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Pediatric Cervical Spine
A variety of diseases and congenital anomalies may affect the pediatric cervical spine and increase the risk for neurologic compromise from instability or encroachment of the spinal cord. Multiple anomalies of the upper cervical spine are common within a single patient, so when a single anomaly is seen in a patient, others should be sought. An average of 3.4 cervical spine osseous anomalies per patient has been reported.
Normal Embryology and Growth and Development
Most disorders of the spine are the result of aberrant growth and developmental processes. Knowledge of the normal embryology, growth, and development of the pediatric cervical spine is necessary to aid in the understanding of these conditions. In embryonic development of the spine, 42 to 44 pairs of somites (4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8 to 10 coccygeal) will form craniocaudally from the mesoderm on either side of the notochord. Each somite differentiates into either sclerotomes or dermomyotomes. Sclerotomes, precursors of the vertebral arch and body, collect at the embryonic midline, surrounding the neural tube and notochord, and proceed to separate into cranial and caudal portions. The cranial portion of each sclerotome then recombines with the caudal portion of the direct superior sclerotome, eventually forming vertebrae. In the cervical spine, eight pairs of embryonic somites create seven cervical vertebrae, with the cranial portion of the first cervical sclerotome contributing to the development of the occiput and the caudal portion of the eighth cervical sclerotome contributing to the formation of the T1 vertebrae.
The mechanism in the formation of the occiput-cervical junction is different and more complex. The first four spinal sclerotomes fuse to form the occiput and posterior foramen magnum. The cranial portion of the first cervical sclerotome remains as half a segment, eventually becoming part of the occipital condyle and tip of the odontoid (proatlas). The atlas is formed by cell contributions from the first cervical sclerotome and the fourth occipital sclerotome. However, unlike the other sclerotomes, the vertebral arch of the first sclerotome separates from the centrum to become the ring of C1 and fuses with the proatlas above and the centrum of C2, becoming the odontoid process and body of C2. Thus, the axis is created by cell contributions from the cranial half of the first cervical sclerotome (tip of the odontoid), the second cervical sclerotome, and the centrum, which become the body of the odontoid. The inferior portion of the axis body is formed from the second cervical sclerotome.
The HOX and PAX regulatory genes are believed to have a role in embryonic differentiation. HOX genes specify the vertebral morphology phenotype along the embryonic axis. The PAX genes are also integral in vertebral development and are thought to establish the intervertebral boundaries of the sclerotomes. Abnormalities of the PAX1 sequence in humans are associated with Klippel-Feil syndrome.
At birth, the atlas has three ossification centers, one for the body and one for each neural arch. Although the posterior arches usually fuse by 3 years of age, occasionally the posterior synchondrosis between the two fails to fuse, resulting in a bifid arch. The neurocentral synchondroses that connect the neural arches to the body close by 7 years of age.
The axis has four separate ossification centers: one for the dens, one for the body, and two for the neural arches. The neurocentral synchondroses connect the body to the adjacent lateral masses, and the dentocentral synchondrosis connects it to the dens. The dentocentral synchondrosis closes by 6 to 7 years of age; it may persist as a sclerotic line until 11 years. The neural arches of C2 fuse at 3 to 6 years of age. Occasionally, the tip of the odontoid is V shaped (dens bicornum), or a small separate summit ossification center may be present at the tip of the odontoid (ossiculum terminale).
Ossification of the third through seventh cervical vertebrae is similar: a single ossification center for the vertebral body and one for each neural arch. Between the ages of 2 and 3 years, the neural arch fuses posteriorly, and by 3 to 6 years the neurocentral synchondroses between the neural arches and the vertebral body fuse. Until 7 to 8 years of age, these vertebrae are normally wedge-shaped.
The clinical presentations of patients with pediatric cervical spine disorders are variable; however, most common presentations are deformity, pain, limited motion, and neurologic compromise.
Anomalies of the Odontoid
Although congenital anomalies of the odontoid are rare, they can cause significant atlantoaxial instability. These anomalies usually are detected as incidental findings after trauma or when symptoms occur. Atlantoaxial instability can cause a compressive myelopathy, vertebral artery compression, or both.
Congenital anomalies of the odontoid can be divided into three groups: aplasia, hypoplasia, and os odontoideum ( Fig. 43.1 ). Aplasia or agenesis is complete absence of the odontoid. Hypoplasia is partial development of the odontoid, and the bone varies from a small, peg-like projection to almost normal size. Odontoid hypoplasia and aplasia have been associated with spondyloepiphyseal dysplasia and mucopolysaccharidosis (Hunter, Hurler, Morquio, and Maroteaux-Lamy syndromes). In os odontoideum, the odontoid is an oval or round ossicle with a smooth, sclerotic border. It is separated from the axis by a transverse gap, leaving the apical segment without support ( Fig. 43.1D ). The ossicle is of variable size and usually is in the position of the normal odontoid (orthotopic), although occasionally it appears near the occiput in the area of the foramen magnum (dystopic). Because this lesion is frequently asymptomatic and remains undiscovered until it is brought to the physician’s attention by trauma or the onset of symptoms, the exact incidence of os odontoideum is unknown, but it is probably more common than appreciated. Odontoid anomalies have been reported to be more common in patients with Down syndrome, Klippel-Feil syndrome, Morquio syndrome, and spondyloepiphyseal dysplasia.
Knowledge of the embryology and vasculature of the odontoid is essential to understanding the etiologic theories of congenital anomalies of the odontoid. The odontoid is derived from mesenchyme of the first cervical vertebra. During development, it becomes separated from the atlas and fuses with the axis. A vestigial disc space between C1 and C2 forms a synchondrosis within the body of the axis. The apex, or tip, of the odontoid is derived from the most caudal occipital sclerotome, or proatlas. This separate ossification center, called ossiculum terminale , appears at age 3 and fuses by age 12. Anomalies of this terminal portion are rarely of clinical significance ( Figs. 43.1C and 43.2 ).
The arterial blood supply to the odontoid is derived from the vertebral and carotid arteries ( Fig. 43.3 ). The vertebral artery gives off an anterior ascending artery and a posterior ascending artery that begin at the level of C3 and ascend anterior and posterior to the odontoid, meeting superiorly to form an apical arcade. The most rostral portion of the extracranial internal carotid artery gives off “cleft perforators,” which supply the superior portion of the odontoid. This peculiar arrangement of blood supply is necessary because of the embryologic development and anatomic function of the odontoid. The synchondrosis prevents direct vascularization of the odontoid from C2, and vascularization from the blood supply of C1 cannot occur because of the synovial joint cavity surrounding the odontoid.
Congenital and acquired causes (posttraumatic) of odontoid anomalies have been suggested. Trauma has been reported in up to 50% of patients. Congenital causes include failure of fusion of the apex or ossiculum terminale and failure of fusion of the odontoid to the axis, neither of which explains all the findings in os odontoideum. The ossiculum terminale is usually too small to influence stability significantly, and the theory of failure of fusion of the odontoid to the axis does not explain the fact that the space between the ossicle and the axis is at the level of the articulating facets of C2, rather than below the level of the articulating facets where the synchondrosis occurs during development. A congenital etiology is supported by the increased incidence among patients with Down syndrome, Klippel-Feil malformation, multiple epiphyseal dysplasia, and other skeletal dysplasias compared with the general population. Os odontoideum can be acquired after infection or trauma or can result from osteonecrosis. Several authors have suggested that an unrecognized fracture at the base of the odontoid is the most common cause. A distraction force by the alar ligament pulls the tip of the fractured odontoid away from its base to produce a nonunion. Osteonecrosis after halo-pelvic traction has been reported.
Diagnosis
The presentation of os odontoideum varies. Signs and symptoms can range from minor to frank compressive myelopathy or vertebral artery compression. Presenting symptoms may include neck pain, torticollis, or headache caused by local irritation of the atlantoaxial joint. Neurologic symptoms vary from transient episodes of paresis after trauma to complete myelopathy caused by cord compression. Symptoms may consist of weakness and loss of balance with upper motor neuron signs, although upper motor neuron signs may be completely absent. Proprioceptive and sphincter disturbances are common findings. Vertebral artery compression causes cervical and brainstem ischemia, resulting in seizures, syncope, vertigo, and visual disturbances. Lack of cranial nerve involvement helps differentiate os odontoideum from other occipitovertebral anomalies because the spinal cord impingement occurs below the foramen magnum.
Radiographic findings
Odontoid anomalies can be diagnosed on routine cervical spine radiographs that include an open-mouth odontoid view ( Fig. 43.4 ). CT scans with reconstruction views and MRI are helpful in making the initial diagnosis of os odontoideum. Lateral flexion and extension radiographs can detect any instability. Odontoid aplasia appears as a slight depression between the superior articulating facets on the open-mouth odontoid view. Odontoid hypoplasia is seen as a short, bony remnant. With os odontoideum, a space is present between the body of the axis and a bony ossicle. The free ossicle of os odontoideum is usually half the size of a normal odontoid and is oval or round with smooth, sclerotic borders. The space differs from that of an acute fracture, in which the space is thin and irregular instead of wide and smooth. This space should not be confused with the neurocentral synchondrosis in children younger than 6 to 7 years of age.
The amount of instability can be documented by lateral flexion and extension plain films that allow measurement of the amount of anterior and posterior displacement of the atlas on the axis. In children, motion between the odontoid and the body of the axis must be shown before instability with os odontoideum can be diagnosed because the ossicle is fixed to the anterior arch of C1 and moves with it during flexion and extension. Measurement of the relation of C1 to the free ossicle is of little value because this moves as one unit. A more significant measurement is made by projecting a line superiorly from the body of the axis to a line projected inferiorly from the posterior border of the anterior arch of the atlas. Measurements of more than 4 to 5 mm in children indicate significant instability.
The space available for the spinal cord also is a helpful measurement. This space is determined by measuring the distance from the posterior aspect of the odontoid or axis to the nearest posterior structure. Fielding reported that most symptomatic patients in his study had an average of 1 cm of movement. Cineradiography can also be helpful in determining motion around the C1-2 articulation.
Watanabe, Toyama, and Fujimura described two radiographic measurements that correlate with neurologic signs and symptoms. They found that if there is a sagittal plane rotation angle of more than 20 degrees or an instability index of more than 40%, a patient is likely to have neurologic signs and symptoms. The instability index is measured from lateral flexion and extension radiographs. Minimal and maximal distances are measured from the posterior border of the C2 body to the posterior arc of the atlas. The instability index is calculated by the following equation:
The sagittal plane rotation angle is measured by the change in the atlantoaxial angle between flexion and extension ( Fig. 43.5 ). MRI can be useful in identifying reactive retrodental lesions that can occur with chronic instability. This reactive tissue is not seen on routine radiographs but can be responsible for a decrease in the space available for the spinal cord and compressive myelopathy. The prognosis of os odontoideum depends on the clinical presentation. The prognosis is good if only mechanical symptoms (torticollis or neck pain) or transient neurologic symptoms exist. It is poor if neurologic deficits slowly progress.
Treatment
The primary concern in congenital anomalies of the odontoid is that an already abnormal atlantoaxial joint can subluxate or dislocate with minor trauma and cause permanent neurologic damage or even death. Patients with local symptoms usually improve with conservative treatment and immobilization. The indications for operative stabilization are: (1) neurologic involvement (even if this is transient), (2) instability of more than 5 mm anteriorly or posteriorly, (3) progressive instability, and (4) persistent neck complaints associated with atlantoaxial instability and not relieved by conservative treatment ( Box 43.1 ).
BOX 43.1
Indications for Operative Stabilization of Os Odontoideum
- ▪
Neurologic involvement (even transient)
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Instability of greater than 5 mm posteriorly or anteriorly
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Progressive instability
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Persistent neck complaints
Prophylactic operative stabilization of odontoid instability of less than 5 mm in asymptomatic patients is controversial. Because it may be difficult or impossible to restrict a child’s activities, the safety of stability without restriction of activity must be weighed against the possible complications of surgery. The decision concerning prophylactic arthrodesis must be made after discussion with the patient and family concerning potential risks of operative and nonoperative treatment. Delayed neurologic injury has been reported in three patients who initially received conservative treatment. We, therefore, recommend prophylactic stabilization of os odontoideum.
In patients with neurologic deficits, skull traction can be used before surgery to achieve reduction. Achieving and maintaining reduction are probably the most important aspects in the treatment of this anomaly. Dlouhy et al. found that the transverse ligament anterior and inferior to the ossicle was the most common factor preventing reduction of an os odontoideum.
Before C1-2 fusion, the integrity of the posterior arch of C1 must be documented. Incomplete development of the posterior ring of C1 is uncommon (3 cases in 1000) but is reported to occur with increased frequency in patients with os odontoideum.
Posterior cervical approaches
Atlantoaxial Fusion
Many variations of two basic techniques of atlantoaxial fusion exist ( Box 43.2 ). The Gallie and the Brooks and Jenkins techniques have been the most frequently used for posterior atlantoaxial fusion ( Figs. 43.6 to 43.8 ). The Gallie technique has the advantage of using only one wire passed beneath the lamina of C1, but tightening the wire can cause the unstable C1 vertebra to displace posteriorly and fuse in a dislocated position ( Fig. 43.6 ). The Brooks and Jenkins technique has the disadvantage of requiring sublaminar wires at C1 and C2 but gives greater resistance to rotational movement, lateral bending, and extension. The wire varies in size from 22 gauge to 18 gauge, depending on the age of the patient and the size of the spinal canal. Songer cables may also be used instead of wires for the Brooks and Jenkins fusion. In a very young child, wire fixation may be unnecessary; instead, the graft is placed along the decorticated fusion site, and a halo or Minerva cast is used for postoperative immobilization. With the use of fluoroscopy and image-guided systems, C1-2 transarticular screws or C1-2 screw and rod fixation can be used for stabilization in appropriately sized children and is often the preferred fixation method.
BOX 43.2
Posterior Fusion Techniques
Atlantoaxial Fusion
Gallie
-
Advantage: One wire passed beneath lamina of C1.
-
Disadvantage: Wire may cause unstable C1 vertebra to displace posteriorly and fuse in dislocated position; need for postoperative halo immobilization.
Brooks and Jenkins
-
Advantage: Greater resistance to rotational movement, lateral bending, and extension.
-
Disadvantage: Requires sublaminar wires at C1 and C2.
Harms and Melcher
-
Advantage: Individual placement of polyaxial screws simplifies technique and involves less risk to C1-C2 facet joint and vertebral artery.
-
Disadvantages: Possible irritation of the C2 ganglion from instrumentation. Technique is not possible in patients with aberrant course of the vertebral artery (20%).
Magerl and Seeman
-
Advantage: Significant improvement in fusion rates over traditional posterior wire stabilization and bone grafting techniques.
-
Disadvantage: Technically demanding and must be combined with Gallie or Brooks fusion for maximum stability.
Occipitocervical Fusion
Occipital Rod and Screw Fusion
Cone and Turner; Willard and Nicholson; Rogers
-
Required when other bony anomalies occur at occipitocervical junction.
Wertheim and Bohlman
-
Wires passed through outer table of skull at occipital protuberance instead of through inner and outer tables near foramen magnum.
-
Lessens risk of danger to superior sagittal and transverse sinuses (which are cephalad to occipital protuberance).
Koop, Winter, Lonstein
-
No internal fixation used.
-
Autogenous corticocancellous iliac bone graft.
Dormans et al.
-
Stable fixation is achieved by exact fit of autogenous iliac crest bone graft and fixation of the spinous process with button wire and fixation of the occiput with wires through burr holes.
-
Can be used in high-risk patients (Down syndrome) with increased stabilization and shorter immobilization time.
Contoured Rod, Screw, or Contoured Plate Fixation
-
Has the advantage of achieving immediate stability of the occipitocervical junction.
Posterior Atlantoaxial Fusion
Technique 43.1
(Gallie)
- ▪
Carefully intubate the patient in the supine position while the patient is on a stretcher. Place the patient prone on the operating table with the head supported by traction, maintaining the head-thorax relationship at all times during turning. Obtain a lateral cervical spine radiograph to ensure proper alignment before surgery.
- ▪
Prepare and drape the skin in a sterile fashion and inject a solution of epinephrine (1:500,000) intradermally to aid hemostasis.
- ▪
Make a midline incision from the lower occiput to the level of the lower end of the fusion, extending it deeply within the relatively avascular midline structures, the intermuscular septum, or ligamentum nuchae. Do not expose any more than the area to be fused to decrease the chance of spontaneous extension of the fusion.
- ▪
By subperiosteal dissection, expose the posterior arch of the atlas and the laminae of C2.
- ▪
Remove the muscular and ligamentous attachments from C2 with a curet or periosteal elevator; dissect laterally along the atlas to prevent injury to the vertebral arteries and vertebral venous plexus that lie on the superior aspect of the ring of C1, less than 2 cm lateral to the midline.
- ▪
Expose the upper surface of C1 no farther laterally than 1.5 cm from the midline in adults and 1 cm in children. Decortication of C1 and C2 is generally unnecessary.
- ▪
From below, pass a wire loop of appropriate size upward under the arch of the atlas directly or with the aid of a nonabsorbable suture, which can be passed with an aneurysm needle.
- ▪
Pass the free ends of the wire through the loop, grasping the arch of C1 in the loop.
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Take a corticocancellous graft from the iliac crest and place it against the laminae of C2 and the arch of C1 beneath the wire.
- ▪
Pass one end of the wire through the spinous process of C2 and twist the wire on itself to secure the graft in place.
- ▪
Irrigate the wound and close it in layers with suction drainage tubes.
Fielding described several modifications of the Gallie fusion, as shown in Figure 43.7 .
Postoperative Care
The patient is immobilized in a Minerva cast, halo cast or halo vest, or a cervicothoracic orthosis. Immobilization usually is continued for 12 weeks.
Posterior Atlantoaxial Fusion Using Laminar Wiring
Technique 43.2
(Brooks and Jenkins)
- ▪
Intubate and turn the patient onto the operating table as for the Gallie technique (Technique 43.1). Prepare and drape the operative site as described.
- ▪
Expose C1 and C2 through a midline incision.
- ▪
Using an aneurysm needle, pass a Mersilene suture from cephalad to caudad on each side of the midline under the arch of the atlas and then beneath the laminae of C2 ( Fig. 43.8A ). These sutures serve as guides to introduce two doubled 20-gauge wires. The size of the wire used varies depending on the size and age of the patient.
- ▪
Obtain two full-thickness bone grafts 1.25 to 3.5 cm from the iliac crest and bevel them so that the apex of the graft fits in the interval between the arch of the atlas and the lamina of the axis ( Fig. 43.8B ).
- ▪
Fashion notches in the upper and lower cortical surfaces to hold the circumferential wires and prevent them from slipping.
- ▪
Tighten the doubled wires over the graft and twist them on each side ( Fig. 43.8C and D).
- ▪
Irrigate and close the wound in layers over suction drains.
Postoperative Care
The postoperative care is the same as that for the Gallie technique.
C1-2 Fixation with Transarticular Screws and with Screw and Rods (Harms Technique)
Adult instrumentation and fusion techniques may be used in the pediatric cervical spine. The use of this instrumentation is dependent on the preoperative anatomy that would allow appropriate size screws to be placed safely. Adult instrumentation of the cervical spine usually can be used in adolescents and preteens. For smaller children, the use of these adult instrumentation techniques becomes more difficult but can be used safely in certain patients. Wang et al. reported good results in the management of pediatric atlantoaxial instability with C1-2 transarticular screw fixation and fusion, using a 3.5-mm screw in children of 4 years of age. Originally described for adult patients, it is technically demanding and requires fluoroscopic or stereotactic assistance for the proper placement of the transarticular screw ( Fig. 43.9 ). Harms and Melcher reported posterior C1-C2 fusion using polyaxial screw and rod fixation in adults and children with good results. They cited the following advantages: individual placement of polyaxial screws in C1 and C2 allows direct manipulation of C1 and C2, simplifying reduction and fixation; superior and medial placement of the C2 screw carries less risk to the vertebral artery; the integrity of the posterior arch of C1 is not necessary for stable fixation ( Fig. 43.10 ). Please refer to Chapter 41 for transarticular screw fixation technique in adults.
Translaminar Screw Fixation of C2
Translaminar screw fixation can be used as an alternative to polyaxial screw and rod fixation when the C2 isthmus or pedicle cannot be instrumented. Approximately 20% of patients have an abnormal path of the vertebral artery that will prevent placement of the C2 screw in Harms and Melcher’s technique. Translaminar screw fixation may also be used in the lower cervical spine if needed.
Technique 43.3
- ▪
Place the patient prone with the head in a neutral position in a Mayfield head holder.
- ▪
Expose the posterior arch of C1 and the spinous process, laminae, and medial and lateral masses of C2.
- ▪
Create a small cortical window at the junction of the C2 spinous process and the lamina on the left, close to the rostral margin of the C2 lamina ( Fig. 43.11A ).
- ▪
Using a hand drill, carefully drill along the length of the contralateral (right) lamina, with the drill visually aligned along the angle of the exposed contralateral laminar surface.
- ▪
Palpate the length of the drill hole with a small ball probe to verify that no cortical breakthrough into the spinal canal has occurred.
- ▪
Insert a 4-mm diameter polyaxial screw along the same trajectory. In the final position, the screw head is at the junction of the spinous process and lamina on the left, with the length of the screw within the right lamina.
- ▪
Create a small cortical window at the junction of the spinous process and lamina of C2 on the right, close to the caudal aspect of the lamina.
- ▪
Using the same technique as above, insert a 4-mm diameter screw into the left lamina, with the screw head remaining on the right side of the spinous process.
- ▪
Place appropriate rods into the screw heads and attach to C1 screws or lateral mass screws below C2 ( Fig. 43.11B ).
Postoperative Care
The patient is immobilized in a cervical or cervicothoracic orthosis for 8 to 12 weeks.
Occipitocervical Fusion
When other bony anomalies occur at the occipitocervical junction, such as absence of the posterior arch of C1, the fusion can extend up to the occiput. The following technique for occipitocervical fusion includes features of techniques described by Cone and Turner, Rogers, Willard and Nicholson, and Robinson and Southwick.
Technique 43.4
- ▪
Approach the base of the occiput and the spinous processes of the upper cervical vertebrae through a longitudinal midline incision, extending it deeply within the relatively avascular intermuscular septum.
- ▪
Expose the entire field subperiosteally.
- ▪
Dissect the posterior occiput laterally to the level of the external occipital protuberance.
- ▪
Make two burr holes in the posterior occiput about 7 mm from the foramen magnum and 10 mm lateral to the midline ( Fig. 43.12 ).
- ▪
Separate the dura from the inner table of the skull by blunt dissection with a right-angle dissector.
- ▪
Pass short lengths of wire through the holes in the occiput and through the foramen magnum.
- ▪
Pass wires beneath the posterior arch of C1 on either side if the arch is intact.
- ▪
Drill holes in the outer table of the spinous processes of C2 and C3, completing them with a towel clip or Lewin clamp, and pass short lengths of wire through the holes.
- ▪
Obtain a corticocancellous graft from the iliac crest and make holes at appropriate intervals to accept the ends of the wires.
- ▪
Pass the wires through the holes in the graft and lay the graft against the occiput and the laminae of C2 and C3.
- ▪
Tighten the wires to hold the graft firmly in place ( Fig. 43.12 , inset ).
- ▪
Lay thin strips of cancellous bone around the cortical grafts to aid in fusion.
- ▪
Inspect the graft and wires to ensure that they do not impinge on the dura or vertebral arteries. Irrigate and close the wound in layers over suction drains.
Robinson and Southwick passed individual wires beneath the laminae of C2 and C3 instead of through the spinous processes ( Fig. 43.12 ).
Postoperative Care
Some form of external support is recommended. This support may vary from a Minerva cast or halo vest or halo cast to a cervicothoracic brace, depending on the degree of preoperative instability and the stability of fixation.
Occipitocervical Fusion Passing Wires Through Table of Skull
Wertheim and Bohlman described a technique of occipitocervical fusion similar to that described by Grantham et al. in which wires are passed through the outer table of the skull at the occipital protuberance instead of through the inner and outer tables of the skull near the foramen magnum. Superior to the foramen magnum the occipital bone is very thin, but at the external occipital protuberance, it is thick and allows passage of wires without passing through both tables. The transverse and superior sagittal sinuses are cephalad to the protuberance and are out of danger.
Technique 43.5
(Wertheim and Bohlman)
- ▪
Stabilize the spine preoperatively with cranial skeletal traction with the patient on a turning frame or cerebellar headrest.
- ▪
Place the patient prone and obtain a lateral radiograph to document proper alignment.
- ▪
Prepare the skin and inject the subcutaneous tissue with a solution of epinephrine (1:500,000).
- ▪
Make a midline incision extending from the external occipital protuberance to the spine of the third cervical vertebra.
- ▪
Sharply dissect the paraspinous muscles subperiosteally with a scalpel and a periosteal elevator to expose the occiput and cervical laminae, taking care to stay in the midline to avoid the paramedian venous plexus.
- ▪
At a point 2 cm above the rim of the foramen magnum, use a high-speed diamond burr to create a trough on either side of the protuberance, making a ridge in the center ( Fig. 43.13A ). With a towel clip, make a hole in this ridge through only the outer table of bone.
- ▪
Loop a 20-gauge wire through the hole and around the ridge and loop another 20-gauge wire around the arch of the atlas.
- ▪
Pass a third wire through a drill hole in the base of the spinous process of the axis and around this structure; three separate wires are used to secure the bone grafts on each side of the spine ( Fig. 43.13B ).
- ▪
Expose the posterior iliac crest and obtain a thick, slightly curved graft of corticocancellous bone of premeasured length and width.
- ▪
Divide this horizontally into two pieces and place three drill holes in each graft ( Fig. 43.13C ).
- ▪
Decorticate the occiput and anchor the grafts in place with the wires on both sides of the spine ( Fig. 43.13D ). Pack additional cancellous bone around and between the two grafts.
- ▪
Close the wound in layers over suction drains.
Postoperative Care
A rigid cervical orthosis or a halo cast is worn for 6 to 16 weeks, followed by a soft collar that is worn for an additional 6 weeks.
Occipitocervical Fusion Without Internal Fixation
Koop, Winter, and Lonstein described a technique of occipitocervical fusion without internal fixation for use in children. The spine is decorticated, and autogenous corticocancellous iliac bone is placed over the area to be fused. In children with vertebral arch defects, an occipital periosteal flap is reflected over the bone defect to provide an osteogenic tissue layer for the bone grafts. A halo cast is used for postoperative stability.
Technique 43.6
(Koop Et Al.)
- ▪
After the administration of endotracheal anesthesia, apply a halo frame with the child supine.
- ▪
Turn the child prone and secure the head with the neck in slight extension by securing the halo frame to a traction frame.
- ▪
Make a midline incision. In patients with intact posterior elements, expose the vertebrae by sharp dissection.
- ▪
Decorticate the exposed vertebral elements and lay strips of autogenous cancellous iliac bone over the decorticated bone. Expose only the vertebrae to be included in the fusion. In patients with defects in the posterior elements, do not expose the dura, if possible.
- ▪
At the level of the occiput, dissect the nuchal tissue from the periosteum and retract it laterally ( Fig. 43.14A ).
- ▪
Elevate the occipital periosteum in a triangular-based flap attached near the margin of the foramen magnum.
- ▪
Reflect this flap caudally to cover the defects in the posterior vertebral elements and suture it in place ( Fig. 43.14B ).
- ▪
Decorticate the occiput and the remaining exposed vertebral elements with an air drill ( Fig. 43.14C ).
- ▪
Lay strips of autogenous cancellous bone in place over the entire area ( Fig. 43.14D ).
- ▪
Close the wound in layers over a suction drain.
- ▪
Turn the child supine and apply a halo cast.
Postoperative Care
The halo cast is worn until union is radiographically evident, usually at about 5 months. When union is documented by lateral flexion and extension radiographs, the halo cast is removed, and a soft collar is worn for 1 month.
Occipitocervical Fusion Using Crossed Wiring
Dormans et al. described occipitocervical fusion using a different wiring technique in 16 children with an average age of 9.6 years (range 2.5 to 19.3 years). Fusion was achieved in 15 patients. Complications included pin track infection (four patients), pneumonia (one patient), additional level of fusion (one patient), and graft fracture and nonunion (one patient). The use of wire fixation, combined with inherent stability of the bone-graft construct, allowed for removal of the halo device relatively early (6 to 12 weeks).
Technique 43.7
(Dormans Et Al.)
- ▪
After halo ring application, place the patient prone and secure the halo frame to the operating table. Confirm alignment of the occiput and cervical spine with lateral radiographs.
- ▪
Expose the midline from the occiput to the second or third cervical vertebra. Limit the lateral dissection to avoid damaging the vertebral arteries.
- ▪
In patients who require decompression because of cervical stenosis or for removal of a tumor, remove the arch of the first or second cervical vertebra, or both, with or without removal of a portion of occipital bone to enlarge the foramen magnum.
- ▪
Use a high-speed drill to make four holes through both cortices of the occiput, aligning them transversely with two on each side of the midline and leaving a 1-cm osseous bridge between the two holes of each pair. Place the holes caudad to the transverse sinuses ( Fig. 43.15A ).
- ▪
Fashion a trough into the base of the occiput to accept the cephalad end of the bone graft.
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Obtain a corticocancellous graft from the iliac crest and shape it into a rectangle, with a notch created in the inferior base to fit around the spinous process of the second or third cervical vertebra ( Fig. 43.15B ). The caudal extent of the intended fusion (the second or third cervical vertebra) is determined by the presence or absence of a previous laminectomy, congenital anomalies, or level of instability.
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Pass a looped 16- or 18-gauge Luque wire through the burr holes on each side and loop it onto itself.
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Pass Wisconsin button wires (Zimmer, Warsaw, IN) through the base of the spinous process of either the second or the third cervical vertebra ( Fig. 43.15C ). Pass the wire that is going into the left arm of the graft through the spinous process from right to left. Place the graft into the occipital trough superiorly and around the spinous process of the vertebra that is to be at the caudal level of the arthrodesis (the second or third cervical vertebra).
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Contour the graft precisely so that it fits securely into the occipital trough and around the inferior spinous process before the wires are tightened.
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Cross the wires, twist, and cut ( Fig. 43.15D ).
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Obtain a radiograph at this point to assess the position of the graft and wires and the alignment of the occiput and cephalad cervical vertebrae. Extension of the cervical spine can be controlled by positioning of the head with the halo frame, by adjustment of the size and shape of the graft, and, to a lesser extent, by appropriate tightening of the wires.
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For patients who have not had a decompression, pass the sublaminar wire caudally to the ring of the first cervical vertebra to secure additional fixation. In young children, this may be difficult or undesirable because of the small size of the ring of the first cervical vertebra or the failure of formation of the posterior arch of the first cervical vertebra.
Postoperative Care
A custom halo orthosis or halo cast is worn until a solid fusion is obtained; thereafter, a cervical collar is worn for 1 month.
Occipitocervical Fusion Using Contoured Rod and Segmental Rod Fixation
Occipitocervical fusion using a contoured rod and segmental wire or cable fixation, which has been described by several authors, has the advantage of achieving immediate stability of the occipitocervical junction. This stability allows the patient to move in a cervical collar after surgery, avoiding the need for halo cast immobilization. Smith et al. described occipitocervical arthrodesis using a contoured plate instead of a rod for fixation.
Technique 43.8
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Approach the base of the occiput and the spinous processes of the upper cervical vertebrae through a longitudinal midline incision, extending it deeply within the relatively avascular intermuscular septum.
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Expose the entire field subperiosteally.
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Carry the dissection proximally above the inion and laterally to the level of the external occipital protuberance.
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Make a template of the intended shape of the stainless-steel rod with the appropriate length of Luque wire.
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Make two burr holes on each side, about 2 cm lateral to the midline and 2.5 cm above the foramen magnum. Avoid the transverse and sigmoid sinus when making these burr holes. Leave at least 10 mm of intact cortical bone between the burr holes to ensure solid fixation.
- ▪
Pass Luque wires or Songer cables in an extradural plane through the two burr holes on each side of the midline. Pass the wires or cables sublaminar in the upper cervical spine.
- ▪
Bend the rod to match the template; this usually has a head-neck angle of about 135 degrees and slight cervical lordosis. A Bend Meister (Sofamor/Danek, Memphis) may be helpful in bending the rod.
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Secure the wires or cables to the rod.
- ▪
Decorticate the spine and occiput and perform autogenous cancellous bone grafting.
Postoperative Care
A Philadelphia collar or an occipitocervical orthosis is worn until the fusion is stable.
Occipitocervical Fusion Using a Contoured Occipital Plate, Screw, and Rod Fixation
This technique uses an adjustable-angle rod and a contoured occipital plate (Vertex Select, Medtronic, Memphis, TN) for fixation.
Technique 43.9
- ▪
Expose the spine posteriorly as described in Technique 43.8.
- ▪
Adjust the angle of each rod for the most preferable alignment; tighten the internal set screws to lock the angle. Further bend the rods to best fit the patient’s anatomy. Cut both ends of the rods to the required lengths.
- ▪
Position the rods in the previously placed cervical implants to determine the proper occipital plate size and make adjustments, if necessary, to align the rod.
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Position the occipital plate in the midline (occipital keel) between the external occipital protuberance and the posterior border of the foramen magnum. Contour the plate for an anatomic fit against the occiput. Avoid repeated bending of the plate because this may compromise its integrity. It may be necessary to contour the bone of the occiput.
- ▪
With an appropriate-size drill bit and guide that match the screw diameter, drill a hole in the occiput to the desired predetermined depth. Drilling must be done through the occipital plate to ensure proper drilling depth.
- ▪
Tap the hole, using a gauge to verify the depth. The occipital bone is very dense, and each hole should be completely tapped.
- ▪
Insert the appropriate size occipital screw and provisionally tighten it. Insert the rest of the screws as above and hand-tighten each.
- ▪
Place the rods into the implants and stabilize them by tightening the set screws. Perform final tightening of the occipital plate set screws and recheck all connections of the final construct before wound closure.
Postoperative Care
Immobilize the cervical spine in an orthosis for 8 to 12 weeks.
Anterior cervical approaches
C1-2 subluxation or dislocation sometimes cannot be reduced with traction. If a patient has no neurologic deficits, a simple in situ posterior fusion can be done with little increase in risk. Posterior decompression by laminectomy has been associated with increased morbidity and mortality. Posterior decompression increases C1-2 instability unless accompanied by fusion from the occiput to C2 or C3. If posterior stabilization cannot be performed because of the clinical situation or anterior subluxation associated with cord compression is present, then an anterior approach should be considered. A subtotal maxillectomy, lateral retropharyngeal approach, or transoral approach can be used. The retropharyngeal approach usually is preferred because of the increased incidence of wound complications and infection associated with the transoral and maxillectomy approaches ( Box 43.3 ).
BOX 43.3
Anterior Cervical Approaches
Transoral (Fang et al.)
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High incidence of wound complications and infection
Transoral Mandible-Splitting and Tongue-Splitting (Hall, Denis, and Murray)
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More extensive exposure of upper cervical spine
Subtotal Maxillectomy (Cocke et al.)
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Extended maxillotomy and subtotal maxillectomy are used when exposure of base of skull is necessary and cannot be obtained by other approaches
Lateral Retropharyngeal (Whitesides and Kelly)
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Extension of classic Henry approach to vertebral artery
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Sternocleidomastoid muscle everted and retracted posteriorly
-
Dissection in plane posterior to carotid sheath
-
Potential for postoperative edema and airway obstruction
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