Skoliosis

01Pathophysiology

Scoliosis is defined as a lateral curvature of the spine measuring 10 degrees or more on a standing radiograph, measured by the Cobb angle. It is not simply a side-bending deformity but a three-dimensional distortion involving lateral deviation, axial rotation, and alterations in the sagittal profile (kyphosis or lordosis changes). This rotational component is what produces the clinically visible rib hump on forward bending: as the thoracic vertebrae rotate, they carry the attached ribs posteriorly on the convex side and anteriorly on the concave side.

In adolescent idiopathic scoliosis, the exact mechanism remains poorly understood, but current evidence points to a multifactorial model involving genetic predisposition, abnormal neuroendocrine signaling (melatonin and calmodulin pathways), asymmetric growth of the vertebral endplates, and biomechanical feedback loops. Relative anterior spinal overgrowth compared to the posterior column is thought to create a rotational instability that worsens during the adolescent growth spurt. This is why skeletal immaturity is the strongest predictor of curve progression: the more growth remaining, the greater the risk the curve will worsen.

In congenital scoliosis, the pathology begins during embryogenesis (weeks 4 to 6 of gestation) with failure of vertebral formation (hemivertebra), failure of segmentation (unsegmented bar), or a combination. These structural anomalies create an inherent asymmetry in longitudinal growth. A fully segmented hemivertebra has the worst prognosis for progression because it retains two growth plates, whereas an unsegmented bar on one side with a contralateral hemivertebra is the most aggressive combination.

In neuromuscular scoliosis, the curve develops because of asymmetric muscular pull or loss of trunk muscle support. Conditions like cerebral palsy, spinal muscular atrophy, or Duchenne muscular dystrophy result in long C-shaped collapsing curves that typically involve the pelvis (pelvic obliquity). These curves progress even after skeletal maturity because the underlying muscle dysfunction persists.

In degenerative (adult or de novo) scoliosis, asymmetric disc degeneration and facet joint arthropathy in the lumbar spine lead to progressive lateral listhesis and rotational subluxation. Patients present in their 50s to 70s with back pain, radiculopathy, and neurogenic claudication. Curve magnitude tends to be smaller than idiopathic curves but is symptomatic because of associated spinal stenosis.

02Classification and Clinical Manifestation

Classification by Etiology

Lenke Classification (Adolescent Idiopathic Scoliosis, Surgical Planning)

Clinical Manifestation by Curve Location

03Diagnostic Workup

The diagnostic approach begins with the Adam's forward bend test, which is the standard clinical screening maneuver. The examiner stands behind the patient and asks them to bend forward at the waist with arms hanging freely and palms together. A visible rib hump or paraspinal prominence indicates vertebral rotation and raises suspicion for scoliosis. A scoliometer placed across the back quantifies the angle of trunk rotation; a reading of 7 degrees or more is the accepted threshold for radiographic referral.

The standing posteroanterior (PA) full-spine radiograph is the best initial diagnostic test and also serves as the confirmatory study. The PA projection (rather than AP) is deliberately chosen to reduce radiation exposure to the breast tissue and thyroid in adolescent females, who constitute the majority of patients. On this film, the Cobb angle is measured by drawing lines along the superior endplate of the most tilted vertebra above the curve apex and the inferior endplate of the most tilted vertebra below. The angle between these two lines (or their perpendiculars) defines the curve magnitude. A Cobb angle of 10 degrees or more with vertebral rotation establishes the diagnosis.

The Risser sign is assessed on the same iliac crest visible on the spinal radiograph. It grades the ossification of the iliac apophysis from lateral to medial. Risser 0 means no ossification has begun and the patient is pre-growth-spurt or in early growth spurt. Risser 4 to 5 indicates near-complete or complete skeletal maturity, meaning the curve is unlikely to progress significantly. This grading directly determines whether observation, bracing, or surgery is appropriate.

MRI is not routine for typical right thoracic adolescent idiopathic scoliosis. It is reserved for red flags: a left thoracic curve (which is atypical and associated with intraspinal pathology in up to 20% of cases), neurological findings on exam, onset before age 10, pain as the primary symptom, or rapid curve progression. The MRI must cover the entire spine from the craniocervical junction to the conus to rule out Chiari malformation, syringomyelia, or a tethered cord.

04Management and Treatment

Observation

For curves below 25 degrees in a growing patient, the standard approach is serial monitoring. Clinical examination and standing radiographs are obtained every 4 to 6 months during periods of rapid growth (Risser 0 to 2 or pre-menarchal females) and every 6 to 12 months as the patient approaches skeletal maturity. The goal of observation is to detect progression early enough to initiate bracing before the surgical threshold is reached. A curve is considered to have progressed if the Cobb angle increases by 5 degrees or more between two consecutive radiographs (accounting for a 3 to 5 degree measurement error inherent to the Cobb method).

Bracing

Bracing is the only non-operative treatment with strong evidence of efficacy in preventing curve progression. The landmark BrACT (Bracing in Adolescent Idiopathic Scoliosis Trial) study demonstrated that bracing significantly reduced the rate of curve progression to the surgical threshold compared to observation alone, with a success rate of 72% in braced patients versus 48% in observed patients.

The indications for bracing are a Cobb angle of 25 to 40 degrees in a skeletally immature patient (Risser 0 to 2). The prescribed orthosis is typically a thoracolumbosacral orthosis (TLSO), with the Boston brace being the most commonly used underarm design. The brace must be worn for a minimum of 16 hours per day, with evidence showing a dose-response relationship: wearing the brace for 18 hours or more per day yields the best outcomes. Bracing continues until the patient reaches skeletal maturity (Risser 4 to 5 or at least 2 years post-menarche in females).

Bracing is not indicated in the following scenarios: curves below 25 degrees (observation is sufficient), curves above 45 degrees (the deformity is too large for brace correction), skeletally mature patients (Risser 4 to 5, as there is no remaining growth to influence), and neuromuscular scoliosis (bracing does not address the underlying muscle pathology, though it may be used for sitting support).

Surgical Treatment

The primary surgical indication is a Cobb angle of 45 to 50 degrees or greater in an adolescent or a curve demonstrating relentless progression despite compliant bracing. The standard procedure is posterior spinal fusion with segmental pedicle screw instrumentation. The goals of surgery are to halt progression, achieve a balanced spine in the coronal and sagittal planes, and preserve as many motion segments as possible.

Key surgical principles include selecting fusion levels based on the Lenke classification, performing intraoperative neuromonitoring (somatosensory evoked potentials and motor evoked potentials) to reduce the risk of spinal cord injury, and correcting the curve to approximately 50% of its preoperative magnitude on average. Patients are typically mobilized on postoperative day 1 and do not require postoperative bracing in most cases.

For adult degenerative scoliosis, surgical management is reserved for patients with disabling pain, progressive neurological deficits, or significant functional impairment that has failed conservative therapy (physical therapy, analgesics, epidural injections). Surgery often involves a longer fusion construct with possible interbody fusion and osteotomies, carrying a higher complication rate than adolescent surgery.

Complications of scoliosis surgery to be aware of for testing purposes include: spinal cord injury (detected by intraoperative neuromonitoring changes, managed by a wake-up test or reversal of corrective maneuvers), surgical site infection (incidence 1 to 3%), pseudarthrosis (failure of fusion, presenting with late pain and hardware failure), proximal junctional kyphosis (excessive kyphosis above the fusion construct), and superior mesenteric artery syndrome (rare, postoperative duodenal compression presenting with bilious vomiting after correction of severe curves).

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common mistake students make with scoliosis questions is confusing who needs bracing versus who needs surgery versus who just needs observation. Test-writers exploit this by giving a vignette of a 12-year-old girl with a 30-degree curve and Risser 1, then listing observation, bracing, physical therapy, and surgery as answer choices. The correct answer is bracing, not observation (the curve has crossed 25 degrees in a skeletally immature patient) and not surgery (the curve has not reached 45 to 50 degrees). Physical therapy alone has no proven efficacy in halting curve progression and is a classic distractor.

A second high-yield trap involves the atypical curve pattern. When a vignette describes a left thoracic curve, an onset before age 10, neurological findings, or pain as the primary complaint, the question is testing whether you recognize the need for MRI of the entire spine before attributing the curve to an idiopathic etiology. Skipping the MRI and jumping to bracing or surgery is wrong in this setting.

Another tested concept is the Risser sign and its relationship to growth. Risser 0 does not mean the patient has already completed growth; it means the opposite. Misinterpreting the Risser grade leads to choosing observation when bracing is needed or vice versa.

Finally, be alert to the vignette that describes an adolescent presenting with bilious vomiting after scoliosis surgery. The answer being tested is superior mesenteric artery syndrome, a rare but classic postoperative complication where the duodenum is compressed between the aorta and the SMA after the spine is straightened. Treatment begins with nasogastric decompression, intravenous fluids, and nutritional support. This is a low-frequency but high-yield association that appears because it tests the ability to connect a surgical procedure to an unusual postoperative complication.

The core competency being tested across all scoliosis questions is the ability to risk-stratify patients using the Cobb angle and skeletal maturity and then match the correct intervention to the correct stage, while recognizing red flags that demand further workup before any treatment decision.