Morphometric analysis of the thoracic pedicle: An anatomico-radiological study

Background: Knowledge of the morphometric anatomy of the pedicles in thoracic spine is essential for the surgeon attempting thoracic pedicle screw placement.
Aim: To study the morphometry of the pedicles in the thoracic spine in Indian subjects and note the anatomical landmarks required for safe and accurate pedicle screw placement.
Settings and Design: An anatomico-radiological study with cadaveric confirmation was conducted in a medical college and tertiary care center.
Materials and Methods: Morphometric anatomy of 720 pedicles from T1-T12 was studied. The study consisted of 15 separated thoracic vertebral cadavers and 15 computed tomographic scans of undiseased thoracic spine. Transverse and sagittal pedicle diameters, transverse pedicle angle, chord length and the pedicle entry point landmarks were studied. Using the results, accuracy of the pedicle screw placement was confirmed in 120 pedicles from five unseparated cadavers.
Results: Transverse pedicle diameter was narrowest at T4 and gradually increased craniocaudally. Twenty-two percent of the pedicles from T4 to T6 were less than 4.5 mm, but none were less than 3.5 mm. The transverse pedicle angle was widest at T1 (26.50) and decreased caudally to T12 (8.10). The chord length gradually increased caudally from a minimum of 30.4 mm at T1 to a maximum of 43.3 mm at T12. Landmarks (transverse and vertical distance) for the pedicle entry point were measured from the reference point taken as the center of the junction of lamina and the transverse process. The pedicle entry point was always superolateral to this reference point.
Conclusion: Knowledge of the pedicle diameter and chord length is essential for choosing the appropriate pedicle screw, whereas the pedicle angle and the entry point are important for accurate screw placement.

Keywords
Chord length, pedicle, pedicle angle, pedicle diameter, pedicle screw entry point, thoracic spine