The Ventral Lamina and Superior Facet Rule: The Key to Accurate Placement for Thoracic Pedicle Screws

Abstract

Methods 115 thoracic spine vertebral levels(n=230 pedicles) were evaluated. After the vertebral body was removed, K-wires were inserted retrograde along the four boundaries of the pedicle. Using digital calipers, we measured width of the SAF and pedicle at the isthmus, and from the borders of the superior articular facet(SAF) to the boundaries of the pedicle. We calculated the morphologic relationship of the VL and center of the pedicle, to the SAF. Results 229 pedicles were measured(1 excluded due to SAF fracture). The VL was identifiable in all specimens medial to midline SAF, forming the roof of the spinal canal, and confluent with the medial pedicle wall(MPW). The mean distance from SAF midline to the MPW was 1.34±1.25mm medial. The MPW was lateral to SAF midline in 34(14.85%) pedicles, with a mean distance of only 0.52±0.51mm lateral. The mean distance from SAF midline to center of the pedicle(COP) was 2.22±1.49mm lateral. The COP was medial to SAF midline in only 9(3.39%) pedicles. The mean distance from the SAF superior border to the COP was 13.15±2.47mm.