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 15° in the cephalad aspect of
the thoracic spine, decreased to 7° at the twelfth thoracic vertebra,
and increased again to 16° 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 scoliosis.