Paediatric, Scoliosis (Adolescent)

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Adolescent Scoliosis

• Scoliosis is defined as >10° abnormal lateral curvature of the spine in the coronal plane, often associated with axial rotation 1, 2
• Scoliosis can be classified as structural or non-structural (functional). Functional scoliosis can be postural or compensatory. It is non-progressive and correctable by ipsilateral bending 1, 3
• Structural scoliosis can be classified into 5 aetiological causes: idiopathic (80%), congenital (10%), or associated with neuromuscular, developmental and other miscellaneous diseases 3
• Idiopathic scoliosis is a diagnosis of exclusion and can be subdivided based on age of onset: infantile (from birth to 3 years – <1% of cases), juvenile (4 to 10 years - 12-21%) and adolescent (>10 years and before skeletal maturity - 2-4%) 1-6
• Adolescent idiopathic scoliosis has a prevalence of 0.5-3% and is the most common form of the disease. Females are predominantly affected (female : male ratio 5-10:1) and are more likely to have more progressive disease and severe curves 2, 4, 6
• Adam's test was 92% sensitive and 60% specific for detecting thoracic curves >20° and 73% sensitive and 68% specific for lumbar curves >20°, when compared with Cobb’s angle as the gold standard 7

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Plain Radiography

• The primary imaging modality for evaluating adolescent scoliosis should include a posteroanterior erect film of the entire spine and including the iliac crests 1, 2, 4, 5
• The PA view is standard as it reduces the radiation dose to thyroid and breast tissue despite delivering increased radiation absorption to bone marrow. Bone marrow is only one-sixth as sensitive to radiation as breast tissue 3
• Authors are also increasingly recommending a lateral film as part of the initial radiographic investigation 3, 4, 8
• The lateral view is necessary to determine the absence of apical segment lordosis of the thoracic spine (i.e. the presence of normal thoracic kyphosis or hyperkyphosis) which is considered an atypical curve pattern and found to be associated with increased incidence of neuroaxis abnormalities 4, 9, 10
• The scoliosis curve is described as “right” or “left” depending on their convexity and named by the location of the apex vertebrae
• The Cobb method is used to quantify the degree of scoliosis. A line parallel to the superior end plate of the most cephalic tilted vertebra and a line parallel to the inferior end plate of the most tilted caudal vertebra are drawn. Perpendicular lines to these are drawn and the Cobb angle is measured where the lines intersect 5, 11
• Factors which reduce the reproducibility include patient position, radiographic technique and diurnal variation (5%deg; reported in one study) 1, 3
• Hence, in the monitoring of scoliosis a 10° difference of the Cobb angle between radiographs taken at different times is necessary in order to be 95% confident that a true change in scoliosis has occurred 3
• The PA film compared to the AP view, reduces cumulative radiation dose to the thyroid gland and breast by 3 to 7 fold and would reduce the estimated risk of lifetime cancer by 3 to 4 fold 1, 6
• A retrospective cohort study of 5573 female patients with scoliosis diagnosed before the age of 20 has shown that scoliosis patients are exposed to an average of 25 radiographs per patient with a mean estimated cumulative radiation dose to the breast of 10.8 cGy. The relative risk of dying from breast cancer was 1.7 (95% CI = 1.2-2.1) after an average of 40 years follow-up (77 observed breast cancer deaths vs 45 expected deaths in this population) 1, 3, 6

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Preoperative Lateral Bending Views

• Passive lateral bending view in the frontal plane enables the surgeon to measure the degree of correction and determine the levels included in the operation 1, 3, 8
• A chest radiograph is required to exclude any associated cardiopulmonary abnormalities 3, 8

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Magnetic Resonance Imaging (MRI)

• MRI is the modality of choice for assessment of the spinal cord and paraspinal soft tissues in patients with scoliosis 5
• Spinal cord abnormalities are seen in 2-3% of patients with presumed adolescent idiopathic scoliosis 9, 12
• Abnormalities detected by MRI include tethered spinal cord, Chiari malformations, hydromyelia, syringomyelia, intramedullary tumours, diastamatomyelia and intra-spinal lipomas 13-15
• Commonly accepted indications for MRI include 4, 5, 14
  • Neurological findings including headache, neck pain, absence of abdominal reflex and asymmetric lower-extremity atrophy
  • A typical curve pattern: examples are thoracic levoscoliosis, short segment curve (less than six segments), decreased vertebral rotation, rapid progression, and kyphosis near the apex of curve. Other features on scoliosis radiographs requiring MRI may be an underlying tumour or infection, widening of an intervertebral foramen or thickening of the paraspinal line. 14 In one study, there was a 25% prevalence of neuroaxis abnormalities when both an atypical curve and neurological findings were present 9
  • Age of onset 3
• The presence of abnormalities on MRI in those without any of the above features is variable depending on the series. Some studies report a 2-3% prevalence of which none required prior neurosurgical intervention or had postoperative neurological complications. (12) Others have reported prevalence up to 8% of which 15% required a neurosurgical procedure 16
• In view of this, many neurosurgeons advocate preoperative MRI to exclude spinal cord abnormality (e.g. tethering of the cord) that requires surgical intervention prior-to or in conjunction with scoliosis correction 4, 13

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Computed Tomography (CT)

• Thin section CT is the most accurate confirmatory test if there is concern regarding spondylolysis. Spondylolysis at L5 is common in patients with adolescent idiopathic scoliosis so CT can be limited to the lumbo-sacral junction. Spondylolysis is important to identify since the surgeons may choose to include this area while extending posterior fusion to pelvis 14
• CT ’s superior ability to display bony anatomy as well as its multiplanar and 3D capabilities make it useful in characterising spinal segmentation anomalies which may accompany a structural scoliosis, particularly for preoperative planning 14

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