This chapter explores the vascular complications associated with cervical spine surgery for both anterior and posterior approaches. Recognizing that cervical decompression and instrumentation are common procedures, it is important to understand the complications that can occur. Knowledge of the spine anatomy and potential anomalies allows for successful outcomes. Vertebral artery injury (VAI) is the most common vascular complication in both anterior and posterior approaches to the cervical spine. Although VAI can be life-threatening, early recognition and appropriate management more often than not will lead to acceptable outcomes.
Keywordsvertebral artery injury, cervical spine anatomy, cervical spine complication managment
Vertebral artery injury is the most common type of vascular complication in both anterior and posterior approaches to cervical spine surgery. Vertebral artery injury can occur during exposure, decompression, or instrumentation.
Vertebral artery injury can result in catastrophic bleeding, permanent neurologic damage, and death.
Direct tamponade is the most common method used in the management of vertebral artery injuries, but there are important immediate and delayed consequences of this type of management. Direct repair and endovascular techniques such as embolization and stenting are being used increasingly.
It is imperative that the surgeon studies the preoperative films to avoid these types of injuries, is able to quickly assess when such an injury has occurred, and is able to quickly manage these injuries intraoperatively and the sequelae postoperatively.
Cervical decompression and instrumentation are common in spinal surgery practice. Vascular complications can occur in both anterior and posterior approaches to cervical spine surgery. Vertebral artery injury (VAI) is the most common type of vascular complication in both approaches. Although rare, VAI can be a life-threatening complication. The incidence of VAI is reported to be 0.08% to 0.5%. VAI can occur during exposure, decompression, or instrumentation of the cervical spine. The highest reported rates are associated with posterior instrumentation of the high cervical spine (such as C1−2 fusion) and anterior corpectomies. As with other surgical complications, it is imperative that the surgeon studies the preoperative films to avoid these types of injuries, is able to quickly assess when such an injury has occurred, and is able to quickly manage these injuries intraoperatively and the consequences postoperatively.
Understanding the anatomy of the vertebral artery is critical for the surgeon to avoid VAI injuries and to manage these injuries if they occur. It is critical to study the vertebral artery anatomy in all patients undergoing cervical spine surgeries. Traditional imaging for spine pathology such as magnetic resonance imaging (MRI) or computed tomography (CT) is usually sufficient, but dedicated vascular imaging in the form of MR, CT, or catheter angiography may be helpful in more complex procedures.
Normally, the vertebral artery branches off of the first part of the subclavian artery and divides into four segments as it ascends to provide circulation to the posterior fossa and brainstem ( Fig. 53.1 ). The first segment, known as V1, starts with the branching of the vertebral artery from the subclavian artery and travels anterior to the transverse foramen of C7 and enters the transverse foramen of C6. The V2 region determines a convergent course of the arteries as it passes through the transverse foramina from C6 to C1. The vertebral artery is typically at least 1.5 mm lateral to the uncovertebral joint. It is important to note that the vertebral artery may enter the transverse foramen at a level other than C6 in almost 10% of cases. The third segment, V3, includes the superior section of the arch of the atlas to the foramen magnum and can be encountered during posterior cervical approaches. It is important to note that as the vertebral artery exits the transverse foramen at C1, it runs medially on the vertebral artery groove (VAG), which is also known as the sulcus arteriosus, and then about 8 to 19 mm from midline and then turns abruptly upward toward the foramen magnum. This is especially important during posterior approaches; as such, one should refrain from monopolar cautery when dissecting the ring of C1 laterally, especially along its superior border. The last segment, V4, extends from the foramen magnum to unite with contralateral vertebral artery. The vertebral arteries on either side join to form the basilar artery.
Understanding this anatomy should allow surgeons to avoid injuries to the vertebral arteries. In a multiinstitutional survey of spine surgeons, it was found that the most common procedures associated with VAIs are posterior instrumentation of the high (C1−2) spine (34%) and anterior corpectomies (23%), followed by posterior exposures more generally. The relatively high rates of vertebral injuries during high cervical instrumentation can be understood by the fact that the vertebral artery has a winding course between C1 and C2, the course through C2 is highly variable, and that much of the instrumentation placed here runs very close to the normal course of the vertebral artery.
Numerous methods are employed by surgeons for posterior C1−C2 fixation. The most common are Gallie-type fusion, transarticular screw placement, and C1 lateral mass with C2 pedicle screw (Harms fusion). In both transarticular screw placement and C2 pedicle screw placement, the vertebral artery is at risk ( Fig. 53.2A and B ). Two characteristics that appear to be important in stratifying the risk of VAI during the placement of these screws is the size of the pedicle and the presence of a “high-riding” vertebral artery. The exact definition of a high-riding vertebral artery is somewhat vague but refers to the situation when the VAG is too medial and too high within the isthmus of the C2 pedicle to allow for the safe insertion of a C2 pedicle screw ( Fig. 53.3 ). It is crucial that the surgeon studies the course of the vertebral artery as it passes through C2 preoperatively for each individual patient before attempting to place C2 pedicle screws. If there is not a good trajectory for placement of a pedicle screw, it is our practice to place a shorter pars screw in C2, which most often provides more than adequate fixation. Several studies have shown that the vertebral artery is less susceptible to injury with C2 pedicle screws compared with transarticular screws, and as such, we have limited our practice to only C2 pedicle or pars screws. A further benefit of C2 screws is that the trajectory can be modified to accommodate an aberrant course of the vertebral artery without the obligation to traverse the C1–2 joint.
Anatomic anomalies increase the likelihood of injury, especially if not appreciated preoperatively. Anomalies can be intraforaminal, extraforaminal, or arterial. Intraforaminal anomalies, also known as vertebral artery tortuosities, occur when the vertebral artery is located medial to the uncovertebral joint. This can cause erosion into the vertebral body, making the vertebral artery susceptible to injury, especially in corpectomy cases. Extraforaminal anomalies are instances where the vertebral artery traverses anterior to the transverse foramen at levels between C6 and C1. Arterial anomalies include dual-lumen and triple-lumen arteries or a hypoplastic vertebral artery. It is important to note a hypoplastic vertebral artery in the case of VAI because if the injury occurs on the dominant side, neurologic consequences may ensue if sacrifice of the artery is the only method available for management.
Carotid injuries during cervical spine surgery are extremely rare. Carotid injuries usually occur in anterior cervical spine surgery. In a retrospective, multicenter review of over 17,000 patients undergoing anterior cervical spine surgery in 21 centers, there were no cases of carotid artery injury (CAI) or cerebrovascular accidents (CVA). In a review of the literature, these same authors were able to find only a few cases of carotid injury during anterior cervical procedures. Risk factors for carotid injury appeared to be extensive retraction on the carotid and long operative times. Interestingly, in long anterior cervical procedures, it has been shown that the carotid artery may have up to an 80% decrease in its cross-sectional area, leading to the suggestion that during long anterior cases, the surgeon should release the retraction on the carotid intermittently.