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Anterior access to the CTJ is significantly restricted by osseous and vulnerable soft tissue structures. Management of trauma patients requires an understanding of the neurovascular anatomy of this region as well as the interrelationship of the sternum and the upper thoracic spinal column. Direct anterior approaches to the CTJ of the spine are caudally restricted by the manubrium and the broad medial edges of each of the clavicles. Protected behind these stout osseous structures are significant vessels, major neural structures, and mediastinal organs. Specifically, the trachea, thyroid gland, and esophagus block direct midline access to the spine, with the aortic arch more caudally crossing the midline around the T3 level. The right and left subclavian arteries tether the aortic arch to the posterior mediastinum, with the right vagal nerve usually crossing the right subclavian artery, whereas the recurrent laryngeal nerves emerge beneath each of the subclavian arteries and course rostrally along the anterolateral surface of the vertebral bodies.1,2 The brachiocephalic veins are formed by the confluence of the internal jugular and subclavian veins and usually lie immediately anterior to the subclavian arteries. Together the large brachiocephalic veins merge into the superior vena cava, which lies to the right of the aorta.

The anterior cervicothoracic vascular anatomy has great variability, such as an innominate vein (or artery) coursing underneath the aortic arch prior to ending in the superior vena cava.³ The large thoracic duct usually drains into the vein system at the junction of the left internal jugular and subclavian veins, whereas the smaller right thoracic duct enters into the right subclavian vein.⁴ The main thoracic duct lies medial to the subclavian artery and arches lateral to its insertion point in the vein system.¹ The longus colli muscles, which originate at the base of the axis, are segmentally joined by further muscle trunks from each of the uncovertebral joints until they caudally terminate in the C7-T1 joints. This leaves no meaningful anterior spinal muscle group crossing the CTJ.

This brief description omits other structures, such as the vagal nerves and the inferior thyroid arteries and vein, which further impede surgical access to the anterior CTJ. The anterior neural anatomy of the upper thoracic spinal column would also not be complete without reference to the sympathetic plexus, which emanates from the ventral rami of the respective spinal nerves starting with the T1 root caudalward and runs along either side of the anterolateral surface of the spinal column.⁵ From a surgical approach perspective, adequate access to this area is also challenging due to the physiological inclination angle of the upper thoracic spine with the inherent downward tilt of the vertebral end plates. This alignment for most patients requires an upward directed visualization trajectory to facilitate adequate anterior decompression and reconstruction of the upper thoracic spine. Awareness of the spatial interrelationship of the rostral end of the manubrium and the upper end-plate angle of the T1 vertebral body has been consequently suggested as an additional planning tool to identify suitable exposure needs should an anterior cervicothoracic surgery be contemplated.^6,7 (Fig. 5.1).

From an osteology standpoint, it is further relevant to remember that the vertebral density of the upper thoracic vertebral bodies can be expected to be 10 to 20% less dense than adjacent vertebral body segments of the lower cervical or thoracic spine. This physiological factor is likely induced by a stress-shielding effect brought about by the stouter rib cage attaching and buttressing the upper thoracic spine and may limit anterior fixation in the vertebral bodies of the upper thoracic spine, in addition to the inherent adverse biomechanical factors of the transition region itself.⁸ Thus, the bony and soft tissue environment of the CTJ makes anterior surgery a challenge.

Posterior Anatomy

The appearance of the posterior osseous and that of the lower cervical and thoracic spine distinctly differ. The cervical spine features lateral masses on either side of the lamina as its outer boundary, whereas the larger thoracic vertebrae feature prominent transverse processes, which project out posterolaterally, but without lateral mass equivalent. The lateral masses of the C7 segment differ from those of the adjacent lower cervical segments in the form of a much steeper facet joint inclination angulation of between 60 and 80 degrees and a much more shallow anteroposterior sagittal bone depth. The vertebral artery passage through the transverse processes typically seen in the lower cervical spine usually bypasses the C7 vertebral segment laterally in all but about 6% of patients or even fewer. Consequently, there is usually no vertebral artery within the bony structures of C7. Instead, one can usually find either absent or vestigial foramina within the wide transverse processes without intrinsic vertebral artery passage.⁹

In contrast to the more rostral segments, C7 pedicles are usually stouter and are angulated medially between 30 and 45 degrees, analogous to the upper thoracic pedicles (Fig. 5.2). Thoracic vertebral segments are defined as such by the articulated rib attachments to the superior lateral vertebral bodies just anterior to the transverse processes on either side. A rudimentary cervical rib may emanate from the lateral surface of the C7 segment in fewer than 1% of individuals. They may occur uni- or bilaterally and may or may not be ossified with their vertebral point of origin or the adjacent first thoracic rib. In general, these vestigial ribs have very little or no direct clinical implications; however, they may cause confusion in terms of intraoperative identification or on imaging-based level identification.10

Fig. 5.1a–e (a–d) The C7-T1 junction is typified by steeply inclined large facet joints and a relatively broad vertebral body dimension. Despite the transition from a relatively well-protected thoracic to a very mobile cervical spinal column, there are no significant additional ligamentous reinforcements to protect this region. The nuchal ligament as a broad fascial aponeurosis is part of the lower cervical ligamentous complex and serves as muscle attachment for paraspinal and some of the shoulder girdle muscles. It does not, however, directly contribute to the passive stability of the cervicothoracic junction (CTJ). (a) The anteroposterior perspective of the CTJ is typefied by the relatively broad and squat T1 and T2 vertebral bodies, as well as the disc space crossing medial rib attachments on either side. (b) In the lateral plane note the slope or inclination angle of the upper endplates of T1, T2 and T3. These have a foundational impact on the alignment of the cervical spine. (c) In the axial plane note the relatively large size of the transverse processes just posterior to the broad based lateral rib insertions. The pedicles are relatively broad and usually angulated medially in an about 30 (± 10) degree angle and have broad facet joints emanate from their dorsal ends. (d) Shows a three-dimensional view of the emergence of the T1 and T2 roots as they exit the foraminae laterally. (e) The long sloping transition of the CTJ is well represented in this anatomic specimen. Note the broad prominence of the T1 transverse process, which typifies the transition from C7 to the first thoracic vertebra.

The spinous processes of the CTJ are particularly robust as well as prominent and serve as caudal attachment points for the nuchal ligament, an aponeurosis of the supraspinous ligament emanating in the caudal direction from the posterior arch of the atlas and in itself constituting an inflection of the fasciae of each of the sets of the generally vertically oriented para spinal muscles. This resulting relatively broad and thick fascial aponeurosis serves as a primary stabilizer of the posterior spinal elements against bending forces and also enables attachment of the more horizontally oriented shoulder girdle muscles. Muscles such as the trapezius, the rhomboids, the serratus anterior, and others find their origins in this fascial aponeurosis, which finds its cruciform manifestation exactly at the dorsal CTJ.11

Fig. 5.2 Radiographic example of acquired cervicothoracic kyphosis with loss of CTJ alignment and resultant kyphosis. The two vertical lines identify the impact of acquired CTJ kyphosis on the overall cervical spine alignment, with the center of the C2 vertebral body being over 4 cm anterior to the center of the T1 vertebral body. Patients will typically correct this with a compensatory hyperlordosis of the upper cervical spine. Note also the importance of upright radiographs, as recumbent imaging such as magnetic resonance imaging (MRI) and computed tomography (CT) may not demonstrate the impact of gravity.

The spinal cord in its cervical region is broadened and enables egression of the cervical roots with the T1 root as its most caudal segment. The spinal cord at the CTJ usually has a capacious passage space, occupying 60% of the spinal canal.12 Aside from pathological conditions such as congenital stenosis and ossification of the posterior longitudinal ligament, the CTJ usually is exempt from the severe cord impingement sometimes seen in other subaxial fractures. In terms of foraminal passage space, the lower cervical roots typically egress in a straight lateral and slightly rostrally directed angle, which entails a slightly greater distance of passage to their respective upper pedicle compared with their next lower pedicle.¹² From the T2 roots onward, the exiting roots mainly fulfill a segmental dermatomal sensory role and provide some crossover innervation of the intercostal muscles. Clinical deficits to the roots in the CTJ mainly affect grip strength, with C8 root deficits notoriously eluding detection even by experienced clinicians. The T2 root provides sensory function to the medial aspect of the upper arm but usually does not contribute to meaningful hand function.

Biomechanics

Throughout the aging process of a human, the CTJ allows for some relatively unchanged excursion in sagittal flexion and extension motion and to a lesser degree lateral tilt. Due to its nearly vertical alignment of its facet joint architecture at the C7–T2 level, however, it affords minimal axial rotational motion. As the kyphotically aligned CTJ sits on top of the torso, the remaining cervical spine alignment is highly dependent on this inclination angle of the rostral thoracic spine. The T1 vertebral inclination angle has just recently become a more focal point of investigation. Perhaps historically overlooked due to traditional radiographic obfuscation, the T1 inclination angle determines cervical lordosis and influences the composite spinovertebral angle (SVA). The most common physiological alignment of the upper end plate of T1 of between 10 and 20 degrees relative to the horizon creates a forward tilt of the CTJ that places the dorsal soft tissues of this area under a constant tension strain. An increase of the forward tilt of T1 increases the flexion moment arm placed on the CTJ disproportionally, and creates a propensity toward further forward rotation in the sagittal plane around this pivot point. As thoracic kyphosis and positive sagittal balance typically increase with aging, it can be expected that the CTJ will undergo an age-related increase of tension in the moment arm with any destabilizing event.13 Other events, such as ankylosing disorders, will also entail an increase in major stress at the very junction of the formerly mobile cervical spine and the always more rigid thoracic spine.

Anatomy: Summary

The fundamental anatomy of the CTJ places a substantial flexion-rotational moment arm on this transition zone of the spine. Considerable anatomic obstacles preclude ready access to the anterior spinal column, making posteriorly based surgical approaches and concomitant reconstruction efforts preferable.¹⁴ Thus, taken in context with the biomechanical alignment of this region and its unique transition anatomy, posteriorly based instrumentation solutions are strongly preferred over available anterior techniques for treatment of an unstable CTJ. Anterior surgeries for the CTJ in trauma retain a largely supplemental role in rare cases where anterior column reconstruction is necessary and feasible.

Diagnosis

The CTJ has commonly eluded conventional lateral C-spine assessment due to overriding shoulder shadows, especially in larger patients. With lateral radiographs barely revealing the C7 vertebral body in a majority of trauma patients in the supine position, and frequently ending at a much higher level in larger patients, missed CTJ injuries were a common phenomenon in the era of plain radiographs. A commonly cited study found a 30% missed diagnosis rate for CTJ injuries despite secondary attempts at visualizing this area with techniques such as the swimmer’s view, the shoulder pull-down view, and oblique fluoroscopic spot images.^15–17 Historically, this left the anteroposterior radiographic projection as the most important conventional imaging modality to detect serious cervicothoracic injuries. By all accounts the emergence of rapid-acquisition computed tomography (CT) scans in routine applications for select trauma patients has dramatically reduced this number of missed injuries, as long as sagittal and coronal reformats of this transition zone are part of the C-spine imaging protocol.¹⁸ Missed injuries, however, remain a reality. They seem to be of particular concern in three distinct patient populations:

• Occult ligamentous injuries of the CTJ. Disruption of the PLC of the CTJ may be missed on CT scan, which, due to the recumbent patient positioning inherent to CT imaging, may result in spontaneous reduction of traumatically induced injuries of this area.

• Ankylosing spines with fractures. Due to the unfavorably large stiffness gradient of cervical and thoracic spine segments, and the long moment arm of an immobile cervical spine subjected to head impact in the context of falls and similar relatively low injury mechanisms, the CTJ is a typical location for primary or associated noncontiguous fracture in patients with ankylosing disorders to the spine.

• Severe polytrauma with life-threatening injuries. Patients subject to major deceleration trauma such as falls from a great height and high-speed motor vehicle accidents may elude conventional trauma imaging algorithms in favor of initial lifesaving emergency interventions. Unless there is an efficient protocol for secondary surveys, however, this scenario may lead to missed spine injuries.

Although there is no conclusive information regarding how often CTJ injures are missed in the era of readily available and fully integrated rapid CT scans in most trauma care environments, there are several steps that clinicians can take to help reduce missed injuries in these populations further:

• Careful physical evaluation: Primary-directed physical evaluation of spine trauma patients remains a key to detecting possibly obscure injuries, especially in a transition zone such as the CTJ. The evaluation should include meticulous and systematic documentation of the neurologic status of the patient. Unexplained neurologic deficits or asymmetry in reflex status are helpful pointers in identifying more severe underlying injuries. Inspection and palpation of the posterior situs of a trauma patient provides concrete physical examination findings in this critical area. This increasingly overlooked simple core trauma evaluation technique, conducted under proper log-rolling technique of the affected trauma patient, facilitates identifying typical ecchymosis, swelling, fluctuating mass effects as well as focal tenderness and other telltale signs such as gaps or crepitus on direct interspinous palpation. Identification of any of these abnormalities ideally prompts further diagnostic imaging evaluation. Another frequently overlooked directed physical examination modality is the assessment of the anterior thoracic cavity to assess sternal integrity and congruency and the stability of the medial sternoclavicular joints.

• Neurologic assessment: As in any spine trauma patient, a differentiated neurologic assessment is important. Due to space constraints this will not be discussed in detail here. However, C7 and C8 as well as T1 root functions can be frequently overlooked in neurologic assessments and may not be adequately documented.19

• Magnetic resonance imaging (MRI): If available, this imaging modality readily identifies with very high sensitivity but less than perfect specificity diskoligamentous injuries to the CTJ, and demonstrates otherwise occult fractures, such as in patients with ankylosing spine disorders.²⁰

• Upright radiographs: For patients with unclear stability of the CTJ, upright radiographs usually show structural integrity of this region, regardless of treatment with brace or surgery. Look for a change in the increase of the T1 upper endplate inclination angle or an otherwise unexplained increase in upper cervical spine lordosis.

Most importantly perhaps, awareness of the propensity of the CTJ to harbor occult spine injuries, adherence to evaluation principles, and a secondary risk evaluation protocol for patients at increased risk for injuries are key strategies to diminish the adverse effects of missed CTJ injuries. For patients with severe dissociative spine trauma, vascular imaging studies remain desirable to address possibly life-threatening vertebral artery and carotid trauma.

Nonoperative Treatment

Emergent closed reduction of known fracture dislocations of the cervicothoracic region has been notoriously difficult due to the near-vertical alignment of the T1 facet joints, the increasing muscle spasms associated with delayed reduction attempts, and the common concurrent presence of fractures in this area. Delays in reduction, which are commonly encountered in patients with CTJ injuries, predictably worsen muscle spasms further and thus make such reduction efforts of the lower cervical spine even harder with the passage of time. Attempts at reducing fractures in neurologically intact patients with ankylosing spinal disorders are actually discouraged due to the inability to achieve a true coaxial vertical distraction effect of the caudal end of the cervical spine relative to the upper thoracic spine. A failed closed reduction rate of over 30% for such efforts has been historically identified.¹⁵ With the debate on closed reduction of lower cervical spine dislocations yet to be completely resolved, the basic principles applicable to closed reduction remain applicable to CTJ dislocation injuries, and the earliest possible closed reduction of dislocations in the CTJ remains preferable.

In patients with spinal cord injury, attempts of closed reduction using skeletal cranial traction following the principles established by White and Panjabi remain a primary treatment preference prior to getting advanced imaging such as MRI.

For neurologically intact patients and those not amenable to neurologic evaluations during reduction efforts, a pre-reduction MRI scan is recommended to search for potential anterior cord impingement due to bone fragments, disk herniation, and other mass effects.

In cases of failure of closed reduction efforts, expedient surgical reduction is ideally performed from a posterior approach with careful disengagement of the facet joints followed by segmental posterior fixation under neuromonitoring using baseline signals for comparison.

The CTJ is notoriously difficult to treat with nonoperative means. Regardless of the type of cervicothoracic orthosis or the addition of a halo ring attached to a vest, the CTJ remains a fulcrum point for forward sagittal rotation at the intersection of the lower C-spine and upper torso.21 The main rate-limiting step of effective nonoperative care of the CTJ remains inadequate contact of a brace to the chest. This is of particular importance in patients with a large torso or individuals with preexisting cervicothoracic kyphosis.²² The typical end result of an unstable CTJ injury is painful kyphosis, usually due to a combination of anterior spinal column failure and concurrent distraction of the PLC dorsally. The typical presenting patient complaint with failed nonoperative treatment of an unstable CTJ is severe and progressive pain, hand dysfunction from C8, T1 root impingement, and, in more advanced cases, myelopathy.

The treatment of an established fixed posttraumatic kyphotic deformity is invariably much more involved than a primary fracture reduction and limited internal fixation²³ (Fig. 5.3). Therefore, it is preferable that patients selected for nonoperative treatment be closely observed for the first 3 weeks following injury, regardless of the type of external immobilization device used, to enable timely detection of lost reduction and to permit early primary surgical intervention. In principle, injuries that are doubtful for successful nonoperative treatment in terms of maintaining an acceptable alignment are probably better treated surgically a priori rather than subjecting the patient to a far more complex procedure on a delayed basis when a deformity has become fixed. Patients with ligamentous CTJ injuries or fractures in the presence of an ankylosing disorder will do better with primary open reduction and surgical stabilization, if their general medical status permits.

Surgical Care

Challenges

As discussed earlier, patients who require CTJ surgery for fracture-dislocations are almost categorically preferably treated from a posterior midline approach with segmental stabilization compared with anterior reconstruction efforts. Anterior procedures for an unstable CTJ are realistically limited by a caudal exposure restriction between the C6 and T2 vertebrae, depending on patient body habitus and underlying spinal conditions. Attempts at restoring stable alignment through an anterior procedure are limited not only in their caudal access but also by an adverse biomechanical environment. All in all, access-related morbidity is clearly higher for anterior procedures compared with posterior CTJ surgery, and therefore anterior procedures are less desirable in a trauma population. Posterior surgery provides a setting in which the surgeon has a much better chance to achieve a physiological realignment of the patient in this critical area and can provide implant stiffness commensurate with the patient’s needs by choosing from a variety of rod and screw configurations. Should a supplemental anterior procedure of the anterior column be necessary, for instance in the presence of a significant destruction of the anterior column, alternative CTJ reconstruction can be achieved either through a modified costotransversectomy approach or a supplemental anterior procedure on a delayed basis.

Posterior surgery for instrumentation of the CTJ is mainly affected by three problems:

• Safe placement of segmental instrumentation of the posterior screw fixation can be very challenging from an intraoperative imaging standpoint, especially in patients with large body habitus, osseous deformities, and severe osteopenia.

• The posterior CTJ can be subject to impaired soft tissue healing, for instance in the form of dehiscence of the nuchal ligament and fascia as well as soft tissue infections.

• Alignment and general fit of posterior cervical lateral mass and upper thoracic pedicle screw fixation can be very challenging.

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