Instruments and implants approved by the AO Foundation
USS Variable Axis Screw (VAS)System. For posterior fixation of thelumbar spine.
Technique Guide
Introduction
Surgical Technique
Product Information
Table of Contents
USS Variable Axis Screw (VAS) System 2
AO Principles 4
Indications 5
Prepare Pedicles 6
Insert Screws 7
Insert Rods 8
Place Collars and Nuts 9
Apply Distraction or Compression 10
Tighten Nuts 11
Optional Techniques 14
Instruments 16
Set List 21
Synthes Spine
USS Variable Axis Screw (VAS) System
Designed to restore lordosis– Variable axis head offers ±25° of angulation for minimal rod contouring
– Precontoured rods designed to mimicspinal curvature
– Permits sagittal and lateral screw off-set and reduces the need to contourthe rod precisely
– Technique permits posterior compression
Provides stable internal fixation – Dual core screw design creates rigid fixation by engagement of cortical threads within the pedicleand cancellous threads inside the vertebral body
– Rounded, blunt screw tip design allows bicortical fixation
2 Synthes Spine USS Variable Axis Screw (VAS) System
Provides optimal environment– Variable axis head offers ±25° of angulation to provide optimal rodplacement and simplify construct assembly
Uses atraumatic technique– Preassembled head reduces operativetime and minimizes trauma to patient
– Double-lead thread increases speedof screw insertion for 5.2 mm,6.2 mm, and 7.0 mm screws
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AO Principles
In 1958, the AO formulated four basic principles, which have become the guidelines for internal fixation.1 They are:– Anatomical reduction
– Stable internal fixation
– Preservation of blood supply
– Early, active mobilization
The fundamental aims of fracture treatment in the limbs andfusion of the spine are the same. A specific goal in the spineis returning as much function as possible to the injured neural elements.2
AO Principles as Applied to the Spine3
Anatomic alignmentRestoration of normal spinal alignment to improve the biomechanics of the spine.
Stable internal fixationStabilization of the spinal segment to promote bony fusion.
Preservation of blood supplyCreation of an optimal environment for fusion.
Early, active mobilizationMinimization of damage to the spinal vasculature, dura, andneural elements, which may contribute to pain reduction andimproved function for the patient.
4 Synthes Spine USS Variable Axis Screw (VAS) System
1. M.E. Müller, M. Allgöwer, R. Schneider, and H. Willenegger: Manual ofInternal Fixation, 3rd Edition. Berlin; Springer-Verlag. 1991.
2. Ibid.3. M. Aebi, J.S. Thalgott, and J.K. Webb. AO ASIF Principles in Spine
Surgery. Berlin; Springer-Verlag. 1998.
Indications
The Synthes USS VAS variable axis components consist ofnon cervical spinal fixation devices intended for use as a posterior pedicle screw fixation system (T1–S2) or as an anterolateral fixation system (T8–L5). Pedicle screw fixation is limited to skeletally mature patients, with the exception ofthe Small Stature USS.
These devices are indicated as an adjunct to fusion for all ofthe following indications regardless of the intended use:– Degenerative disc disease (defined as discogenic back painwith degeneration of the disc confirmed by history and radiographic studies)
– Spondylolisthesis
– Trauma (i.e., fracture or dislocation)
– Deformities or curvatures (i.e., scoliosis, kyphosis, and/orlordosis, Scheuermann’s disease)
– Tumor
– Stenosis
– Failed previous fusion (pseudoarthrosis)
When treating patients with degenerative disc disease (DDD),transverse bars are not cleared for use as part of a posteriorpedicle screw construct.
When used with the 3.5 mm/6.0 mm parallel connectors,the USS VAS variable axis components can be linked to theCerviFix system. In addition, when used with 5.0 mm/6.0 mm parallel connectors, the Synthes Small Stature USS canbe linked to the USS VAS variable axis components.
In addition, USS VAS variable axis components can be inter-changed with all USS 6.0 mm rods and transconnectors.
Please refer to product insert (GP0001) for complete systemdescription, indications, contraindications and warnings.
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Prepare Pedicles
1Prepare pedicles
Instruments
388.532 Pedicle Reamer
388.539 Pedicle Probe, for 7.0 mm, 8.0 mm and 9.0 mm screws
or388.54 Probe
388.55 Awlor388.552 Awl, for 8.0 mm and 9.0 mm screws
Locate pedicles as described in AO ASIF Principles in SpineSurgery.4 Use the awl to open the cortex of the pedicles to adepth of 10 mm. Continue opening the pedicles using theprobe with markings at 30 mm, 40 mm, and 50 mm. Deter-mine the required lengths of the USS variable axis screws.
Note: For 8.0 mm or 9.0 mm screws, use the awl for 8.0 mmand 9.0 mm screws and the pedicle probe for 7.0 mm–9.0 mm screws.
To ensure mobility of the polyaxial screwhead, insert the tipof the pedicle reamer into the prepared pedicle. Use rotatingmovement to remove excess bone. Repeat this procedure foreach pedicle.
6 Synthes Spine USS Variable Axis Screw (VAS) System
4. Ibid.
Insert Screws
2Insert screws
Instruments
314.132 3.0 mm Hexagonal Screwdriver with T-Handle
388.38 Holding Sleeve, for Screwdriver
388.61 Hook or Screw Holderor388.621 Handle for Hook or Screw Holder
Alternative Instruments
313.892 3.0 mm Hexagonal Screwdriver Shaft
388.652 Ratchet T-Handle, 6 mm hex coupling
Insert screws using the 3.0 mm hexagonal screwdriver withT-handle and holding sleeve or the ratchet T-handle, 3.0 mmhexagonal screwdriver shaft and holding sleeve.
Remove the selected self-tapping variable axis screw fromthe screw rack. Insert the screw into the prepared pediclesuntil the screwheads are well seated. Turn the T-handle counterclockwise one-half turn in order to ensure that thescrewhead is fully flexible. Align the side opening on thescrewhead to one side to receive the rod. Repeat for eachscrew.
Note: Before inserting the rod, make sure each of the screwheads is mobile.
To facilitate collar and nut placement, use the hook or screwholder. Insert one hook or screw holder into each screwheadand tighten in order to guide the collar and nut in Step 4.
Alternatively, use the handle for hook and screw holder toinsert the hook and screw holder.
Note: The knob on the handle can be turned to tighten orloosen the screw on the hook or screw holder, or it can bepressed down to release the hook or screw holder from thehandle.
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Insert Rods
3Insert rods
Instruments
388.44 Rod Holding Forceps, for 6.0 mm rods
388.902 Coated Rod Template for 6.0 mm rod, 150 mm
388.961 Rod Bender, with bend radius adjustment
Determine the correct rod contour and length using thecoated rod template. The polyaxial mobility of the screwhead aids in compensation for a lateral screw offset. Select the appropriate length 6.0 mm titanium rod and, if necessary, bend the rods using the rod bender.
8 Synthes Spine USS Variable Axis Screw (VAS) System
Insert the rods into the side-opening polyaxial screwheadsusing the rod holding forceps.
Place Collars and Nuts
4Place collars and nuts
Instrument
388.15 Socket Wrench with straight handle
Load a collar and a nut directly onto a loading post in the tray.Align the socket wrench with straight handle directly over theloading post and press down until the nut and collar are secured in the wrench. Place the loaded wrench over the hookor screw holder and onto the screwhead. Hand-tighten nuts to hold the rod, while allowing some movement for final adjustments.
Note: For constructs with more than two screws on eachside, start with the medial screwhead.
Repeat for all remaining screws. Although the rods are nowsecured in the side opening, the screwheads remain mobile.
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Apply Distraction or Compression
5Apply distraction or compression (optional)
Instruments
388.410 Distraction Forceps, curved
388.422 Compression Forceps
Distraction or compression with variable axis screws is possible only before the nuts have been tightened.
To distract, use the distraction forceps and then tighten thenuts as described in Step 6.
To achieve compression, use the compression forceps andthen tighten the nuts as described in Step 6.
10 Synthes Spine USS Variable Axis Screw (VAS) System
Tighten Nuts
Synthes Spine 11
6Tighten nuts
Instruments
388.13 Socket Wrench with L-Handle
388.261 10 Nm Torque Wrench
388.263 Internal Counter Torque
Alternative Instruments
388.14 Socket Wrench with straight handle
388.61 Hook or Screw Holder
Each nut can be tightened using the socket wrench with L-handle. Either the internal counter torque or the socketwrench with straight handle and a hook or screw holder canbe used for countertorque.
Tightening method using the internal counter torqueInsert the internal counter torque into the socket wrench withL-handle. Hold the internal counter torque stationary andturn the socket wrench with L-handle to secure the nut. This reduces the torque on the bone while tightening the nut.
Tighten Nuts continued
6Tighten nuts continued
Tightening method using socket wrench with straighthandle for countertorquePlace the socket wrench with L-handle over the hook or screwholder and insert the socket wrench with straight handle.Hold the socket wrench with straight handle stationary andturn the socket wrench with L-handle to secure the nut. This reduces the torque on the bone while tightening the nut.
Note: Any distraction or compression maneuvers must be completed before tightening.
12 Synthes Spine USS Variable Axis Screw (VAS) System
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The 10 Nm torque wrench must be used for the finalconstruct tighteningBefore final tightening, check that the rod is properly positioned in the USS VAS screw. Place the 10 Nm torquewrench over the nut. Insert the internal counter torque intothe 10 Nm torque wrench. Hold the internal counter torquestationary while turning the 10 Nm torque wrench. Thewrench will “click” at the preset torque of 10 Nm.
Optional Techniques
Adding transconnectors
Instruments
388.31 Long Small Hexagonal Screwdriver
388.865 Measuring Template, for Low ProfileTransconnectors
The low profile transconnector is designed to be used as aconstruct stabilizer to reduce rotation.
Use the measuring template for low profile transconnectorsto measure the distance between the two rods.
Choose a transconnector of the appropriate length. With thetransconnector setscrews loosened, apply it to the rods. Usethe long small hexagonal screwdriver to secure the trans con -nector to the rods by tightening the setscrews on each end.
Note: For transconnectors with stargrind, tighten the stargrind setscrew to lock the angle between the rods.
When using an adjustable length transconnector, adjust thedistance between the rods, if desired, by compressing or distracting; then tighten the center setscrew on the rotatingshaft using the long small hexagonal screwdriver.
Note: If any part of the construct requires further adjust-ment, all transconnector setscrews must be loosened. Afterfinal adjustment, retighten the setscrews.
14 Synthes Spine USS Variable Axis Screw (VAS) System
Remobilization
Instrument
388.357 Locking Ring Extractor
Remove the nut, collar, and rod from the construct. Prior toremobilization using the locking ring extractor, loosen thepusher by turning the T-handle counterclockwise to themarked thread and move the tube back.
Slide the slotted part of the extractor over the cam of thescrewhead’s locking ring and push the tube down.
Slowly turn the T-handle clockwise until resistance is encountered.
Continue turning until the screwhead is remobilized.
Caution: Further turning of the T-handle will cause removalof the locking ring from the construct. If the locking ring isremoved, the variable axis screw must be removed and replaced.
Synthes Spine 15
Instruments
Taps for Dual Core Screws311.602 5.2 mm311.603 6.2 mm311.604 7.0 mm311.605 8.0 mm311.606 9.0 mm
Cannulated Taps for Dual Core Screws311.612 5.2 mm 311.613 6.2 mm311.614 7.0 mm311.615 8.0 mm311.616 9.0 mm
388.274 Universal Spinal System Tap Handle
Taps for dual core screws penetrate the pedicle prior to screw insertion. They preparea pathway with the same pitch as the screwand smaller cancellous core diameter.
388.532 Pedicle Reamer
Removes excess bone around the pedicle toenable rotation of USS Variable Axis ScrewHead.
388.539 Pedicle Probe, for 7.0 mm, 8.0 mm and9.0 mm screws
Used to open the pedicle canal and determinethe proper screw length.
388.54 Probe
388.545 Straight Ball Tip Probe
Used to palpate the walls of the pedicle andto determine proper screw length using thedepth markings at 25 mm, 30 mm, 40 mm,50 mm, 60 mm, and 70 mm.
16 Synthes Spine USS Variable Axis Screw (VAS) System
For pedicle preparation
388.546 Curved Ball Tip Probe
388.55 Awl
Used to perforate the posterior cortex of the pedicle.
388.552 Awl, for 8.0 mm and 9.0 mm screws
313.892 3.0 mm Hexagonal Screwdriver Shaft
314.132 3.0 mm Hexagonal Screwdriver with T-Handle
388.38 Holding Sleeve, for Screwdriver, for side-opening implants
388.652 Ratchet T-Handle, 6 mm hex coupling
Synthes Spine 17
For screw insertion
Instruments continued
388.44 Rod Holding Forceps, for 6.0 mm rods
Used to place the rod into the Variable AxisScrew. Ratchet-locking mechanism ensures aconsistent and stable grip on the 6.0 mm rod.Quick release permits one-handed applicationfor easy maneuvering and rod placement.
388.902 Coated Rod Template for 6.0 mm rods,150 mm
Used to determine the length and contour of the rod.
388.94 Rod Pusher, for 6.0 mm rods
Assists rod placement into the side-openingimplants.
388.961 Rod Bender, with bend radius adjustment
Used to contour the rod. Knob is used to adjust the bend radius.
388.13 Socket Wrench with L-Handle, 11 mm widthacross flats
Used to tighten the nut once it has beenloaded onto the implant.
388.14 Socket Wrench with straight handle, 6 mmwidth across flats
Used with Hook or Screw Holder (388.61) forcountertorque during tightening.
18 Synthes Spine USS Variable Axis Screw (VAS) System
For rod preparation and insertion
For construct assembly
388.261 10 Nm Torque Wrench, 11 mm width across flats
Important: For final tightening of the construct, this wrench must be used to apply the proper amount of torque.
388.262 Counter Torque Sleeve
This instrument is used in conjunction withthe Hook or Screw Holder to reduce torqueon the bone while tightening the nut.
388.263 Internal Counter Torque
Used with the 11 mm Hex Socket Wrench to reduce the torque on the bone while tightening the nut.
388.31 Long Small Hexagonal Screwdriver
Used to secure transconnector to the rods.
388.61 Hook or Screw Holder
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388.15 Socket Wrench with straight handle, 11 mmwidth across flats
Used to load the collar and nut directly ontothe implant and secure them to the rod. Theinstrument retains both the collar and nut forease of construct assembly.
Instruments continued
388.410 Distraction Forceps, curved
388.422 Compression Forceps
388.357 Locking Ring Extractor, for USS Variable AxisScrews
20 Synthes Spine USS Variable Axis Screw (VAS) System
For distraction and compression
For extraction
388.621 Handle for Hook or Screw Holder
Facilitates positioning of the USS VAS collar and nut, acting as an extension to the implants.
388.865 Measuring Template, for Low ProfileTransconnectors
Universal Spinal System Variable Axis Screw Instrument Set (145.252)
Synthes Spine 21
Graphic Case690.034 USS Variable Axis Screw Instrument Set
Graphic Case
InstrumentsTaps for Dual Core Screws311.602 5.2 mm311.603 6.2 mm311.604 7.0 mm311.605 8.0 mm311.606 9.0 mm
Cannulated Taps for Dual Core Screws311.612 5.2 mm311.613 6.2 mm311.614 7.0 mm311.615 8.0 mm311.616 9.0 mm
313.892 3.0 mm Hexagonal Screwdriver Shaft314.132 3.0 mm Hexagonal Screwdriver with
T-Handle, 2 ea.388.13 Socket Wrench with L-Handle, 11 mm width
across flats388.14 Socket Wrench with straight handle, 6 mm
width across flats388.15 Socket Wrench with straight handle, 11 mm
width across flats, 2 ea.388.261 10 Nm Torque Wrench, 11 mm width
across flats388.262 Counter Torque Sleeve388.263 Internal Counter Torque 388.274 Universal Spinal System Tap Handle388.31 Long Small Hexagonal Screwdriver388.357 Locking Ring Extractor, for USS Variable
Axis Screw388.38 Holding Sleeve, for Screwdriver, for
side-opening implants, 2 ea.388.410 Distraction Forceps, curved388.422 Compression Forceps 388.44 Rod Holding Forceps, for 6.0 mm Rods, 2 ea.388.532 Pedicle Reamer388.539 Pedicle Probe, for 7.0 mm, 8.0 mm and
9.0 mm screws388.54 Probe388.545 Straight Ball Tip Probe388.546 Curved Ball Tip Probe
388.55 Awl388.552 Awl, for 8.0 mm and 9.0 mm screws388.61 Hook or Screw Holder, 8 ea.388.621 Handle for Hook or Screw Holder, 2 ea.388.652 Ratchet T-Handle, 6 mm hex coupling388.865 Measuring Template, for Low Profile
Transconnectors388.902 Coated Rod Template for 6.0 mm rods388.94 Rod Pusher, for 6.0 mm rods388.961 Rod Bender, with bend radius adjustment
Titanium Universal Spinal System Variable Axis Screw Implant Set (145.251)
22 Synthes Spine USS Variable Axis Screw (VAS) System
7.0 mm Titanium USS Variable Axis Screws*499.351 30 mm thread, 2 ea. 499.352 35 mm thread, 6 ea.499.353 40 mm thread, 8 ea. 499.354 45 mm thread, 8 ea. 499.355 50 mm thread, 6 ea. 499.356 55 mm thread, 2 ea. 499.357 60 mm thread, 2 ea. 499.358 65 mm thread, 2 ea.
8.0 mm Titanium USS Variable Axis Screws499.361 30 mm thread, 2 ea. 499.362 35 mm thread, 6 ea. 499.363 40 mm thread, 8 ea. 499.364 45 mm thread, 8 ea. 499.365 50 mm thread, 6 ea. 499.366 55 mm thread, 2 ea. 499.367 60 mm thread, 2 ea. 499.368 65 mm thread, 2 ea.
Graphic Case690.064 Titanium USS Variable Axis Screw Implant Set
Graphic CaseImplants497.140 Titanium Collar, for USS Variable Axis Screws,
16 ea.498.003 Titanium Nut, 11 mm across flats, 16 ea.
Titanium Low Profile Transconnectors497.796 31.5 mm–34 mm, 2 ea.497.797 35 mm–41 mm, 2 ea.497.798 42 mm–55 mm, 2 ea.497.799 56 mm–83 mm, 2 ea.
6.0 mm Titanium Curved Rod498.139 45 mm, 2 ea.498.140 55 mm, 2 ea.498.141 65 mm, 4 ea.498.142 75 mm, 4 ea.498.143 85 mm, 4 ea.
6.0 mm Titanium Soft Rod498.150 50 mm, 4 ea.498.151 75 mm, 4 ea.498.152 100 mm, 4 ea.498.153 125 mm, 4 ea.498.154 150 mm, 4 ea.
5.2 mm Titanium USS Variable Axis Screws*499.331 30 mm thread, 2 ea. 499.332 35 mm thread, 6 ea.499.333 40 mm thread, 6 ea.499.334 45 mm thread, 4 ea.499.335 50 mm thread, 2 ea.499.336 55 mm thread, 2 ea.
6.2 mm Titanium USS Variable Axis Screws*499.341 30 mm thread, 2 ea.499.342 35 mm thread, 6 ea.499.343 40 mm thread, 8 ea. 499.344 45 mm thread, 8 ea.499.345 50 mm thread, 6 ea. 499.346 55 mm thread, 2 ea.499.347 60 mm thread, 2 ea.499.348 65 mm thread, 2 ea.
*Double lead thread
Synthes Spine 23
Also Available
Implants
4.2 mm Titanium USS Variable Axis Screws*
499.640 25 mm thread499.641 30 mm thread499.642 35 mm thread499.643 40 mm thread
5.2 mm Titanium, USS Variable Axis Screw*
499.644 25 mm thread
6.2 mm Titanium USS Variable Axis Screw*
499.645 25 mm thread
7.0 mm Titanium USS Variable Axis Screws*
499.650 25 mm thread499.651 70 mm thread499.652 75 mm thread499.653 80 mm thread499.654 90 mm thread499.655 100 mm thread
8.0 mm Titanium USS Variable Axis Screws
499.660 25 mm thread499.661 70 mm thread499.662 75 mm thread499.663 80 mm thread499.664 90 mm thread499.665 100 mm thread
9.0 mm Titanium USS Variable Axis Screws
499.371 30 mm thread499.372 35 mm thread499.373 40 mm thread499.374 45 mm thread499.375 50 mm thread499.376 55 mm thread499.377 60 mm thread499.378 65 mm thread499.670 70 mm thread499.671 75 mm thread499.672 80 mm thread499.673 90 mm thread499.674 100 mm thread
*Double lead thread
Synthes Spine1302 Wrights Lane EastWest Chester, PA 19380Telephone: (610) 719-5000To order: (800) 523-0322Fax: (610) 251-9056
Synthes (Canada) Ltd.2566 Meadowpine BoulevardMississauga, Ontario L5N 6P9Telephone: (905) 567-0440To order: (800) 668-1119Fax: (905) 567-3185
© 2002 Synthes, Inc. or its affiliates. All rights reserved. CerviFix and Synthes are trademarks of Synthes, Inc. or its affiliates. Printed in U.S.A. 1/10 J3911-F
www.synthes.com
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