Safety Entry Point, Size and Direction for Placement of
Thoracic Pedicle Screw - A Cadaveric Study
Torphong Bunmaprasert MD*,
Amornsak Roobsoong MD*, Suthipas Pongmanee MD*,
Songsak Khunsree MD*, Sikrai Laowatthanaphong MD**
Affiliation :
* Department of Orthopaedics, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
** Department of Anatomy, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
Background : Understanding of the pedicle anatomy is necessary for pedicle screw placement; however, there have been
few Thai studies reporting on thoracic pedicle morphometry.
Objective : To determine important anatomical measurements for thoracic pedicle screw fixation.
Material and Method: T1-T12 vertebral pedicles were evaluated in 27 cadavers. The diameter, angle, length and entry
point of the pedicle were measured.
Results : The transverse diameter was smaller than the sagittal diameter at all levels. The narrowest transverse diameter
was at the T5 level in males and T4 level in females. The pedicle diameter in males was statistically significantly greater
than in females at all levels except at the T12 level. Most pedicles with a transverse diameter of 5.0 mm or less were found
at the T4, T5, T6 and T7 levels. The transverse angle was widest at the T1 level; it faced medially at all levels. The sagittal
angle was widest at the T12 level and faced cephaladly at all levels. The axis length was shortest at the T1 level. Most entry
points were at the inferolateral zone.
Conclusion : A 4-mm diameter screw should be used carefully at the mid-thoracic levels for Thai people, especially females.
Screw lengths of less than 30 mm are safe for placement at all levels. The safe zone for the pedicle entry point is in the
inferolateral zone.
Keywords : Thoracic, Pedicular screw, Pedicle diameter, Cadaveric anatomical study
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