http://upload.orthobullets.com/topic/2070/images/pedicle diameter illustration 3.jpg
http://upload.orthobullets.com/topic/2070/images/thoracic vert.jpg
http://upload.orthobullets.com/topic/2070/images/endplate area.jpg
http://upload.orthobullets.com/topic/2070/images/spinal canal diameter.jpg
http://upload.orthobullets.com/topic/2070/images/cervical facets.jpg
http://upload.orthobullets.com/topic/2070/images/rom.jpg
Alignment
Osteology
  • Vertebral prominens
    • the long prominent spinous process found at T1
  • Costal facets
    • articulation between ribs and vertebral segments
    • present on all vertebral bodies and transverse processes from T1 to T9
    • articulation with ribs leads to increased rigidity of thoracic spine (most rigid in axial skeleton)
  • Vertebral body size  
    • increases progressively from T1 to T12
  • Spinal canal dimensions  
    • varies from T1 to T12
Motion
  • The orientation of the facets (zygapophyseal) joints determines the degree and plane of motion at that level
    •  varies throughout the spine to meet physiologic function
    • cervical spine (C3-7)
      • planes
        • 0° coronal
        • 45° sagittal (angled superio-medially) 
      • function
        • allows flexion-extension, lateral flexion, rotation
    • thoracic spine
      • planes
        • 20° coronal
        • 55° sagittal (facets in coronal plane) 
        • 6 degrees of freedom  
      • function
        • allows some rotation, minimal flexion-extension (also limited by ribs)  
        • prevents downward flexion on heart and lungs  
    • lumbar spine
      • plane
        • 50° coronal
        • 90° sagittal (facets in sagittal plane)  
      • function
        • allows flexion-extension, minimal rotation
        • helps increase abdominal pressure 
Thoracic Pedicle Anatomy
  • Pedicle diameter
    • the pedicle wall is twice as thick medially as laterally
    • T4 has the narrowest pedicle diameter (on average)  
    • T7 can be irregular and have a narrow diameter on the concave side in AIS
    • T12 usually has larger pedicle diameter than L1
  • Pedicle length
    • pedicle length decreases from T1 to T4 and then increases again as you move distal in the thoracic spine
      • T1: 20mm
      • T4: 14mm (shortest pedicle)
      • T10: 20 mm
  • Pedicle angle
    • transverse pedicle angle  
      • varies from 10deg (mid thoracic spine) to 30deg (L5)
    • sagittal pedicle angle  
      • 15-17deg cephalad for majority of thoracic spine
      • neutral (0deg) for lumbar spine except L5 (caudal) 
Erector Spinae Muscles
  • Characteristics  
    • functions to extend the trunk
    • located dorsal to vertebral column
    • innervated by dorsal rami of spinal nerves
  • Erector spinae muscles include
    • spinalis
      • most medial
      • origin and insertion: spinous process to spinous process
    • longissimus
      • intermediate 
      • origin and insertion: transverse process to transverse process
    • iliocostalis
      • most lateral
      • origin: ilium and ribs 
      • insertion: ribs and transverse process
Surgical Approaches
  • Surgical approaches for thoracic disc herniation  
    • laminectomy/hemilaminectomy
    • transpedicular
    • costotransversectomy
    • lateral extracavitary
    • anterior intracavitary
      • thoracotomy
      • VATS (video assisted thoracoscopic surgery)
 

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Questions (1)

(OBQ08.190) In the adult spine, which of the following pedicles have the smallest average transverse diameter. Review Topic

QID:576
1

T1

21%

(472/2234)

2

T6

66%

(1477/2234)

3

T12

10%

(229/2234)

4

L3

1%

(30/2234)

5

L5

1%

(22/2234)

Select Answer to see Preferred Response

PREFERRED RESPONSE 2

Of the levels listed, T6 has the smallest pedicle diameter.

Knowledge of pedicle diameter is important when placing pedicle screws. On average, thoracic pedicle diameter is maximal at T1 and T12, and gradually "dips" to its smallest diameter at the T4 to T6 region.

Scoles et al. performed an anatomic study of 50 normal adult vertebral columns ranging in age from 20 to 40 years at the time of death. They found the average pedicle diameter was smallest at T6 and largest at L5.

Ofiram et al. is an anatomic study of 100 patients comparing the pedicle isthmic width from T10 to L1 using magnetic resonance imaging. In this area they found the smallest pedicle isthmic width was at L1, while T12 had the largest pedicle width in the thoracolumbar junction.

Illustration A shows the finding of pedicle diameter in the Scoles et al study, with the smallest diameter being at T6. Illustration B shows a composite average of multiple studies and depicts the average pedicle diameter from C1 to the sacrum. Notice the "dip" in thoracic diameter from T4 to T6. Notice and additional dip in the lumbar spine at L1, so the diameter of T12 is actually greater than that of L1.

Incorrect Answers:
Answer 1: T1 has the largest pedicle diameter in the upper cervicothoracic spine. It is an important fixation point in cervicothoracic fusions.
Answer 3: On average T12 has the largest diameter in the thoracolumbar region,.
Answer 4 & 5: Lumber pedicle diameter continues to increase in the caudal direction, making L5 the largest diameter in the lumbar spine.

ILLUSTRATIONS:

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