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| Chapter Synopsis | The upper cervical spine encompasses the area spanning the occiput, the atlas (C1), the axis (C2), and the C2-C3 motion segment. The authors discuss four main approaches to the upper cervical spine: the dorsal or posterior, the posterolateral transcondylar, the transoral transpalatopharyngeal, and the transcervical extrapharyngeal. The indications for, applications of, and descriptions of each approach are reviewed. |
| Important Points | Selection of the appropriate approach, technique, and construct depends on the patient’s age, pathologic process, bony anatomy, and alignment. |
| Clinical and Surgical Pearls |
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| Clinical and Surgical Pitfalls |
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The upper cervical spine is defined by the area encompassing the occiput, the atlas (C1), the axis (C2), and the C2 to C3 motion segment. The anatomic complexity of this region is related to the uniqueness of the bony anatomy of each of these segments and the relation to neural and vascular structures. A comprehensive and detailed knowledge of this intriguing region is key not only to surgical management of the protean disorders affecting this area but also to avoidance of complications.
Selection of the appropriate approach, technique, and construct depends on the patient’s age, pathologic process, bony anatomy, and alignment ( Fig. 2-1 ).
Surgical Approaches and Techniques
Dorsal (Posterior) Approach
The dorsal or posterior approach is the most common approach to the upper cervical spine. Through this exposure, atlantoaxial and occipitocervical decompression and fusions can be accomplished. The indication for atlantoaxial fusions is C1 and C2 instability, whereas the indications for occipitocervical fusion include occipitocervical instability and C1-C2 fusion failure. In adults, trauma, tumors, and rheumatoid arthritis are the primary causes of occipitocervical and atlantoaxial instability. In children, congenital abnormalities, Down syndrome, Klippel-Feil syndrome, and various causes of basilar invagination and impression lead to instabilities in this area. Bony components alone or in combination with ligamentous attachments (primarily the transverse and alar ligaments) can be affected by all these processes, with resulting instability.
General Consideration in Dissection
Exposure is achieved through a midline incision from the inion to the C4 spinous process down to the deep cervical fascia. The occiput and the C2 spinous process are identified early during the dissection. Incising through the avascular ligamentum nuchae aids in keeping the dissection midline and avoids unnecessary muscle bleeding.
The points of insertion of suboccipital musculature are the posterior arch of C1, the spinous process, and the lamina of C2. These muscles are detached through subperiosteal dissection with monopolar electrocautery in a mediolateral direction. Dissection beyond 12 mm is transitioned to bipolar cutting current or dissection with a Freer elevator in a subperiosteal fashion, by staying ventral to the suboccipital fascia. This procedure should be done carefully because the vertebral artery courses around the lateral mass of C1 medially in the superior aspect of the posterior arch of C1. Another vascular structure of concern is the suboccipital venous plexus behind the occiput-C1 and C1-2 interspace.
Occipitocervical Fusion
Occipitocervical fusion can be semirigid or rigid. Semirigid fixation includes contoured loop and wire instrumentation. This procedure is supplemented with a postoperative halo vest or a molded rigid orthosis. Rigid fixation encompasses rod and screw fixation. Selection of the type of instrumentation is dictated by the patient’s age, disease process, and associated bony anatomy.
In young patients (3 to 6 years of age), semirigid fixations are employed to allow for additional growth and remodeling. Moreover, the small size of the spine and the incomplete ossification in these patients render rod and screw constructs infeasible. Intraoperative traction to improve and maintain alignment is critical. Thus, the authors most often use crown halo traction resting on a Mayfield headrest, rather than the Mayfield three-point pin headrest for positioning.
Occipitoatlantoaxial Fixation Using Autograft and Wire or Cable
After awake intubation, the patient is positioned prone on the operating table. The head is placed in the cerebellar headrest. Attention should be paid to ensure that no pressure is placed on the eyes. Between 5 and 7 pounds of traction is maintained throughout the operation for satisfactory alignment of the craniocervical junction.
A lateral radiograph using a C-arm fluoroscope is obtained to confirm that appropriate occipitocervical alignment has been maintained.
Subperiosteal electrocautery is used to expose the occipital bone and the dorsal upper cervical spine in a subperiosteal fashion. A notch is placed inferiorly and superiorly on each lamina at its junction with the facet, and a hole is drilled through each side of the occipital bone lateral to the foramen magnum. Titanium cables are passed in a sublaminar fashion and from the occipital trephines to the foramen magnum, to gain occipital purchase. These cables have the advantage of being more pliable yet have equivalent strength compared with wire.
Autologous bone is harvested from the rib or iliac crest, with the former having the advantages of a lower complication rate, improved strength, and less donor site pain. The graft is notched adjacent to the lamina, and notch or a hole is placed in the rostral end for the occipital cable. The graft is then secured to the recipient laminar surface, or the occipital bone, or both, and the cables are tightened. Postoperatively, patients are immobilized in a custom-made occipitocervical brace for 5 to 6 months ( Fig. 2-2 ).
Occipitoatlantoaxial Fixation Using Rod or Loop and Wire
This semirigid fusion technique offers immediate stabilization. Its advantages are ease of use, a low incidence of neurologic complications, and the ability to place the instrumentation even after wide decompression.
With the same previously described exposure, the titanium loop is placed against the dorsal occipitocervical articulation, and it is custom contoured to the occipitocervical articulation. Cables secure the loop at the points of fixation to the occiput, as well as at the dorsal aspects of the lamina from C1 to C2. The construct should extend to two or three levels below the area of instability. In cases of axial instability, the loop can be designed to incorporate C3 as well. The titanium cables are tightened to 30 pounds of torque pressure at the occiput and C2, whereas at C1 and C3, 15 to 20 pounds of torque pressure is applied. Rib grafts are placed medial to the instrumentation to contact bony surfaces and are secured in place with suture ( Fig. 2-3 ).
Occipitoatlantoaxial Fixation Using Screw Plate and Rod
Occipitocervical fusion using plate and rod instrumentation provides the most rigid construct with higher fusion rates and fewer reported implant failures. Modern occipital plates allow multiple bicortical points of fixation to the midline keel. Moreover, polyaxial screw heads located more laterally on the plate allow easy accommodation of both bent and hinged rod systems.
Patient positioning and exposure are similar to the standard dorsal approach to the upper cervical spine described earlier. Preoperative identification of the location of the torcula and the transverse sinus and of bone thickness at the proposed area of plate placement is crucial. While the plate is held opposing the proposed position, screw placement is conducted through penetration of the outer cortex with either an awl or a high-speed electric or pneumatic drill. This is followed by hand drilling. The trajectory is then tapped, and the screw is placed. After the occipital plate is secured, various options for atlantoaxial arthrodesis are available. These include C1 and C2 transarticular screws and C1 lateral mass screws combined with C2 pars interarticularis, pedicle, or laminar screws ( Fig. 2-4 ).
C1 to C2 transarticular screw fixation is technically demanding, with potential serious complications. Determination of the course of the vertebral artery is crucial through preoperative computed tomography and magnetic resonance imaging (MRI). The point of entry is usually 3 mm cranial to the C2-C3 facet joint and 3 mm medial to the lateral border of the C2 inferior facet. The steep superior angulation aiming at the anterior tubercle of C1 requires that the incision be extended to the T1 or T2 level. An alternative way to avoid a long incision is to perform a stab incision at that level approximately 2 cm lateral to the midline and, through a trocar with an obturator, introduce a high-speed drill or an awl to decorticate the entry point.
A straight-up or mild medial angulation trajectory though the pars interarticularis is then created with a hand drill until the C1-C2 joint is encountered. Penetration of this joint is completed with a high-speed drill, and advancement into the lateral mass of C1 on the lateral radiographic view is continued. Identifying the medial border of the pars interarticularis with a Freer elevator or a dissector and keeping the drill just lateral to the Freer elevator or dissector avoids medial violation of the pedicle. Care should be maintained not to stray too laterally and thus place the vertebral artery at risk.
If transarticular screw placement is not possible because of unusual bony anatomy or malalignment or because the vertebral artery is in the way of the trajectory, or if the surgeon prefers, then C1-C2 arthrodesis through C1 lateral mass screws combined with C2 pars interarticularis or laminar screws can be employed. Placement of C1 lateral mass screws requires dissection conducted in a subperiosteal fashion along the inferior edge of the posterior arch of C1 with a Freer or Penfield elevator. After retracting the C2 nerve root inferiorly, the medial and lateral borders of the C1 lateral mass are defined. The point of entry for the screw is in the middle, frequently coinciding with an emissary vein. With a hand drill, the trajectory for placement is superior and slightly medial, aiming at the tubercle of C1. Lateral violation places the carotid arteries in jeopardy.
The point of entry for a C2 pars interarticularis screw is approximately 5 mm superior to the C2-C3 facet joint and 3 mm medial to the lateral border of the inferior facet of C2. The medial border of the C2 pedicle is identified with the use of subperiosteal dissection, thus freeing the atlantoaxial membrane from the bony attachment. The trajectory is drilled using a hand drill 25 degrees cranially and 15 to 25 degrees medially. If the pars interarticularis and pedicles are small, C2 laminar screw placement remains another option.
The translaminar screw can provide solid fixation without placing the vertebral artery at risk, although ventral penetration of the lamina can place the spinal cord at risk. A hole is created with a high-speed drill at the junction of the spinous process and the lamina. A trajectory is drilled using a hand drill in the contralateral lamina. This maneuver is followed by tapping the trajectory and placing the screw. A more complete description of the technique is described in Chapter 41 .
After securing all instrumentation and achieving satisfactory alignment, the surgeon then places the autograft lateral to the construct. Rib grafts or occipital bone shavings are generally used. Although controversial, in high-risk patients the authors consider the use of recombinant human bone morphogenetic protein. However, caution with regard to potential serious complications should be noted with its use and discussed with the patient. Complications include, but limited to, ectopic bone growth causing compressive lesions, tissue edema, seroma formation, and potential increased cancer risks.
Atlantoaxial (C1-C2) Fixation
Atlantoaxial fixation can be semirigid or rigid. Semirigid fixation encompasses wire or cable constructs combined with autologous grafts and requires external immobilization with a halo vest or, in certain situations, a rigid collar. Rigid fixation encompasses C1-C2 screw rod constructs and transarticular screws and usually requires only rigid collar supplementation.
Atlantoaxial Fixation Using Graft and Cable
Various techniques use graft and cable fixation. These include the original Gallie, interspinous, Brooks, and modified Brooks techniques. Because of their inferior fusion rates compared with screw-rod constructs, these techniques are usually applied to the pediatric population or to patients with anomalous vertebral arteries or small posterior elements.
A standard dorsal approach dissection is employed with exposure of the posterior arch of C1 and the spinous process and lamina of C2. The Gallie technique requires a wire or cable that loops around the spinous process of C2 and the posterior arch of C1 with a graft placed in between them. In a standard Brooks technique, two wires or cables are looped around the posterior arch of C1 and the lamina of C2 on each side while the graft is placed in between them.
Rib or iliac crest autografts are typically the grafts of choice. They are positioned between C1 and C2.
Atlantoaxial Fixation Using Transarticular Screws
This technique provides excellent fixation and fusion rates, although it is demanding and requires expertise. Attention should be paid to the course of the vertebral artery and the bony anatomy. Exposure and placement are described previously in the section on occipitoatlantoaxial fixation using screw plate and rod; however, the initial step of plate placement obviously is skipped ( Fig. 2-5 ).
