Anatomic Considerations for the Video-Assisted Thoracoscopic Surgery Approach

The rib cage and chest wall form a rigid open space in which endoscopic surgery may be performed. Unlike the abdomen, CO₂ insufflation is not required to maintain a working space. Through most of the thoracic spine, ribs articulate at the disc space level. The rib number corresponds to the lower vertebral body at the disc space (e.g., the sixth rib comes off the T5-6 disc space). Because the rib comes directly off the disc space from demifacets arising on the vertebral body just above and below the disc, rib resection is required for adequate access to the posterolateral corner of the disc. In the lower thoracic region, T11 and T12, the rib head may be well caudal to the disc space, permitting unobstructed access.

The segmental vessels lie in the waist of the vertebral bodies, entering the epidural space via the foramina. When approaching the spine endoscopically, it is important not to inadvertently lacerate these vessels. Some spine procedures, including corpectomy and instrumentation, require unilateral and occasionally bilateral sacrifice of the segmental vessels. Discectomy and ventral release procedures, on the other hand, usually do not require vessel sacrifice. One cadaver study demonstrated adequate discectomy without sacrifice of the intercostal or segmental vessels once an adequate mobilization of the esophagus and azygos vein had been carried out. The authors concluded that the segmental vessels ought to be preserved to reduce the risk of spinal cord ischemia.¹⁰ In a two-phase goat study, thoracoscopic discectomy and fusion were undertaken both with and without sacrifice of the segmentals.²⁷ In the first phase, the area of disc excision was slightly higher in the vessel-ligated group, but the investigators did not believe this to be significant. Operative times were the same. In the second phase, biomechanical testing of the resulting fusion was undertaken, and the vessel-spared group revealed less flexibility in lateral bending. The authors concluded that the segmental vessels in the thoracic spine can be effectively spared without injury during disc excision and fusion. They noted that while slightly more disc area was excised with ligation of the vessels, sparing the segmental vessels may provide a blood supply that aids in fusion. They recommended sparing the segmental vessels in patients with a higher risk for cord perfusion–related neurologic injury, such as revision surgery, severe kyphosis, paraparesis, and congenital anomalies.

These studies have been criticized for not adequately modeling the intraoperative conditions of spine deformity.³ Many authors report that sacrificing the segmental vessels provides better visualization through improved pleural reflection and more complete discectomy.^21,22,28,29 In a report of 1197 procedures in which more than 6000 vessels were sacrificed, there were no adverse neurologic consequences.³⁰ It may be reasonable to use both vessel-sparing and vessel-sacrificing techniques as a function of the clinical situation. For example, in congenital deformity cases in which spinal cord blood supplies may be anomalous, vessel sparing may be more important.²¹ Also, if the intervention requires the sacrifice of one or more segmental arteries in the mid to lower thoracic region, especially T9 to T11, a right-sided approach should be considered to avoid ligation of the artery of Adamkiewicz. The artery of Adamkiewicz can be visualized with either CT or MRI angiography, and this is recommended if a left-sided approach is being considered.

Other surgically important structures include the superior intercostal veins and the sympathetic chain. The veins empty into the azygos circulation at or about the T3-4 interspace.¹ Branches from the sympathetic chain run over the rib heads, just below the parietal pleura.³¹ Over the 5th through 10th ribs, these coalesce as the greater splanchnic nerve that courses into the abdomen.

There are critical regional differences in thoracoscopic anatomy that dictate different exposure techniques. In the upper thoracic region, for example, the surgeon should elevate and support the ipsilateral arm to rotate the scapula away. Here, unless there are apical adhesions, the collapsed lung readily falls away from the spine, allowing excellent visualization.³² In the midthorax, there is more available space that allows more variation in placement of the camera and retractor ports. On the other hand, a fan retractor or strategically placed sponges are typically needed to keep the collapsed lung out of the operative field. Similarly, a second retracting port may be needed to move aside a bullous or stiff lung.³² Tilting the operating table forward may improve visualization with less forceful lung retraction. In the lower thoracic region, it may be necessary to retract the diaphragm, but here, as at the apices, lung retraction is not usually a problem.

Indications and Contraindications

Anesthesia

Cooperation between the anesthesia team and a thoracoscopic spine surgeon begins with a careful preoperative evaluation, followed by meticulous room and intubation setup. An experienced anesthesiologist with expertise in thoracic surgery is strongly recommended. Selective double-lumen endotracheal intubation allows collapse of the lung on the operative side. The tube may easily migrate, and frequent bronchoscopic assessment of tube position is mandatory.³⁵ In small patients (<45 kg), even the smallest double-lumen endotracheal tube may not fit. In these cases, bronchial blockers are required.^3,21 Blockers are technically more difficult to use and have a higher rate of incomplete lung deflation, which may seriously impair visualization.³ Prone positioning in deformity cases may allow single-lumen intubation.³⁶

General anesthetic options include total intravenous technique, isolated volatile agent, or a combination of volatile and intravenous agents. Initially, intravenous technique was recommended because of the potential risk of hypoxic pulmonary vasoconstriction with inhalational agents during single-lung ventilation. Recently, however, a series of 85 patients found no difference among these techniques.³⁵ Hemodynamic monitoring includes a double-lumen central venous catheter. Alternatively, pulmonary artery catheterization may be undertaken.³⁵ Hypotensive anesthesia should be avoided in myelopathic patients or in those undergoing segmental artery sacrifice.²³

Once the tube position has been confirmed, the ipsilateral lung is deflated by clamping the lumen of its endotracheal tube. Once the chest has been entered with the first portal, the lung should collapse. If inadequate collapse is noted, a short period of positive pressure CO₂ insufflation may assist in collapsing the lung. Usually, this insufflation is not necessary.³⁷

Patient and Operating Room Positioning

A radiolucent operating frame is preferred for either lateral decubitus or prone positioning. Lateral decubitus, identical to open thoracotomy positioning, is most typical for VATS spine surgery. A beanbag or bolsters may be used to maintain laterality. If intraoperative imaging is to be used, it is necessary to assess the location and lucency of the positioning aids. The patient should be well padded, and an axillary roll is typically used.

The patient is belted into place so that the table may be tilted into the Trendelenburg or reverse Trendelenburg position or even tilted right or left as necessary to improve intraoperative visualization. It is important to ensure that the patient stays in a strict lateral position during the initial approach to the spine to maintain surgeon orientation. Some surgeons prefer to “airplane” the table up for portions of the procedure, but given the loss of tactile feedback and three-dimensional information associated with endoscopy, a strict knowledge of the patient’s body position in space is necessary. In some settings, particularly in the lower thoracic spine, it may be useful to “jackknife” the table to improve access to the lateral body wall. However, in patients with significant spinal cord compression, excessive “jackknifing” may increase the risk of iatrogenic neurologic progression.³⁷

Prone positioning may be used as part of a simultaneous ventral/dorsal approach.^20,36 Simultaneous surgery eliminates the need to stage the procedures, as well as the added time and costs for repositioning, redraping, and a new operating room setup. Prone position is particularly advantageous in cases of marked instability. For example, in ankylosing spondylitis or trauma, the spine may suddenly translate at the osteotomy site during repositioning. Prone position also allows a gravity reduction of hyperkyphosis.³⁶ Finally, prone positioning confers the additional advantage of allowing the lungs to fall away from the spine, decreasing the need for retraction.

A large operating room is typically needed to accommodate the special equipment required in VATS cases.³³ The gowned and sterile team typically includes two surgeons, one assistant, and one scrub nurse. Additional personnel include the anesthesia team, somatosensory-evoked potential monitoring personnel, cell saver transfusion technicians, and circulating nursing staff. Beyond the usual complement of anesthesia machines and back tables for instruments and implants, endoscopic spine surgery requires two video monitors, a fluoroscope, and neurologic monitoring equipment (usually sensory-evoked and motor-evoked potentials). The endoscopic surgeon and spine surgeon typically work on the same side of the patient (facing the patient in the lateral decubitus position). Alternatively, they can work opposite one another. Video mixers can convert image orientation so that no mirror image instrument manipulation is required.¹ More and more frequently, voice-activated robotics are being used to replace the assistant surgeon in camera positioning. Robotics may improve visualization by providing a steady image.

Instruments for an open thoracotomy should be readily available for emergency use. In the prone position, open access can be achieved with an extended costotransversectomy approach. Because the lung has already been mobilized, it is easy to enter the chest. Once in, the surgeon is readily able to access, identify, and control the major vascular structures.²⁰ Immediate potential access to a thoracic surgeon is also recommended.

Equipment

The workhorse of spinal endoscopy is the video equipment. This begins with the endoscope itself. A number of standard 10-mm endoscopes are used, most commonly 0-degree and 30-degree scopes. Occasionally, 70-degree scopes are needed. The 0-degree scope is standard for thoracoscopy, but a 30-degree scope decreases instrument crowding and allows better visualization around bony corners.^24,38 Typically, a 10-mm, 15-inch end-viewing scope is used; however, in pediatric cases and, with increasing frequency in adults, a 5-mm scope may be preferred.²⁴ The smaller scope provides less illumination, but with improvements in high-resolution, three-chip technology is adequate in most cases. Three-dimensional endoscopes are becoming increasingly available and help visualize landmarks and render improved depth perception.²⁴

Instruments are introduced into the chest through trocars. Initially, these trocars were hard. Hard trocars may protect the thoracoscope against the rigid fulcrum of the rib cage.¹⁵ More recently, soft trocars have been developed that may be less traumatic to the neurovascular bundle on the inferior rib undersurface. Standard trocars are either 5 mm or 10 mm and are selected based on the size of instrument to be passed and the intercostal distance, which in adults is less than 12 mm.³⁷

Typical spine instruments are customized for endoscopic applications by creating an extended shank of uniform diameter to match standard trocar sizes (Fig. 127-1). These include long-handled curets, Cobb elevators, pituitary rongeurs, disc shavers, nerve hooks, and Penfield dissectors. High-speed burs with long extenders are often required, as are more specialized types of endoscopic equipment such as Endo Shears, a bipolar endoscopic electrocautery, the harmonic scalpel, endovascular clips and loop ligatures, as well as endoscopic fan retractors.

FIGURE 127-1 Spinal thoracoscopy benefits from an ever-increasing array of available instruments. Important among these are the endoscope itself (A); standard endoscopic instruments, including a fan retractor and autosuture device (B); endoscopic dissecting tools (C); and typical spine instruments modified for thoracoscopic use with long hands and uniform diameter shafts (D).

A variety of spinal surgical implants are also available for the task required, including disc interbody cages, screw and rod combinations, and vertebrectomy cages.

Surgical Technique and Avoidance of Complications

A left-sided or right-sided approach to the thoracic spine may be used depending on the eccentricity of the pathology (Fig. 127-2). With a left-sided approach, the thick resilient aorta is less prone to injury than the large friable tortuous veins of the azygos system. Some authors prefer a right-sided approach when the pathology is not lateralized, because there is a greater spinal surface area lateral to the azygos vein than the aorta.¹⁴ This difference can be assessed with preoperative axial CT or MRI images. Below T9, one may consider a left-sided approach to avoid the more cranial diaphragm reflection on the right.

FIGURE 127-2 Lateral thoracoscopy. A, Operating room setup. B, Clinical photograph of lateral thoracoscopy. Note the assistant in the foreground holding the fan retractor. C, Visualization is improved when the lungs fall away from the spine with a ventral tilt of the operating room table of 20 to 30 degrees.

(C, From Regan JJ, Jarolem KL: Thoracoscopy of the spine. In Herkowitz HN, Garfin SR, Balderston RA, et al, editors: Rothman-Simeone: the spine, ed 4, Philadelphia, 1999, WB Saunders, p 601.)

The initial trocar creates the main viewing portal and is placed in the anterior axillary line at the sixth or seventh intercostal space, giving an unobstructed view of the entire hemithorax. The trocar is inserted in the manner of a tube thoracostomy with blunt dissection with a Kelly forceps just over the top of the rib to avoid damage to the neurovascular bundle or deep structures. A digital exploration is undertaken to exclude adhesions and avoid parenchymal lacerations of the lung. Some recommend Bovie dissection through the musculature to prevent bleeding around portals, which can obscure the camera image.¹

This first portal is the only one to be inserted blindly. Once open to the atmosphere, the lung falls away from the thoracic wall, allowing insertion of the thoracoscope. The endoscope is inserted, and an exploratory thoracoscopy is performed. Minor lung adhesions are released. If complete atelectasis is not achieved, a brief period of CO₂ insufflation may help collapse the lung.

The camera assistant must maintain the camera orientation and keep the operative field centered in view with a steady hand. The camera and instruments should be in the same 180-degree arc to avoid working in a mirror image. The camera assistant and the operating surgeon should work in unison with small movements. The camera should be removed for cleaning at various intervals. It should be reinserted carefully, because the lung may have partially reinflated, and injury to the lung parenchyma is possible.³⁷ Self-cleaning and defogging arthroscopes are very helpful in this regard.²⁴

It is necessary to manipulate only one object at a time. The camera operator zooms into the operative site. Then, as new instruments are introduced, the operator pans the camera out to follow the instrument into the operative field, preferably without changing the camera angle. Similarly, retractors and other instruments should be removed under direct visualization. Fan retractors should be removed in the fully closed position only. Levering instruments on the rib cage should be avoided to decrease pressure on the intercostal nerve.³⁹

Once in the chest, surgical levels are identified. Operating at the wrong level is always a concern in the thoracic spine. It is important to screen for variant anatomy, such as accessory ribs, with preoperative radiographs, then find the level by counting down from the first rib. The first rib may be difficult to identify. It is necessary to mark the disc space and obtain radiographic confirmation. A Steinmann pin can be passed directly through the chest wall into the pathologic level.³³ A radiograph confirms level localization, and the pin also demonstrates the optimal location for the working portal. Only quality radiographic images are acceptable. Anteroposterior radiographs are typically more helpful than lateral radiographs.³¹ In some centers, marking beads are placed at each spinal level, and radiographs or fluoroscopy are obtained prior to entering the operating suite. The appropriate level bead is maintained on the patient for intraoperative confirmation.³²

To manipulate the spinal tissues, additional instruments need to be inserted into the chest through additional trocars. Typically, two working portals are created under direct video visualization with the lung protected. The chest is percussed, and by visualizing the percussions from within the chest, additional sites are chosen. As an alternative, 18-gauge spinal needles can be placed through the interspace to verify the level and trajectory. It is necessary to organize the remaining portals to center the instruments at the level of pathology. A number of portal patterns have been described and are covered in more detail in subsequent sections. Typically, an L or V shape at the dorsal axillary line two interspaces cephalad and caudad to the viewing portal is created, depending on the chest wall morphology and the intended spinal level. Portals should be spaced far enough apart that instruments do not “fence” with each other. The final viewing portal should be far enough away from the lesion to allow a panoramic view and to allow room to manipulate instruments.³ During the procedure, the instruments and scope are interchanged between the portals to facilitate work at different levels. It is preferable to make another portal perpendicular to the operative level than to operate at an acute angle to the pathology.³²

When the appropriate portals have been placed and the correct level identified, the surgeon incises the parietal pleura with monopolar cautery. Alternatively, he or she uses the harmonic scalpel to dissect with less smoke and char.^12,40 It is necessary to avoid monopolar cautery over the inferior margin of the rib head, where electrocautery injury to the intercostal nerve may occur.³⁷ The degree of pleural dissection depends on the extent of the intended surgery but may include longitudinal approaches parallel to the spine or transverse approaches parallel to each disc space. If the segmental vessels are to be preserved, smaller pleural incisions are created parallel to the disc space. Bluntly dissect the incised parietal pleura rostrally, caudally, and ventrally to expose as much of the vertebral margins as is necessary.

At each step, meticulous hemostasis is required. Methods to control bleeding include monopolar or bipolar electrocautery, harmonic scalpel, argon beam coagulation, and hemostatic packing. Uncontrolled bleeding may necessitate conversion to an open procedure.

At the conclusion of the procedure, it is necessary to irrigate out any disc or bony debris. Most authors do not attempt to close the parietal pleura. Some recommend an intercostal bupivacaine block to decrease postoperative pain.⁹

A chest tube is then selected—20F, 24F, or 28F—depending on the patient’s chest size. One inserts the tube through the inferiormost portal and runs it cranially along the vertebral column. Rosenthal uses two chest tubes: one, an apical tube for air and second, a basilar tube for effusions.⁴¹ Depending on the nature of the procedure, the tube can be maintained at water seal or at 20 cm of water suction. Typically, the tube can be removed 1 to 2 days postoperatively.

In the postoperative period, most patients are extubated immediately. A chest radiograph is obtained in the recovery room to verify full inflation of the lungs.⁷ A brief period of postoperative ICU monitoring is recommended. Aggressive respiratory care and physical therapy are required to prevent “down lung” atelectasis and pneumonia.

Results and Complications

Indications and Contraindications