Overview
The cervicothoracic junction (CTJ) represents a unique feature of the spinal column with significant biomechanical, anatomic, and functional aspects because of the transition between the cervical and thoracic spine. Most consider the CTJ to involve C7 to T3; therefore stabilization of the CTJ commonly involves instrumentation of these vertebrae.
The CTJ represents a transitional region from the mobile cervical spine to the rigid thoracic spine, which is splinted by rib attachments that greatly limit its mobility. The CTJ is also unique in that it represents a change from the lordotic cervical spine to the kyphotic thoracic spine. As a result of this curvature shift, a significant stress riser can develop during instances of instability.
The CTJ is often a difficult region to image adequately, because the shoulders obscure the lateral radiographs acquired with the C-arm fluoroscope. Careful study of the preoperative imaging, in particular, the computed tomography (CT) scan, is of utmost importance in planning accessibility and surgical approach, and it also serves as a guide to placement of instrumentation.
The major reasons for stabilization at the CTJ include structural instability and lesions that result in spinal canal compromise. Structural deformities include those arising from trauma and potential deformities at the CTJ, whereas causes of spinal compromise include tumors, infections, and disk herniations at these levels.
Stabilization of the CTJ may be performed from either an anterior or a posterior approach. Each approach has its own unique indications, operative considerations, and pitfalls.
Operative Anatomy
Some key anatomic considerations apply to the stabilization of the CTJ:
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The C7 vertebra is a transitional vertebra, and it is different from the rest of the subaxial spine in that it has small, thin lateral masses compared with the rest of the subaxial cervical spine. Lateral mass thicknesses decrease from 11 mm at C5 to 8.7 mm at C7 on average; therefore often bone is lacking for screw placement.
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Although lateral mass decreases in size, pedicle size increases gradually in width from 5.2 mm at C5 to 6.5 mm at C7. However, the height of the C7 pedicle still averages 6.9 mm.
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C7 is better placed to take a pedicle screw for insertion, rather than a lateral mass screw, and numerous studies have been done to confirm the safety and adequacy of such a screw.
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In the remaining subaxial cervical spine (C3–C6), the placement of pedicle screws is demanding and poses particular hazards. As a result, lateral mass screws are often more appropriate at these levels.
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Translaminar screws are another option for fixation, particularly at C2 and C7. They are not considered as safe for the remaining subaxial spine, because the laminar thickness of these segments is usually less than 3.0 mm; thus it is usually unrewarding to place a 3.5-mm or bigger diameter screw.
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The C3–C5 pedicles are often too small and narrow to allow good screw placement. The angle of the pedicles also decreases from around 50 degrees medially at C5 to approximately 11 degrees medially at T5.
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Biomechanically, posterior fixation at the CTJ has been shown to be superior to stand-alone anterior stabilization unless accompanied by posterior fixation as well.
Surgical Approaches
Selection of the surgical approach is dependent on the goals of the surgery. Stabilization may be achieved with a posterior, anterior, or combined approach. Current implant technology provides excellent reconstruction and stabilization options for many pathologic conditions. The surgeon must be able to tailor the stabilization to the specific case and thus must be familiar with all the devices currently available in the spine surgeon’s armamentarium.
Anterior Surgical Approaches to the Cervicothoracic Junction
Exposure of the lower CTJ is often limited by important anatomic structures in the region; namely, the great vessels, clavicle, sternum, rib cage, thoracic duct, laryngeal nerves and sympathetic chain, and esophagus and trachea. Fortunately, most stabilization procedures can be performed from the posterior or posterolateral approaches. However, two specific indications have been established for ventral stabilization of the CTJ:
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Resection of structural lesions of the body of C7 to T3–T4. Structural lesions can include intervertebral disk herniation at these levels as well as infections and tumors.
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Kyphotic deformity of the CTJ. Such deformities may need to be corrected through both an anterior and posterior stabilization.
At the CTJ, the indication for anterior-only fixation is limited. Although uncommon for disk pathology, single-level anterior diskectomy and fusion at the C7–T1 level have been used ( Fig. 29-1 ). Because of the biomechanical forces mentioned earlier, anterior plating is recommended at this level. Likewise, single-level corpectomies, either at C7 or T1, are successfully managed with anterior plate stabilization and strut graft or cage, providing no posterior pathology or instability is present. When two or more levels of corpectomy are done at the cervical–thoracic level, supplemental posterior fixation is also recommended ( Fig. 29-2 ).
Technique
Low Cervical Approach
This is an extension of the cervical approach to the anterior C- spine.
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A longitudinal incision is made just medial to the sternocleidomastoid (SCM), and dissection is carried down to the vertebrae; the carotid sheath is kept lateral, and the esophagus and trachea are kept medial. We usually use a left-sided approach to minimize injury to the recurrent laryngeal nerve, which has a more constant course on the left side. Note the thoracic duct is at greater risk on the left and can be found as high as C7.
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Radiolucent retractor systems are placed to allow maximal visualization and to retract viscera away ( Fig. 29-3, A ). Care is taken to ensure no undue excessive pressure is put on viscera, such as the esophagus and carotid sheath. Intermittent deflation of the endotracheal tube cuff may also be helpful to reduce pressure on the recurrent laryngeal nerve.
Figure 29-3
Use of ( A ) translucent retractors to achieve access for a C7 corpectomy and ( B ) allograft insertion for subsequent fusion ( C ). Postoperative plain radiograph shows the construct with a translatable plate placed between C6–T1.
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We use a translatable plate and allograft (see Fig. 29-3, B ) for our anterior approaches, but we typically use a titanium cage in patients with tumor.
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Using the low-cervical approach, the T1–T2 level can be approached in most cases. A transsternal or transmanubrial approach is usually needed for access to the T3–T4 level. This can be combined with a low-cervical incision for access to the lower cervical spine.
Transsternal-Transmanubrial Approach
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The original technique has been modified to involve a manubriectomy with osteotomies of the clavicle and resection of part of the SCM.
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A more modern approach has involved either a unilateral manubriectomy or a median manubriectomy, in which the sternoclavicular joints are left intact. In this technique, exposure down to T5 has been attained.
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Once exposure is achieved and the esophagus has been satisfactorily retracted, care must be taken with regard to the great vessels, because great anatomic variation is possible with respect to position. Typically, the superior portions of the great vessels overlie T3–T4; however, in the kyphotic patient, this can extend as high as T2.
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A corpectomy can be performed after removing the disk at the superior and inferior margin of the planned resection area. The intervertebral bone is then removed with the aid of a high-speed burr.
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Once the pathology at the CTJ has been rongeured or drilled away, an appropriately sized and shaped interbody graft is placed. We use allograft for degenerative conditions and titanium mesh cage for tumor. For tumor or infection, these cages are typically packed with allograft bone before being tamped into place.
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An anterior cervical plate is positioned over the inferior and superior vertebral body end plates, and we use the shortest adequate plate to stay away from adjacent disk spaces. The plate is fixed with appropriately sized screws based on lateral fluoroscopy.
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If the manubrium has been split, it is reapproximated with miniplates or with sternal wires. If the clavicle or clavicular head has been removed, this is also reapproximated with miniplates.
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Potential complications include injury to the recurrent laryngeal nerve, thoracic duct, esophagus, carotid sheath—which includes the carotid, internal jugular vein, and vagus nerve—and the great vessels, including the innominate, brachiocephalic, and aortic arteries.
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Great attention must be paid to preoperative imaging to identify the position of the vessels as well as to obtain as much information about the angle of the approach to avoid instrumentation malpositioning.
Thoracotomy
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When access below T4 is required, a thoracotomy may be necessary. Unfortunately, a thoracotomy cannot be used to access the lower cervical spine, unless a “carotid” incision is extended to the sternum and swung around horizontally at the fourth intercostal space to the midaxillary line. In this way, a sternotomy can be followed by a thoracotomy to achieve access from C3 potentially down to T4–T5.
Posterior Approach
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Many situations at the cervical–thoracic junction will need only secure posterior stabilization. In this situation, no fixed deformity should be present, and the cervical lordosis can be restored during extension.
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Posterior-only fixation can provide restoration of the tension band or prevent progressive deformity in cases of multilevel decompression for spondylotic myelopathy.
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Interspinous wiring and hook constructs have been successfully used when posterior elements are sufficient.
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Hook-and-wire constructs may need to include nondecompressed motion segments into the fusion construct to ensure stability. The strongest posterior construct that maintains motion in the nondecompressed segments is the lateral mass subaxially from C3–C6 and the pedicle screw system at C7.
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Excellent results have been reported with first-generation systems (plate and screw), but long constructs that cross the cervicothoracic junction are more challenging. Second-generation polyaxial screw-and-rod systems are constrained and lock the screw onto the rod. Because the screw is placed independently of the rod, there is more freedom of screw placement into lateral masses or pedicles.
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Polyaxial screw-rod systems are much less challenging in the longer constructs, because variations in the lateral position of the screws are managed by the mobile polyaxial screw head and offset connectors.
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Several rod-to-rod connecting devices, both side-to-side and end-to-end, are now available to connect thin-rod cervical constructs into the cervical and thoracic regions with wider rods ( Fig. 29-4 ).
Related posts:
Craniovertebral Junction Instabilities and Surgical Fixation Techniques
Surgical Approaches to the Craniovertebral Junction in Rheumatoid Arthritis
Thoracic Microdiskectomy: Lateral and Posterolateral Approaches
Lumbar Facet Screw Fixation Techniques
Surgical Management of Scheuermann Kyphosis
Primary Malignant and Benign Tumors of the Spine
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