4: Odontoid Screw Fixation

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Procedure 4 Odontoid Screw Fixation

Michael A. Finn, Daniel R. Fassett, Ronald I. Apfelbaum

image

Indications

image For surgical fixation of recent (less than 6 months old) type II and some high type III odontoid fractures (Figure 4-1, A and B)

image Offers several advantages

• Immediate stability with no need for external orthosis in most cases
• Preservation of normal C1-2 rotational motion. Some loss of motion may occur, however, because of associated injuries to the atlantoaxial lateral mass articulation at the time of trauma.
• High fusion rate
image image

FIGURE 4-1, A-B

Indications Pitfalls

• Contraindications

• Inability to achieve an appropriate screw trajectory because of chest obstructing trajectory for instruments used to place odontoid screw
• Short neck
• Barrel chest
• Straight or kyphotic cervical alignment
• Inability to extend the neck

• Type III fractures with significant vertebral body involvement because of poor proximal screw fixation

• Transverse ligament disruption (atlantodental interval [ADI] >3 mm). Although magnetic resonance imaging (MRI) has been recommended by some for evaluation of transverse ligament rupture, the authors do not recommend this modality unless neurologic deficits or increased ADI are identified. In the authors’ experience, transverse ligament rupture in the setting of odontoid fracture is very rare.

• Chronic nonunion. Fractures older than 6 months or fractures with sclerotic margins have a much lower fusion rate and should be treated by posterior atlantoaxial arthrodesis.

• Nonreducible canal compromise. Intraoperative reduction has been considered more feasible by a posterior approach in combination with atlantoaxial arthrodesis; however, the guide-tube system to be described allows realignment intraoperatively before placement of an odontoid screw. In the authors’ experience, almost all acute fractures are reducible with traction or intraoperatively.

• Anterior oblique fractures (posterior superior to anterior inferior) can be difficult to reduce and maintain in good alignment with odontoid screw fixation (Figure 4-2, A). Because the screw crosses the fracture line at an angle, and thus tends to pull the odontoid anteriorly, these fractures have lower fusion rates. In the authors’ previously reported series, patients with anterior oblique fractures had an approximately twofold greater risk of nonunion after odontoid screw fixation than did those with horizontal or posterior oblique fractures (anterior superior to posterior inferior) (Figure 4-2, B). By fixing these fractures with the odontoid positioned in a slightly posterior position and using a hard collar type of external orthosis, the authors have usually been able to achieve successful fixation and healing in these patients.

image image image

FIGURE 4-2, A-C

Indications Controversies

• Type III fractures (Figure 4-2, C)

• Some surgeons advocate odontoid screw fixation for high type III fractures, but odontoid screw fixation is contraindicated for type III fractures when there is additional vertebral body involvement because of poor proximal screw fixation.
• Careful study of reformatted computed tomography (CT) scans can help in identification of patients with fractures in the body of C2.

• Chronic nonunion. Although it has been reported that chronic nonunion can be treated with curettage and odontoid screw fixation, the fusion rates are very low, and this fracture is probably better treated with posterior C1-C2 fusion.

• Treatment of the elderly. In the authors’ experience, this procedure is well tolerated in older patients and allows for early mobilization with fewer general medical complications. The incidence of temporary postoperative dysphagia is greater in this group.

• Most cost-effective alternative

• A single odontoid screw is less expensive than posterior atlantoaxial arthrodesis instrumentation alternatives.
• Patients have earlier return to work and activity than with external orthosis.

• Procedure is suited for patients of all ages, including the elderly.

Examination/Imaging

image Neurologic and musculoskeletal examination

image Anteroposterior (AP), lateral, and open-mouth cervical spine radiographs to assess alignment and other fractures. Note that plain films alone are only 65% to 95% sensitive for axis fractures.

image Computed tomography

• Greater sensitivity than plain films
• Horizontally oriented fractures may be missed if one is relying on axial images alone; thus sagittal and coronal reconstructions should be evaluated (Figure 4-3, A and B).
• Useful for operative planning if fracture is obliquely oriented
• Helps exclude patients with concomitant body fractures

image Magnetic resonance imaging

• Should be performed in all cases in which a neurologic deficit is present
• May be used to evaluate integrity of transverse ligament rupture. However, unless suspicion is high (ADI greater than 3 mm), the authors do not routinely perform MRI.
image image

FIGURE 4-3, A-B

Treatment Options

• Nontreatment may be considered for severely debilitated elderly patients.

• External orthoses

• Cervical collar: provides least amount of motion restriction
• Cervical orthosis with thoracic extension (Minerva and SOMI braces) is not recommended because cervical orthoses using an under-the-chin support have been shown to increase upper cervical spine motion with talking and eating.
• Halo vest
• Complications include pin-site infection, intracranial pin penetration or infection, loosening of hardware, and respiratory compromise.
• The overall success rate is about 70%.
• Halo vests are not tolerated well in elderly patients, in whom the success rate is much lower.

• External orthoses have poor fusion rates except in younger patients. The worst fusion rates occur in older patients, patients with fractures with large gaps or subluxations, and those with comminuted fractures.

• Treatment with all forms of external orthosis requires close follow-up and 3 to 6 months of significant activity restrictions.

• Posterior C1-C2 arthrodesis

• Options include transarticular screw fixation, polyaxial C1 and C2 screws with rods, and bone grafting with wiring constructs.
• Results in loss of atlantoaxial motion (approximately 50% of normal axial rotation of the head and 10% of cervical flexion/extension occurs at this joint)
• Greater surgical morbidity
• Longer postoperative recovery
• If noninstrumented atlantoaxial arthrodesis procedures are done, they should be supplemented with a rigid external orthosis until fusion is documented.

Surgical Anatomy

image Knowledge of the neck anatomy is imperative

• Platysma
• Sternocleidomastoid fascia
• Carotid sheath contents
• Trachea and esophagus
• Longus colli
• C2 vertebral body

Anatomy Pearls

• Biplanar fluoroscopy is advantageous (Figure 4-4, A).

• C-arms should be placed for views in the lateral and AP planes.
• One C-arm can be used but requires additional time for frequent rotation.
• A radiolucent mouth gag is used to ensure better AP open-mouth view. A notched wine bottle cork has worked well in the authors’ experience (Figure 4-4, B).

• A folded blanket is placed behind the patient’s shoulders to allow maximal cervical extension, which may be needed to obtain an appropriate odontoid screw trajectory.

• The head is initially kept in neutral position until reduction can be achieved. Halter traction with 10 lb of traction is used to stabilize the head and neck and elevate the chin (Figure 4-4, C).

• If the fracture reduces in extension, the neck is carefully placed into extension under fluoroscopic control to ensure that canal compromise does not occur.
• If the fracture does not reduce in extension, or if the fragment is retrolisthesed, the patient is kept in a neutral position until the spikes on the guide tube are engaged into C3. With the aid of the guide tube, the fracture can be reduced and then, under fluoroscopic control, the neck is placed into extension to improve screw trajectory.
image image image

FIGURE 4-4, A-C

Positioning

image Awake nasotracheal or fiberoptic intubation is used if there is instability in extension.

• Traditional laryngoscopic intubation is safe if the fracture reduces in extension.

image The patient is placed in the supine position with the head immobilized in 10 lb of halter traction (see Figure 4-4, C).

Positioning Equipment

• Two C-arms

• Halter traction

• Bite block

• Shoulder bump

Portals/Exposures

image The initial approach is a standard Cloward or Smith-Robinson approach to the C5-6 level.

image A small unilateral skin incision is made along the natural skin crease at approximately C5. Either side can be approached, but the right side is often preferred by right-handed surgeons.

image The platysma muscle is divided horizontally.

image The sternocleidomastoid muscle is identified and the fascia along the medial border of this muscle is opened sharply.

image The carotid artery is palpated to ensure that the approach is continued medial to this structure.

image Blunt dissection of natural tissue planes provides easy access to the prevertebral space. The trachea and esophagus are retracted medially.

image The prevertebral fascia is incised in the midline at the C5-6 level, and the longus colli muscles are elevated to allow retractor placement.

image Caspar sharp-toothed retractor blades are inserted under the longus colli bilaterally at approximately C5 and attached to a modified retractor blade holder (Figure 4-5).

image Blunt dissection with a Kittner dissector in the prevertebral fascial plane is carried out to C1 and confirmed on lateral fluoroscopy.

image A superior angled retractor blade is inserted to retract the pharyngeal tissues off the anterior upper cervical spine and protect them (see Figure 4-5). This superior retractor is secured to the modified Caspar retractor (Apfelbaum odontoid retractor system).

image image

FIGURE 4-5, A-B

Portals/Exposures Pearls

• Under fluoroscopy, a straight instrument can be placed alongside the neck for optimal location of the skin incision.

• Firm fixation of the Caspar blades beneath the longus muscles is crucial for proper fixation of the retractors during the procedure.

• Deflation and reinflation of the endotracheal tube cuff after placing the lateral retractor allows the endotracheal tube to be recentralized within the larynx, which may reduce the risk of recurrent laryngeal nerve injury.

Portals/Exposures Pitfalls

• Too high an incision prevents proper screw trajectory from the inferior anterior end plate of C2 to the odontoid tip.

Portals/Exposures Instrumentation

• Caspar sharp-toothed cervical retractor blades

• Modified Caspar retractor blade holder

• Superior angled retractor blade (comes in six sizes to fit patient’s anatomy)

Procedure

Step 1

image An entry site on the anterior inferior edge of C2 is chosen and confirmed on AP and lateral fluoroscopy.

• One midline site for one screw
• Two paramedian sites about 2 to 3 mm from the midline for two screws

image A 2-mm Kirschner wire (K-wire) is impacted 3 to 5 mm into the desired entry site (Figure 4-6, A).

image A 7-mm hollow-core hand-twist drill is passed over the K-wire. A groove to accommodate the drill guide is drilled into the anterior face of C3 and the annulus of C2-3 (Figure 4-6, B-D).

image The inner and outer drill guides are mated and placed over the K-wire.

image The outer guide has forward-projecting spikes that are walked up the vertebral column, under live fluoroscopy, to overlie the C3 body.

• The K-wire is trimmed so that no more than 1 cm protrudes from beyond the inner guide tube.
• A plastic impactor is placed over the inner guide tube and a mallet is used to drive the spikes into the C3 body, securing the apparatus (Figure 4-7). These spikes in C3 allow for reduction maneuvers with the guide tube to align C2-3 with the odontoid-C1 complex. They then are used for maintenance of alignment during drilling, tapping, and placement of the screw, establishing the trajectory to reach the tip of the odontoid.

image The inner guide tube is then advanced in the previously created groove (see Figure 4-7, B, large arrow) up to the bottom of C2 (see Figure 4-7, B, small arrow). At this stage, the K-wire can be removed.

image image image image

FIGURE 4-6, A-D

image image

FIGURE 4-7, A-B

Step 1 Pearls

• All steps are monitored on biplanar fluoroscopy.

Step 1 Instrumentation/Implantation

• 2-mm K-wire

• 7-mm hollow-core hand-twist drill

• Inner and outer drill guide tubes

Step 2

image A pilot hole is drilled through the body of C2, across the fracture gap, and into the odontoid fragment using a calibrated drill bit, with attention to drill the distal cortex of the odontoid (Figure 4-8, A).

• The odontoid fragment is realigned by depressing or lifting the guide tube that has been securely fixed to C3.
♦ Further extension of the neck, which may improve screw trajectory, can be accomplished by removing padding from behind the head while keeping the odontoid and C2 aligned with the guide-tube system.
• The apical cortex of the odontoid should be penetrated.
• A 3-mm drill is used for the 4-mm cortical screws, as these screws have a 2.9-mm minor (core) diameter. The drill has excellent directional stability, allowing corrections to be made to the trajectory if needed.
• The depth of the drilling is noted on the calibrated drill shaft. Adjustments in length are made for any gap between the fractured odontoid and C2.

image The inner guide is removed, and the calibrated tap is inserted into the outer guide tube.

• The tap is rotated by hand to tap (cut threads) along the previously drilled pathway.
• The entire length of the pilot hole, including the apical cortex, should be tapped before placement of the screw (Figure 4-8, B).

image A 4-mm, buttress-threaded cortical titanium lag screw (threaded distally only) is inserted into the guide tube and the tapped hole.

• A lag screw is placed across the fracture into the distal odontoid cortex to pull the fractured dens into better approximation with the body of C2 (Figure 4-9, B, arrows). Care must be taken to ensure that the distal cortex of the odontoid is engaged. Because the screw trajectory is tangential to the canal, the dura is not endangered if the screw is advanced several millimeters beyond the odontoid tip.
• The head of the screw should be recessed into the C2-3 annulus or the C2 body.
• Traction should be removed from the patient’s head as the screw is tightened.

image A second screw can placed in the same fashion if anatomy allows.

• Biomechanical studies have failed to show a difference in the immediate stability of one or two screws.
• Although some clinical studies have failed to show a benefit to the placement of two screws, a large retrospective series showed a significant improvement in stability rates (96% vs. 56%) in elderly patients (age >70) undergoing the procedure.

image Stability can be confirmed by flexing and extending the patient’s neck under fluoroscopy.

image The retractors are removed, the wound is irrigated, hemostasis is ensured, and the wound is closed in layers.

image image

FIGURE 4-8, A-B

image image

FIGURE 4-9, A-B

Postoperative Care and Expected Outcomes

image The authors observe all patients in a monitored setting overnight for acute complications, including hematoma development and respiratory compromise.

image The authors do not use external orthoses in most cases. They recommend the use of a rigid collar in the case of an anterior oblique fracture (posterior superior to anterior inferior) and in patients who are very osteoporotic.

image AP and lateral plain radiographs are sufficient, but CT scanning should be considered if any concern exists about screw placement.

image Early ambulation is critical, especially in elderly patients.

image Fusion rates of 85% to 95% have been demonstrated in numerous studies.

• Age, sex, and degree and direction of displacement have no effect on fusion.
• Anterior oblique fracture orientation (anterior inferior to posterior superior) decreases the rate of fusion: 50% fuse in anatomic position, 25% fuse in nonanatomic position, and 25% fail to fuse.

image Full range of cervical motion was present in 83% of patients after fusion.

Evidence

Although no prospective randomized trials have examined the efficacy of odontoid screw fixation, a multitude of retrospective studies have demonstrated consistent fusion rates in the 80% to 90% range when it is used to treat acute fractures. Additionally, preserved motion at the C1-2 joint and the minimal associated morbidity make odontoid screw fixation the treatment of choice for acute odontoid fractures.

Apfelbaum RI, Kriskovich MD, Haller JR. On the incidence, cause and prevention of recurrent laryngeal nerve palsies during anterior cervical spine surgery. Spine. 2000;25:2906-2912.

The authors describe a maneuver of deflating and reinflating the endotracheal (ET) tube cuff after placement of cervical retractors to allow the ET tube to centralize within the larynx to prevent recurrent laryngeal nerve injury (RLN). With this maneuver, they reduced the rate of RLN injury from 6.4% to 1.7% (Level IV evidence [case series]: a retrospective review of the incidence of RLN injury associated with anterior cervical spine surgery in 900 consecutive patients).

Apfelbaum RI, Lonser RR, Veres R, Casey A. Direct anterior screw fixation for recent and remote odontoid fractures. J Neurosurg. 2000;93(Suppl 2):227-236.

This study examines the optimum timing and results of odontoid screw surgery. Surgery performed within 6 months of injury and a fracture oriented in a horizontal or posterior oblique plane (anterior superior to posterior inferior) resulted in significantly higher fusion rates than fractures treated more than 18 months after injury and those oriented in an anterior oblique fashion (anterior inferior to posterior superior) (Class IV evidence: retrospective review of 147 patients).

Dailey AT, Hart D, Finn MA, Schmidt MH, Apfelbaum RI. Anterior fixation of odontoid fractures in an elderly population. J Neurosurg Spine. 2010;12:1-8.

This study demonstrates a significantly increased stability rate in patients over age 70 undergoing odontoid screw fixation with two screws versus one screw. Elderly patients and those with osteoporotic bone may benefit from the placement of two screws. (Class IV evidence: retrospective review of 57 patients).

Fountas KN, Kapsalaki EZ, Karampelas I, et al. Results of long-term follow-up in patients undergoing anterior screw fixation for type II and rostral type III odontoid fractures. Spine. 2005;30:661-669.

The authors report on the high fusion rate of odontoid screw fixation with a mean follow-up time of 58.4 months, confirming the long-term success of the procedure (Class IV evidence: retrospective review of 31 patients).

Greene KA, Dickman CA, Marciano FF, et al. Acute axis fractures: analysis of management and outcome of 340 consecutive cases. Spine. 1997;22:1843-1852.

Report on treatment of type II fractures with halo immobilization with a 26% overall nonunion rate, but a 67% nonunion rate in fractures displaced greater than 6 mm (Class IV evidence [case series]: retrospective review of 340 axis fractures with 119 type II odontoid fractures in the case series).

Jenkins JD, Coric D, Branch CLJr. A clinical comparison of one- and two-screw odontoid fixation. J Neurosurg. 1998;89:366-370.

The study demonstrated no difference in fusion rate with the use of one or two screws. A good discussion of this controversial topic is provided (Class IV evidence: retrospective review of 42 patients).

Majercik S, Tashjian RZ, Biffl WL, Harrington DT, Cioffi WG. Halo vest immobilization in the elderly: a death sentence? J Trauma. 2005;59:350-357.

The authors report on the use of halo vest immobilization in the elderly and increased morbidity associated with this treatment (Class IV [case series]: retrospective review of 456 consecutive cervical spine fractures).

Montesano PX, Anderson PA, Schlehr F, Thalgott JS, Lowrey G. Odontoid fractures treated by anterior odontoid screw fixation. Spine. 1991;16(Suppl 3):S33-S37.

The authors report on their results with this treatment and comment on its usefulness in polytrauma patients (Class IV evidence [case series]: retrospective review of 14 patients).

Sasso R, Doherty BJ, Crawford MJ, Heggeness MH. Biomechanics of odontoid fracture fixation: comparison of the one- and two-screw technique. Spine. 1993;18:1950-1953.

This study found that odontoid screw fixation provides 50% of the stability of the unfractured odontoid and that two screws offer slightly more stiffness in extension loading only (cadaveric study).

Subach BR, Morone MA, Haid RWJr, et al. Management of acute odontoid fractures with single-screw anterior fixation. Neurosurgery. 1999;45:812-819. discussion 819-20

The authors report a 96% fusion rate in 26 patients with acute fractures treated with odontoid screw surgery (Class IV evidence: retrospective review of 26 patients).

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