Analysis of the Vertebral Morphology in Idiopathic Scoliosis with MRI Using Multiplanar Reconstructions

Department for Orthopedic Surgery, Westfälische Wilhelms-Universität, Münster, Germany

PURPOSE: There is a paucity in the current literature concerning the vertebral morphology in idiopathic scoliosis.

METHODS: The morphology of the pedicles and the vertebral bodies as well as the distance between the pedicles and the dural sac (epidural space) were analyzed in twenty-six patients with idiopathic right-sided thoracic scoliosis with magnetic resonance imaging (MRI) using multiplanar reconstruction. In total, 307 vertebrae (614 pedicles) were investigated.

RESULTS: There was a distinct vertebral asymmetry at the apical region of the thoracic curves with significantly smaller pedicles on the concavity than on the convexity (p ‹ 0.05). The degree of intravertebral deformity diminished further from the apex with symmetrical vertebrae at the neutral level, again. The endosteal transverse pedicle width measured between 2.3 and 3.2 millimeters on the concavity of the thoracic apical region, and between 3.9 and 4.4 millimeters on the convexity (p ‹ 0.05). In the lumbar spine, the pedicle width measured between 4.6 millimeters at the upper and 7.9 millimeters at the lower lumbar spine. The chord length and the pedicle length increased from thirty-four and seventeen millimeters, respectively, at the fourth thoracic vertebra gradually to fifty-one and twenty-five millimeters, respectively, at the third lumbar vertebra. The transverse pedicle angle measured fourteen degrees in the upper thoracic spine and decreased to seven degrees at the twelfth thoracic vertebra and increased to sixteen degrees at the fourth lumbar vertebra, again. The width of the epidural space was less than 1 millimeter on the concavity of both the thoracic and lumbar apex whereas on the convexity the epidural width measured between three and five millimeters (p ‹ 0.05).

CONCLUSION: In idiopathic scoliosis there is a distinctive intravertebral deformity with smaller pedicles on the concavity and a shift of the dural sac towards the concavity. Pedicle screw instrumentation in the apical region on the concavity may be jeopardized by the small pedicle width and the limited epidural safe-zone in thoracic scoliosis. Scoliosis surgeons should be aware of these altered conditions when considering pedicle screw instrumentation in thoracic scoliosis.