Technique of Sublaminar Wire Passage

40 Technique of Sublaminar Wire Passage

Vincent J. Devlin and Marc A. Asher

Goal of Surgical Treatment

To achieve secure segmental fixation of the posterior spinal elements.

Indications

1. Scoliosis

2. Kyphosis

3. Hyperlordosis

4. Fractures

5. To provide supplementary fixation for adjacent hook or screw fixation sites (Figs. 40–1 and 40–2)

Contraindications

1. Deficient lamina (e.g., postlaminectomy deformity)

2. Conditions where the epidural space is compromised (e.g., tumor) or where the spinal cord is enlarged (e.g., syrinx)

Advantages

1. Sublaminar wires provide an inexpensive, versatile, and rapid technique for fixation of multiple spinal segments.

2. Sublaminar wires are excellent implants for translating vertebral segments.

3. Sublaminar wires provide a variable position connection that facilitates rod-anchor linkage in severe spinal deformities.

Disadvantages

1. Sublaminar wires do not provide axial or rotational stability to the instrumented spinal segments.

2. Sublaminar wires may directly traumatize the spinal cord and cause neurologic injury.

Procedure

Laminotomy

The goal of this step is to provide a clear view of the entrance and exit sites for wire passage. Interspinous ligaments and capsular soft tissue are removed to permit visualization of the interlaminar space at each level where wires will be placed. In the thoracic region, a small amount of the spinous process and the inferior lamina edge overlying the interlaminar space are removed to facilitate exposure because these caudal structures overlie the interlaminar space. This step is not generally required in the lumbar region. A double-action rongeur is then used to remove ligamentum flavum from the midline of the interlaminar space, thereby exposing the epidural space (Fig. 40–3A). A Penfield No. 4 dissector is used to gently develop a working plane and separate the epidural fat and the internal venous plexus from the underside of the ligamentum flavum (Fig. 40–3B). Epidural bleeding can be minimized by attention to these steps. A 45-degree Kerrison rongeur is then used to remove residual ligamentum flavum from the interspace along with a small portion of the inferior laminar margin to achieve adequate visualization of the epidural space (Fig. 40–3C). The majority of the spinous process is saved, as this provides a bed for soft tissue reattachment and a site for fusion mass to accumulate. This sequence of preparation is repeated at every level where wires will be placed. Gelfoam soaked in thrombin along with cottonoids, cotton oxacil, or bipolar electrocautery may be used to control epidural bleeding encountered at this stage.