The quantitative anatomy of the thoracic facet and the posterior projection of its inferior facet.

STUDY DESIGN: This study evaluated the dimensions of the thoracic facet from T1 to T12 and determined the posterior projection of the inferior facet using thoracic spine specimens.

OBJECTIVES: To evaluate quantitatively the thoracic facet and determine the projection of the inferior facet on the posterior aspect of the lamina relative to facet hook placement in the thoracic spine.

SUMMARY OF BACKGROUND DATA: Anatomic evaluation of the thoracic facet has not been extensively addressed. No detailed studies of the thoracic facet relative to posterior facet hook fixation exist.

METHODS: Forty-three thoracic spines from T1 to T12 were directly evaluated for this study. Anatomic evaluation of the thoracic superior and inferior facets included the facet width, height, and angulation relative to sagittal plane. The projection of the inferior facet on the posterior aspect of the lamina was constructed and measured.

RESULTS: In general, the male linear and angular parameters were larger than the female ones. The average transverse angle of the facets at T1-T12 for both men and women ranged approximately from 74 degrees to 88 degrees for the superior facet and 74 degrees to 108 degrees for the inferior facet. The average inferior thickness from T1 to T12 for both sexes ranged from 3 to 5 mm. The posterior projection height of the inferior facet was found to be 9 to 12 mm from T1 to T12 for both men and women. The distance between the posterior midline and the inferior facet projection ranged from 7 to 11 mm at T1-T12 for both sexes.

CONCLUSIONS: This study may aid in the understanding of the location, angulation, and dimensions of the facet and proper placement of hooks into the thoracic facet joint.