Posterolateral (Costotransversectomy) Approach to the Thoracic Spine

The classic posterolateral approach to the thoracic spine was developed for the drainage of tuberculous abscesses in this part of the spine. Its major advantage is that it does not involve entering the thoracic cavity. However, the approach is less extensive than a formal thoracotomy and offers a poorer exposure. It probably is best for limited exposures in patients who are at high risk. This approach can also be combined with a posterior/posterolateral approach to the spine to decompress the vertebral canal circumferentially.

Its uses include the following:

1.   Abscess drainage23,24

2.   Vertebral body biopsy

3.   Partial vertebral body resection

4.   Limited anterior spinal fusion

5.   Anterolateral decompression of the spinal cord

6.   Tumor debulking

Position of the Patient

Place the patient prone on the operating table, with bolsters positioned longitudinally on each side of the rib cage to allow for chest expansion. Drape widely over the rib cage area so that the rib cage can be exposed laterally (see Fig. 6-101).

Landmarks and Incision

Landmarks

Palpate the spinous processes in the area. If the patient has a gibbous deformity, use it as a landmark for surgery. In any case, a needle should be placed into the spinous process of the vertebra to be exposed so that a lateral x-ray film can pinpoint the position. Remember that the spinous processes of the thoracic area are long and slender, and tend to overlap the vertebrae below. Note that the rib in the area to be exposed often is more prominent.

Figure 6-83 Make a curved linear incision lateral to the appropriate spinous process. Center the incision over the rib involved in the pathologic process.

Incision

Make a curved linear incision about 8 cm lateral to the appropriate spinous process and 10 to 13 cm long. Center the incision over the rib that is involved in the pathologic process (Fig. 6-83).

Internervous Plane

There is no true internervous plane in this approach; it involves splitting the trapezius muscle and cutting through the paraspinal muscles. Because the paraspinal muscles are innervated segmentally, no significant denervation occurs. The trapezius receives its supply from the spinal accessory nerve higher up.

Superficial Surgical Dissection

Incise the subcutaneous fat and fascia in line with the skin incision, cutting through the trapezius muscle parallel with its fibers close to the transverse processes. Deep to it are the paraspinal muscles (Fig. 6-84).

Cut down onto the posterior aspect of the rib to be resected all the way to bone. The plane often is bloody; a cutting cautery (diathermy) is useful (Fig. 6-85).

Deep Surgical Dissection

Carefully separate all the muscle attachments from the rib that has been approached, using subperiosteal dissection with a periosteal elevator (Fig. 6-86). Dissect laterally along the superior border of the rib and medially along the inferior border. Continue dissection subperiosteally on to the anterior surface of the rib. Divide the rib about 6 to 8 cm from the midline. Then, lift it up and carefully cut any remaining muscle attachments and the costotransverse ligament. Twist the rib’s medial end to complete the resection (Figs. 6-87 and 6-88). At this point, the field may flood with a gush of pus from the opened abscess cavity.

Remove all muscle attachments from the transverse process; divide the process at its junction with the lamina and pedicle, using a rongeur biting instrument. Remove the transverse process to gain wider exposure (see Fig. 6-88, cross section).

Figure 6-84 Incise the subcutaneous fat and fascia in line with the skin incision.

Incise the trapezius muscle parallel with its fibers.

Carefully enter the retropleural space by digital palpation and dissection, removing the parietal pleura from the vertebral body. Note that this plane is safe only if the pleura is thickened by disease. Careful blunt dissection is essential to avoid entering the pleural cavity. At this point, the vertebral body and disc space should have been exposed.

Dangers

Nerves

If dissection is extensive around the vertebral body, the central canal can be entered accidentally. If the dura is damaged, it must be closed to prevent spinal fluid leaks.

Vessels

The segmental intercostal arteries often are damaged when the ribs are stripped. They lie on the inferior border of the rib and should be ligated if they are cut (see Fig. 6-94).

Figure 6-85 Cut down onto the posterior aspect of the rib to be resected. Strip the muscles laterally and medially onto the transverse process. Incise the periosteum over the rib.

Figure 6-86 Separate all the muscle attachments from the rib, using subperiosteal dissection.

Figure 6-87 Divide the rib about 6 to 8 cm from the midline. Lift it up and carefully cut any remaining muscle attachments and the costotransverse ligament.

Figure 6-88 Twist the rib’s medial end to complete the resection and remove the rib. The abscess cavity now is exposed. The abscess cavity may extend along the lateral and anterior borders of the vertebra (cross section). Resect the transverse process if greater exposure is necessary.

Lungs

The pleura often is thickened by infections of the underlying lung. As dissection proceeds, damage to the pleura can be minimized by using blunt dissection to strip the pleura from the anterolateral surface of the affected vertebral body. The approach can cause a pneumothorax, however. If there is a sucking sound or a tear in the pleura, it should be treated by inserting a chest tube after closure.

How to Enlarge the Approach

Local Measures

If the musculature is too tight, divide the paraspinal muscles transversely in line with the transverse process to facilitate retraction.

Extensile Measures

The incision cannot be extended, but it can be enlarged to include adjacent ribs and vertebrae either cephalad or caudad.