Analysis of vertebral morphology in idiopathic scoliosis with use of magnetic resonance imaging and multiplanar reconstruction

Background: Several studies have provided data on the vertebral morphology of normal spines, but there is a paucity of data on the vertebral morphology in patients with idiopathic scoliosis. Methods: The morphology of the pedicles and bodies of 307 vertebrae as well as the distance between the pedicles and the dural sac (the epidural space) in twenty-six patients with right-sided thoracic idiopathic scoliosis were analyzed with use of magnetic resonance imaging and multiplanar reconstruction. Results: A distinct vertebral asymmetry was found at the apical region of the thoracic curves, with significantly thinner pedicles on the concave side than on the convex side (p < 0.05). The degree of intravertebral deformity diminished farther away from the apex, with vertebral symmetry restored at the neutral level. In the thoracic spine, the transverse endosteal width of the apical pedicles measured between 2.3 mm and 3.2 mm on the concave side and between 3.9 mm and 4.4 mm on the convex side (p < 0.05). In the lumbar spine, the pedicle width measured between 4.6 mm at the cephalad part of the curve and 7.9 mm at the caudad part of the curve. The chord length and the pedicle length gradually increased from 34 mm and 18 mm, respectively, at the fourth thoracic vertebra to 51 mm and 25 mm, respectively, at the third lumbar vertebra. The transverse pedicle angle measured 150 in the cephalad aspect of the thoracic spine, decreased to 7degrees at the twelfth thoracic vertebra, and increased again to 16degrees at the fourth lumbar vertebra. The width of the epidural space was <1 mm at the thoracic apical vertebral levels and averaged 1 mm at the lumbar apical vertebral levels on the concave side, whereas it was between 3 mm and 5 mm on the convex side (p < 0.05). Conclusion: Idiopathic scoliosis is associated with distinctive intravertebral deformity, with smaller pedicles on the concave side and a shift of the dural sac toward the concavity. Clinical Relevance: Care must be exercised during pedicle-screw instrumentation, especially in the apical region of the concavity of thoracic curves, because of the small pedicle width and the limited epidural safe zone in this area. Surgeons should be aware of these altered conditions when considering pedicle-screw instrumentation for patients with thoracic scollosis.