Interspinous, Laminar, and Facet Fusion

Published on 02/04/2015 by admin

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Chapter 47 Interspinous, Laminar, and Facet Fusion

Basic to the details of therapeutic intervention, either operative or nonoperative, is an understanding of the biomechanical principles of cervical spine function. These considerations permit the most effective planning of a specific treatment, especially the details of surgical intervention. Generally, in the cervical region, the major mechanism of injury is transmission of force through the head. The corresponding changes are usually related to flexion, extension, or rotation, with associated axial compression or distraction. Clarification of these factors assists the surgeon in designing the most appropriate procedure. A surgeon therefore desires to counteract the major force vectors responsible for the principal injury pattern. (One would not accentuate an extension-compression or extension-distraction injury by increasing extension forces with certain posterior fixation procedures.) The selected method of treatment should be based on the biomechanics of the injury and the experience and preference of the surgeon. This chapter covers the factors predisposing to instability in the subaxial (C3-7) cervical spine and the management of instability, using wire and cable techniques. Allen et al.1 proposed a mechanistic classification based on biomechanical considerations of the injury vectors. Panjabi and White2 proposed a working classification, especially for acute instability, in which more than 3.5 mm of anterolisthesis or more than 11 degrees of angulation constitutes instability in the lower cervical spine; this classification may be helpful in evaluation. In awake patients who fail to demonstrate radiologic evidence of instability with routine cervical spine films, flexion-extension lateral radiographs should be obtained. Dynamic radiographs, however, should be approached with a level of caution. The situation is often best approached initially by CT, with sagittal reconstruction for full definition of the possible injury patterns. If instability is not demonstrated with the aforementioned studies yet is suspected from the increased prevertebral soft tissue swelling and the severe neck pain, these patients should be placed in a firm cervical collar and the flexion-extension films repeated in 2 weeks. The elapsed time allows muscle spasm to abate and allows demonstration of ligamentous instability on the flexion-extension radiographs.

Operative Techniques

Exposure

The neck (up to the occiput) and the area around the iliac crest and posterior superior iliac spine are routinely prepared and draped. A midline incision is made in the neck; the length of the incision depends on the number of segments to be addressed. It is critical to stay in the midline to avoid excessive bleeding. The paracervical muscles are stripped subperiosteally from the spine and laminae and retracted laterally. The possibility of preexisting bony or ligamentous incompetence with associated instability or dural exposure cautions the surgeon to exercise care in the exposure of the dorsal elements. Supported by preoperative imaging information, dissection is accomplished sharply. Blunt dissection and monopolar cautery are avoided. The dissection is carried to the lateral edge of the facet joints. When possible, the supraspinous and interspinous ligaments are preserved. Once the spine is exposed, a lateral radiograph is obtained with a marker on the spinous process to identify the levels to be fused.

Reduction of preoperatively unreduced, unilateral, or bilateral locked (“jumped”) facets should be attempted at this time. The tip of the superior facet is drilled. Using two straight curettes between the adjacent laminae in the “tire-lever” B-type maneuver and working from medially to laterally toward the facet joint, the surgeon removes the superior facet ventral to the inferior facet (Fig. 47-2). In cases in which there is a facet fracture with encroachment into the neural foramen, this fragment of bone should be removed to relieve pressure on the exiting nerve root. The surgeon should always be aware of the potential for a lateral mass fracture that mimics a unilateral facet displacement.

Wire and Cable Fixation

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