positive coronal balance. In neutral sagittal balance the C7 plumb line touches the posterior-superior corner of S1. If the C7 plumb line falls anterior to S1 there is positive sagittal balance, and if it falls posterior to S1 there is negative sagittal balance.
In the coronal plane, the spine should be straight (<10 degrees of curvature), but on the sagittal plane the lumbar spine typically has 20-55 degrees of lordosis (inward curving, as seen from the side), while the thoracic spine has a physiologic kyphosis (an outward curve or hunching of the spine) of 20-45 degrees.
Adolescent idiopathic scoliosis is classically described as a painless condition. Low back pain is becoming
increasingly more common among adolescent patients, and some of them will have scoliosis; but scoliosis should
be the default explanation of the symptoms.
A common complaint of adolescent idiopathic scoliosis patients is the appearance of the back and posture from a pronounced rib “hump,” trunk shift, and uneven shoulders. Appearance issues can range from mild dysphoria to debilitating psychosocial distress.
Scoliosis may progress with growth. It is therefore important to establish the patient’s growth history and document growth at each follow-up visit. On average, boys grow until the age of 16 and girls grow until the age of 14, or 2 years after menarche. Predicting growth is difficult, but some tools to help predict remaining growth include the Risser sign and Sanders stage (discussed below).
A complete physical exam begins with inspection of the patient standing upright facing away from the examiner. Scapular prominence, waist crease asymmetry and arm-side space can be observed. From a lateral view, the hypokyphosis of the thoracic spine can also be noted. Shoulder asymmetry, trunk shift and pelvic asymmetry can be observed and palpated. During the examination, it is important to identify a potential leg length discrepancy that can mimic scoliosis. If leg length difference is noted, the examiner can place a block under the shorter leg to assess if the curve corrects.
The Adam’s forward bending test is an easy screening test. It is performed by having the patient lock his or her knees in extension and attempt to bend forward and touch toes. The patient is then observed from behind, to note the presence of an asymmetries of the rib cage and shoulder blades. Any rib prominence should be measured using a scoliometer (Figure 3). A rib prominence deformity greater than 7 degrees should prompt an evaluation by a pediatric spine specialist. As a rule of thumb, 7 degrees of prominence on Adam’s forward bending test corresponds curve measuring about 10 to 20 degrees on x-ray.
There are important radiographic parameters to help with diagnosis and management of adolescent idiopathic scoliosis:
- Cobb angle: The angle between intersecting lines drawn perpendicular to the two end vertebrae (see Figure 1).
- End Vertebrae: Top and bottom vertebrae maximally tilted into the concavity.
- Neutral vertebra: Vertebra that are not rotated. Identified by symmetric pedicles in the coronal radiograph.
- Stable vertebra: Most cephalad vertebra distal to end vertebra that is most closely bisected by the central sacral vertical line.
- Apical vertebrae: Central vertebra within a curve, typically least tilted and most rotated.
- Risser sign: Radiographic predictor of growth based on the amount of iliac crest apophysis ossification (Figure 4).
- Sanders staging: Radiographic predictor of growth based on hand x-ray (Figure 5). In general, the bone epiphysis in the hand fuse from distal (phalangeal bones) to proximal (distal radius) and thus supports a staging system that ranges from 1 (skeletally immature) to 8 (skeletally mature).
Adolescent idiopathic scoliosis is relatively rare, with a prevalence of 3% in the general population. The prevalence of severe curves (>30) is much lower, approximately 0.03%. When considering only large curves, females are ten times more commonly affected than males, but the ratio is closer to 1:1 for cases with smaller curves.
There is thought to be a genetic component to adolescent idiopathic scoliosis, though the mode of inheritance is unknown. The risk of having adolescent idiopathic scoliosis is increased 50-fold when both parents have a history of scoliosis. In females whose mother has a curve >15º, the risk is 27%.
So-called neuromuscular scoliosis is found when there are irregular spinal curvatures in the presence of the central nervous system or muscular disorders. In contrast to adolescent idiopathic scoliosis, neuromuscular curves tend to progress more rapidly, involve more vertebral levels, progress after maturity, and are usually associated with pelvic obliquity.
Scheuermann’s Kyphosis is a spinal deformity causing rigid thoracic hyperkyphosis (>45 degrees). In general, adolescent idiopathic scoliosis is associated with “flat back,” or loss of normal kyphosis and lordosis.
A leg length discrepancy can cause an apparent scoliosis. If present, leg length discrepancy will result in pelvic obliquity, and with it, a compensatory curve to keep the head and upper body over the center of the pelvis (see Figure 6).
It is important to identify red flags during adolescent idiopathic scoliosis evaluation, which will warrant further investigation such as MRI to assess for intraspinal abnormalities such as syrinx, Chiari malformation, or cord tethering that may need to be addressed prior to curve correction. These include left thoracic curves (right thoracic curves are far more common), apical kyphosis (kyphosis is rare in adolescent idiopathic scoliosis), rapid progression of a curve, structural abnormalities such as a hemivertebrae, neurologic findings such as pathologic reflexes or radicular pain, and foot deformities.
Treatment Options and Outcomes
The plan of treatment depends on the severity of the curve and patient age. After achieving skeletal maturity, curves <30 degrees are unlikely to progress in adulthood. In contrast curves >50 degrees are likely to progress 1 degree per year; and even higher rates are seen during pregnancy and menopause.
Curves smaller than 20 degrees have a low probability of progressing and require only surveillance with periodic physical exams until skeletal maturity. (After skeletal maturity is reached, curves smaller than 20 degrees do not need close monitoring.)
Curves measuring more than 20 degrees on initial presentation require intervention. The goal in treating patients with curves of more than 20 degrees but less than ~50 degrees (see Figure 7) is to prevent progression - not correction. This goal can often be achieved with thoraco-lumbar bracing. A landmark multicenter, prospective, randomized trial known as the Bracing in Adolescent Idiopathic Scoliosis Trial (BrAIST) demonstrated a 72% success rate at preventing curve progression to 50 degrees or more compared to 48% in the observation cohort. Given the effectiveness of bracing, the trial was terminated early. Multiple societies, including the Scoliosis Research Society (SRS), Pediatric Othopaedic Society of North America (POSNA), American Academy of Orthopaedic Surgeons (AAOS), and American Academy of Pediatrics (AAP) all recommend bracing in cases of adolescent idiopathic scoliosis with growth remaining and curves between 20-40 degrees to prevent progression and avoid surgical intervention. Needless to say, patient compliance is key: brace therapy is effective only if the brace is worn.
For patients with curves measuring more than 45 to 50 degrees, surgery may be the best option to correct the deformity and halt curve progression. In addition to the severity of the curve, it is ideal that patients be close to or have reached skeletal maturity.
(The precise indication for surgery is based on expert opinion. According to the website of the American Academy
Orthopaedic Surgeons in August 2020, “Most scoliosis surgeons agree that children who have very severe curves
(45-50° and higher) will need surgery to lessen the curve and prevent it from getting worse.”)
Surgical techniques are variable and continue to evolve with emerging technology, but the ultimate goal is to help correct deformity and achieve a solid fusion. A common technique used today is stabilization of the spine with pedicle screws and long rods until posterior spinal fusion is achieved (Figure 8).
Surgery is usually successful. In some patients who undergo posterior spinal fusion at a young age, the anterior column of the spine can continue to grow, creating a rotation deformity. This complication can be prevented by delaying surgery until skeletal maturity or performing anterior based spinal fusions to halt growth of the anterior vertebrae
Risk Factors and Prevention
Currently, there are no known preventable risk factors for adolescent idiopathic scoliosis. As such, much effort
been focused on screening to help with early diagnosis and bracing to prevent the need for surgery.
A few studies have reported on the relationship with scoliosis and exercise and/or posture. Although healthy ergonomic posture and core strengthening are encouraged, there is no Level 1 evidence that demonstrates prevention or reversal of scoliosis based on posture and exercise or physical therapy programs.
Although adolescent idiopathic scoliosis is considered to be painless, residual curves (especially those measuring 50 degrees or more) may be associated with increased incidence of low back pain in adulthood.
Scoliosis need not interfere with high level athletic performance. Usain Bolt (Figure 9), one of the fastest sprinters in history, reported in his autobiography that he has scoliosis.
Scoliosis, Cobb angle, Risser/Sanders Assessment of Skeletal maturity, Bracing, Posterior spinal fusion
Define scoliosis. Be able to measure the coronal plane Cobb angle on plain film radiographs. Identify coronal and sagittal plane global balance. Recognize red flags on history and physical exam that warrant advanced imaging with MRI in patients that present with Adolescent idiopathic scoliosis. Understand criteria for bracing and surgery based on curve severity and skeletal maturity.