Posterior Spinal Fusion for Idiopathic Scoliosis



Posterior Spinal Fusion for Idiopathic Scoliosis


Peter O. Newton

Vidyadhar V. Upasani





ANATOMY



  • The spinal deformity is divided into three areas: proximal thoracic, main thoracic, and thoracolumbar/lumbar.


  • A proximal thoracic curve has an apex between T2 and T5. A main thoracic curve has and apex between T5 and T12 and a thoracolumbar/lumbar curve has an apex between T12 and L4.


  • Vertebral definitions (FIG 1)



    • The end vertebrae define the extent of each curve and are most tilted from horizontal in the coronal plane.


    • The stable vertebra is defined as the vertebra most closely bisected by the center sacral vertical line (CSVL).


    • The neutral vertebra is defined as the least rotated vertebra in the axial plane based on the radiographic symmetry of its pedicles.






FIG 1 • Vertebral definitions: The end vertebrae (EV) define the extent of each curve and are most tilted from horizontal in the coronal plane; the stable vertebra (SV) is defined as the vertebra most closely bisected by the CSVL; the neutral vertebra (NV) is defined as the least rotated vertebra in the axial plane based on the radiographic symmetry of its pedicles. (©SD PedsOrtho.)


PATHOGENESIS



  • Twin studies and observations of familial aggregation reveal significant genetic contributions to deformity progression.1,13


  • Increased calmodulin (which regulates the contractile properties of muscles and platelets) and decreased melatonin (a calmodulin antagonist) levels have been found in patients with progressive scoliosis.7,11


  • Differential growth rates in the anterior and posterior spinal column may cause imbalance in the sagittal plane with subsequent buckling of the vertebral column.5


NATURAL HISTORY



  • Risk factors for deformity progression include female gender, greater growth potential, thoracic curve location, and larger curve magnitude.6,15


  • Radiographic markers of skeletal maturity (state of the triradiate cartilage, Risser sign, carpal ossification, growth centers around the elbow) can be used to define a patient’s remaining growth potential.


  • After skeletal maturity, curves less than 30 degrees tend not to progress, whereas curves greater than 50 degrees tend to progress about 1 to 2 degrees per year.19,21


  • Thoracic lordosis and severe scoliosis (>80 degrees) result in restrictive lung disease and decreased pulmonary function.14,22


PATIENT HISTORY AND PHYSICAL FINDINGS



  • Document medical history, developmental milestones, growth history, and family history.


  • Observation should assess for asymmetries of the neck, shoulders, ribs, waist, and hips. Cutaneous lesions such as hairy patches or sinuses may suggest spinal dysraphism, whereas café-au-lait spots or axillary freckling may suggest neurofibromatosis.


  • Adams forward bend test is used to identify a unilateral prominence of the thoracic rib cage or lumbar paraspinal muscles due to axial rotation of the spine.


  • Coronal decompensation can be identified as lateral translation of the C7 spinous process in relation to the gluteal cleft.


  • Clinical assessment of maturity based on Tanner stage. Peak growth velocity occurs approximately 6 to 12 months prior to the onset of menses in girls and the onset of axillary and facial hair in boys.17


  • Assessment of functional capacity is performed by analyzing gait, stance, motor and sensory function, and reflexes.



  • Abdominal reflexes should be assessed to rule out intramedullary lesions. Unilateral absence of the reflex suggests the need for a spine magnetic resonance imaging (MRI).


  • Limb length discrepancy can result in apparent scoliosis.






FIG 2 • Posteroanterior (A) and lateral (B) radiographs demonstrating a typical right thoracic deformity with apical lordosis. (©SD PedsOrtho.)






FIG 3 • Posteroanterior (A) and lateral (B) EOS images with representative coronal (C) and sagittal (D) three-dimensional (3-D) reconstructions. (©SD PedsOrtho.)


IMAGING AND OTHER DIAGNOSTIC STUDIES



  • Full-length, upright posteroanterior (FIG 2A), and lateral (FIG 2B) spinal radiographs are adequate for routine assessment.


  • Three-dimensional reconstructions using advanced, low-radiation imaging technology can provide important insights into the true scoliotic deformity (FIG 3).4


  • Lateral bending radiographs are important for preoperative planning to determine curve flexibility but are not required otherwise.


  • Advanced imaging studies including computed tomography and MRI can be used to identify neurologic or congenital abnormalities.


DIFFERENTIAL DIAGNOSIS



  • Congenital scoliosis (failure of vertebral formation or segmentation)


  • Neuromuscular scoliosis (cerebral palsy, spinal muscular atrophy, Duchenne muscular dystrophy)


  • Syndromic scoliosis (osteochondrodystrophies, neurofibromatosis, Marfan syndrome)


NONOPERATIVE MANAGEMENT



  • Periodic observational monitoring is appropriate for skeletally immature patients with curves between 11 and 25 degrees. During periods of peak growth, more frequent evaluations (every 4 to 6 months) should be performed.


  • Skeletally immature patients (less than Risser 2) with documented curve progression to greater than 25 degrees or 30 degrees on initial presentation can be treated with a rigid thoracolumbosacral orthosis.2



  • Bracing has been shown to successfully decrease the progression of high-risk curves during the adolescent growth spurt. A dose-dependent relationship between hours of brace wear and success with bracing has been identified.16,20


  • A coordinated effort between the patient, the treating physician, and the orthotist is required to optimize success with bracing.


SURGICAL MANAGEMENT



  • Surgical goals are as follows:



    • Obtain three-dimensional and well-balanced deformity correction while fusing as few motion segments as possible.


    • Obtain a solid arthrodesis to prevent deformity progression.

Jul 24, 2016 | Posted by in ORTHOPEDIC | Comments Off on Posterior Spinal Fusion for Idiopathic Scoliosis

Full access? Get Clinical Tree

Get Clinical Tree app for offline access