Background : Spinal fusion with S1 dorsal screw placement has been used successfully in the management of lumbosacral instability. A detailed knowledge on the morphology of the first sacral vertebra is necessary in order to avoid fracture of pedicle cortex, injury of nerve root, facet joint and adjacent vital structures.
Objective : To determined the morphological parameters of the first sacral vertebra of Thais.
Design: Descriptive study based on numerical survey.
Setting: Bone Collection Unit, Department of Anatomy, faculty of Medicine, Chiangmai University, Thailand
Subjects: Human skeleton S1 pedicles from Thai skeletons, 59 males and 41 females between 35 and 87 years of age
Material and Methods: The cephalad-caudad height (H), anterior posterior width (W), XP distance, T angle and S angle of S1 pedicle were determined and record.
Result: Results show that the mean height, width and XP distance of S1 pedicle were significantly different between male and female (p< 0.05) The mean height of the pedicle were 25.2+2.0 mm. and 23.7+1.9 mm., the mean width were 25.1+2.5 mm. and 22.8+1.8 mm., and the mean XP distance were 50+3.6 mm. and 47.13+3.4 mm for male and female, respectively. However, there was no stastically significant difference in T angle and S angle between male and female. The mean T angle of male pedicle were 36.72+3.4o and female were 37.58+2.9o. The mean S angle were 16.45+4.5o in male and 16.9+5.1o in females.
Conclusion : The present study revealed that height, width and XP distance of S1 pedicles were statistically different between males and females, whereas T angle and S angle were not (different between two groups. Morphological parameters of the first sacral vertebra provide useful information for spinal fusion with S1 screw placement among male and female
Key words: S1 pedicle, lumbosacral instability, spinal fusion