Morphological Parameters of the Thoracic Pedicle in an Asian Population: A Magnetic Resonance Imaging–Based Study of 3324 Pedicles

STUDY DESIGN: A cross-sectional magnetic resonance imaging (MRI)–based anatomical study. OBJECTIVES: Instrumentation of the thoracic spine may be challenging due to the unique pedicle morphology and the proximity of vital structures. As prior morphological studies have mostly been done in Caucasians, our study aims to determine the optimal pedicle screw size for transpedicular fixation in an Asian population. METHODS: A retrospective analysis of 400 patients who had undergone MRI of the thoracic spine was performed. A total of 3324 pedicles were included. Pedicle morphology was graded qualitatively based on the size of its cancellous channel, and quantitatively with the following parameters: pedicle transverse diameter, pedicle screw path length, and pedicle angle. Subgroup analysis based on gender was performed. RESULTS: Mean pedicle transverse diameter was the narrowest at the T4 (2.9 ± 1 mm) and T5 (3.1 ± 1.1 mm) level. The mean pedicle screw path length progressively increased from T1 (34 ± 4.6 mm) to T12 (47 ± 4.6 mm). The mean pedicle angle was the largest at T1 (34° ± 7.9°) and decreased caudally, to 9.4° ± 3.8° at the T12 level. Females had significantly lower mean pedicle diameter and screw path length than males at every vertebral level; however, they had a larger pedicle angle at T8 to T10. The most common size of the pedicle cancellous channel was more than 4 mm. CONCLUSION: Morphological differences in the Asian pedicle suggest that caution needs to be taken during thoracic spine instrumentation, particularly in Asian females who have significantly smaller pedicles. In such cases, the use of alternative techniques or intraoperative navigation may be useful.