Thoracic Pedicles Morphometry in Vertebrae from Scoliotic Spines

Introduction: There exists a lot of controversy in the literature concerning the shape and size of thoracic pedicles in idiopathic scoliosis. In recent years, thoracic pedicle screws are being used more frequently in corrective spine surgery but few studies have evaluated the morphology of scoliotic thoracic pedicles.

Purpose: The objective of this study was to quantify the changes occurring in thoracic pedicles affected by a scoliotic deformity.

Material and Method: Thirty scoliotic specimens with curves presenting a various degree of severity were studied using a 3D digitizing protocol developed to create a precise 3D reconstruction of the vertebrae. Eighteen parameters analysing specifically the pedicles were then calculated for each vertebra from these reconstructions. Every scoliotic specimen was then matched with a normal specimen to provide for a representative control group. One-way and two-way ANOVA were calculated between parameters of scoliotic and normal vertebrae regarding pedicle width, length, height, surface and orientation.

Summary of Results: A total of 683 thoracic vertebrae were measured (325 scoliotic and 358 normal vertebrae). Pedicles located on the concavity of typical right thoracic curves were found to be significantly smaller than their normal counterparts with a maximal mean difference of 1.37 mm at T8. The pedicles on the concavity of the high thoracic compensatory curve were also found to be significantly diminished with a maximal mean difference of 1.68 mm at T4. Mean left pedicle width at T8 (concavity) and mean right pedicle width at T4 (concavity) were found to be 4.08 mm and 2.60 mm respectively. Pedicle length was found to be slightly increased and pedicle height was found to be slightly decreased in pedicles from scoliotic spines with no preference for concavity or convexity. Pedicle orientation and elevation were unchanged.

Conclusion: These results are of critical importance for clinicians performing spinal corrective surgery in patients with AIS. Pedicle width is significantly diminished on the concavity of scoliotic curves. Our results advocate caution in the use of pedicle screws in the thoracic spine, especially on the concave side of the curve.