SURGICAL MANAGEMENT

 

 

Operative intervention in the posterior subaxial cervical spine is frequently carried out for decompression or stabilization.

 

 

Fusion and instrumentation of the posterior cervical spine may be required for unstable fractures or after extensive decompressive procedures.

 

Instrumentation reduces the need for postoperative immobilization and orthosis wear, augments fusion success, and allows better maintenance of sagittal alignment of the cervical spine.

 

Interspinous Wiring

 

Interspinous wiring can be an alternative to lateral mass or pedicle screw fixation in stabilization of the posterior cervical spine.

 

 

Although it resists flexion reasonably well, it is generally not as strong in resisting extension, axial load, rotation, and lateral bending.

 

The most commonly used implants are 18- or 20-gauge stainless steel wire or 1- to 1.2-mm titanium braided cable.

 

 

Alternatives include braided stainless steel or polyethylene cable. Multistrand braided steel, titanium, or polyethylene cables show superior fatigue resistance, greater flexibility, and improved stability on flexion-extension testing compared to a single-filament stainless steel wire.38,44

 

In modern spine surgery, wiring techniques are g enerally limited to cases in which biomechanically superior techniques such as lateral mass fixation cannot be used, a somewhat less invasive midline-only exposure is desired, or the additional rigidity of lateral mass fixation is not necessary (eg, for posterior repair of relatively stable pseudarthroses or to provide a tension band effect as an adjunct to anterior instrumentation).

 

Techniques of wiring include simple interspinous wiring (eg, Rogers), Bohlman triple wiring (can be used also for occipitocervical fixation), and oblique wiring.

 

 

As a result of the direction of its stabilizing forces, oblique wiring may counter rotational instability better than simple interspinous wiring.

 

Lateral Mass Screw Fixation

 

The lateral mass of the subaxial cervical vertebra is a quadrangular column of bone formed by the complex of the superior and inferior articular processes and the intervening bone.

 

Lateral mass screws are the most commonly used and widely evaluated implants for posterior fixation of the subaxial cervical spine.

 

Lateral mass screws are versatile in that they can be used when the spinous processes and laminae are unavailable as fixation points (eg, from trauma, tumors, or surgical resection for decompression).

 

Lateral mass screw fixation techniques provide superior flexion and torsional stiffness compared to posterior wiring.8,42

 

The improved strength of fixation allows instrumentation to be limited to the levels of fusion. When wiring techniques are used, the construct occasionally needs to be extended proximally or distally to obtain additional points of fixation.

 

A lower incidence of postoperative kyphosis is achieved with lateral mass screws versus wiring techniques.13

 

Lateral mass screws are easier to insert and have a low incidence of complications when compared to pedicle screws.

 

The Magerl technique of lateral mass screw fixation has been shown to have superior pullout strength and

higher load to failure when compared to screws inserted with the Roy-Camille technique.30 This may be related to the longer screw length generally possible with the Magerl technique.

 

 

Anatomic variations in screw lengths occur at each subaxial level, with either technique; from C3 to C6, the Magerl technique can safely afford a screw length of 14 mm as compared to the Roy-Camille technique which can afford a screw length of 12 mm. At C7, the reported screw lengths are 2 mm shorter for the Roy-Camille technique and 3 to 4 mm shorter for the Magerl technique. Screw lengths are greater in males compared to females at all levels. Assessment of lateral masses on preoperative computed tomography

 

(CT) scans is recommended to ascertain screw lengths while using either technique.9,39 Pullout strength is significantly greater with a bicortical screw than with a unicortical purchase.

 

Because bicortical purchase engenders potential risk to nerve roots and the vertebral artery, unicortical purchase is used in most cases.

 

Pedicle Screw Fixation of the Cervical Spine

 

Pedicle screw fixation allows simultaneous stabilization of all three columns of the cervical spine and has been reported to be biomechanically superior to lateral mass fixation.20

 

Although cervical pedicle screws are commonly used in Asian countries, they are not as popular in United States. The risk of neurovascular injury from broaching the walls of the small cervical pedicles from C3 to C6 and variability in pedicle size sometimes even at the same level (FIG 1) makes this procedure technically

difficult and restricts its widespread use.12,21,32,33

 

Pedicle screws are most commonly used at C2 and C7 where the pedicles are largest in the cervical spine and the risk of neurovascular injury is lower.

 

 

P.5145

 

 

 

FIG 1 • Axial CT image of a subaxial cervical vertebra depicting variability in the pedicle diameter at the same level.

 

 

At C7, most patients do not generally have a vertebral artery in the foramen transversarium, making pedicle screw fixation safer at this level.

 

 

At C2, the vertebral artery is generally lateral to the insertion site and trajectory of the pedicle, making pedicle screw fixation feasible.

 

From C3 to C6, the proximity of the vertebral artery and the small diameter of the pedicles make pedicle screw fixation challenging and not feasible for routine use.

 

Whenever pedicle screw fixation in the cervical spine is contemplated, careful scrutiny of preoperative CT and magnetic resonance imaging (MRI) scans is essential to measure the dimensions and angulation of the pedicles and rule out congenital anomalies.

 

The cervical pedicle is generally taller than it is wide, with the mean height of all cervical pedicles around 7 mm (range 6 to 11 mm).12,32,33

 

The width of the pedicle is the critical dimension for feasibility of pedicle screw placement.

 

Table 1 Cervical Pedicle Outer Width

Pedicle Width (mm)

C2

6.9 ± 1.6

 

C3

5.3 ± 0.8

C4

5.4 ± 0.8

C5

5.7 ± 0.8

C6

5.9 ± 0.9

C7

6.7 ± 1.0

 

 

 

Pedicle outer diameters less than 4 mm generally preclude pedicle screw insertion.12

 

Multiple morphologic studies have found that the mean cervical pedicle outer width varies from 4 to 7 mm, with significant variation in the width at different levels (Table 1).12,28,32,33

 

The pedicles of C2 and C7 are however generally large enough to accommodate either 3.5- or 4-mm screws.

 

The length of the pedicles from C3 to C6 ranges from 12 to 18 mm.12,33 Screw lengths are generally slightly longer to obtain purchase within the vertebral body.

 

The axial angle of the pedicle (medial angle to the sagittal plane) is the least at C2 (25 to 30 degrees)10 and increases to a mean of 44 degrees (25 to 55 degrees) at C3. From C3 to C7, it gradually reduces to a mean of 37 degrees (33 to 55 degrees).28

 

Preoperative CT-based navigation35,41 and, more recently, the use of intraoperative three-dimensional

imaging-based navigation19 has been reported to reduce the cervical pedicle screw malpositioning and, consequently, the risk of neurovascular complication.

 

TECHNIQUES

• Posterior Cervical Fusion

Although it is tempting to focus on instrumentation techniques, performing a meticulous fusion technique is just as important, if not more so, to the success of surgery.

In virtually all cases, posterior fusion is supplemented by some form of instrumentation.

To maximize the surface area for fusion, all posterior bony surfaces that do not need to be resected for the decompression should be left intact for fusion.

Following exposure, all soft tissues, including the interspinous ligaments and muscles, facet joint capsules, and paraspinal soft tissue, are meticulously resected so that the posterior cortical surfaces lie exposed.

In patients who require a laminectomy, the lateral masses and facet joints form the fusion bed.

 

 

 

 

TECH FIG 1 • Decortication of the laminae and facet joints at the levels selected for fusion. Only iliac crest bone graft is placed over the decorticated areas.

 

 

P.5146

 

Facet joint cartilage is removed with a curette or 3-mm burr within the facet joint. It is easier to decorticate the facet joints if done before the insertion of lateral mass screws.

 

The posterior cortical surfaces of the lateral masses, laminae, and spinous processes are decorticated with a 3-mm burr to expose bleeding subcortical bone (TECH FIG 1).

 

Bone graft obtained from the iliac crest or local bone from laminectomy is morselized into small cancellous and corticocancellous chips and onlaid over the bleeding bone.

 

Cancellous chips of bone are inserted directly into the facet joint.

• Interspinous Wiring

Simple Interspinous Wiring

 

The spinous processes and laminae at the level to be instrumented should be confirmed to be intact and

instrumentable on preoperative imaging studies.

 

Closed or operative reduction of spinal fracture-dislocations should be carried out before instrumentation if possible.

 

 

 

TECH FIG 2 • Simple interspinous wiring. A. Safe position of the drill hole for passage of spinous process wire is dorsal to the spinal laminar line. B. The wire or cable selected is passed through and around the base of the cranial and caudal spinous processes at the levels selected for fusion so that both ends of the wire are on the same side of the spine. C. Ends of wire are twisted together after releasing any cervical traction.

 

 

In some cases of flexion-distraction injury, sequential tightening of the wires can be done to reduce the spine.

 

Two- to 3-mm drill holes are made through the cortex at the junction of the spinous process and laminae bilaterally at the levels to be included in the fusion.

 

Attention should be paid to the ventral location of the dural sac, and the drill should be directed coronally to minimize the risk of inadvertent spinal cord injury (TECH FIG 2A).

 

P.5147

 

The drill holes should be positioned at the proximal aspect of the cephalad spinous process and the distal aspect of the caudal spinous process to provide the widest margin of safety against the wire cutting through the spinous process.

 

The tips of a towel clip or a tenaculum clamp are placed in the cortical holes on either side of the base of the spinous process.

 

A gentle side-to-side rocking movement is used to create a continuous tract in the cancellous bone at the base of the spinous process.

 

The wire or cable selected for use is passed through and around the base of the cranial spinous process (TECH FIG 2B).

 

One end of this wire is similarly passed through and around the base of the caudal spinous process so that both the ends of the wire end up on the same side of the spine.

 

The free ends of the wire are tightened (TECH FIG 2C).

 

Cancellous bone graft is placed bilaterally on the decorticated laminae and spinous processes and within the facet joint at the fusion levels.

 

Modification of the technique can include a plate of corticocancellous bone graft harvested from the iliac crest and placed under the wire or cable bilaterally prior to tightening.

Triple Wire Technique

 

The wire or cable selected is passed through and around the spinous processes at the cephalad and caudal ends of the fusion levels, as with routine interspinous wiring.

 

A pair of corticocancellous plates of bone graft including the full thickness of the cancellous bone of the iliac crest but excluding the inner cortical table is harvested from the posterior iliac crest.

 

The length of the bone block should be adequate to span the fusion construct and wide enough to cover the decorticated laminae within the fusion levels.

 

Two- to 3-mm drill holes are created in the proximal and distal portions of the harvested bone grafts.

 

Two additional 22-gauge wires are passed through the holes in the proximal and distal spinous processes.

 

These wires are then passed on either side through the holes made in the bone graft.

 

The wires are tightened over the grafts on both sides to hold the bone graft rigidly against the decorticated lamina and spinous process (TECH FIG 3).

Oblique Wiring

 

A periosteal elevator is carefully inserted into the facet joint to slightly distract and clearly identify the plane of the facet joint.

 

A 2-mm drill bit is used to make a channel in the sagittal plane through the midportion of the inferior articular process, exiting through the articular surface into the joint.

 

The periosteal elevator within the joint confirms penetration by the drill and prevents overpenetration by the drill (TECH FIG 4A).

 

A 20-gauge wire or cable is passed through this drill hole and is guided distally through and out of the facet joint using a periosteal elevator in a “shoehorn” fashion.

 

One end of the wire is then passed either around or through a hole in the intact spinous process of the vertebra one or two levels caudal to the level of injury.

 

 

 

TECH FIG 3 • Triple wiring technique. After simple interspinous wiring, additional wires are passed through the cranial and caudal spinous processes at the levels selected for fusion. These wires are used to firmly hold corticocancellous plates of bone graft against the decorticated laminae at the fusion levels.

 

 

This procedure is done bilaterally, and the free ends of the ipsilateral wires are twisted together to the appropriate tension (TECH FIG 4B). The absence of laminae or spinous processes is often a reason to consider oblique wiring over interspinous wiring.

 

Supplemental midline interspinous or triple wiring is frequently added when the bony anatomy permits.

Multilevel Buttress Facet Wiring

 

Posterior stabilization after multilevel laminectomy can also be obtained by posterolateral facet fusion with multilevel facet wiring.7

 

Oblique facet wires are passed bilaterally through the inferior articular processes at all facet joints included in the fusion.

 

Two wires are passed through a hole in the spinous process of the most caudal vertebra.

 

Rib grafts, iliac crest strut grafts, or metal rods have all been used for stabilization with the multilevel facet wires (TECH FIG 5).7,14

 

The bone graft is placed over the decorticated lateral masses and in between the free ends of the wires, and the wires are twisted together at each level to the appropriate tension.

Postoperative Immobilization

 

Rigid external bracing is recommended in all posterior cervical wiring procedures until solid bony fusion is obtained. Six to 12 weeks of halo vest or rigid cervicothoracic bracing should be used after interspinous or oblique wiring, depending on the stability of the construct and the number of levels included in the fusion.

 

Radiographs should show a continuous fusion mass and absence of mobility in flexion and extension before immobilization is discontinued.

 

P.5148

 

 

 

TECH FIG 4 • Facet wiring techniques. A. A channel is drilled in the sagittal plane through the midportion of the inferior articular process, exiting through the articular surface into the joint. A periosteal elevator held within the joint space prevents overpenetration by the drill and can be used to guide the wire out through the joint space. B. Facet wires may be obliquely looped around the spinous process when the lamina is deficient at a level.

 

 

 

TECH FIG 5 • Facet wires may be tightened over rib grafts bilaterally in cases of multilevel laminectomy.

 

 

P.5149

• Lateral Mass Screw Fixation

   

  The quadrilateral posterior surface of the lateral mass is clearly exposed.

   

  A ridge between the lamina and lateral mass helps identify the medial border. This distinction is less prominent at C7.

   

  The lateral edge of the lateral mass can be easily palpated.

   

   

  The joint lines above and below delineate the superior and inferior borders. The center of the quadrilateral posterior surface of the lateral mass is identified.

   

  Several techniques have been described for lateral mass screw insertion. The goal is to avoid damage to

  the vertebral artery, the nerve root in the foramen, and avoid violating the facet joint while inserting a lateral mass screw of adequate length.

   

  Roy-Camille et al37 proposed an entry point for the lateral mass screw at the center of the posterior

  surface of the lateral mass.

   

  The screw is directed perpendicular to the posterior surface of the lateral mass, angled laterally 10 degrees to the sagittal plane.

   

   

   

  TECH FIG 6 • Lateral mass screw insertion techniques. A-C. In the Roy-Camille method, the entry point is at the center of the posterior surface of the lateral mass, with the screw directed perpendicular to the posterior surface of the lateral mass and angled laterally 10 degrees to the sagittal plane. D,E. In the Magerl technique, the entry point is 1 mm medial to the center of the posterior surface of the lateral mass, and the screw is directed parallel to the plane of the facet joint and angled laterally 25 degrees to the sagittal plane.

   

   

  This trajectory aims to exit lateral to the vertebral artery and inferior to the exiting nerve root (TECH FIG 6A-C).

   

  Magerl et al29 proposed an entry point 1 mm medial to the center of the posterior surface of the lateral mass.

   

  The screw is directed parallel to the plane of the facet joint with 25 degrees of lateral angulation in the axial plane.

   

  Magerl et al29 recommended inserting a needle into the facet joint to determine the plane of the joint.

   

  Lateral plane fluoroscopy can help accurately determine the direction of the screw in the sagittal plane, aiming to keep the screw parallel to and between the articular surfaces of the lateral mass.

   

  This trajectory aims to exit lateral to the vertebral artery and superior to the exiting nerve root (TECH FIG 6D,E).

   

  P.5150

   

  A modification of the Magerl et al technique by An et al5 uses a similar starting point but recommends angling the screw 30 degrees laterally in the axial plane and 15 degrees cranially in the sagittal plane.

   

  This trajectory again aims to exit laterally to the vertebral artery and superiorly to the exiting nerve root at the junction of the transverse process and the lateral mass.

   

  Enlarged and bulbous tips of the spinous processes can be ronguered if they interfere with appropriate angulation of the instruments.

   

  When the lateral masses are sclerotic, a high-speed 2-mm burr is used to penetrate the outer cortex of the lateral mass at the entry point before a drill is used. This will also prevent the drill tip slipping on the surface of the lateral mass.

   

  A tap is used prior to screw insertion in sclerotic bone.

   

  Most current instrumentation systems use a rod to connect the screws after they have been precisely positioned and inserted into the lateral mass.

   

  Lining up the screw heads for subsequent rod fixation is easier if the most proximal and distal screws are inserted initially followed by the screws in between.

   

  Polyaxial screw heads compensate for minor variations in insertion or anatomy.

   

  The rods can be contoured in multiple planes and allow for application of compressive, distractive, and rotatory forces for correction of deformity.

   

  A rod-screw construct can easily be extended to the occipital and thoracic region.

   

   

  Bicortical screws provide better pullout strengths as compared to unicortical screws16; however, they can cause nerve root irritation or damage if too long. Bicortical screws should be considered in certain cases:

   

  Patients with rheumatoid arthritis or metastatic bone tumors in whom bone quality may be suboptimal

   

  Longer fixation constructs extending to the occipital or thoracic regions to reduce the chances of implant pullout

• Pedicle Screw Fixation of the Cervical Spine

Insertion of Pedicle Screws from C3 to C7

 

Preoperative radiographs and CT images should be reviewed to assess pedicle dimensions and orientation and to confirm the feasibility of obtaining intraoperative radiographs; this is especially important in patients with short, stocky necks.

 

Inserting pedicle screws before decompression allows better identification of morphologic landmarks and reduces the risk of inadvertent injury to an exposed spinal cord during the insertion process.

 

Anatomic studies provide broad guidelines on locations of the pedicle entry point at each subaxial

cervical level.12,32,33

 

The most commonly used technique relies on identification of topographic landmarks combined with fluoroscopy.1

 

The entry point to the pedicle is 1 to 2 mm inferior to the caudal edge of the inferior articular process and 2 to 3 mm lateral to the midline of the lateral mass or 2 to 3 mm medial to the lateral edge of the lateral mass.

 

 

Occasionally, degenerative changes at the joint obscure true landmarks. The dorsal cortex of the lateral mass is penetrated using a high-speed burr.

 

The cancellous bone of the pedicle in many cases can be visualized in this pilot hole.

 

A blunt, fine pedicle probe is advanced through this cancellous bone to find the medially angled pedicle (TECH FIG 7A).

 

Fluoroscopy is used to guide the trajectory in the sagittal plane.

 

In general, the screws should be parallel to the superior endplate of the vertebral body from C5 to C7 and angled slightly rostral to the endplate from C2 to C4.

 

Some authors recommend that a keyhole laminoforaminotomy be performed after locating the entry point.4

 

The superior and medial walls of the pedicle are directly palpated through this foraminotomy with a right angled nerve hook to direct the trajectory of the pedicle probe (TECH FIG 7B).

 

The pilot hole is tapped before inserting the screw.

 

 

Size 3.5- or 4-mm screws are generally used based on preoperative imaging of pedicle dimensions. Small pedicle diameters may require a 2.7-mm screw.20

 

The length of the screw ranges from 18 to 26 mm, depending on the length of the pedicle as determined

on preoperative CT scans.

 

The screw should be inserted to a depth no longer than two-thirds of the anteroposterior width of the vertebral body, as confirmed on the lateral fluoroscopy image.

 

Because the C7 pedicle is longer, a screw up to 30 mm can usually be inserted at this level.

 

Computer-assisted image guidance systems have been used for pedicle screw insertion in the cervical spine.

 

Preoperative CT data are used by the computer-assisted system to prepare a three-dimensional model of the vertebra.

 

Alternatively, intraoperative CT of the cervical spine is obtained following exposure. This data is transferred to the navigation system.

 

After registration of surface landmarks during surgery, a registered probe or drill bit can be used to locate the pedicle screw entry point and trajectory, and guide a fine drill bit through the pedicle into the

vertebral body.41

 

 

P.5151

 

 

 

TECH FIG 7 • A. Comparative trajectories of cervical pedicle screw and lateral mass screw in the axial plane. B. Palpation of the superior and medial pedicle walls through the laminoforaminotomy window helps determine the trajectory of the pedicle probe.

C2 Pedicle Screw Insertion

 

The entry point for the C2 pedicle is located on the superior medial quadrant of the posterior aspect of the lateral mass of C2, 3 mm lateral to the medial edge of the isthmus, and in line with or slightly distal to the superior margin of the C2 lamina.

 

The entry point and trajectory for subsequent drilling are confirmed by palpating the medial and superior margins of the C2 pedicle with a Penfield probe to determine medial angulation and with fluoroscopy to determine sagittal angulation.

 

The cortex is penetrated with a 3-mm burr.

 

The underlying cancellous bone is probed with a fine curette or pedicle probe to locate the pedicle channel. A 2.7-mm drill bit can also be used under fluoroscopy control to cannulate the pedicle.

 

The drill is generally angled 15 to 25 degrees medially and 20 to 30 degrees cranially.

 

The integrity of the drilled hole is verified with a blunt probe and tapped, and a 3.5- to 4.0-mm screw is inserted.

 

Twenty- to 22-mm screw lengths are generally used. C2 pedicle screws longer than 24 mm are likely to penetrate the anterior surface of the vertebral body and may provide superior fixation in some

situations.34 The pullout strength of C2 pedicle screw is reported to be twice that of C2 pars screw.40

 

The varying screw entry points and trajectories in the cervical spine occasionally create challenges in contouring the connecting rods. Using a polyaxial screw head provides some tolerance in placement of the rod connecting C2 to subaxial levels.

C2 Pars Screw Insertion

 

The entry point for a C2 pars screw is located on the lateral mass of C2, 3 mm cranial and 3 mm lateral to

medial edge of the inferior articular facet of C2.

After a pilot hole is drilled at this location, a 2.7-mm drill bit is used to cannulate the pars under fluoroscopy control. The drill is angled 10 to 15 degrees medially. A Penfield dissector can be used to feel the medial edge of the C2 pars, which can help with directing the drill. Fluoroscopy is used to assist with sagittal trajectory, which is generally around 25 degrees cranially directed, more caudally oriented than a C1-C2 transarticular screw.

The C2 pars screw is shorter than the C2 pedicle and can measure up to 16 mm.

 

 

P.5152

 

PEARLS AND PITFALLS

 

Posterior cervical infusion

• The surgeon should ensure meticulous decortication of the laminae and spinous processes within the fusion levels.

• Facet joint cartilage should be resected at fused levels.

 

Posterior cervical instrumentation

• Insert lateral mass or pedicle screws before neural decompression. This allows better identification of morphologic landmarks and offers a degree of protection against inadvertent injury to the spinal cord.

   

  Posterior wiring techniques

  • Drill holes should be positioned at the proximal aspect of the cephalad spinous process and the distal aspect of the caudad spinous process to allow greater purchase of the wires in bone.

  • Wires should be positioned dorsal to the spinolaminar line.

 

Lateral mass fixation

• Preoperative templating allows selection of appropriate screw length to minimize the risk of spinal nerve injury.

• Linking the screws to the rod is easier if the most proximal and distal screws are inserted initially followed by the screws in between.

 

Pedicle screw fixation

• Pedicle screw dimensions and orientation should be identified on preoperative imaging studies.

• Osteophytes can distort bony margins and should be resected to allow identification of morphologic landmarks for screw insertion.

• A burr is used to expose cancellous bone at the pedicle screw insertion point. A blunt, fine pedicle probe is advanced through this cancellous bone to find the medially angled pedicle.

• The screw should be inserted to a depth no greater than two-thirds of the anteroposterior width of the vertebral body.

 

OUTCOMES

Posterior Wiring Techniques

Long-term successful fusion rates of 94% to 96% have been reported with interspinous wiring techniques

 

 

when used for trauma, degenerative conditions, and tumors of the cervical spine.25,36

 

Weiland and McAfee43 reported a fusion rate of 100% when a triple-wire technique was used for subaxial posterior cervical fusion in 60 patients.

 

Two of the 60 patients required halo vest immobilization, whereas the rest fused with a two-poster orthosis.

 

Cahill et al6 reported stable fusion and acceptable alignment in all 18 patients with facet dislocations treated using bilateral oblique wiring.

 

Fusion generally occurred within 3 to 4 months. No patients developed neurologic deterioration after wiring.

 

Callahan et al7 reported solid fusion in 50 of 52 cases with multilevel facet fusion done after, using iliac crests or rib graft for fixation along with facet wires.

 

Two patients who failed to achieve solid fusion were followed up with regular assessments and did not require any further management.

 

Fusion rates with interspinous wiring have been found to be comparable to those obtained from lateral mass plating.26

Lateral Mass Screw Fixation

 

Ebraheim et al11 retrospectively reviewed the radiographic and clinical outcomes in 36 patients treated with lateral mass plate-screw fixation for traumatic instability, postlaminectomy instability, or metastatic disease. Fusion occurred at an average of 3 months in all patients. One patient demonstrated postoperative neurologic deterioration, but this is resolved with subsequent decompression.

 

Fehlings et al13 reported successful arthrodesis in 39 (93%) of 42 patients treated with lateral mass plate-screw fixation for cervical instability at a mean follow-up of 46 months. Revision of posterior plating was required in 2 patients for a screw pullout. Another patient required supplementary anterior plating for progressive postoperative kyphosis.

 

Katonis et al23 reported on insertion of 1662 lateral mass screws in 225 patients. The fusion rate in their group was 97.4% at the mean follow-up of 18 months. Intraoperatively, 27 (1.6%) screws were associated with lateral mass fracture without any neurovascular deficits. Screw removal was required in 3 (1.3%) patients for radiculopathy due to bicortical screws causing nerve root irritation. Screw pullout as a late complication developed in 3 (1.3%) patients within 14 weeks of surgery. The total reoperation rate was 6.2% (14 cases) for nerve injury, hematoma formation, pseudarthrosis, and screw pullout.

Cervical Pedicle Screws

 

Screw loosening or pullout has not been an issue with cervical pedicle screw use.

 

Abumi et al3 used pedicle screw-rod fixation after correction of cervical kyphosis in 30 patients and reported excellent correction and no adverse mechanical or neurovascular sequelae related to the pedicle screws.

 

Yukawa et al48 reported on cervical pedicle screw fixation in 100 patients with unstable cervical injuries. A total of 419 pedicle screws were inserted. They reported a 4% incidence of pedicle perforation (more than 50% of the screw diameter outside the pedicle). Instrumentation failure associated with loss of correction was found in two patients, whereas an additional three patients had a loss of correction of more than 10 degrees on follow-up. Local vertebral alignment around the injured segment measured 6

degrees of kyphosis preoperatively and 6.7 degrees of lordosis postoperatively. Successful bony fusion

was achieved in all patients other than three patients who died shortly after surgery.

 

 

 

P.5153

 

 

COMPLICATIONS

Wiring

The most common complication reported with interspinous wiring is loss of reduction and recurrence of the deformity.

Loss of reduction is more common when posterior wiring is done across a level with fractured posterior elements by bypassing that level.25

Osteoporosis or excessive tensioning of the wires can result in intraoperative or postoperative fracture of a spinous process.

Wire breakage can occur with use of a single-strand wire.

Use of multistrand cable reduces the risk of wire breakage.18,44

Inadvertent passage of spinous process wire through the spinal canal can lead to spinal cord injury.

Appropriate placement of drill holes at the spinolaminar line and avoiding a ventrally placed tract between the holes on either side should avoid this complication.

Lateral Mass Screw Fixation

In a cadaveric comparison of different screw placement techniques, Xu et al45 found that violation of either the dorsal or ventral nerve root was least likely using the modification of the Magerl technique

described by An et al.5

Clinical studies with lateral mass screw insertion have reported a 6% incidence of nerve root injury17 and a 6% incidence of screw malposition.15

Three percent of the patients required screw removal for radiculopathy.15

Screw loosening is reported to occur with an incidence ranging from 2% to 6%.13,15,17

In addition to direct contact of the nerve root by the screw, radiculopathy can also occur from foraminal stenosis as the lateral mass gets pulled up to the rod during final tightening of the construct.

Precise screw length and placement and appropriate contouring of the rod should minimize the incidence of this problem.

Vertebral artery injuries have not been reported after lateral mass plating.

Cervical Pedicle Screws

The medial pedicle wall is the thickest, making medial perforation and spinal cord injury less likely.

The lateral pedicular wall is thin, increasing the risk of lateral perforation during pedicular screw insertion.

There is little to no space between the superior border of the pedicle and the superior nerve root, whereas there is a mean gap of 1.4 to 1.6 mm between the inferior border of the pedicle and the inferior nerve root.46

 

Thus, cortical perforations of the pedicle walls by the pedicular screws are more likely to damage the vertebral artery or superior nerve roots.

 

Abumi et al2 reported a 6.7% (45/669 pedicle screws) incidence of cortical perforation by the screw in 180 consecutive patients.

 

Three of the 180 patients developed screw-associated neurovascular complications, with two patients developed radiculopathy that resolved with nonoperative management.

 

One patient developed vertebral artery injury without neurologic sequelae.

 

 

Kast et al22 reported lateral cortical perforation with more than 25% narrowing of the vertebral artery foramen in 4 of 94 pedicular screws implanted in 26 patients.

 

No vascular or neurologic sequelae occurred with these breaches.

 

Three screws encroached on the intervertebral foramen; one of these screws was revised for a sensory radiculopathy.

 

Nakashima et al31 reported data from a multicenter study on complications of pedicle screw fixation in 84 patients. A total of 390 cervical pedicle screws were inserted. The incidence of pedicle screw misplacement was 19.5%, with 16 (4.1%) of these screws showing more than 50% of the screw diameter outside the pedicle. Complications directly attributable to screw insertion were observed in 5 patients, with nerve root injury in 3 and vertebral artery injury in 2 patients.

 

Yukawa et al47 reported on insertion of 620 cervical pedicle screws in 144 cervical trauma patients. The incidence of pedicle breach (<50% of the screw diameter outside the pedicle) was 9.2%, whereas the incidence of pedicle perforation (>50% of pedicle diameter outside the pedicle) was 3.9%. There was one patient in whom a pedicle probe penetrated the vertebral artery without further complications and one patient with transient radiculopathy.

 

Kotani et al24 reported an improvement in the incidence of pedicle perforation when an image-guided

system was used, whereas other authors27 have not shown significant improvement in safety or accuracy with these systems.

 

Ishikawa et al19 reported on use of intraoperative CT-assisted navigation system for cervical pedicle screw insertion. Of the 108 pedicle screws inserted, 88.9% were completely contained inside the pedicle with no perforation, 8.3% perforated the pedicle with less than 50% of the screw diameter exposed, and 2.8% perforated the pedicle with more than 50% of the screw diameter exposed. There were no instances of complete pedicle perforation with 100% of the screw diameter outside the pedicle.

 

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