Posterior Stabilization in the Thoracic Spine

Published on 02/04/2015 by admin

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Last modified 02/04/2015

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Chapter 36 Posterior Stabilization in the Thoracic Spine

POSSIBLE OPTIONS IN THORACIC INSTRUMENTATION

Several posterior stabilization techniques have been used in patients with spinal tumors.1,2 Harrington distraction rods have long been used after resection of lesions of the thoracic and lumbar spine. But the Harrington three-point fixation system is likely to fail because of excessive bending loads when the anterior and middle vertebral columns are eroded by tumor. Segmental spinal fixation with a wire and rod system, introduced by Luque, provided more rigid fixation than the Harrington system. The major concerns associated with this system were complications related to the epidural passage of multiple sublaminar wires and limitations on the ability to resist axial forces. The hook system offered rigid segmental fixation and improved the ability to achieve spinal alignment in three dimensions. However, hook segmental fixation requires the presence of intact laminae and facets, and multiple motion segments above and below the level of tumor involvement should be fitted with the construct. The pedicle screw system provides the most rigid and stable construct, covering three columns with short segment application.3,4 Systems with increased stiffness and stability allow early mobilization without external immobilization. The rod hook/rod pedicle screw system has a stiffer construct compared with Luque rods or with wiring to Harrington rods.5

THORACIC WIRING

Sublaminar wires are often used in conjunction with the rods to provide rigid segmental stability to the posterior spine.6 Wire placement at the end of the instrumentation construct resists implant pullout in the sagittal plane (Fig. 36-1). The risk of bone/implant failure is lessened with this technique because of the multitude of points of fixation contact (Fig. 36-2).

Wires and cable constructs are reported to be stiffer than the intact spine. Less canal encroachment is observed with cables than with wires.

TECHNIQUES OF WIRING

The radius of curvature of the bent sublaminar wire should be at least equal to the width of the lamina. The wires should be passed anterior to the lamina in a caudal to cranial direction and a lateral to medial direction. The tip of the wire should remain in contact with the undersurface of the lamina as it is advanced cranially (Fig. 36-3). The wire should be rolled so that the tip emerges at the upper end of the lamina in the midline. The looped leading edge can then be grasped with a nerve hook or narrow needle holder. The wire is then pulled through with a firm posterior force on the leading and trailing edge of the wire. The wire ends are bent to conform to the posterior lamina. Once the wire is passed, it should be twisted over the respective posterior lamina to prevent inadvertent canal migration.

Harrington distraction rods with segmental wiring provide the best axial load stability. Luque segmental wiring, a semi-rigid fixation device, is best for rotational stability for burst fracture management (Fig. 36-4).7 The rod on each side of the midline is cut to the appropriate length and placed along the lamina. The wires are twisted around the rods. L-shaped rods are usually used. The L-shape aids in settling of the spine and prevents rod rotation. The L should be passed across the midline through an interspinous space and underneath the straight aspect of the opposing rod. This prevents the dorsal protrusion of the L-aspect of the rod. Wires are tightened down alternately, and double wires are recommended at the ends of the construct.

TRANSPEDICULAR SCREW FIXATION IN THORACIC SPINE