Open Techniques for Pedicle Screw Placem ent Know Your Anatom y Alexander R. Vaccaro, MD, PhD, MBA Professor, Chairman Department of Orthopaedics and Neurosurgery Thomas Jefferson University President Rothman Institute Philadelphia, PA
Disclosure Grant Support/ Royalties/ Stock options/ Consulting/ Editorial Board: Depuy, Nuvasive, Medronics, Stryker, Globus, Stout Medical, Aesculap, Alphatec, Paradigm Spine, Replication Medica, Spinology, Bonovo Spine, Dimension Orthotics, Gamma Spine, IT, SBI, RI related holdings, Gerson Lehrman, Guidepoint Global, Medacorp, ISD, ASIP, PST, ICOM, Orthobullets, Vertiflex, Vexim, SpineWave, Atlas Spine, Avaz Surgical, AO Spine, Spine, ESJ, JNS, PSI Board Member: CSRS Editor in Chief : Clinical Spine Surgery President: Rothman Institute Rothman Institute of Orthopaedics at Thomas Jefferson University
“Every pedicle screw can be worth ten million dollars…”
BASICS Understand Topical Landmarks Understand Pedicle anatomy Understand at risk Structures Understand Different Insertion methods Rothman Institute of Orthopaedics at Thomas Jefferson University
Basic Technique for Screw Placement • Expose start point and relevant anatomy • Burr/rongeur outer cortex • Cannulate tract – drill/curette/probe/etc. • Check for breaches with ball-tip probe • Tap? • Check again for breaches • Place screw
C2 Pedicle Screw Where is the pedicle? • – The cranial margin of the C2 lamina is the craniocaudal landmark – A nerve hook can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the C2 pedicle Where is it going? • – Preop imaging and intraop pedicle palpation help determine medial angulation (Black Arrow) – Fluoro for cephalocaudad angulation
Vertebral Artery Course in Upper Cervical Spine
Vertebral Artery Course in Upper Cervical Spine FIA Fenestrated
Preop Imaging
Subaxial Cervical Pedicle Screws
C7 Pedicle Screw • Where is the pedicle? – Slightly lateral to the center of the articular mass – Close to the inferior margin of the inferior articular process of the cranially adjacent vertebra – Use laminotomy to find pedicle – The lateral margin of the articular mass of the cervical spine can have a notch approximately at the level of the pedicle
C7 Pedicle Screw -Use preop imaging to determine medial angulation • Where is it going? -If difficulty finding pedicle, use a funnel technique 1 2 3 4
Thoracic Pedicle Screws • Where is the pedicle? – Medial-Lateral – Can use Superior Facet Rule – Removal of IAP aids with identifying SAP, avoid at upper instrumented vertebra to avoid destabilization IAP SAP
Thoracic Pedicle Screws • Where is the pedicle? – Cephalocaudal
Thoracic Pedicle Screws T1 • Where is it going? T12
Thoracic Pedicle Screws • Where is it going? – Anatomic (AT) versus Straightforward (SF) AT SF AT
Thoracic Pedicle Screw • What is in my way?
Pearls for Improved Fixation • Undertapping – 1mm undertapping increases POS by 93% • OD and ratio of OD/ID – Larger screws with larger ratios increase POS – ID affects bending strength • Length of screw – ~75% of max POS achieved with engagement of neurocentric junction – Max POS with ~80% of way to anterior cortex
Pearls for Improved Fixation • Screw convergence – 30 degrees of convergence increased pullout 28.6% in the lumbar spine • Try not to remove/replace screw – Insertional torque decreased 34% by removing and replacing same size screw • Avoid hubbing – Decrease in POS by 43% with hubbing of screw
Thoracolumbar Pedicle Screws T12 • Where is the pedicle? – Transitional surface anatomy – Use a funnel technique through the base of the SAP • Place screws in a location to L1 facilitate rod placement crossing the TL spine
Lumbar Pedicle Screws • Where is the pedicle? – Midpoint TP – Upslope of facet versus mamillary process versus 1-3mm lateral to MLP – “Inside-out” when needed • Palpate pedicle directly through decompression
Lumbar Pedicle Screws L1 • Where is it going? L5
Lumbar Pedicle Screws • Where is it going? – Remember the sagittal trajectory intraoperatively!
Pedicle Sizes L5 Pedicle size width > height T1-L4 Pedicles size height > -still large enough to width accommodate most screws -use pedicle width to size these pedicle screws
Sacral • Where is the “pedicle”
Sacral Pedicle Screw • Where is it going? – Approx 35-40 deg medial • What is in the way? – Prominent iliac wing/PSIS
Sacral Pedicle Screw • Bicortical versus Promontory/Tricortical – Sacral promontory screw improved maximum insertional torque by 99% versus bicortical screw
T/L Fluoroscopic Pedicle Screw -Commonly 4cm from midline -Can be longer or shorter • Initial Imaging depending on body habitus
How to Traverse the Pedicle Starting point - Left pedicles start at approximately 10 to 11 o’clock at lateral border of pedicle - Right pedicles start at approximately 2 to 3 o’clock at lateral border of pedicle -Ensure level appropriate medial angulation and proper sagittal trajectory Traversing the Pedicle -After advancing the wire approximately 15mm , check AP and lateral imaging -When the guidewire is at the medial border of the pedicle on the AP , the guidewire should be AT or BEYOND the neurocentric junction on the lateral view
T/L Fluoroscopic Pedicle Screw • Technique Start Point Tapping Traversing the Pedicle Screw
Thank You
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