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

      • open triradiate cartilage 

         

      • 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

    • 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