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Scoliosis (plural: scolioses) is defined as an abnormal lateral curvature of the spine. It is quite common in young individuals and is often idiopathic and asymptomatic. In some cases, however, it is the result of underlying structural or neurological abnormalities.
Early onset scoliosis refers to scoliosis with a onset <10 years regardless of cause 8.
Scoliosis imaging has extensive terminology that should be used precisely to avoid confusion 1.
By definition, scoliosis is any lateral spinal curvature with a Cobb angle >10°. Asymptomatic lateral curvature of the spine that is stable, with a Cobb angle ≤10° is known as spinal asymmetry 2.
Each curve of a scoliosis can be described in terms of the direction of convexity as
levoscoliosis: curvature towards the left
dextroscoliosis: curvature towards the right
The most pronounced curve is usually the one at which the main structural abnormality is present and thus in most patients the terms primary curve, major curve and structural curve are interchangeable 1. Secondary curves, minor curves and non-structural curves usually all refer to the less pronounced compensatory curves that develop above and/or below the primary curve to maintain balance 1.
The apex is the vertebral body or disc space which demonstrates the greatest rotation and/or furthest deviation from the expected center of the vertebral column 1. The endplates of the apical vertebra are often horizontal or near horizontal.
The end vertebrae are present on either side of the apex and are the vertebrae that are most tilted towards each other 1,4. They form the basis of the Cobb angle.
Neutral vertebrae are present on either side of the apex and are the vertebrae that demonstrate no rotation (axial plane). In some cases, they will be the same as the end vertebrae although usually, they will be few segments more distal to the apex. They are never closer to the apex than the end vertebrae 1.
The stable vertebra is the first vertebra below the lowest curve which is roughly bisected by the central sacral vertical line (CSVL).
In most instances, scoliosis is obvious if severe. On examination, the Adams forward bend test (a clinical test for assessing scoliosis) may be positive where a rib hump forms on the side of the convexity.
The majority (80%) of scolioses have no apparent underlying cause and are termed idiopathic 1. Idiopathic scoliosis can be broken down into infantile, juvenile and adolescent based on the age of the patient.
The remaining 20% of scolioses are the result of other causes. There are many ways to potentially group these causes, but a simple three-pronged grouping strategy is:
neuromuscular: conditions that cause neurological or muscular deficits that result in asymmetric muscular tone resulting in spinal curvature
congenital bony: an underlying bony abnormality of the vertebra that results in a relatively fixed spinal curve
tumor or treatment: this is a bit of a catch-all for the remainder of causes, most of which relate to an adjacent tumor, or previous treatment, e.g. radiotherapy or cardiac surgery
pars interarticularis defect (spondylolysis): ~5% in idiopathic scoliosis 9
Assessment and monitoring of scoliosis is primarily achieved with long-spine plain films. CT and MRI have roles to play in assessing for underlying abnormalities as well as, in certain situations, preoperative planning.
Scoliosis imaging will vary depending on patient and treatment particulars but will generally include a long (full spine) PA with or without lateral projections. Additionally, lateral bending films can be obtained to help determine structural vs non-structural curves 1.
Examination of spinal films should be systematic, and the following features should be assessed and commented upon 1:
presence of structural osseous abnormalities
major and minor curves
Structural osseous abnormalities
Sagittal and coronal balance
Lateral flexion views
Lateral flexion views, often with a bolster, are designed to determine how fixed a curve is. If a curve cannot be straightened to below a Cobb angle of 25° it is considered structural, otherwise, it is a non-structural compensatory minor curve 1.
Note: In some centers, scoliosis radiographs are displayed laterally (left to right) flipped to all other imaging to replicate what the clinician views when standing behind the patient who is facing away. Care must be taken to examine side markers.
Treatment and prognosis
Management depends on the magnitude of the curve(s), their rate of progression and (in a child) whether they are still growing. In general, treatment can be broken down into three main groups:
bracing (moderate and still growing)
surgical intervention (severe: over 50 degrees) 6
History and etymology
The Cobb angle was first described in 1948 by American orthopedic surgeon John R Cobb (1903-1967) 7.