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`PEDICLE SCREW FIXATION 2
`
`
`Guyer et al
`
`
`
`The Wiltse Pedicle
`Screw Fixation System
`
`
`David W. Guyer, MD
`Leon L. Wiltse, MD
`Richard D. Peek, MD
`
`
`
`
`the screws are inserted, a soft aluminum mastering
`rod is fastened into the saddle clamp on each pedicle
`screw. The aluminum master creates a precise model
`of the spinal contour. The model is then taken to a
`special bending apparatus and a perfect stainless
`steel replica is made. The replica is positioned along
`the pedicle screws and the saddle clamps are again
`tightened.
`,
`The Wiltse System has several distinct advantages
`over other pedicle screw fixation systems. The rod/
`saddle/screw junction provides rigid transfer of load,
`decreasing the chance of loosening or fatigue frac—
`ture within the system. The use of rods allows adapt—
`ability to spinal contour despite severe deformity
`(Fig. 2). Because of the saddle size and orientation,
`the superior facet joint of the instrumented cephalad
`vertebra always remains undisturbed. The system
`also makes it possible to reduce displaced vertebrae.
`Another unique feature is that either one or two
`rods can be used on each side of the spine ie, two or
`four rods in total (Fig. 1). Each of these methods has
`certain advantages. The advantage of the two—rod
`system is strength. It is most often used when a long
`gap exists between screws, for example, when one
`vertebra has to be bridged. The one-rod system saves
`time because only one rod has to be bent per side and
`the possibility of damaging the facet at the upper end
`of the fusion is decreased.
`.
`
`There are many indications for use of the Wiltse
`System (Table l). The principle indication is existing
`painful spinal instability or potential instability.
`Instability is seen in post-laminectomy spon-
`dylolisthesis, where wide decompression has caused
`compromise of the posterior elements, or in painful
`pseudarthrosis, where previous attempts at fusion
`have been unsuccessful and motion still exists.
`
`Examples of potential instability include spinal ste—
`
`1455
`
`
`
`ABSTRACT: This article illustrates the
`
`application of the Wiltse pedicle screw fixation
`system and the general principles of pedicle
`screw insertion. The system is designed for sta-
`bilization of the lumbOsacral spine. Indications,
`complications, and personal results are re—
`viewed.
`
`Special problems confront surgeons who perform
`adult reconstruction of the lumbar spine. A high rate
`of pseudarthrosis complicates simple fusions of this
`highly mobile area. Instability in this area,
`especially following surgical decompression, causes
`pain, deformity, and fusion failures. Distraction
`instruments have caused problems by eliminating
`lumbar lordosis. The lack of posterior structures
`following decompression in the lumbar spine some-
`times precludes the use of distraction instrumenta-
`tion or segmental wiring. These and other complica—
`tions have impeded the use of instrumentation,
`although many believe that rigid internal fixation
`increases the success of fusion mass consolidation.
`
`Pedicle screws were first used in the 1950s. They
`have been reintroduced recently and have the advan-
`tage of solid fixation to vertebral bodies from a
`posterior approach. Pedicle screws do not rely on
`posterior elements, nor do they require distraction or
`compression to hold a position rigidly. The Wiltse
`System relies, on pedicle screws connected to
`stainless steel rods by saddle clamps (Fig. 1). Once
`
`From the California Spine Surgery Medical Group, Inc, Long
`Beach, California.
`Reprint requests: David W. Guyer, MD, Vancouver Orthope-
`dic Group, 505 NE 87th Avenue, Vancouver, WA 98664-6440.
`
`2
`
`

`

` %
`
`.21v
`
`
`
`ORTHOPEDICS
`
`' October 1988 Vol Ii/No It)
`
`
`
`Fig. 1: The Wiltse System assembled on a model spine.
`The double-rod system is shown on the right. The
`single-rod system is displayed on the left.
`
`nosis. and degenerative scoliosis, where wide
`decompression is planned and compromise of the
`supporting structures is expected. A second indica—
`tion is unstable fracture of the thoracolumbar or
`
`lumbar spine. The solid fixation obtained by this
`system obviates instrumentation of multiple levels
`above and below the fracture site. Thirdly, it is indi-
`cated where posterior augmentation is necessary to
`support anterior vertebrectomy and strut grafting, as
`with tumor or infection. The system may also be used
`to stabilize spinal osteotomies.
`Contraindications for the Wiltse System include
`recent, or in many cases, old infections of the spine;
`decompressions that will not cause instability; and
`fusions which are normally successful without inter~
`nal fixation.
`
`Technique
`
`The patient is positioned on a kneeling frame,
`unless AP flUOroscopic visualization of the pedicle is
`
`1456
`
`TABLE 1W
`PRINCIPAL INDICATIONS
`Existing painful spinal instability:
`Post-laminectomy spondylolisthesis
`Painful pseudarlhrosis
`Potential instability:
`Spinal stenoSiS
`Degenerative scoliosis
`Unstable fractures.
`
`Augmenting anterior strut grafting:
`Tumor
`Infection
`Stabilizing spinal osteotomies.
`CONTRAINDICATIONS
`
`Recent infection.
`Laminectomies that will not cause instability.
`Fusions which are normally successful without fixation.
`
`
`necessary. The authors use the Andrews frame with
`adjustable chest support. This position reduces
`engorgement of epidural veins and promotes lumbar
`lordosis. When both AP and lateral fluoroscopic
`images are needed, the patient is placed in the prone
`position, using the Pheasant frame and Skytron
`table, both penetrable by radiographs. The adjusta—
`ble chest support is also used. The AP image is
`essential when patients have had previous attempts at
`fusion and normal landmarks are obliterated. By
`using AP fluoroscopy, one is able to rotate the table
`and look down the shaft of the pedicle. If both views
`are needed, drape the C—arm for the AP View first,
`then swing it to the lateral position while carefully
`adjusting the drapes. If only the lateral view is
`needed, the portable C—arm can be placed either over
`the top or underneath the table, and draping is no
`problem.
`The midline approach is used for cases where it is
`necessary to do a central decompression.
`In the
`thoracolumbar area, the midline approach works
`very well. Below the third lumbar vertebra, a para—
`spinal approach is preferred because retracting the
`muscles and soft tissue wide enough in order to aim
`the pedicle screws correctly can be very difficult1
`(Fig. 3).
`The transverse process is located, then traced
`medially to the lateral mass of the vertebra. The
`pedicle is deep to the base of the transverse process in
`the lateral plane and directly under the superior artic-
`ular facet of the involved vertebra in a coronal plane.
`A starting point for the pedicle screw is made in the
`cortical bone with the awl at the middle of the base of
`
`
`
`3
`
`

`

`Guyer et al
`
`PEDICLE SCREW FIXATION
`
`4
`
`‘:p
`
`
`
`J
`
`
`
`Fig. 2D: Pdstopéffitive lateral View.
`
`1457
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`4
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`

`

`
`
`
`
`ORTHOPEDICS
`October 1988 Vol il/No 10
`
`
`mmAmwvmnmwmm-M
`
`
`
`
`
`0...».”W...“a»,.
`
`
`
`Fig. 3: The paraspinal approach with correct screw
`placement.
`
`the transverse process and slightly up onto the lateral
`aspect of the superior articular process (Fig. 4). At
`the first sacral vertebra, the starting point should be
`caudal and just lateral to the superior articular pro-
`cess. The best starting point for 82 is midway
`between the first and second sacral foramen.
`
`After a hole is made in the cortex, a pedicle probe
`is introduced to identify the medullary cavity of the
`pedicle. Gently twisting the probe allows the blunt
`end of the instrument to find the cancellous bone
`
`within the pedicle “cortical tube. ” All screws should
`be aimed medially except at the S2 position.2 As a
`rule of thumb, one should add approximately 5° of
`medial angulation to each subsequent lumbar ver«
`tebra, progressing from 5° at L1, to 10° at L2, 15° at
`L3, 20° at L4, and 25° at L5. The Si screw should
`also be angulated approximately 25° medially while
`82 is angulated 40°»50° laterally and 10°—15° cepha-
`lad (Table 2). Once the pedicle is probed, a small
`Kirschner wire with a rounded end is inserted and
`
`tamped in while its progress is monitored fluo—
`roscopically.
`When the direction of the Kirschner wire is cor—
`
`rect, the hole is. tapped. The tap is inserted approx—
`imately 2 cm, which is about the length of the pedi—
`cle, and then removed. A speCial nerve hook with a
`smaller “probe” edge is then used to feel for threads
`out along sides of the hole made by the tap. If threads
`are felt circumferentially to the depth of the pedicle,
`it is safe to proceed. Great care should be taken to
`avoid thread protrusion out of the pedicle. The tap is
`then turned until the anterior cortex of the vertebral
`
`1458
`
`
`
`Fig. 4: Starting point for the pedicle screw is shown on
`a spine model.
`
`body is reached but not penetrated. After the tap is
`removed, a small Kirschner wire is again inserted to
`check the integrity of the anterior cortex and then
`measured. The length of the screw to be used is
`gauged by the depth of the Kirschner wire in the
`vertebral body. A shorter screw is used if the anterior
`cortex has been penetrated. However, in osteoporotic
`bone, it is important that the anterior cortex of the
`vertebral body be engaged by the screw.
`The screws come in four sizes: 5.0 mm and 5.8
`mm diameter screws are used in thoracic and smaller
`
`lumbar vertebrae; 6.5 mm diameter screws are used
`for lower lumbar vertebrae. and S2; and, a 7 mm
`screw is usually more appropriate at $1. Flattened
`shanks on the screws prevent rotation of the saddle
`clamps. There are two types of saddles to accommo—
`date either single or double rods on each side. The
`choice depends on the stability required. The saddle
`clamps and stainless steel rods are serrated. The
`
`5
`
`

`

` PEDICLE SCREW FEXATEON
`Guyer et at
`
`TABLE 2
`RECOMMENDED SCREW SIZE AND ANGULATION
`
`
`
` Level Screw Size Angulation (°)
`
`
`
`T11
`T12
`L1
`L2
`L3
`L4
`L5
`S]
`$2
`
`——
`—
`0—10 medially
`10 medially
`10—15 medially
`15-20 medially
`20—25 medially
`25 medially
`40-50 laterally and
`10—15 cephalad
`
`
`5.0 mm
`5.0 mm
`5.8 mm
`5.8 mm
`6.5 mm
`6.5 mm
`6.5 mm
`7.0 mm
`6.5 mm
`
`interlocking contact between them prevents rotation
`of the rod in the saddle. Jam nuts are tightened on the
`threaded end of the pedicle screw to secure the rod/
`saddle/screw junction (Fig. 5).
`the
`When the screws and saddles are in place,
`surgeon is ready to mold the aluminum rods which
`are used as templates for the stainless steel rods.
`Templates are bent by hand to approximate the
`length of the needed rod, then lowered into place.
`The saddle clamp of the center screw is tightened
`first. The soft aluminum rods are then easily con-
`toured to the remaining saddle positions. Once the
`aluminum rods are in place, the saddle positions are
`marked with a small chisel to facilitate orientation of
`
`the rods in the bending apparatus where the final
`steel rods are produced.
`A separate table is prepared for the bending
`assembly. This apparatus consists of base plate, slide
`assembly, center towers, varied angle post assembly,
`and rod bending tools (Fig. 6). The template contour
`is transferred to the slide bending assembly by
`adjusting the post and slide assemblies to fit the
`corresponding saddle positions on the aluminum
`rod. The aluminum rod is then removed, and a steel
`rod is chosen and inserted into the center tower.
`
`Using the bending tools, the rod is carefully bent to
`fit the position held by the post aSSemblies. Simple
`bends may be accomplished with the handheld
`French bender.
`
`While the rod bending is taking place, exposed
`bone at the fusionvsite is decorticated with a high
`speed burr or rongeur. A bone graft
`is obtained
`through the same incision from the posterior superior
`iliac crest. Prior to rod placement, a small amount of
`soft cancellous bone is tamped into every available
`area. The surgeon has the option of using a spacer
`
`
`
`
`
`Fig. 5: Pedicle screw at the 81 position With spacer,
`saddle clamp, serrated rod, and,jam nuts.
`
`under a lower saddle to create a greater bone fusion
`area (Fig. 5). The stainless steel rods are then laid in
`the appropriate position. Saddle clamps, jam nuts,
`and locking nuts are then tightened using a special
`wrench to prevent rotation of the pedicle screw. The
`machine end of the screw is staked using a small
`chisel, which removes any possibility of loosening.
`The wound is closed routinely; a drain is advisable.
`Patients are permitted to be mobile as soon as they
`feel able, occasionally even on the first postsurgery
`day. An overhead trapeze is not used. Patients are
`trained to get out of bed minimizing rotation. COrsets
`are often used to remind the patient not to bend
`excessively. Other forms of external support are gen~
`erally not necessary.
`Additional instrumentation has been developed to
`facilitate reduction of degenerative scoliosis, spon-
`dylolisthesis, and acute fractures, but their discus—
`
`1459
`
`6
`
`

`

`7
`ORTHOPEDICS
`October 1988 Vol li/No it)
`
`
`
`
`
`
`Fig. 6: The bending assembly for transferring tem-
`plate contour to stainless steel rods. Slide assemblies
`are horizontal on the base plate and post assemblies
`are vertical.
`
`sion is beyond the scope of this article.
`A recurrent problem with long, complicated revi—
`sion surgeries is infection. To counter this,
`the
`authors use every possible precaution including: 1)
`perioperative antibiotics; 2) wound drainage; 3) dou—
`ble—glove technique; 4) laminar airflow operating
`rooms; 5) use of the largest operating rooms avail—
`able so equipment can be moved around safely; 6)
`limiting flow of personnel in and out of the operating
`room during the procedure; 7) scrupulous care in
`draping the patient and C—arm; and 8) most impor-
`tantly, delaying the opening of the instrument system
`until the approach and decompression are made.
`
`Complications
`
`Out of 170 cases, there have been 6 infections: 4
`resolved with appropriate treatment and 2 required
`removal'of the instrumentation; 5 cases have had
`postoperative radiculopathy. Exploration of the
`involved root has demonstrated accurately placed
`screws within an intact pedicle and no foraminal
`impingement. Pain has been relieved by removal of
`the instrumentation. The cause of the radiculopathy
`
`is uncertain. One rod broke early in the test series, in
`which the system was used unilaterally. The break
`may have been related to machining techniques for
`the rods, which have been changed. The rod size has
`also been increased by 15%. However, unilateral use
`of the system is not recommended. Two 5.8 mm
`screws have broken at the Si location in a patient 7
`months after an L3 to $1 fusion. L3 to L5 had fused,
`leaving firmly anchored rods holding the small
`screWs at $1. The sacrum then cycled these screws
`until fatigue fractures occurred. There was no evi~
`dence of bent screws. A one-rod branch and anchor
`
`at S2 could have helped support the Si screw. It is
`uncertain whether the system itself or lack of fusion
`was at fault. At the Si position, 7 mm screws are
`recommended. A total of ten cases had poor results
`or fusion failure. Failure has been attributed to infec-
`
`tion, partial system failure, patient smoking habits,
`or extensive prior surgery. Most of these cases were
`repaired with additional implant work and appropri—
`ate therapy.
`
`Conclusion
`
`Results of 2V2 years of experience with use of the
`Wiltse pedicle screws fixation system in 170 patients
`are very encouraging. Pedicle screw fixation offers
`greater stability for spine fusion, faster results,
`shorter patient recovery periods, and applications to
`a greater variety of surgical problems than other
`systems of instrumentation. Precision, versatility,
`safety, and increased Stability resulting from its
`unique features have made the Wiltse System the
`most promising pedicle screw system to date. As this
`system is improved and better surgical techniques
`develop, success rates may become even higher.
`
`References
`
`l. Wiltse LL, Bateman JG, Hutchinson RN, et al: The para-
`spinal sacrospinalis—splitting approach to the lumbar spine. J
`Bone Joint Surg 1968; 50A29l9.
`2. Zindrick MR, Wiltse LL, Widell EH, et a]: A bio-
`mechanical study of intrapeduncular screw fixation in the lum—
`bosacrai spine. Clin Orrlzop 1986; 203:99.
`
`1460
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`7
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