Anterior Cervical Stabilization in Tumor Surgery

Published on 02/04/2015 by admin

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Last modified 02/04/2015

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Chapter 34 Anterior Cervical Stabilization in Tumor Surgery

TECHNIQUES OF PLATING

DIRECTION OF SCREWS

The screw is usually directed 10 to 15 degrees to the horizontal plane.3 However, pull-out tendency is greatest when the screw lies tangent to the arc of rotation around the instantaneous axis of rotation (IAR) and least when the screw lies perpendicular to the arc of rotation around the IAR. The IAR lies toward the ventral inferior aspect of the vertebra but is altered under the influence of a rigid load-bearing device. The screws that lay more perpendicular to the vector of pullout should have greater resistance to pullout (Fig. 34-1).

SELECTION OF THE DEVICE

The classification of devices is according to the motion at the plate-screw interface.4

Restricted-Constrained Device (Unicortical Locked Bone Screw)

In this system, the screw purchase is unicortical and the screw-plate interface is constrained (Fig. 34-3). There is a predetermined (rigid) screw trajectory in the plate. The locking mechanism prevents screw migration even if screw breakage occurs. The CSLP (cervical spine locking plate) and Orion plate (constrained type) are included in this category.

OTHER OPTIONS IN ANTERIOR CERVICAL PLATING

Surgeons can choose a variety of plates based on plate, biomaterials, sagittal/coronal contour, profile, and concavity of the plate.

Telescopic Plate Spacer

The Telescopic Plate Spacer (TPS; Interpore Cross International, Irvine, CA) is a new option after corpectomy (Fig. 34-5). The device is a titanium cervical plate-interbody spacer hybrid, which can be used in either one-level or two-level corpectomy defects.5 The spacer portion of the device is hollow and may be packed with bone graft. The plate portion of the device can be fixed to the adjacent vertebral bodies with screws. Through the telescopic effect, the device can be expanded to fit corpectomy defects to restore anterior column height and correct kyphotic deformity. By applying distraction anterior to the IAR, the TPS restores lordosis in the cervical spine.

The TPS increases stability through the integration of constrained screws, flanges, and a large spacer contact area. The 45-degree-angle screw in the TPS is more favorable because it allows the use of a 20- to 22-mm screw without violation of the posterior cortex. The 45-degree-angle screws are more perpendicular to the vector of pullout force.

Junctional Plate

This is a technique in which a small anterior cervical plate is fixed at one end of the construct, usually at the lower vertebra graft because dislodgment often occurs at the inferior end of the construct (Fig. 34-6). It overlaps the end of the strut graft-vertebra junction and is able to block the end of the graft so that it does not dislodge anteriorly. An advantage of this system is that it does not create a tension band anteriorly, which would lead to large stresses on the strut graft. It allows load sharing by the graft and lets the graft settle gradually into the endplates without distraction force.