Adolescent Idiopathic Scoliosis

Adolescent idiopathic scoliosis is a three dimensional deformity of the spine, with a lateral curve of 10 degrees or more (measured by the Cobb angle) with vertebral rotation, arising between age 10 and skeletal maturity, with no underlying cause. It is the commonest form of scoliosis, and accounts for about 80% of all idiopathic scoliosis.

It affects 2 to 3% of adolescents (curves of 10 degrees or more), but only 0.1 to 0.3% have curves over 30 degrees that need treatment. Girls and boys are equally affected for small curves, but girls are 5 to 10 times more likely to have progressive curves needing treatment. A family history is common (a polygenic pattern, with heritability of about 40 to 90%). The commonest curve is a right thoracic curve.

The risk of progression is highest around the peak of growth (a Risser sign of 0 to 1, before or at menarche, and a curve of 20 to 30 degrees). Curves over 50 degrees continue to progress in adulthood by about 0.5 to 1 degree a year.

Complications are cosmetic deformity, back pain in adulthood (no more frequent than in people without scoliosis), reduced pulmonary function in severe thoracic curves (over 70 to 100 degrees), psychological distress, and rarely cardiopulmonary compromise.

Pathophysiology

The cause is multifactorial: genetic factors (many loci, including LBX1 and GPR126), asymmetric growth of the spine (relative anterior spinal overgrowth with hypokyphosis), neuromuscular and proprioceptive differences, abnormal melatonin signalling, and biomechanical factors. Asymmetric loading of the growth plates leads to wedging of vertebrae and a vicious cycle of progression during growth spurts.

Often detected by school screening or by the family as shoulder or waist asymmetry, a prominent shoulder blade, uneven hemlines or a rib hump. Pain is not typical (about 20 to 30% have mild back pain), and pain, neurological symptoms, or rapid progression suggest another cause.

Examine standing posture (shoulder height, trunk shift, waist crease asymmetry), the Adams forward bend test with a scoliometer (angle of trunk rotation of 5 to 7 degrees or more needs radiographs). Also examine leg lengths, the skin of the back (café-au-lait spots, hairy patch, dimple), neurological state (abdominal reflexes, power, tone, gait, sensation), foot deformities, and Tanner stage and menarche.

• Standing posteroanterior (and lateral) full spine radiographs, taken at a low radiation dose (or with a low dose biplanar imaging system). They show the Cobb angle (angle between the end vertebrae of the curve), curve pattern (Lenke classification), vertebral rotation, apical vertebra, skeletal maturity (Risser sign, triradiate cartilage, bone age), and sagittal alignment.
• Bending films or traction views to assess curve flexibility before surgery.
• MRI of the whole spine is needed for atypical features: a left thoracic curve, onset before 10 years, rapid progression (over 1 degree a month), significant pain, neurological signs, abnormal reflexes, a short and stiff spine, or a foot deformity. It excludes syringomyelia, Chiari malformation, tethered cord and tumours.
• Pulmonary function tests for curves over 60 to 70 degrees; echocardiography when a syndrome is suspected.
• Blood tests are not needed unless another diagnosis is suspected.

Differential diagnosis.

• Congenital scoliosis and neuromuscular scoliosis.
• Syndromic scoliosis (neurofibromatosis, Marfan syndrome, Ehlers-Danlos syndrome).
• Scoliosis from osteoid osteoma, spinal tumour or syrinx.
• Postural curve from leg length difference or pain, and Scheuermann kyphosis.

Treatment depends on the curve size, skeletal maturity and risk of progression.

Observation. Curves under 25 degrees in a growing child: clinical review and radiographs every 4 to 6 months (every 6 to 12 months for curves under 20 degrees in a nearly mature child). Curves under 10 degrees are normal variation. Physiotherapy based scoliosis specific exercises may help trunk control and are an adjunct, but they do not replace bracing.

Bracing (curves of 25 to 45 degrees with a Risser sign of 0 to 2, or curves of 20 to 25 degrees that progress by 5 degrees or more).

• A thoracolumbosacral orthosis (Boston type brace) worn for 16 to 23 hours daily (the dose is critical), or a night time bending brace for flexible lumbar and thoracolumbar curves worn for 8 to 10 hours.
• Bracing continues until skeletal maturity (Risser 4 or 5, and 2 years after menarche, with growth under 1 cm in 6 months), then is weaned. It reduces progression to surgery in about 70% of patients who wear it as prescribed, against about 50% with observation alone.
• Check fit, skin, wear time (temperature sensor), and psychological well being. Exercises and sport are encouraged out of the brace.

Surgery (curves of 45 to 50 degrees or more in a growing child, or over 50 degrees at maturity, or rapidly progressive with unacceptable deformity).

• Posterior spinal instrumentation and fusion with pedicle screws and rods, with osteotomies and derotation, is the usual treatment and corrects about 60 to 80% of the curve. Selective fusion preserves motion segments. Fusion is from the upper to the lower instrumented vertebra, selected by the Lenke type.
• Anterior vertebral body tethering or growth modulating systems in skeletally immature patients with flexible thoracic curves of 35 to 60 degrees in selected centres (off label for some devices; risk of overcorrection, tether breakage and reoperation).
• Intraoperative spinal cord monitoring (motor and sensory evoked potentials) and a wake up test when needed.
• Complications of surgery: bleeding, infection (about 1 to 3%), neurological injury (about 0.3 to 0.5%), implant failure, pseudarthrosis, adding on, junctional kyphosis, and rarely vascular or visceral injury.

Operative antibiotic prophylaxis. Cefazolin 30 mg/kg to a maximum of 2 g intravenously (2 g in adolescents; 3 g when weight is 120 kg or over) within 60 minutes before incision, repeated every 4 hours or after blood loss over 1500 mL (or 25 mL/kg). With severe penicillin allergy, clindamycin 10 mg/kg (maximum 900 mg) intravenously or vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Intrawound vancomycin powder 1 g is used in some centres.

Tranexamic acid (spinal fusion). Tranexamic acid 50 mg/kg intravenously over 15 minutes before incision, followed by 5 mg/kg/hour until wound closure (maximum 100 mg/kg in total, or 4 g). Avoid with a history of thromboembolism, active intravascular clotting, seizures, or severe renal impairment (reduce the dose at creatinine clearance under 50 mL/min). Watch for seizures at high doses.

Analgesia (perioperative, multimodal).

• Paracetamol 15 mg/kg intravenously or orally every 6 hours (maximum 75 mg/kg daily and not exceeding 4 g daily; reduce with hepatic impairment or weight under 50 kg to 3 g daily).
• Morphine by patient controlled analgesia: bolus 10 to 20 micrograms/kg with a lockout of 5 to 10 minutes (maximum 0.3 mg/kg in 4 hours), usually for 24 to 72 hours. Then oral morphine 0.1 to 0.2 mg/kg every 4 hours as needed (maximum 10 mg a dose). Monitor sedation, respiratory rate and oxygen saturation.
• Prescribe a laxative and antiemetic. Avoid with severe respiratory disease without monitoring.
• Gabapentin 5 mg/kg orally (maximum 300 mg) at night, up to 5 to 10 mg/kg three times daily (maximum 900 mg three times daily; reduce at creatinine clearance under 60 mL/min) for up to 2 weeks, to reduce opioid need; monitor sedation and dizziness.
• Ibuprofen 10 mg/kg orally every 6 to 8 hours with food (maximum 40 mg/kg daily and not exceeding 2400 mg daily) is used after the first 24 to 48 hours in many centres. This is because of the lack of clear evidence that short courses impair fusion.
• Avoid with kidney impairment, dehydration or active bleeding, and omit when the surgeon has concerns about pseudarthrosis.

Monitoring. After bracing starts: review at 4 to 6 months with a standing radiograph in the brace and out of it. After surgery: wound and neurological check daily in hospital, review at 2 weeks, 6 weeks, 3 months, 6 months, 12 months and 24 months with standing radiographs. Pulmonary function in severe curves. Psychological well being and body image.

Referral and escalation. Refer any child with a scoliometer reading of 7 degrees or more, a Cobb angle of 20 degrees or more, or a progressive curve to a paediatric spinal service. Urgent referral for a rapidly progressive curve, a left thoracic curve, neurological signs, severe pain, or cardiopulmonary symptoms. Emergency referral for a new neurological deficit after surgery.

Special groups.

• Early onset or immature children: growth sparing techniques and casting; avoid early fusion.
• Boys: curves progress less often, and a larger share has an underlying cause (MRI).
• Adults with untreated curves over 50 degrees: monitor for progression, pain and pulmonary function; surgery for decompensation.
• Pregnancy and young women: scoliosis does not usually affect pregnancy; avoid radiographs where possible.