Open Techniques for Pedicle Screw Placement Know Your Anatomy
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Open Techniques for Pedicle Screw Placement Know Your Anatomy Alexander R. Vaccaro, MD, PhD, MBA Professor, Chairman Department of Orthopaedics and Neurosurgery Thomas Jefferson University President Rothman Institute Philadelphia, PA
Open Techniques for Pedicle Screw Placement Know Your Anatomy
Rothman Institute of Orthopaedics at Thomas Jefferson University
Understand Topical LandmarksUnderstand Pedicle anatomyUnderstand at risk StructuresUnderstand Different
Insertion methods
BASICS
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 craniocaudallandmark
– 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 cephalocaudadangulation
Presenter
Presentation Notes
Start point is along the lamina, direct palpation of the pedicle allows for placement of the M/L start point. Use fluoro to assist with angulation https://www.researchgate.net/profile/Michael_Kaiser9/publication/6699021/figure/fig14/AS:277903976747030@1443268879584/Fig-14-The-drawings-demonstrate-the-trajectories-required-for-appropriate-cervical.png Start point superior and medial to center of C2 lateral mass Laminotomy to palpate c2 pedicle – assists with M/L angulation – usually about 10 medial Use fluoro for cephalocaudad angulation – usually about 15 cephalad The cranial margin of the C2 lamina is the craniocaudal landmark for the screw insertion point for C2. To confirm the screw insertion points in C2, a small spatula can be inserted into the spinal canal along the cranial margin of the C2 lamina to the medial surface of the C2 pedicle. Figure 13-7 shows the pedicle screw insertion point for C2. The cranial margin of the C2 lamina (white broken line) is the landmark for the screw insertion point for C2 (asterisk). To confirm the screw insertion points in C2, a small spatula can be inserted into the spinal canal along the margin cortex of the C2 pars interarticularis to the medial surface of the C2 pedicle. The black broken arrow indicates the screw direction toward the C2 pedicle. https://www.researchgate.net/profile/Michael_Kaiser9/publication/6699021/figure/fig14/AS:277903976747030@1443268879584/Fig-14-The-drawings-demonstrate-the-trajectories-required-for-appropriate-cervical.png Approx 20% of patients will have anatomic variations of the path of the VA -use CTA when needed Check CT prior to ensure adequate path for 3.5mm screw According to previous studies by Panjabi and colleagues and by Karaikovic and colleagues, the pedicle of the cervical spine in a normal population has a sufficient diameter to allow insertion of a screw with a diameter of 3.5 mm or more Karaikovic and colleagues defined the inner morphology of the cervical pedicles. They revealed that the thinnest pedicle cortex was always the lateral cortex, and some pedicles had no medullary canal (i.e., where solid cortical bone is expected: 0.9% for C2, 2.8% for C3 and C4, and 3.8% for C5 pedicles).
Vertebral Artery Course in Upper Cervical Spine
Presenter
Presentation Notes
Its important to briefly talk about VA course In upper cspine – relevant aberracy can be ssen in 2 places – course of VA b/t C2-3 and traversing C1. C2 aberrancy is more common Lee spine 2014 – C2 groups found in 18% of population. C is a medialized VA, and 2 is a high riding subtype
Vertebral Artery Course in Upper Cervical Spine
FIA
Fenestrated
Presenter
Presentation Notes
If C2 anomalies weren’t enough, heres something further to keep you awake at night… Uchino neuroradiology 2012 – persistent first intersegmental artery 3.2%, VA fenestration in 0.9%, PICA C1/2 origin 1.1%
While we rarely even consider this technique, its worth mentioning. Entry point – notch level in the sagittal plane, medial to the lateral border of SAP approx 1/4th of its width. Medial wall is thicker. Use up/down motion as you advance probe, stay aimed medial to avoid VA. Curved tip used initially, then probe, then straight tip awl to widen tract Park et al, spine 2015 – 256 screws, 94% accuracy, no complete VA occlusions, no VA stenosis related symptoms – accuracy based on postop CT
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 notchapproximately at the level of the pedicle
Presenter
Presentation Notes
The screw insertion points for the C3 to C7 pedicles are slightly lateral to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. The lateral margin of the articular mass of the cervical spine has a notch approximately at the level of the pedicle. The pedicles are located approximately below the lateral vertebral notch at C2, at the notch at C3 through C6, and at or slightly above the notch at C7. The screw insertion points for the C3 to C7 pedicles are slightly laterally to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. Craniocaudal orientation of the screw insertion point can be confirmed by a lateral image intensifier. By making the funnel-shaped hole bigger and deeper with a curette or high-speed burr, the surgeon can see the medial cortex of the posterior portion of the pedicle and the pedicle cavity directly in most cases. This funnel-shaped resection of the outer portion of the articular mass toward the entrance of the pedicle cavity allows more freedom and potential angulation for positioning the screw The intended angle of screw insertion in the sagittal plane is parallel to the upper end plate for the pedicles of C5 to C7, and it is slightly in the cephalad direction for C2 to C4 The length of the screw is usually 20 to 24 mm for C3 to C7. A screw length of 24 mm or more is sometimes required to penetrate the anterior cortex of the vertebral body to increase the C2 screw stability.
C7 Pedicle Screw-Use preop imaging to determinemedial angulation-If difficulty finding pedicle, use a funnel technique
• Where is it going?
1 2
3 4
Presenter
Presentation Notes
Use preop imaging and intraoperative palpation of pedicle to help determine angle Pictured above is a laminotomy – avoid facet overresection https://www.jkns.or.kr/journal/view.php?number=158 http://www.ijoonline.com/articles/2015/49/3/images/IndianJOrthop_2015_49_3_272_156186_f7.jpg
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
IAPSAP
Presenter
Presentation Notes
Sup Fac rule – start 2mm lateral to mid TP. This means you have to expose the whole superior facet! Also vent lam rule to help guide traj watanabe/lenke MAST 2006 – thoracic pedicle types – lg cancellous channel 42%, sm canc channel 44%, cortical channel, but still channel possible 10%, absent channel 4%
Thoracic Pedicle Screws
• Where is the pedicle?– Cephalocaudal
Thoracic Pedicle Screws
• Where is it going?T1
T12
Thoracic Pedicle Screws
• Where is it going?– Anatomic (AT) versus Straightforward (SF)
SF
AT
AT
Presenter
Presentation Notes
SF with 39% incr in MIT vs ANA, 27% incr in pullout strength c/w ANA. Lehman spine 2003 Should use multiaxial for anatomic path, can use fixed vs multiaxial for Straight forward
Thoracic Pedicle Screw
• What is in my way?
Presenter
Presentation Notes
The TP can block appropriate medialization, causing lateral breeches Fix this problem by rongeuring the TP in the way of the pedicle tract
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
Presenter
Presentation Notes
Kuklo lehman spine 2003, 1mm undertap vs LTL – 93% increased in MIT (1.37 vs 2.61 in-lbs, 0.5 vs 1mm undertap 47% incr in MIT (1.22 vs 1.79) OD and OD/ID ratio important for pullout strength, bending strength depends on ID. Skinner spine 1990 SF with 39% incr in MIT vs ANA, 27% incr in pullout strength c/w ANA. Lehman spine 2003. 75% of pullout strength achieved with engagement of NC junction, max strength about 80% of way to ant cortex Kang jpo2014 immature calf skeletons – 747N vs 922N for nonhubbed
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
Presenter
Presentation Notes
Cross links can improve torsional control. Kuklo imast 2007. Improved after PSO 2CL (35%), 1CL (20%), more important with ant column destruction (PSO, VCR) look up free hand vs power Barber JSDT 1998 – 30deg convergence increased pullout 28.6% (Lspine) polly spine 1998 – insertional torque decreased 34% by replacing screw, incr diameter 2mm increased insert torque ~8.4%
Thoracolumbar Pedicle Screws
• Where is the pedicle?– Transitional surface
anatomy– Use a funnel technique
through the base of the SAP• Place screws in a location to
facilitate rod placement crossing the TL spine
T12
L1
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
Presenter
Presentation Notes
MLP-Mid lateral Pars
Lumbar Pedicle Screws
• Where is it going?L1
L5
Lumbar Pedicle Screws• Where is it going?
– Remember the sagittal trajectory intraoperatively!
Pedicle SizesT1-L4 Pedicles size height > width
-use pedicle width to size these pedicle screws
L5 Pedicle size width > height-still large enough to accommodate most screws
Sacral
• Where is the “pedicle”
Presenter
Presentation Notes
Start point is downslope of S1 SAP
Sacral Pedicle Screw• Where is it going?
– Approx 35-40 deg medial
• What is in the way?– Prominent iliac wing/PSIS
Presenter
Presentation Notes
If you need to dissect over the PSIS or resect the PSIS anyways for an iliac screw, do this before placing S1 screw or else you may end up laterally breeching screw
Sacral Pedicle Screw
• Bicortical versus Promontory/Tricortical– Sacral promontory screw improved maximum
insertional torque by 99% versus bicortical screw
Presenter
Presentation Notes
Lehman spine 2002
T/L Fluoroscopic Pedicle Screw
• Initial Imaging-Commonly 4cm from midline-Can be longer or shorter depending on body habitus
How to Traverse the PedicleStarting 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
![Surgical Outcomes and Complications of Pedicle Screw ... · Cervical pedicle screw fixation is superior to other techniques . in terms of promoting mechanical strength [9,12].The](https://img.dokumen.tips/doc/110x75/5f2d8a662433d87bd01b81be/surgical-outcomes-and-complications-of-pedicle-screw-cervical-pedicle-screw.jpg)
![CT Assessment of accuracy of lumbar pedicle screw insertion · pedicle screw insertion is crucial for the efficacy and outcome of the procedure [4]. Potential complications of screw](https://img.dokumen.tips/doc/110x75/5e7f205077def362b9478726/ct-assessment-of-accuracy-of-lumbar-pedicle-screw-insertion-pedicle-screw-insertion.jpg)
