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- Draw cross hair on lateral mass; superomedial quadrant
- Direction - 20 deg divergent , along facet joint
- Alternative: Cervical spine lateral mass vs transpedicle screw
- Thoracic spine = lateral border of SAP and mid transverse process line (Same as lumbar spine)
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- Starting point = Lateral border of SAP and mid transverse process line
- Direction = parallel to end plates
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- We balance safety with vertebral artery, using lateral mass from C1-C6. C7 can use pedicle screw
- Pedicle screws sustain a significantly higher axial load to failure than lateral mass screws
- https://journals.lww.com/spinejournal/Abstract/1997/05010/Cervical_Pedicle_Screws_Versus_Lateral_Mass.9.aspx#:~:text=The results of this study,the likelihood of hardware loosening.
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- Identify entry point
- Decorticate entry site with bur
- Place gearshift probe into pedicle until resistance at anterior cortex - introduced with concave facing outwards, before rotating it to turn inwards
- Ball tip probe (sound) to check floor, medial, inferior walls of pedicle
- Tap (if required)
- Insert screws
- Triggered EMG to test screws to ensure no pedicle wall breach
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- “in-out-in” technique
- In the thoracic spine, the “in-out-in” technique, where screws are intentionally placed more laterally to decrease the risk of medial breach and potentially increase bony rib purchase, is often also utilized.
- The “in-out-in” technique can also be used in situations where patients have congenitally small thoracic pedicles.
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- Any Breach - medial, lateral, inferior, anterior
- Lateral view - screws should pass midline
- BUT Not more than 2/3 from posterior because the vertebrae is round)
- AP view - Screws should not pass midline
- Screw should pass medial wall but not midline
- Screws should not pass lateral wall
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- Larger screw diameter
- Cement augmentation
- Expandable screws
- Screw thread design - variable pitch (maximise purchase in pedicle), dual thread screws show greater pull our strength
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- Trajectory - cortical bone trajectory which is divergent and oblique rather than convergent
- Bicortical purchase
- Avoid re-insertions
- Load sharing with anterior column support
- Supplementary fixation with laminar wires and hooks; cross linking
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- Optimise osteoporosis, start teriparatide 4-6 weeks before surgery and continue post op for 10 weeks
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- Bone Morphogenic Protein - BMP
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- It is an osteoinductive growth factors that stimulate bone growth
- Commonly use BMP 2 and 7, currently mainly used in tibia fractures
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- Early complications
- Seroma formation so keep the drain for longer period; avoid in cervical spine surgeries
- Can cause radiculitis –inflammation around nerve roots. (Jacob Oh likes to mention retrograde ejaculation if irritate the hypogastric nerve in ALIF)
- Late complications
- Can cause ectopic bone formation ➔ cause compression
- Can lead to osteolysis
- Risk of malignancy, avoid in patients with risk of Ca
- Contraindicated in patients in skeletal immature
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- Laminotomy = Partial hemilaminectomy
- Can be unilateral or bilateral
- Hemilaminectomy = removal of one side lamina
- Laminectomy = removal of entire lamina and spinous process
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- 50%
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- Screws - nerve root injury (ensure do under II, Neuromonitoring), injury to large vessels
- Interbody cage - displacement, cage subsidence, cage back out, nerve root injury
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- 6.5/ 7mm screws
- Length about 45mm
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- PEEK = PolyEtherEtherKetone
- Titanium cages also available.
- Meta-analysis shows that both similar rate of fusion but increased rate of subsidence with titanium cage
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- Controversial and evidence is based on retrospective studies with low levels of evidence; do not allow to draw clear conclusion
- However, in my instution, we regularly put vancomycin powder
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- Need to drill cement and tap cement prior to screw insertion
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- Screw augmentation
- Vertebroplasties
- Void fillers in spinal mets
Fixation Technique Buzzwords
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- “I will use 3 column fixation with the 4th generation technique of pedicle screws to achieve a stable spine”
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- 1st - harrington rods
- 2nd - sublaminar wires
- 3rd - segmental hooks
- 4th - monoaxial and polyaxial pedical screws
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Dural Leak
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- Ask for help
- Principle is to expose to ensure adequate visualization
- Optimize visualisation
- Head down to reduce CSF pressure
- Anesthesia to reduce BP
- Remove more lamina to improve visualization
- Repair options
- Direct suture repair with 6/0 ethilon
- Sealant glue
- Augmented closure with fat, muscle tissue of fascial graft (if hole not opposable)
- Post op
- RIB, head up
- Drain is controversial, can increase infection. Consider if big leak, and need to monitor leak post op.
- Warn patient about headache
- monitor wound as CSF has lytic enzymes which may lead to poor wound healing
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- Clinically - headache
- Drain findings - High persistent clear output, Glucose stick
- Double halo sign on filter paper
- Special tests - beta-2 transferrin assay