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Updated: Feb 15 2024

Adolescent Idiopathic Scoliosis

Images
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https://upload.orthobullets.com/topic/2053/images/ais standing.jpg
https://upload.orthobullets.com/topic/2053/images/ais forward bending.jpg
  • summary
    • Adolescent Idiopathic Scoliosis is a coronal plane spinal deformity which most commonly presents in adolescent girls from ages 10 to 18.
    • Diagnosis is made with full-length standing PA and lateral spine radiographs. 
    • Treatment can be observation, bracing, or surgical management depending on the skeletal maturity of the patient, magnitude of deformity, and curve progression.
  • Epidemiology
    • Incidence
      • most common type of scoliosis
        • incidence of 3% for curves between 10 to 20°
        • incidence of 0.3% for curves > 30°
    • Demographics
      • most commonly presents in children 10 to 18 yrs
      • 10:1 female to male ratio for curves > 30°
        • 1:1 male to female ratio for small curves
        • right thoracic curve most common
          • left thoracic curves are rare and indicate an MRI to rule out cyst or syrinx
  • Etiology
    • Pathophysiology
      • unknown
      • potential causes
        • multifactorial
        • hormonal (melatonin)
        • brain stem
        • proprioception disorder
        • platelet
        • calmodulin
        • abnormal development of neurocentral synchodrosis (NCS)
          • cartilaginous plate that forms between the centrum and posterior neural arches
          • closure occurs in characteristic order
            • cervical NCS by 5-6 years old
            • lumbar NCS by 11-12 years old
            • thoracic NCS by 14-17 years old
      • most have a positive family history
    • Curve Progression
      • risk factors for progression (at presentation)
        • curve magnitude
          • before skeletal maturity
            • > 25° before skeletal maturity will continue to progress
          • after skeletal maturity
            • > 50° thoracic curve will progress 1-2° / year
            • > 40° lumbar curve will progress 1-2° / year
        • remaining skeletal growth
          • younger age
            • < 12 years at presentation
          • Tanner stage (< 3 for females)
          • Risser Stage (0-1)
            • Risser 0 covers the first 2/3rd of the pubertal growth spurt
            • correlates with the greatest velocity of skeletal linear growth
          • peak growth velocity
            • is the best predictor of curve progression
              • in females it occurs just before menarche and before Risser 1 (girls usually reach skeletal maturity 1.5 yrs after menarche)
              • most closely correlates with the Tanner-Whitehouse III RUS method of skeletal maturity determination
            • if curve is >30° before peak height velocity there is a strong likelihood of the need for surgery
        • curve type
          • thoracic more likely to progress than lumber
          • double curves more likely to progress than single curves
  • Classification
    • King-Moe Classification
      • five part classification to describe thoracic curve patterns and help guide surgeons implanting Harrington instrumentation
      • link to King-Moe classification (not testable)
    • Lenke Classification
      • more comprehensive classification based on PA, lateral, and supine bending films
      • helps to decide upon which curves need to be included within the fusion construct
      • link to Lenke classification (not testable)
  • Presentation
    • School screening
      • patients often referred from school screening where a 7° curve on scoliometer during Adams forward bending test is considered abnormal
        • 7° correlates with 20° coronal plane curve
    • Physical exam
      • special tests
        • Adams forward bending test
          • axial plane deformity indicates structural curve
        • forward bending sitting test
          • can eliminate leg length inequality as cause of scoliosis
      • other important findings on physical exam
        • leg length inequality
        • midline skin defects (hairy patches, dimples, nevi)
          • signs of spinal dysraphism
        • shoulder height differences
        • truncal shift
        • rib rotational deformity (rib prominence)
        • waist asymmetry and pelvic tilt
        • cafe-au-lait spots (neurofibromatosis)
        • foot deformities (cavovarus)
          • can suggest neural axis abnormalities and warrant a MRI
        • asymmetric abdominal reflexes
          • perform MRI to rule out syringomyelia
  • Imaging
    • Radiographs
      • recommended views
        • standing PA and lateral
      • Cobb angle
        • > 10° defined as scoliosis
        • generated by drawing lines parallel to the vertebrae that are most tilted towards each other and then the angle created by those lines
        • intra-interobserver error of 3-5°
      • spinal balance
        • coronal balance is determined by alignment of C7 plumb line to central sacral vertical line
        • sagittal balance is based on C7 plumb from center of C7 to the posterior-superior corner of S1
      • stable zone
        • between lines drawn vertically from lumbosacral facet joints
      • stable vertebrae
        • most proximal vertebrae that is most closely bisected by central sacral vertical line
      • neutral vertebrae
        • rotationally neutral (spinous process equal distance to pedicles on PA xray)
      • end vertebrae
        • end vertebra is defined as the vertebra that is most tilted from the horizontal apical vertebra
      • apical vertebrae
        • the apical vertebraeis the disk or vertebra deviated farthest from the center of the vertebral column
      • clavicle angle
        • best predictor of postoperative shoulder balance
    • MRI
      • should extend from posterior fossa to conus
      • purpose is to rule out intraspinal anomalies
      • indications to obtain MRI
        • atypical curve pattern (left thoracic curve, short angular curve, apical kyphosis)
        • rapid progression
        • excessive kyphosis
        • structural abnormalities
        • neurologic symptoms or pain
        • foot deformities
        • asymmetric abdominal reflexes
        • a syrinx is associated with abnormal abdominal reflexes and a curve without significant rotation
  • Treatment
    • Based on skeletal maturity of patient, magnitude of deformity, and curve progression
    • Nonoperative
      • observation alone
        • indications
          • cobb angle < 25°
        • technique
          • obtain serial radiographs to monitor for progression
      • bracing
        • indication
          • cobb angle from 25° to 45°
          • only effective for flexible deformity in skeletally immature patient (Risser 0, 1, 2)
          • goal is to stop progression, not to correct deformity
        • outcomes
          • 50% reduction in need for surgery with compliant brace wear of at least 13 hours a day
          • poor prognosis with brace treatment associated with
            • poor in-brace correction
            • hypokyphosis (relative contraindication)
            • male
            • obese
            • noncompliant (effectiveness is dose-related)
          • the number needed to treat (NNT) is four in highly compliant patients 
          • Sanders staging system
            • predicts the risk of curve progression despite bracing to >50 degrees in Lenke type I and III curves
            • uses anteroposterior hand radiograph and curve magnitude to assess risk of progression despite bracing
    • Operative treatment
      • posterior spinal fusion
        • indications
          • cobb angle > 45°
          • can be used for all types of idiopathic scoliosis
          • remains gold standard for thoracic and double major curves (most cases)
      • anterior spinal fusion
        • indications
          • best for thoracolumbar and lumbar cases with a normal sagittal profile
      • anterior / posterior spinal fusion
        • indications
          • larges curves (> 75°) or stiff curves
          • young age (Risser grade 0, girls <10 yrs, boys < 13 yrs)
            • in order to prevent crankshaft phenomenon
  • Techniques
    • Bracing
      • recommended for 16-23 hours/day until skeletal maturity or surgical intervention deemed necessary (actual wear minimum 12 hours required to slow progression)
      • brace types
        • curves with apex above T7
          • Milwaukee brace (cervicothoracolumbosacral orthosis)
            • extends to neck for apex above T7
        • apex at T7 or below
          • TLSO
          • Boston-style brace (under arm)
          • Charleston Bending brace is a curved night brace
      • bracing success is defined as <5° curve progression
      • bracing failure is defined
        • 6° or more curve progression at orthotic discontinuation (skeletal maturity)
        • absolute progression to >45° either before or at skeletal maturity, or discontinuation in favor of surgery
      • skeletal maturity is defined as
        • Risser 4
        • <1cm change in height over 2 visits 6 months apart
        • 2 years postmenarchal
    • Posterior spinal fusion
      • fusion levels
        • goals
          • fusion should include enough levels to adequately maintain sagittal and coronal balance while being as minimal as safely possible to preserve motion
          • typical fusion from proximal end vertebra to one or two levels cephalad to the stable vertebra
          • double and triple major curves fuse to the distal end vertebra
        • Harrington technique
          • recommends one level above and two levels below the end vertebrae if these levels fall wilthin the stable zone
        • Moe technique
          • recommends fusion to the neutral vertebrae
        • Lenke technique
          • recommends including all major curves in the fusion and minor curves that are not flexible or are kyphotic
        • L5 level
          • Cochran found increase incidence of low back pain with fusion to L5, and to a lesser extent L4.
            • therefore, whenever possible, avoid fusion to L4 and L5
        • pelvis
          • it is almost never required to fuse to the pelvis in idiopathic scoliosis
      • pedicle screw fixation
        • screw insertional torque correlates with resistance to screw pullout
        • resistance to screw pullout increases by
          • undertapping by 1mm
      • curve correction
        • segmental pedicle screw fixation allows increased coronal plane correction while lessening the need for anterior releases
    • ASF with instrumentation
      • advantage
        • better correction while saving lumbar fusion levels
      • disadvantage
        • increased risk of pseudarthrosis when thoracic hyperkyphosis is present
      • fusion levels
        • typically fuse from end vertebra to end vertebra
    • Neurologic Monitoring
      • monitoring with somatosensory-evoked potentials (SSEPs) and/or motor-evoked potentials (MEPs) is now the standard of care
        • motor-evoked potentials can provide an intraoperative warning of impending spinal cord dysfunction
      • neurologic event defined as drop in amplitude of > 50%
      • if neurologic injury occurs intraoperatively consider
        • check for technical problems
        • check blood pressure and elevate if low
        • check hemoglobin and transfuse as necessary
        • lessen/reverse correction
        • administer Stagnaras wake up test
        • remove instrumentation if the spine is stable
  • Complications
    • Neurologic injury
      • paraplegia is 1:1000
      • increased risk with kyphosis, excessive correction, and sublaminar wires
    • Pseudoarthrosis (1-2%)
      • presents as late pain, deformity progression, and hardware failure
        • an asymptomatic pseudarthrosis with no pain and no loss of correction should be observed
    • Infection (1-2%)
      • presents as late pain
      • incision often looks clean
      • Propionibacterium acnes most common organism for delayed infection (requires 2 weeks for culture incubation)
      • attempt I&D with maintenance of hardware if not loose and within 6 months
    • Flat back syndrome
      • early fatigability and back pain due to loss of lumbar lordosis
      • rare now that segmental instrumentation addresses sagittal plane deformities
        • decreased incidence with rod contouring in the sagittal plane and compression/distraction techniques
      • treat with revision surgery utilizing posterior closing wedge osteotomies
        • anterior releases prior to osteotomies aid in maintenance of correction
    • Crankshaft phenomenon
      • rotational deformity of the spine created by continued anterior spinal growth in the setting of a posterior spinal fusion
        • can occur in very young patients when PSF is performed alone and the anterior column is allowed continued growth
        • avoided by performing anterior diskectomy and fusion with posterior fusion in very young patients
    • SMA syndrome (superior mesenteric artery [SMA] syndrome)
      • compression of 3rd part of duodenum due to narrowing of the space between SMA and aorta
      • SMA arises from anterior aspect of aorta at level of L1 vertebrae
      • presents with symptoms of bowel obstruction in first postoperative week
        • associated with electrolyte abnormalities
        • nausea, bilious vomiting, weight loss
      • risk factors
        • height percentile <50%; weight percentile < 25%
        • sagittal kyphosis
      • treat with NG tube and IV fluids
    • Hardware failure
      • late rod breakage can signify a pseudarthrosis
    • Emergency department visits
      • most often for minor medical complaints 
        • associated with older age at the time of surgery and more fusion levels
  • Prognosis
    • Natural history
      • increased incidence of acute and chronic pain in adults if left untreated
      • curves > 90° are associated with cardiopulmonary dysfunction, early death, pain, and decreased self image
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