Thoracic Spine Anatomy Clinical Applications Michael S Chang

Thoracic Spine Anatomy: Clinical Applications Michael S. Chang, MD Clinical Faculty BGSMC Orthopaedic Residency Sonoran Spine Center Phoenix, Arizona February 16, 2013 CA# 11004 A 1

Disclosures Consultant Globus Integra Speaker’s Bureau Medtronic Depuy/Synthes Stryker CA# 11004 A 2

Acknowledgements CA# 11004 A 3

Thoracic Spinal Surgery • Surgery of the thoracic spine is generally for: – Deformity Correction • Scoliosis • Kyphosis – Decompression/Stabilization • Trauma • Tumor Resection • Herniated Disc CA# 11004 A 4

Instrumentation • Fixation options: – Pedicle screws – Hooks – Sublaminar wires CA# 11004 A 5

Thoracic Pedicle Screws • Advantages Strongest biomechanically • Greatest pullout strength • 84% stronger then hooks –Three column fixation • Segmental • Rotational –Does not encroach upon the canal – CA# 11004 A 6

Thoracic Pedicle Screws • Disadvantage –Limited direct visualization –Requires complete understanding of thoracic vertebra/pedicle anatomy CA# 11004 A 7

Insertion Techniques 1. Free hand 2. Stealth navigation 3. Fluoro assisted 4. K-wire guided CA# 11004 A 8

Why Freehand? • • Less radiation exposure Decreased operative times Uniquely provides tactile feedback With experience is proven to have very low complication rate CA# 11004 A 9

Step 1: Complete exposure 10 CA# 11004 A

Step 2: Entry Point • T 1 -3, 12 – Lateral edge of pars intersection with middle of TP • T 4, 5, 11 – Just medial to lateral edge of pars and inferior to proximal 1/3 of TP • T 7 -9 – Just lateral to middle of superior facet with superior edge of TP • T 6, 10 – Medial to lateral edge of pars with proximal 1/3 of TP CA# 11004 A 11

Step 2: Entry Point • T 1 -3, 12 – Lateral edge of pars intersection with middle of TP • T 4, 5, 11 – Just medial to lateral edge of pars and superior to proximal 1/3 of TP • T 7 -9 – Just lateral to middle of superior facet with superior edge of TP • T 6, 10 – Medial to lateral edge of pars with proximal 1/3 of TP CA# 11004 A 12

Anatomy • Pedicles – Height enlarges caudally • 9. 9 mm at T 1 • 15. 8 mm at T 12 – Width is limiting dimension • 3. 6 – 8. 7 mm • Narrowest between T 4 -T 6 • Wider at T 11, T 12 then L 1 Zindrick, Spine 2000 CA# 11004 A 13

Step 3: Probing Outward Gear Shift until the Base of the Pedicle Inward Gear Shift into the vertebral body After Base of The Pedicle CA# 11004 A 14

Anatomy • Coronal pedicle axis – Gradually decreases from T 1 – T 12 – Most angulated screw at T 1 • Pedicle Length – Increases caudally slightly • 16. 1 – 19. 1 mm Mc. Cormack, Neurosurgery 1995 CA# 11004 A 15

Step 4: Pedicle palpation 1. Palpate all 5 bony walls of the pedicle (cephalad, caudad, medial, lateral, and floor). 2. Mark the length of the tract and measure CA# 11004 A 16

Anatomy • Interpedicular distance – Decreases to T 4, then increases • Least amount of error tolerance for medial breach • Dura within 1 mm from medial wall Liljenqvist, SRS 2001 CA# 11004 A 17

Beware Concavity CA# 11004 A 18

Step 5: Tapping and Re-palpation 1. Tap 1 mm smaller than the proposed screw. 2. Use the sounder a second time to assess pedicle walls CA# 11004 A 19

Step 6 : Screw placement • Better purchase – Increased diameter • Plastic deformation – Increased screw length • 50 -80% body optimal CA# 11004 A 20

Step 7: Confirmation 1. 2. 3. 4. Intraoperative X-rays; Harmonious screw position Triggered EMG; Helpful, but no definite minimum EMG Laminotomy O-arm CA# 11004 A Raynor, Lenke, Spine 2002 21

Safety • • • No postoperative neurologic deficit No thoracic nerve root irritation No radicular chest wall complaints No screw revision No vascular or visceral injuries n=3204 TPS CA# 11004 A Lenke, Bridwell AAOS 2003/SRS 2002 22

Misplaced Screws CONTAINED (CT): inside the pedicle NONCONTAINED GRADE A (GA): <2 mm violation GRADE B (GB): 2 -4 mm violation GRADE C (GC): >4 mm violation CT GA GB CA# 11004 A GC GC GB 23

Early Experience 400 TPS • • No breach <2 mm breach 2 -4 mm breach >4 mm breach 58% 30% 9% (6% lat, 3% med) 3% (lat) CA# 11004 A 24

Late Experience 200 TPS • • No breach < 2 mm breach 2 -4 mm breach > 4 mm breach 91% 7% 2% (lat) 0% CA# 11004 A 25

Conclusion • Modern thoracic spine surgery relies heavily on pedicle screws • Rigorous understanding of anatomy is necessary in order to ensure low complication rates and excellent patient outcomes CA# 11004 A 26

Lenke 1 AN CA# 11004 A 33% Correction on Bending 27

Lenke 1 AN CA# 11004 A Intraop apical derotation 28

Screw Derotation CA# 11004 A Prior to rod placement 29

Concave Rod Placement CA# 11004 A 30

Pre-Derotation Post-Derotation CA# 11004 A 31

Lenke 1 AN PSF-T 4 -L 2 97% Correction CA# 11004 A 32

Preop Scoliometer 22º 5 Days Post Scoliometer 3º CA# 11004 A 8 Mo Post Scoliometer 4º 33

Thanks Michael S. Chang, MD CA# 11004 A 34