12 Occipitocervical Stabilization
Cervical instrumentation surgery started in the early 20th century for management of unstable cervical spine disorders. However, progression of cervical instrumentation surgery has been slow in comparison with instrumentation surgery in the thoracic and lumbar spine. Simple instrumentation such as spinous process wiring and lateral mass wiring had been the representative fixation anchor for stabilization of the cervical spine for ages. Occipitocervical fixation had been similarly dependent on simple cervical fixation until the last decade of the 20th century. However, new fixation anchors for cervical instrumentation surgery appeared in the late 1980s and early 1990s, including the lateral mass screw and pedicle screw.1–3 These rigid cervical fixation anchors allowed major changes in the field of cervical instrumentation surgery, and instrumentation surgery for craniocervical disorders almost simultaneously assumed a new aspect. This chapter reviews the history of craniocervical instrumentation surgery and several methods of fixation, and introduces the authors’ technique of occipitocervical instrumentation.
Historical Review of Occipitocervical Stabilization Surgery
A report by Pilcher in 1910 seems to be the first description of occipitocervical fusion. He reported an unintentional occipitocervical fusion after open reduction of atlantoaxial dislocation by exposing the occiput and the upper cervical spine.4 Foerster in 1927 conducted the first intended occipitocervical fusion with the use of a fibular strut graft without internal fixation for management of atlantoaxial instability caused by fracture of the odontoid process.5 In 1935, Kahn and Yglesias described the use of the autologous iliac crest for bone grafting in occipitocervical fusion.6 Cone and Turner reported a patient who had undergone a fusion from the occiput to the sixth cervical vertebra.7 They used wires placed through occipital burr holes to the spinous process of the cervical vertebra. Subsequently, various occipitocervical fusion techniques supplemented by wires had been developed. Robinson and Southwick described an onlay graft bone method in 1960. Wires passed from two burr holes in the occiput through the foramen magnum accomplished fixation of the grafted bone. The grafted bone was also stabilized by wires to the atlas, axis, and third cervical vertebra.8 Since then, several modifications of wiring techniques have been employed.9,10 Besides these reports, Perry and Nickel, as well as Newman and Sweetnam, reported occipitocervical fusion using chipped bone grafts without internal fixation. They postoperatively kept patients on prolonged bed rest with skull traction, followed by rigid external support, such as a halo cast.11,12 Despite the use of wiring techniques, postoperative stability of the fixed occipitocervical complex was insufficient, and bony union depended heavily on rigid postoperative external support and/or prolonged bed rest.
In the next stage of development of occipitocervical instrumentation surgery, in the 1980s and 1990s, application of a metal rod for use as a longitudinal connector and use of sublaminar wires and laminar hooks for cervical fixation were started. Luque introduced sublaminar wiring for correction of scoliosis in the thoracic and lumbar spine.13 This relatively rigid anchor was also used for cervical and occipitocervical fixation; however, initially, bone graft, such as the ilium, was used as the longitudinal connector, which did not supply sufficient stability to the fixed occipitocervical spine. Therefore, several types of metal rods were employed instead. In 1987, Flint et al. reported using Hartshill rectangular loop rods for occipitocervical fixation in 10 patients.14 A rectangular rod was fixed to the cervical vertebra via stainless steel sublaminar wires, and a firm collar was then used for postoperative external support. The authors noted no cases of pseudarthrosis. Since then, several series of occipitocervical fixation using metal rods and sublaminar wiring have been reported.15–17 According to these descriptions, the rods were contoured to correct kyphosis or maintain lordosis. One of the major disadvantages of using sublaminar wiring for cervical or occipitocervical fixation is the need for extension of construct to fixed segments when laminae had been removed already or if a laminectomy was required for decompression. Another disadvantage of sublaminar wiring is that single-level anchoring is not sufficient to obtain satisfactory stability or to correct a deformity ( Fig. 12.1 ).
More recently, occipitocervical fixation using hooks or clamps as cervical anchors has been attempted.18–20 However, these procedures have not become popular probably because of fear of setting the metal into the spinal canal, causing spinal cord complications ( Fig. 12.2 ). Callahan et al. performed occipitocervical fixation using rods fixed to the lateral mass using wires passed through the articular facets.21 This procedure was useful for patients with missing laminae. In 1988, Goel et al. described the use of occipital screws for occipitocervical fixation.22 With the advent of screws, wire fixation of the lateral masses is not considered an option for occipitocervical fixation.
Current Procedures of Occipitocervical Stabilization
Recent Development of Occipitocervical Instrumentation Surgery
Many reports have demonstrated that simple onlay graft techniques with wiring do not provide sufficient stability for occipitocervical fixation. In addition, occipitocervical stabilization using wiring usually requires longer fixation, especially for patients who need additional posterior decompression and for those whose laminae were removed in earlier surgeries. Therefore, more rigid internal fixations that do not require laminae for stabilization have been popularized. In the 1990s, several procedures were developed using atlantoaxial transarticular screws, lateral mass screws, and pedicle screws in the cervical spine. Regarding occipital anchors, burr holes for setting screws or hooks are generally placed paramedially on the occiput. According to the morphologic studies of the occiput by Zipnic et al. and by Ebraheim et al., the midline of the occiput is thicker than the lateral portion, with the thickest portion of the midline (~1.55 mm average thickness) at the center of the external protuberance.23,24 Therefore, considering the stability of the screw and the minimal risks to neurovascular structures inside the skull, placement of occipitocervical instrumentation into the paramedian of the occiput has been recommended ( Fig. 12.3 ).
The C1–C2 transarticular screw proposed by Magerl and the fixation procedure involving the C2 pedicle screw and C1 lateral mass screws developed by Goel and Laheri have been considered the most rigid internal fixations for atlantoaxial arthrodesis.22,25–27 Grob and colleagues reported using C1–C2 transarticular screws as the anchor for occipitocervical fixation.28,29 A Y-shaped plate was used to connect the occiput and the bilaterally inserted transarticular screws. In 1993, Smith et al. reported their series of occipitocervical fixation using atlanto-occipital reconstruction plates and screws. Screws inserted into the lateral masses were used as the cervical anchor.30 In 1994, Goel and Laheri first described an occipitocervical fixation technique in which the cervical end of the plate was fixed with the help of a C2 pedicle screw alone or in conjunction with C1 lateral mass screws, and the occipital end of the plate was fixed with the help of screws.22,28 Use of C2 pedicle screws to fix the cervical end of the occipitocervical fixation has become a popular method. In 1995, Goel and Achawal described occipitocervical fixation simultaneously with foramen magnum decompression.31 They made a small bone flap incorporating the foramen magnum and turned the flap inside out. The technique was labeled a foramen magnotomy.32
Abumi et al. reported a series of cases with occipitocervical fixation using a combination of occipitocervical rods and cervical pedicle screws.33 In their series, screws were inserted into the C2 pedicles for occipitoatlantoaxial fixation; more caudal pedicles were employed for fixation from the occiput to the middle or lower cervical spine in several cases. Occipitocervical fixation using C1–C2 transarticular screws, pedicle screws, or lateral mass screws is available for use in patients who require one-stage posterior cervical decompression and occipitocervical stabilization, because it requires no laminae for stabilization. In all these cases of cervical anchors used for occipitocervical fixation, both the stabilizing capability of an unstable segment and the pullout strength of the lateral mass screw are inferior to those of C1–C2 transarticular screws and pedicle screws.34–37 Oda et al. demonstrated by biomechanical study that C2 pedicle screws and C1–C2 transarticular screws provide significantly higher stabilizing effects when compared with sublaminar wiring and laminar hooks.38
Despite the high capability for achieving occipitocervical fusion with stabilizing atlantoaxial transarticular screws or C2 pedicle screws, it is difficult to apply a distraction force for correction of alignment. In addition, further correction of atlantoaxial subluxation after insertion of atlantoaxial transarticular screws cannot be obtained. Therefore, correction of vertical subluxation of the odontoid process may be insufficient, and reduction of “irreducible” atlantoaxial dislocation may be difficult by an occipitocervical stabilization procedure using atlantoaxial transarticular fixation. Grob et al. conducted a statistical analysis of surgical reduction of occipitocervical malalignment. According to the results in their published study on occipitocervical fusion using the C1–C2 transarticular screw fixation, no significant differences between the preoperative values of upward migration of the odontoid process and those at the time of follow-up were noted, and 3 of 28 patients remained neurologically unchanged.29 Goel et al. also attempted reduction of vertical odontoid migration in cases with basilar invagination by using C2 pedicle screws and occipital fixation using screws.39 In a series of cases treated by Abumi et al., reduction of upward migration evaluated by the McRae line was 4.2 mm on an average, and only 1 of the 19 patients who had myelopathy before surgery remained in the same neurological grade and the remaining 18 patients obtained neurological recovery.33 The reduction of upward migration of the odontoid process may enhance the decompressive effect by realignment at the atlanto-axial dislocation and may produce better neurological improvement than other procedures, including occipitocervical fusion using the C1–C2 transarticular screw fixation. More recently, Goel and colleagues recommended opening of the atlantoaxial joint and direct distraction of the facets to achieve reduction of the basilar invagination and or irreducible atlantoaxial dislocation.40,41
Occipitocervical Disorders Requiring Reconstructive Surgery
Disorders requiring surgical intervention in the craniocervical junction include rheumatoid arthritis, trauma, metastatic or primary bone tumor, infectious disorders, and instability or deformity by congenital abnormalities. The primary indication for occipitocervical fixation is mechanical instability at the occipitocervical junction. With the development of instability, patients suffer intractable pain and/or neurological deficit. Conservative treatment is usually ineffective for these conditions. Neurological deficits at the craniocervical junction in many patients are caused by compression of neural tissues by tumors, by deformity, by instability, or by a combination of factors. For patients with tumors, if stability of the craniocervical junction has been compromised, or surgical extirpation of the tumor destroys important stabilizing factors at the junction, craniocervical reconstruction must be performed.
Many patients who require craniocervical fixation have a combination of deformities in the sagittal plane. These consist of anterior translation of the atlas on the axis, vertical subluxation of the odontoid process, and flexion deformity caused by anterior subluxation or dislocation of the occipitoatlantal complex on the axis33 ( Fig. 12.4 ). Therefore, the ventral aspect of the junction of the medulla oblongata and the spinal cord is compressed by the tip of the cranially migrated odontoid process. In some patients with a severely anteriorly translated atlas, the tip of the odontoid process anteriorly and the posterior arch of the atlas posteriorly impinge on the neural elements. If anterior atlantoaxial dislocation is the cause of neurological deficits, ventral decompression is required.42,43 However, direct anterior decompressive procedures by a transoral or a mandible-splitting approach involve complicated perioperative management and a risk of infection. It is difficult to obtain solid fusion with these procedures even with postoperative support by rigid external fixation, such as a halo vest or cast. Therefore, direct anterior decompressive procedures are usually followed by additional posterior instrumentation with bone grafting.
Occipitocervical Stabilization Using Cervical Pedicle Screw Fixation
Cervical Pedicle Screw Placement for Occipitocervical Fixation
The combined use of cervical pedicle screws and occipitocervical rods for reconstruction of occipitocervical lesions provides sufficient correction of malalignment of the craniocervical junction by application of the combined force of extension and distraction. As a result of the reduction, indirect decompression of the ventral portion of the medulla oblongata is obtained by decrease of the mechanical stress at the anterior aspect of the neural tissue.33
Pedicle Screw Insertion in the Cervical Spine
In occipitocervical fixation using cervical pedicle screws, many patients can be managed by occipitoatlantoaxial fixation, avoiding extension of the fusion level more caudad than C2. However, vertebrae below C2 should be used for pedicle screw insertion in patients who require longer fixation for reduction or stabilization, or for the patients who do not have a suitable C2 pedicle for screw insertion.44
C2 Pedicle Screw
The cranial margin of the lamina of C2 is the landmark for the point of screw penetration in C2. To confirm the screw insertion point in C2, a slightly curved small spatula can be inserted into the spinal canal along the cranial margin of the C2 lamina to the me-dial surface of the pedicle of C2 ( Fig. 12.5a ). The angle for the C2 pedicle screw insertion should be 15 to 25° medial to the midline in the transverse plane ( Fig. 12.5b ). Prior to screw insertion, a pedicle probe should be inserted to create a route for the insertion of the tap and screw. Lateral C-arm projection should be used to confirm the screw insertion point and direction and to control the depth of the pedicle probe, tap, and screws.
C3–C7 Pedicle Screws
The points of screw penetration for C3–C7 pedicles are lateral to the center of the articular mass and close to the inferior margin of the inferior articular process of the cranially adjacent vertebra. The lateral margin of the articular mass of the cervical spine has a notch at the level of the pedicle.45 The pedicles are located below the lateral vertebral notch at C2, at or slightly above the notch at C3–C6 ( Fig. 12.6 ). The anatomical axis of the pedicle to the midline in the transverse plane is ~45° from C3 to C6 and less in C7. However, the anteroposterior length of the cervical pedicle is shorter than the lumbar or thoracic spine. Therefore, surgeons have more freedom for the insertion angle and can insert a screw at a smaller angle (25–45°) in the cervical spine ( Fig. 12.7 ).
The cortex at the point of screw insertion is penetrated with a high-speed burr. The surgeon can see the pedicle entrance directly in many cases by enlarging the insertion hole using a high-speed burr and a small curet44,46,47 ( Fig. 12.8a,d ). After creating the insertion hole, a small pedicle probe, tap, and screws are inserted into the pedicle with the help of lateral C-arm projection to confirm the direction and insertion depth ( Fig. 12.8b,c,f ). Prior to screw insertion, the surgeon can confirm the proper creation of the screw path using a pedicle sounder ( Fig. 12.8e ). The cortex of the cervical pedicles is always thinnest laterally toward the vertebral artery.48,49 Therefore, the surgeon should keep this in mind while probing and tapping the pedicle and placing the screws. Especially while being pulled out, the tap can easily shift to a direction parallel to the sagittal plane by paravertebral muscle force, and the lateral wall of the pedicle with the thinner cortex can be violated. The direction of the tap must be kept the same as the insertion angle by application of force lateral against the directional force of the paravertebral muscle ( Fig. 12.9 ). A drill bit must never be used to penetrate the cortex of the lateral mass or to make a hole for screw advancement.
The intended angle of screw insertion in the sagittal plane is parallel to the cranial end plate for pedicles of C5–C7 and at a slightly cephalad direction in C2–C4, according to the screw’s angulation in the sagittal plane. The direction of the C2 pedicle screw is almost perpendicular to the ventral surface of the C2 vertebral body ( Fig. 12.10 ). The neurocentral junction in the cervical spine, which is near the base of the pedicle in the vertebral body, is sometimes harder to pass with the pedicle probe than in the thoracic and lumbar spine. In such cases, the junction can be perforated with a Kirschner wire to make a path for the pedicle probe into the vertebral body.29
Related posts:
9 Congenital and Developmental Anomalies of the Craniovertebral Junction
11 Atlantoaxial Transarticular Fixation Techniques
16 Transoral Surgery
20 Intraoperative Neurophysiological Monitoring in Surgery for the Craniovertebral Junction
19 Image-guided Surgery in the Craniovertebral Junction and Upper Cervical Spine
22 Techniques of Occipitocervical Fixation
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
