How is the anterior approach of surgical treatment for idiopathic scoliosis performed?

Updated: Dec 02, 2020
  • Author: Charles T Mehlman, DO, MPH; Chief Editor: Jeffrey A Goldstein, MD  more...
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Answer

After superficial muscle dissection, the surgeon approach proceeds through the bed of the rib that corresponds with the highest vertebra in which instrumentation is planned. This is often either the ninth or tenth rib, with the rib itself being harvested for later use as a bone graft.

Careful dissection is then performed to mobilize the peritoneum (with its contents) in an anterior direction; it is peeled off of the undersurface of the diaphragm. Posterior division of the diaphragm (leaving about a 2-cm cuff for repair) helps to avoid damage to the phrenic nerve. Diaphragmatic division begins with splitting of the costal cartilage and proceeds in a posterior direction with intermittently placed tagging sutures to aid in closure.

The remainder of the retroperitoneal approach to the thoracolumbar spine requires careful superior retraction of the lung, anterior retraction of the peritoneum (with associated aorta and ureter), and posterior retraction of the iliopsoas musculature. Careful identification and division of the segmental vessels (overlying the vertebral bodies) is carried out with either electrocautery or ligatures.

Small sympathetic nerve branches in this same area are sacrificed during this stage of the exposure. This results in at least a transient period in which the left foot (for a left-side approach) will be both pinker and warmer than the contralateral foot. At times, this may result in nursing personnel notifying the surgeon that the contralateral foot is pale and cold, but in reality, it is the foot ipsilateral to the exposure that has changed.

Open thoracotomy might be performed either for anterior thoracic spine release followed by posterior fusion or for anterior thoracic spine fusion with instrumentation. The most common curve pattern to address with this approach would be a right thoracic curve; accordingly, the patient would be positioned with the right side upward.

A similar rib selection and resection technique may be used if desired. From the interior of the chest, the intercostalis musculature (located between each of the ribs) can be seen. Identification of the azygos vein (anteriorly oriented along the vertebral bodies) is necessary. Further medial (ie, central) and running parallel to the azygos vein is the thoracic duct. Several portions of the sympathetic chain may be sacrificed as the segmental vessels overlying the thoracic vertebral bodies are divided and mobilized anteriorly and posteriorly. Blood flow changes similar to those noted in the retroperitoneal approach may be noted in the right foot (for a right thoracotomy).

In addition to this, thoracic surgical dissection carries with it the possibility of sacrificing branches to the greater splanchnic nerve, which would theoretically decrease the visceral referred pain that one might feel from an inflamed gallbladder or similar condition.

Thoracoscopic appreciation of the anatomy of the thoracic spine is becoming more common as endoscopic anterior release and fusion is rapidly moving from being considered an innovation to standard practice. Just as arthroscopic knee surgeons enjoyed an expansion in visualized anatomy in comparison with that visible in knee arthrotomies, the endoscopic spine surgeon benefits from much greater intrathoracic latitude. Most VATS procedures also involve the right thoracic cavity, and this discussion focusses on that particular side.

Proper rib counting and visualization of the superior intercostal vein (formed by the confluence of the second, third, and fourth intercostal veins) as it empties into the azygos vein are necessary steps to orient the surgeon. Beyond this, one also notes the mounds and valleys of the thoracic spine, with the mounds being the disks and the valleys being the vertebral bodies with the segmental vessels that overly them. [126]

The same anatomy outlined in the thoracotomy discussion still clearly applies, but further endoscopic fine points are needed. Specifically, the thoracic spine may be considered to be composed of three separate fields, with important anatomic nuances. [135] The upper field may be considered to be T2-5, the middle field may be considered to be T6-9, and the lower field may be considered to be T10-L1.

The upper field is dominated by the superior intercostal vein, and it is characterized by the fact that the rib heads tend to completely span their respective disk spaces and articulate with two vertebral bodies. This results in a rib such as the third rib coming directly into the region of the T2-3 disk space so that it will articulate with both the T2 and T3 vertebral bodies.

In the middle field, the rib head once again comes directly in toward the disk space, but now, it firmly attaches itself only to the disk space proper.

In the lower field, the rib head articulates directly with its corresponding vertebral body. Thus, in the lower field, the 11th rib is traced to its corresponding vertebral body and then moves directly cephalad to reach the T10-11 disk or directly caudad to reach the T11-12 disk. Once the vertebral bodies have been exposed in a skeletally immature patient, the growth cartilage of the vertebral endplate can be visualized. It has an odd tendency to appear green in color (a quirk of endoscopic optics) and is colloquially referred to as a Wolf line, in honor of Randall K Wolf.


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