Ventral plates increase the stiffness of fusion constructs and increase fusion rates. They also decrease graft-related complications.

Ventral plating systems have been refined through multiple modifications. First-generation plates merely used parallel slots for the screws that did not lock or constrain to the plate. The plate allowed settling at the cost of frequent screw backout and loss of stability (32). Bicortical screw placement into the vertebral bodies could offer improved pullout strength in flexion/extension as compared to unicortical screws as shown by Ryken et al. (33) in a cadaveric study. Bicortical screw fixation provides also additional stability in cyclic loading (34). Unlocked bicortical screw purchase offers no additional stability as compared to a locked unicortical screw/plate system (Fig. 83.2A) (35). These locking systems allow for more rigid fixation with less risk of collapse or cutout. Smith et al. demonstrated in biomechanical studies that locking of cervical screws to the plate provides additional stability under large angular displacement when comparing to nonlocking plates (36,37). Multiple studies have demonstrated the high efficacy of locked unicortical screw/plate systems (Fig. 83.2B and C) in stabilizing degenerative cervical disorders. These rigid implants are criticized because they can prevent load sharing with the interbody graft by stress shielding. Therefore, ventral cervical systems were created that allow dynamic axial compression across a fusion site. There are various ways in which dynamization is permitted, varying from screws toggling within the screw hole, screw translation in a slotted screw hole, and telescoping plates that move together during settling. Such systems theoretically increase the healing rate by allowing for dynamic graft/end plate axial compression while maintaining the rotatory and flexion/extension stability comparable to static locking plates (38). Initial clinical results are encouraging and show a 94% to 95.7% fusion rate with a 4.3% of graft/hardware complications, using dynamic plates (39,40). There have been no
double-blind studies comparing dynamic and rigid ventral cervical plates to date. Dynamic plates systems may not provide rigid enough fixation for unstable fractures, and more long-term results are needed for three- or four-level fixation following multilevel corpectomy.

Vanichkachorn et al. (41) have reported the ventral buttress plate technique as a technique that theoretically may prevent or decrease the incidence of graft or internal fixation dislodgement in long segmental cervical fusions. It must be stressed that three- or four-level corpectomy cases are challenging to restore biomechanical stability with ventral fixation alone, and dorsal supplemental fixation should be considered. If dorsal segmental fixation is used, ventral buttress plate or any internal fixation other than bone graft probably is not needed (31).

For access to the lower cervical spine, the classic ventromedial Smith-Robinson approach is used (42). Incisions in line with Langer’s skin lines are most commonly used and extend from midline to the lateral border of the sternocleidomastoid muscle. Occasionally, oblique or longitudinal incisions can be used for access to more than three cervical levels; however, cosmesis is inferior to transverse incisions due to scarring and contractions. The subcutaneous tissue, platysma, and the deep cervical fascia are cut in line with the skin incision. The platysma muscle can be undermined rostrally and caudally to gain access to more cervical levels. Care must be taken to avoid bleeding from large branches of the anterior jugular vein by their ligation or careful retraction. Next, gentle finger blunt dissection is done through the interval between the medial sternocleidomastoid muscle and the strap muscles. Once a plane is developed, it can be expanded proximally and distally to increase exposure. Care must be taken to retract the carotid sheath and its contents laterally by palpating the carotid pulse. Also commonly encountered, inferior thyroid artery must be protected or suture ligated. A smooth retractor is then used to retract the tracheoesophageal structures medially and the sternocleidomastoid muscle laterally. Tension on the retractors allows for visualization of the pretracheal and the prevertebral fascia directly overlying the ventral cervical spine. Both these layers are then bluntly spread in the longitudinal direction to allow for direct surgical access to the disks and vertebral bodies. The longus colli muscle is then undermined. Self-retaining smooth blade retractors are positioned underneath this muscle to prevent injury to the medially laying tracheoesophageal structures and the lateral carotid sheath. Depending on the level of the skin incision, the levels from C2 to T1 can be visualized with this approach. Next, depending on the degenerative pathoanatomy, decompression is performed by a discectomy or corpectomy, as described elsewhere in the textbook. This is followed by preparation of end plates and graft-docking sites. Next, about 2 mm of distraction is applied and appropriate length allograft or autograft is inserted (43). For ACDF, a 3-mm hole can be made in the middle of the superior and inferior end plate to improve vascularity while preserving the end plate strength (44) (Fig. 83.3).

The instrumentation phase begins with selection of plate length. Using calipers, the distance from midpoints of terminal vertebrae is measured and an appropriate length ventral plate is chosen. An appropriate length plate should not impinge on disk spaces adjacent to the planned fusion, which are not being fused. This has been associated with adjacent-level ossification across the disk space (45). The plate is next contoured to match the radius of cervical lordosis. Ventral osteophytes are removed with a rongeur or burr in order to enlarge the plate contact surface. Prior to placement of the plate, the midline of the vertebral bodies is marked, so that it can be aligned with the long axis of the plate. Several landmarks can be used to identify the midline of each vertebral body: the peak of the convex contour of the body (in the medial-lateral direction) or the middle of the distance from the right to left longus colli. The plate is then fixed with temporary pins, and the plate alignment is assessed. If necessary, portable radiographs can confirm the plate position. Compression is then applied at the terminal vertebrae either indirectly by removing traction or via direct compression (using a Cloward distractor). Depending on the surgeon’s preference, unicortical or bicortical screw holes are then drilled using standard technique. For unicortical screws, a drill stop at 14 to 16 mm is recommended to prevent unwanted dorsal cortex penetration (46). Screws should be either parallel or angled superiorly for the proximal screws, and the inferior screws are parallel to end plate surfaces for optimal stability. Before final tightening, an intraoperative lateral radiograph will confirm proper intraosseous screw placement and the graft position. Most system manufacturers provide larger diameter “salvage” or “emergency” screws, if previously misplaced screws need to be redirected and redrilled. During final tightening, the screw-locking mechanism must be engaged and verified.

For ventral access to C1-C2, modified approaches must be used. A lateral approach of Whitesides, a ventral retropharyngeal approach of McAfee, or a transoraltranspharyngeal decompressive approach as described by Fang et al. can be used (47,48). With either approach, ventral C1-C2 fixation can be performed with a plate or by placement of transarticular ventral to dorsal screws as described by Vaccaro et al. (49,50).