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Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsAnatomy and TechniqueAnatomy and Technique
Frank La Marca M. D.Frank La Marca M. D.
Department of NeurosurgeryDepartment of Neurosurgery
University of MichiganUniversity of Michigan
Department of Neurosurgery, University of Michigan Medical School
Relevant AnatomyRelevant Anatomy
• a = chord lengtha = chord length• b = transverse diameterb = transverse diameter• c = angle of insertionc = angle of insertion• d = pedicle lengthd = pedicle length
Vaccaro et al. JBJS 77(8), 1995.Vaccaro et al. JBJS 77(8), 1995.
Department of Neurosurgery, University of Michigan Medical School
Basic TechniqueBasic Technique
•Starting pointStarting point– Vertical landmarksVertical landmarks– Horizontal landmarksHorizontal landmarks
•Medio-lateral Medio-lateral inclinationinclination•Cephalo-caudad Cephalo-caudad inclinationinclination•Pedicle widthPedicle width•Chord lengthChord length
Department of Neurosurgery, University of Michigan Medical School
Basic TechniqueBasic TechniqueHistoryHistory
•Starting pointStarting point– Mid-articular line Mid-articular line
(vertically)(vertically)– Bisection of transverse Bisection of transverse
process (horizontally)process (horizontally)
•Screw directed Screw directed perpendicular to plane of the perpendicular to plane of the posterior elementsposterior elements•Accuracy not documentedAccuracy not documented
Roy-Camille et al. Clin Orth. 203, 1986.Roy-Camille et al. Clin Orth. 203, 1986.
Department of Neurosurgery, University of Michigan Medical School
Basic TechniqueBasic TechniqueHistoryHistory
•Modified starting pointModified starting point– Mid-articular line Mid-articular line
(vertically)(vertically)– Superior border of Superior border of
transverse process at transverse process at juncture with the lamina juncture with the lamina (horizontally)(horizontally)
Xu et al, Spine. 24(2), 1999.Xu et al, Spine. 24(2), 1999.
Vaccaro et al. JBJS 77(8), 1995.Vaccaro et al. JBJS 77(8), 1995.
Department of Neurosurgery, University of Michigan Medical School
Pedicle MorphometryPedicle Morphometry
•Chord lengthChord length– T4 (39mm) T4 (39mm) – T12 (47mm)T12 (47mm)
•Transverse diameterTransverse diameter– T4 (4.5mm)T4 (4.5mm)– T12 (7.8mm)T12 (7.8mm)
Vaccaro et al. JBJS 77(8), 1995.Vaccaro et al. JBJS 77(8), 1995.
Department of Neurosurgery, University of Michigan Medical School
Pedicle MorphometryPedicle Morphometry
•Sagittal diameterSagittal diameter– T4(10mm)T4(10mm)– T12 (14.7mm)T12 (14.7mm)
•Angle of insertionAngle of insertion– T4 (14 degrees)T4 (14 degrees)– T12 (0.3 degrees)T12 (0.3 degrees)
Vaccaro et al. JBJS 77(8), 1995.Vaccaro et al. JBJS 77(8), 1995.
Department of Neurosurgery, University of Michigan Medical School
Pedicle MorphometryPedicle Morphometry
•Chord lengthChord length– Constant between Constant between
individuals and vertebral individuals and vertebral levelslevels
•Insertion angleInsertion angle– 15 degree angle increases 15 degree angle increases
chord length 1 cmchord length 1 cm
Krag et al. Spine 13(1), 1988.Krag et al. Spine 13(1), 1988.
Department of Neurosurgery, University of Michigan Medical School
Pedicle MorphometryPedicle MorphometryScoliosisScoliosis
• Prospective analysis of 337 Prospective analysis of 337 pedicles in 29 scoliotic ptspedicles in 29 scoliotic pts
•T4 to L4, all standard T4 to L4, all standard measurementsmeasurements
•Concave vs convex Concave vs convex – Endosteal width of concave Endosteal width of concave
pedicle is significantly pedicle is significantly smallersmaller
Liljenqvist et al. Spine. 25(10), 2000.Liljenqvist et al. Spine. 25(10), 2000.
Department of Neurosurgery, University of Michigan Medical School
Pedicle MorphometryPedicle Morphometry
• Medio-lateral Medio-lateral inclinationinclination
– Transpedicular Transpedicular techniquetechnique
– In-out-in techniqueIn-out-in technique
•Cephalo-caudad Cephalo-caudad inclinationinclination
Department of Neurosurgery, University of Michigan Medical School
Surrounding StructuresSurrounding Structures
•MedialMedial– Spinal cordSpinal cord
•LateralLateral– PleuraPleura
•Cephalo/caudadCephalo/caudad– Nerve rootNerve root
•AnteriorAnterior– Vascular/visceral structures Vascular/visceral structures
(5mm)(5mm)
Vaccaro et al. JBJS 77(8), 1995.Vaccaro et al. JBJS 77(8), 1995.
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsBasic Surgical StepsBasic Surgical Steps
1.1. Identify anatomic landmarksIdentify anatomic landmarks2.2. Access pedicle entry zone … sound Access pedicle entry zone … sound
pediclepedicle3.3. TapTap4.4. Screw placementScrew placement
upper thoracic – 4.5mmupper thoracic – 4.5mmmiddle thoracic – 4.5 to 5.5mmmiddle thoracic – 4.5 to 5.5mmlower thoracic – 5.5 to 6.5mmlower thoracic – 5.5 to 6.5mm
Department of Neurosurgery, University of Michigan Medical School
Lenke – 12-Step “Free Hand” Lenke – 12-Step “Free Hand” Technique of Thoracic Pedicle Technique of Thoracic Pedicle
Screw (TPS) PlacementScrew (TPS) Placement1.1. ExposureExposure2.2. Starting pointStarting point3.3. Cortical burrCortical burr4.4. Pedicle gearshift – lateralPedicle gearshift – lateral5.5. Pedicle gearshift – medialPedicle gearshift – medial6.6. Pedicle palpationPedicle palpation7.7. Pedicle length measurementPedicle length measurement8.8. Pedicle tappingPedicle tapping9.9. Repeat pedicle palpationRepeat pedicle palpation10.10. Screw placementScrew placement11.11. Intraoperative x-raysIntraoperative x-rays12.12. Screw EMG stimulationScrew EMG stimulation
Department of Neurosurgery, University of Michigan Medical School
Lenke – 12-Step “Free Hand” Lenke – 12-Step “Free Hand” Technique of Thoracic Pedicle Technique of Thoracic Pedicle
Screw (TPS) PlacementScrew (TPS) Placement1.1. ExposureExposure2.2. Starting pointStarting point3.3. Cortical burrCortical burr4.4. Pedicle gearshift – lateralPedicle gearshift – lateral5.5. Pedicle gearshift – medialPedicle gearshift – medial6.6. Pedicle palpationPedicle palpation7.7. Pedicle length measurementPedicle length measurement8.8. Pedicle tappingPedicle tapping9.9. Repeat pedicle palpationRepeat pedicle palpation10.10. Screw placementScrew placement11.11. Intraoperative x-raysIntraoperative x-rays12.12. Screw EMG stimulationScrew EMG stimulation
Department of Neurosurgery, University of Michigan Medical School
Lenke – 12-Step “Free Hand” Lenke – 12-Step “Free Hand” Technique of Thoracic Pedicle Technique of Thoracic Pedicle
Screw (TPS) PlacementScrew (TPS) Placement1.1. ExposureExposure2.2. Starting pointStarting point3.3. Cortical burrCortical burr4.4. Pedicle gearshift – lateralPedicle gearshift – lateral5.5. Pedicle gearshift – medialPedicle gearshift – medial6.6. Pedicle palpationPedicle palpation7.7. Pedicle length measurementPedicle length measurement8.8. Pedicle tappingPedicle tapping9.9. Repeat pedicle palpationRepeat pedicle palpation10.10. Screw placementScrew placement11.11. Intraoperative x-raysIntraoperative x-rays12.12. Screw EMG stimulationScrew EMG stimulation
Department of Neurosurgery, University of Michigan Medical School
Pedicle Screw EMG Pedicle Screw EMG StimulationStimulation
Screw levelScrew level Recording MuscleRecording Muscle
T6-T12T6-T12 Rectus abdominusRectus abdominus
L1-L2L1-L2 AdductorsAdductors
L3-L4L3-L4 QuadricepsQuadriceps
L5L5 Tibialis AnteriorTibialis Anterior
S1S1 GastrocnemiusGastrocnemius
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsAdvantagesAdvantages
•Biomechanically Biomechanically superior anchor pointsuperior anchor point•Can be performed safelyCan be performed safely•Enhance curve Enhance curve correctioncorrection•Save fusion levelsSave fusion levels•Address all curve typesAddress all curve types
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsDisadvantagesDisadvantages
•Significant learning Significant learning curvecurve•CostCost•Radiation exposure (not Radiation exposure (not with free hand with free hand technique)technique)•Neurologic riskNeurologic risk
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
•Accuracy = rate of fully Accuracy = rate of fully contained screwscontained screws•Accepted and well-Accepted and well-published for large published for large lumbar pedicleslumbar pedicles•Smaller thoracic Smaller thoracic pedicles may preclude pedicles may preclude full containmentfull containment
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
•In vivo studyIn vivo study•71 thoracic screws, T8-T1271 thoracic screws, T8-T12•26% incidence of medial 26% incidence of medial perforationperforation•6% with 4-8mm canal 6% with 4-8mm canal encroachmentencroachment•2 “minor” neurologic 2 “minor” neurologic injuriesinjuries•Hypothesized a 4mm “safe Hypothesized a 4mm “safe zone”zone”
Gertzbein et al. Spine. 15(1), 1990.Gertzbein et al. Spine. 15(1), 1990.
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
•Volumetric canal Volumetric canal intrusion of hooks vs intrusion of hooks vs screwsscrews•Medial perforation of Medial perforation of thoracic pedicle screwthoracic pedicle screw
– >>2mm c/w intrusion of 2mm c/w intrusion of smallest hooksmallest hook
– >>3mm c/w intrusion of 3mm c/w intrusion of largest hooklargest hook
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
•Acceptably positioned Acceptably positioned thoracic pedicle screwsthoracic pedicle screws
– Biomechanically stableBiomechanically stable
– Medial breech < 2-4mmMedial breech < 2-4mm
– Lateral breech < 6mm, Lateral breech < 6mm, violation of CV joint violation of CV joint toleratedtolerated
– No anterior breechNo anterior breech
– Acceptability more relevant Acceptability more relevant than accuracythan accuracy
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
•40 patients, 279 T-screws40 patients, 279 T-screws•Flouroscopic guidance, no Flouroscopic guidance, no laminotomieslaminotomies•Post-op CTPost-op CT•99% of screws were fully 99% of screws were fully contained or inserted with contained or inserted with acceptable medial/lateral acceptable medial/lateral wall breechwall breech•No neurologic deficitsNo neurologic deficits•2 screw revisions from 2 screw revisions from anterior perforationanterior perforation
Level N Out Medial Lateral Level N Out Medial Lateral T1-4 39 27(69%) 11% 89%T1-4 39 27(69%) 11% 89%T5-8 77 47(61%) 34% 66%T5-8 77 47(61%) 34% 66%T9-12 163 46(28%) 42% 58%T9-12 163 46(28%) 42% 58%
Belmont et al. Spine. 26(21) 2001.Belmont et al. Spine. 26(21) 2001.
Department of Neurosurgery, University of Michigan Medical School
Thoracic Pedicle ScrewsThoracic Pedicle ScrewsFundamental ConceptsFundamental Concepts
• 399 T-screws399 T-screws• Flouroscopic guidance, no laminotomiesFlouroscopic guidance, no laminotomies• Post-op CTPost-op CT• Acceptably positioned screwsAcceptably positioned screws
– 98% with coronal plane deformity (curve > 20 degrees)98% with coronal plane deformity (curve > 20 degrees)– 99% without coronal plane deformity99% without coronal plane deformity
• No neurologic deficitsNo neurologic deficits
Belmont et al. Spine. 27(14), 2002.Belmont et al. Spine. 27(14), 2002.
Department of Neurosurgery, University of Michigan Medical School
ConclusionConclusion
•Understanding of pedicle morphometry is essentialUnderstanding of pedicle morphometry is essential
•Free-hand technique safe and effectiveFree-hand technique safe and effective
•Acceptable vs accuracyAcceptable vs accuracy