Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis is a sideways curvature of the spine, combined with rotation of the vertebrae, that appears around puberty in an otherwise healthy child and has no identifiable cause. It is the most common form of scoliosis. Most curves are small and need only observation; a minority progress far enough to need bracing or corrective spinal fusion surgery.

That is the frame Dr. Manoj Miglani, Principal Director Orthopaedics, Fortis Flt. Lt. Rajan Dhall Hospital, Vasant Kunj, New Delhi, India, set for a masterclass for referring doctors in August 2024. His central message was practical: in adolescents the condition is, broadly speaking, a cosmetic deformity rather than a functional one, and the clinician's real job is to judge which curves will progress and act before they become severe. Three companion articles go deeper into diagnosis, the Cobb angle and the Risser sign, observation and bracing thresholds, and surgical correction and its risks.

What is adolescent idiopathic scoliosis?

Scoliosis is a deformity in the coronal plane: seen from behind, the spine bends to one side. When the curve is a fixed, structural deformity, the bend is accompanied by rotation of the vertebral bodies. Dr. Miglani described that rotation as a more or less regular part of every scoliotic deformity, and it is the rotation that produces the visible rib hump.

Rotation also distorts the spine's front-to-back profile. In some segments it creates an apparent kyphosis (a forward, rounded curvature), even in the lumbar spine, where the normal curve is a lordosis (an inward hollow), and the thoracic kyphosis tends to look exaggerated. This is why many of these deformities are described as kyphoscoliotic. In three dimensions, Dr. Miglani noted, the apex of the curve has usually rotated into lordosis, even though on a plain view it appears as a kyphosis.

"Idiopathic" means that no cause is visible. The diagnosis is one of exclusion: the clinician must first rule out the other forms of scoliosis before applying the label.

How it differs from congenital, neuromuscular and syndromic scoliosis

The main alternatives behave differently, mostly in timing:

• Congenital scoliosis arises from malformed vertebrae present from birth, such as a hemivertebra (a half-formed vertebra) or a block vertebra (two or more vertebrae fused together). The deformity has been there since birth and becomes more visible as it progresses.
• Neuromuscular scoliosis follows a condition that weakens the trunk muscles. Dr. Miglani's example was a child who develops poliomyelitis at three or four years of age and then develops scoliosis gradually over the following years.
• Syndromic scoliosis is usually visible by the time the child is a toddler.

Adolescent idiopathic scoliosis develops much later than all three, and it becomes visible without any bony anomaly on the X-ray. For a deeper look at congenital and neuromuscular curves in younger children, see Dr. Puneet Girdhar's guide to scoliosis and kyphosis in children.

Early onset and late onset

Within idiopathic scoliosis, the age of onset matters because it predicts behaviour. The younger the child at onset, the more progressive the deformity, because more growth remains and the curve worsens as the spine grows. Dr. Miglani distinguished early-onset idiopathic scoliosis from late-onset, or adolescent, idiopathic scoliosis. Early-onset curves appear before the age of 10; adolescent curves appear from 10 years of age until skeletal maturity, and most develop just before and during puberty, the period when a girl or boy grows the most.

How common is adolescent idiopathic scoliosis?

Adolescent idiopathic scoliosis accounts for about 80% of all scoliosis cases, according to Dr. Miglani, and it has a worldwide prevalence of around 1% to 3%, the highest of any scoliotic deformity. He stressed that even a 1% prevalence is a substantial load on any health system.

Two patterns stand out, and neither is explained:

• Girls are affected more often than boys.
• Right-sided curves predominate. Because the cause of the condition is unknown, the reason for the right-sided preference is also unknown.

A curve must measure at least 10 degrees on the Cobb angle (the standard angle measured on an X-ray between the most tilted vertebrae at each end of the curve) to be called scoliosis. Curves under 40 degrees rarely produce a deformity that people can see. Curves of 40 degrees or more are the clinically relevant group, and Dr. Miglani put their prevalence at about 0.1%. In other words, most children with a measurable curve will never need corrective surgery.

What causes adolescent idiopathic scoliosis?

The cause has not been established. Dr. Miglani walked through the main hypotheses, none of which has been proven:

• Hormonal factors driving a sudden or asymmetric growth spurt.
• Muscle imbalance around the spine.
• Tissue deficiencies and vertebral growth anomalies, although nobody knows why such growth anomalies would occur.
• Central nervous system anomalies that disturb the body's trunk-balancing system.
• Genetic factors. About 30% of patients have a family member with scoliosis, which supports a genetic hypothesis. But about 70% do not, which is why, in his words, the genetic theory "gets a backseat."

Asked during the session whether the condition is hereditary, Dr. Miglani confirmed the familial presence of around 30% in adolescent idiopathic scoliosis, and added that congenital and some neuromuscular or syndromic scolioses carry a greater chance of being hereditary because of genetic transmission.

Can scoliosis be prevented?

The practical consequence of an unknown cause is that there is no prevention. Dr. Miglani was explicit that no exercise programme at school, special bed or diet prevents idiopathic scoliosis. The only advice is that children stay active, moving around and playing as they normally do. Congenital scoliosis is different: prenatal scans can detect it while the child is still in the womb, and parents can then decide with their obstetrician how to proceed if the anomaly is serious.

Signs and symptoms of scoliosis in adolescents

The typical story is a deformity of the back noticed at around 10 to 13 years of age, often by a parent, a teacher or the child's peers, or by the child. Back pain is usually not part of the picture. The children are young and active, the curve is rarely severe at first, and they have been doing everything normally until someone notices the asymmetry.

Three findings catch the eye: uneven shoulder height, which is usually the first thing people see; a prominent rib hump; and an asymmetric waistline. The diagnosis article covers the full examination and imaging work-up.

Dr. Miglani emphasised three principles for the first consultation:

1. A neurological examination is mandatory. It rules out spinal cord anomalies and other causes of scoliosis. Adolescent idiopathic scoliosis does not cause weakness, paraparesis or paraplegia, so any neurological deficit changes the plan entirely and calls for an MRI to find the reason.
2. Privacy and sensitivity matter. The condition is largely cosmetic and the patients are adolescents, so the examination has to be handled with care.
3. Photographic documentation should be routine. Serial clinical photographs, alongside X-rays, give a regular record of whether a curve is progressing.

Why timing decides almost everything

The growth spurt is the engine of progression. Dr. Miglani noted that in girls the maximum growth spurt occurs about one to one and a half years before menarche (the first menstrual period). A 12-year-old who has already reached menarche and has a 15 to 20 degree curve therefore needs observation only, because little growth, and so little progression, remains.

The clinician weighs four factors together: the size of the curve (Cobb angle), skeletal maturity (the Risser sign and, in girls, menarche), the child's age, and the curve's behaviour over time. A curve of around 35 degrees in a child who is already close to maturity is unlikely to progress. A curve in a 12-year-old with a low Risser grade is highly likely to progress and needs strict monitoring.

The treatment ladder at a glance

Dr. Miglani's decision framework, covered in detail in the article on observation and bracing thresholds, runs as follows:

The aim of treatment is to prevent progression and, where needed, to correct the deformity. Dr. Miglani is openly sceptical of bracing because of poor compliance, and the bracing article sets out his reasoning alongside the trial evidence. For curves that reach the surgical range, modern correction relies on posterior fusion with pedicle screws at every involved level, an approach covered in the article on scoliosis surgery.

What happens if scoliosis is left untreated

Small curves in mature adolescents are benign. Larger curves are not. In Dr. Miglani's account, an untreated curve of more than 45 degrees in a skeletally immature child will progress, and the consequences appear later in life rather than in adolescence:

• Back pain, and pain radiating down the legs.
• Worsening cosmetic deformity.
• Nerve compression, with weakness.
• Restriction of heart and lung function, which is unlikely but becomes possible once the curve exceeds 70 to 80 degrees.

Curves of this size tend to keep progressing at around one degree a year after growth ends. His illustration: a deformity established at 15 years of age may have progressed by a further 25 to 30 degrees by the age of 45, enough to cause cardiac and pulmonary problems.

The reason adolescent curves rarely threaten the heart and lungs during childhood is timing. The deformity usually develops after lung and heart growth is largely complete, by around 10 to 12 years of age. This is the key difference from early-onset curves, which can restrict chest development.

Where scoliosis care is delivered

Dr. Miglani made one closing point that matters for referring doctors and for families weighing where to have surgery. Centres that perform these operations routinely, in high volume, have fewer complications and better results, and the surgery becomes more cost-effective. Families can review the cost of scoliosis correction surgery separately.

Questions from attending doctors on heredity, follow-up intervals, exercises, prevention and a post-traumatic curve are answered in the Live Discussion from this masterclass. For more on Dr. Miglani's practice, see his doctor profile, and for the wider field, the orthopaedics specialty hub.