Anatomy of pedicles and pedicle screw placement

Question 1

Pedicle

Answer 1

• stub of bone connecting the lamina to the vertebra body
  
  • Cylindrical cortical bone with cancellous center
  • Anatomy defers in the different regions

Question 2

What are the anatomic pedicle land markes important to know for the Thoracic and Lumber Spine

Answer 2

1. Transverse pedicle angle
2. Sagittal pedicle angle
3. Transverse pedicle width isthmus
4. Sagittal pedicle width
5. Pedicle length

Question 3

Thoracic spine

Transverse pedicle angle

Answer 3

• Transverse pedicle angle
  
  • Decreases from T1 toT12
  • Largest angle is T1 – 27deg and narrowest T12 which is neg 4.2deg

Question 4

Thoracic spine

Sagittal pedicle angle

Answer 4

• Sagittal pedicle angle
  
  • Angled in a cephalic direction
  • T2 has the greatest angle –17.5deg
  • T12 has the shallowest angle -11.6deg

Question 5

Thoracic spine

Transverse pedicle width isthmus

Answer 5

• T1 has the widest – 7.9mm
• T4 has the narrowest -4.5mm

Question 6

Thoracic spine

Sagittal pedicle width

Answer 6

• T1 – narrowest 9.9mm
• T11 widest -17.4mm

Question 7

Thoracic spine

Pedicle length

Answer 7

• Through pedicle axis
  
  • Longest T8
  • Shortest T1-36.9mm
• Parallel to midline
  
  • Shortest distance- T1-26.7mm
  • Longest T12
  • Except T11/12 -No difference in distance to cortex through pedicle vs. Parallel

Question 8

Lumbar spine

Transverse pedicle angle

Answer 8

• Increases caudally -5deg per level
• Largest angle is L5 – 29.8deg
• Narrowest L1-10.9deg

Question 9

Lumbar spine

Sagittal pedicle angle

Answer 9

• Steep upper lumbar
• Cephalic to caudal direction L1-L5
• L1 - 2.4deg
• L5 - neg 0.8deg (caudal)

Question 10

Lumbar spine

Transverse pedicle width isthmus

Answer 10

• L5: Widest pedicle18mm
• L1: Narrowest -8.7mm
• Most below L1 are >8mm

Question 11

Lumbar spine

Sagittal pedicle width

Answer 11

 L5: Narrowest 14mm (9.5-19mm)

 L1: Widest 15.4mm

Question 12

Lumbar spine

Pedicle length

Answer 12

• Through pedicle axis
  
  • L2/L3- Longest 51.9mm
  • L4 Shortest
• Parallel to the midline axis
  
  • L2- Longest 45.5mm
  • L5-Shortest

Question 13

Placement – entry point

Thoracic spine

Answer 13

1. lower border of the superior articular facet
2. medial border of the transverse process
3. pars interarticularis

these land marks form a triangle, the center of which should be targeted for initial entry

Question 14

Placement – entry point

Lumbar spine

Answer 14

• midpoint of the transverse process used to identify midpoint of pedicle in superior-inferior dimension
• lateral border of pars used to identify midpoint in medial-lateral dimension