Cervical Posterior Lateral Mass Fixation

Patient Selection

Lateral mass instrumentation remains a fundamental technique in the posterior stabilization of the cervical spine. The efficacy of this method of fixation is dependent on patient pathology, anatomy, and load-sharing objectives. At times, lateral mass fixation by itself is adequate to stabilize traumatic facet complex disruptions. Alternatively, it may be used as an adjunct to anterior reconstructions. In the surgical planning, dynamic and static imaging can be useful in determining levels of fixation and aid in complication avoidance. With adequate perioperative planning and intraoperative tools, procedure-specific risks of vertebral artery and nerve root injuries can be minimized.

Focal points of neural compression or irritation are best demonstrated by magnetic resonance imaging, but understanding the bony anatomy is critical to the success of lateral mass screws. Plain X-rays of the cervical spine are a high yield and cost-effective method to define levels of spondylosis and regional lordosis. X-rays in the anterior–posterior and lateral projections enables an evaluation in two dimensions. Given the multidimensional nature of the cervical spine, however, additional considerations have been suggested with standing long cassette films, allowing a relative comparison of the cervical spine to the first thoracic vertebrae, as well as the sacral pelvic angle. The significance of the regional anatomy limited to the cervical spine versus a global balance remains an active area of study. Flexion and extension views of the cervical spine can confirm levels of abnormal motion and may aid in determining levels of instrumentation. Additional understanding of the bony anatomy is gained with computed tomography (CT) scans. It defines the relative anatomy of the transverse foramen to the anticipated lateral mass dimensions. In the setting of longstanding spondylosis, a CT can demonstrate the presence of an erosive arthropathy that would significantly alter the utility of lateral mass screws.

19.2 Preoperative Preparation

Aside from radiographic considerations of anatomy, additional preoperative issues include anesthetic concerns, operative instruments, and intraoperative positioning. Neurophysiologic monitoring is left to surgeon preference. If it is used, muscle relaxants and inhalational anesthetics would be less likely to be used in the induction of anesthesia. Additional anesthetic concerns encompass whether an awake fiberoptic intubation is indicated to minimize unnecessary movement in the setting of severe cervical stenosis. Fluoroscopy can assist in trajectory planning but is not necessary.

Surgery of the posterior cervical spine can be performed on multiple platforms. Of the currently available options, the primary types include the standard surgical table (Skytron, LLC, Grand Rapids, Michigan) or the modular prone spine table (Mizuho OSI, Union City, California). The standard surgical table requires the addition of large gel rolls, whereas the modular prone spine table relies on built-in chest pads. Either option requires the patient’s arms to be tucked and out of the fluoroscopic field of view. Additional options pertain to the device for holding the head and neck in place during the operative fixation. Although many surgeons tend to use the Mayfield (Integra LifeSciences Corporation, Cincinnati, Ohio) head holder, alternative options exist with Gardner-Wells (V. Mueller) tongs. The ultimate end point in using these various options is to achieve a neutral positioning and appropriate amount of lordosis to fixate the cervical spine. A neutral horizontal gaze defines the positioning of the cervical spine, with a level point of view in reference to the head and neck posture.

19.3 Operative Procedure (See Video 19.1)

Once adequate visualization is achieved by taping the shoulders to the foot of the table, clippers can be used to trim hair for adequate exposure. Standard steps should be performed to mitigate infection risk. Antibiotic prophylaxis is typically given within 60 minutes of making an incision, and chlorhexidine, alcohol, or betadine can be used to cleanse the skin. An iodine-impregnated covering can be applied to the skin before incision. The midline incision that is made is developed down the median avascular plane. By using this natural plane and continuing the dissection into a subperiosteal dissection, bleeding and muscle trauma can be minimized.

Adequate exposure of the lateral mass anatomy is critical to the success of screw starting point and placement ( ▶ Fig. 19.1 and ▶ Fig. 19.2). The medial border of the lateral mass is defined by the groove where the lateral mass meets the lamina (medial facet line), and the lateral aspect should be easily identified at the lateral aspect of the exposure (lateral facet line). The superior aspect of the convexity is defined by the articular cartilage of the superior articular process, and the inferior aspect of the convexity is clearly seen as the inferior aspect of the lateral mass. At the center of these landmarks lies the apex of the lateral mass (at the intersection of the lines labeled interfacet line [IFL] and rostrocaudal line [RCL]), which serves as the entry point for screw placement. In some cases of significant spondylotic changes, these landmarks may be difficult to identify. Thus, removing any overlying osteophyte may be helpful to better define these structures. The holes for screw placement should be drilled before the decompression to minimize the trauma risk to an unprotected spinal cord.