Ronald A Lehman1, Daniel G Kang2, Lawrence G Lenke3, Rachel E Gaume2, Haines Paik2. 1. Department of Orthopaedic Surgery and Rehabilitation, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA. Electronic address: armyspine@yahoo.com. 2. Department of Orthopaedic Surgery and Rehabilitation, Walter Reed National Military Medical Center, 8901 Wisconsin Ave., Bethesda, MD 20889, USA. 3. Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Ave, Campus Box 8233, St. Louis, MO 63110, USA.
Abstract
BACKGROUND CONTEXT: With the increasing popularity of thoracic pedicle screws, the freehand technique has been espoused to be safe and effective. However, there is currently no objective, definable landmark to assist with freehand insertion of pedicle screws in the thoracic spine. With our own increasing surgical experience, we have noted a reproducible and unique anatomic structure known as the ventral lamina. PURPOSE: We set out to define the morphologic relationship of the ventral lamina to the superior articular facet (SAF) and pedicle, and describe an optimal medial-lateral pedicle screw starting point in the thoracic spine. STUDY DESIGN: We conducted an in vitro fresh-frozen human cadaveric study. METHODS: One hundred fifteen thoracic spine vertebral levels were evaluated. After the vertebral body was removed, Kirschner 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 SAF to the boundaries of the pedicle. We calculated the morphologic relationship of the ventral lamina and the center of the pedicle (COP) to the SAF. RESULTS: Two hundred twenty-nine pedicles were measured, with one pedicle excluded because of fracture of the SAF during disarticulation. The ventral lamina was clearly identifiable at all levels, forming the roof of the spinal canal and confluent with the medial pedicle wall (MPW). The mean distance from the SAF midline to the MPW was 1.36±1.23 mm medial. The MPW was lateral to SAF midline in 34 pedicles (14.85%) and, on average, was a distance of 0.52±0.51 mm lateral. The mean distance from the SAF midline to the COP was 2.17±1.38 mm lateral. The COP was medial to SAF midline in only 11 pedicles (4.80%). CONCLUSIONS: The ventral lamina is an anatomically reproducible structure located consistently medial to the SAF midline (85%). We also found the COP consistently lateral to the SAF midline (95%). Based on these morphologic findings, the medial-lateral starting point for thoracic pedicle screws should be 2 to 3 mm lateral to the SAF midline (superior facet rule), allowing screw placement in the COP and avoiding penetration into the spinal canal. Published by Elsevier Inc.
BACKGROUND CONTEXT: With the increasing popularity of thoracic pedicle screws, the freehand technique has been espoused to be safe and effective. However, there is currently no objective, definable landmark to assist with freehand insertion of pedicle screws in the thoracic spine. With our own increasing surgical experience, we have noted a reproducible and unique anatomic structure known as the ventral lamina. PURPOSE: We set out to define the morphologic relationship of the ventral lamina to the superior articular facet (SAF) and pedicle, and describe an optimal medial-lateral pedicle screw starting point in the thoracic spine. STUDY DESIGN: We conducted an in vitro fresh-frozen human cadaveric study. METHODS: One hundred fifteen thoracic spine vertebral levels were evaluated. After the vertebral body was removed, Kirschner 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 SAF to the boundaries of the pedicle. We calculated the morphologic relationship of the ventral lamina and the center of the pedicle (COP) to the SAF. RESULTS: Two hundred twenty-nine pedicles were measured, with one pedicle excluded because of fracture of the SAF during disarticulation. The ventral lamina was clearly identifiable at all levels, forming the roof of the spinal canal and confluent with the medial pedicle wall (MPW). The mean distance from the SAF midline to the MPW was 1.36±1.23 mm medial. The MPW was lateral to SAF midline in 34 pedicles (14.85%) and, on average, was a distance of 0.52±0.51 mm lateral. The mean distance from the SAF midline to the COP was 2.17±1.38 mm lateral. The COP was medial to SAF midline in only 11 pedicles (4.80%). CONCLUSIONS: The ventral lamina is an anatomically reproducible structure located consistently medial to the SAF midline (85%). We also found the COP consistently lateral to the SAF midline (95%). Based on these morphologic findings, the medial-lateral starting point for thoracic pedicle screws should be 2 to 3 mm lateral to the SAF midline (superior facet rule), allowing screw placement in the COP and avoiding penetration into the spinal canal. Published by Elsevier Inc.
Entities:
Keywords:
Starting point; Superior articular facet; Superior facet rule; Thoracic pedicle screw; Ventral lamina
Authors: Rafael De la Garza Ramos; Murray Echt; Joshua A Benton; Yaroslav Gelfand; Michael Longo; Vijay Yanamadala; Reza Yassari Journal: J Korean Neurosurg Soc Date: 2020-11-01
Authors: Ulrich J Spiegl; Georg Osterhoff; Philipp Bula; Frank Hartmann; Max J Scheyerer; Klaus J Schnake; Bernhard W Ullrich Journal: Eur J Trauma Emerg Surg Date: 2020-12-02 Impact factor: 3.693