Overview

Although anterior approaches to the thoracolumbar spine date as far back as the 1930s, first-generation anterior column instrumentation was developed in 1968 by Dwyer and colleagues and was composed of a vertebral screw-and-cable system. The first-generation system corrected deformity in the coronal plane but contributed to significant kyphosis and was prone to instrumentation failure secondary to its nonrigid construct. Subsequently, in the 1970s, Zielke and colleagues designed a screw-and-rod system that improved upon the earlier instrumentation. Innovation has continued since, and various systems are currently available that can typically be divided into single screw-and-rod systems or those with dual screws and dual rods that require a staple.

For awhile, the use of anterior correction for scoliotic deformity gained in popularity and became increasingly more widespread. For select curves, an anterior fusion could be performed while preserving more functional levels than a posterior approach. On average, 2.5 fewer levels were fused to achieve similar radiographic outcomes. Furthermore, anterior correction provided greater axial force, permitted greater improvement of the rotation, and also corrected the hypokyphosis often associated with adolescent idiopathic scoliosis when compared with hybrid constructs. Anterior correction also provided better improvement of compensatory unfused curves, and less decompensation over time was observed with these same anterior constructs. However, with the advent of thoracic pedicle screw fixation and posterior direct vertebral body derotation, anterior approaches have become less popular except in select circumstances.

Anterior approaches include the anterior correction and fusion, anterior releases used adjuvantly with posterior instrumentation, or either performed thoracoscopically. This chapter will describe the techniques used to perform open or laparoscopic anterior fusions or releases for scoliotic correction.

Indications

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  Lenke type 1 and 5C curves (single thoracic curves or thoracolumbar curves)

  
  
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  Hypokyphosis (anterior surgery will typically increase kyphosis)

  
  
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  Significant risk of crankshaft (Risser grade 0, open triradiate cartilage); risk of developing crankshaft phenomenon marginalized by anterior fusions

  
  
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  High risk of pseudarthrosis (Marfan syndrome, neurofibromatosis, prior radiation, etc.)

  
  
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  Need for anterior release with rigid, inflexible curves (relative)

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  Single structural thoracic curves

  
  
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  Curvature less than 75 degrees (relative)

  
  
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  Between T5 and L1 (ideally T5 to T12)

Relative Indications

Many of the indications are relative, because changing technology and improved techniques have obviated some of the risks and complications from posterior approaches. Although reportedly frequent in skeletally immature children using hook or hybrid constructs, the risk of developing crankshaft phenomenon using pedicle screw instrumentation is thought to be diminished. Furthermore, pedicle screw fixation has improved the rigidity of constructs and may be sufficient in treating etiologies previously associated with unacceptably high rates of pseudarthrosis (i.e., neurofibromatosis). Significant correction can also be achieved with rigid, inflexible curves through adjuvant posterior techniques, such as pedicle subtraction osteotomies or vertebral column resections.

Endoscopic Contraindications

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  Less than 2 cm between chest wall and vertebral body

Relative Contraindications

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  Severe pulmonary compromise (forced vital capacity <50% predicted)

  
  
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  Inability to tolerate single-lung ventilation

  
  
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  Intrathoracic or abdominal pathology (Marfan syndrome, neurofibromatosis, pleural adhesions)

  
  
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  Significant kyphosis

  
  
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  Double or triple curves (other Lenke-type curves)

  
  
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  Long neuromuscular curves

  
  
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  Severe apical rotation

  
  
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  Severe osteopenia

  
  
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  Insufficient vertebral size to support anterior screws

Selection of Level of Fusion

The selection of instrumented levels for an anterior approach typically involves the end vertebrae (EV). The EV represent the vertebrae on the anteroposterior (AP) radiograph that form the Cobb angle, and which end plates are the most angulated from the horizontal ( Fig. 59-1 ). Selection of levels for an anterior release in conjunction with a posterior fusion is typically limited to the few disk spaces that comprise the apex of the scoliotic curve.

Fundamental radiographic parameters. The end vertebrae (EV) represent the rostral and caudal levels, comprising a curve of which the end plates are measured to form the Cobb angle. The EV represent the levels whose end plates are most angulated from the horizontal. The neutral vertebra (NV) depicts the level with the least rotation, where the spinous process is most centered between the pedicles. The stable vertebra (SV) denotes the level bisected by a vertical line drawn from the midsacrum.

Equipment

Preoperative and Perioperative Considerations

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  Intubation: The patient should be intubated with a double-lumen endotracheal tube (ETT), and the lung on the convex side of the curve should be collapsed at the beginning of the case to safely perform the surgery.

  
  
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  Blood pressure/mean arterial pressure (MAP): Hypotension or hemodilution should be avoided, even at the beginning of the surgery, given the potential risk of spinal cord infarction, especially if segmental vessels are ligated. Particular attention should be paid to ensure that the MAP is above 70 to 80 mm Hg prior to correction of the deformity.

  
  
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  Neuromonitoring: Baseline recordings should be obtained prior to incision, and readings should be verified routinely throughout the case.

  
  
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  Radiography: Fluoroscopy should be arranged at the beginning and draped into the field; it can be useful to verify bicortical purchase of screws and localize the vertebral level.

Positioning

Lateral Decubitus (Endoscopic or Open)

Most commonly, a lateral decubitus position is adopted for a thoracotomy ( Fig. 59-2, A ). Typically, the convex side of the curvature is positioned facing up; however, the surgeon may approach from the alternate side if significant restrictions are present. In the upper thoracic spine, the right brachiocephalic artery and approach has a straighter course and does not risk injury to the thoracic duct and heart. In the thoracoabdominal spine, the artery of Adamkiewicz is often derived from the left side. However, the aorta is also situated closer to the left and is often the preferred side for vascular surgeons, because it is easier to mobilize and repair than the inferior vena cava (IVC). It is also important to remember that with significant axial rotation of a right thoracic curve, the great vessels are farther across the vertebral body and closer to the left side; this may narrow the working space and increase the difficulty from a left-sided approach. Routinely, the convex curve side should be placed upward, and a beanbag can be used to help position the patient in lateral decubitus.

Operative positioning. A, Patient in lateral decubitis for a thoracic approach with placement of operative equipment. B, Illustration of a standard prone position that can be adopted with an anterior release.

A gel roll or padding should be placed under the axilla, and careful attention should be paid to ensure that all pressure points are well padded. The knees are typically slightly flexed, and a pillow is placed between them. The lower arm is usually extended on an arm board, and the more elevated arm is suspended in an armrest flexed at the elbow to rotate the scapula dorsally and rostrally. Tape is placed across the hip; it can be also used to support the shoulder, but caution should be used to avoid having it too caudal, which may restrict the operative field. Surgeons can stand on either side with a screen appropriately placed for proper visualization if thoracoscopy is being used. The diskectomy is easier to perform with the primary surgeon standing on the ventral side of the patient, whereas implantation of instrumentation is easier standing from the dorsal/posterior side.

Operative Technique

Incision/Exposure

The incision should be verified by fluoroscopy to confirm the anticipated exposure. The convex lung should be collapsed prior to entry into the pleural cavity to avoid injury to the pleura or lung. After the initial port is created, the lung can be insufflated with carbon monoxide; the remaining access ports or a lung retractor can be used.

Upper Thoracic Access (T1–T4)

A curvilinear incision paralleling the underside of the scapula should be adopted and aimed toward the ipsilateral nipple ( Fig. 59-3 ). Each of the muscle groups should be identified and tagged to facilitate reapproximation at closure. The scapula can be retracted to help identify the various muscles, and the trapezius can be divided lateral to its medial attachment. The latissimus dorsi, rhomboid major, and serratus anterior can be divided from their rostral attachments, thus allowing finger dissection of the deep plane of the scapula. The scapula can then be further retracted, allowing access to the upper thoracic spine. Generally, rib resection of the lower rib will allow access to the associated disk space (e.g., resection of the T3 rib will allow access to the T2–T3 disk space).

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