Posterior

Behrooz A. Akbarnia

Goals of Surgical Treatment

1. The goals of surgical treatment, which are decompression, realignment, and stabilization, can be reached through this single posterior incision.

2. To improve neurologic recovery when it is done in a timely manner (Ciappetta et al, 1996; Clohisy et al, 1992; Dendrinos et al, 1995; Dimar et al, 1999).

3. To stop the deterioration of neurologic function when the deficit is progressive.

4. To restore sagittal alignment and stability.

Diagnosis

A careful clinical assessment of neurologic function is essential. Plain radiographs and other imaging studies such as computed tomography (CT) scan and magnetic resonance imaging (if soft tissue or disc injury is suspected) are the most helpful studies.

Indications for Surgery

Posterolateral decompression is used in the following conditions:

1. Spinal canal compression caused by bony fragments in patients demonstrating worsening of the neurologic deficit.

2. In patients with incomplete deficit in whom neurologic function has reached a plateau.

3. In patients with normal neurologic function and significant canal compromise (more than 60 %), as well as kyphosis requiring anterior column support to achieve spinal stability. This support is accomplished through a posterior interbody grafting.

4. In some patients with incomplete but nonprogressive neurologic deficit or patients with canal encroachment but intact neurologic function, the natural history of neurologic improvement may not be altered by decompression.

Contraindications

1. When there is a significant comminution (McCormack et al, 1994) of the vertebral body, loss of anterior height (more than 50 %), and kyphosis, especially in the thoracolumbar junction, the anterior approach for decompression and structural grafting may be more appropriate.

2. Mild kyphosis, minimal comminution, no significant canal compromise, and no neurologic deficit.

3. Old posttraumatic kyphosis.

Advantages

1. Posterolateral approach allows decompression and stabilization to be accomplished through a single approach.

2. It provides an alternative when anterior approach carries a higher risk, because of patient’s general condition, associated trauma, and previous abdominal surgery.

3. It provides better visualization of the nerve roots, especially when there is a possibility that they are entrapped in the laminar fractures.

4. In the lower lumbar spine anterior decompression and instrumentation may not be feasible because of vascular proximity, and therefore the posterior approach may be preferable.

5. For lower lumbar spine burst fractures with neurologic deficit, posterolateral decompression is ideal because the spinal canal is wide and the sagittal alignment is not significantly altered.

6. The laminar fractures and entrapment of the neural elements are also more common in the lower lumbar spine burst fractures, which are more accessible posteriorly. Dural tears could be repaired through this approach.

Disadvantages

1. It is not clear whether the presence of fragments in the canal may cause problems such as spinal stenosis at a later date.

2. Because there is no correlation between the degree of canal compromise and the neurologic deficit, especially in the absence of neurologic deficit, removal of bone fragments may be unnecessary (Fidler, 1988).

3. For severe kyphotic deformity requiring strut grafting, the anterior approach is more feasible.

Procedure

The posterolateral approach has been described for decompression of the spinal canal and the removal of retropulsed fragments caused by burst fractures. These techniques have not included extensive removal of the pedicle on a routine basis (Flesch et al, 1977; Garfin et al, 1985). It is difficult to achieve full access to the anterior and middle columns of the spine without removing the major part of the pedicle. Therefore, the technique described in this chapter has been developed to allow better exposure and more effective decompression and grafting via the posterolateral approach.

Using plain radiographs, CT, and other imaging studies, as well as clinical assessment, the pedicle to be approached is selected. This is usually on the side with the worse neurologic deficit. If neurologic deficit is the same bilaterally or in patients with normal neurologic function, the side with more bony fragments or with a larger degree of compression is selected. Surgical approach through a single pedicle is sufficient in most cases. The opposite pedicle is left intact for the purpose of instrumentation. The comminution of the opposite pedicle is determined by preoperative CT scan. It is often possible to use this pedicle as a site of a pedicle screw. It may be necessary to extend instrumentation if more than one level of decompression is required (Akbarnia, 1997).