Thoracic pedicle screws

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


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.


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


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.


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.



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)




•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)




•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.


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.



• Medio-lateral Medio-lateral inclinationinclination

– Transpedicular Transpedicular techniquetechnique

– In-out-in techniqueIn-out-in technique

•Cephalo-caudad Cephalo-caudad inclinationinclination


Surrounding StructuresSurrounding Structures

•MedialMedial– Spinal cordSpinal cord

•LateralLateral– PleuraPleura

•Cephalo/caudadCephalo/caudad– Nerve rootNerve root

•AnteriorAnterior– Vascular/visceral structures Vascular/visceral structures

(5mm)(5mm)



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


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


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


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


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


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



•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.



•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



•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



•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.



• 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.


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

Thoracic pedicle screws

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