Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

26 Anterior Thoracoscopic Vertebral Reconstruction and Instrumentation

Francisco Verdú-López and Rudolf W. Beisse

Abstract

Anterior thoracoscopic surgery with vertebral reconstruction and instrumentation can be used to approach the anterior column of the spine in the area between the third thoracic vertebra and the third lumbar vertebra in most cases.

Acute instability with structural damage to the anterior load-bearing spinal column and posttraumatic deformity represent the most frequent indications for surgery. The application potential includes anterior release procedures, with incision and resection of ligaments and intervertebral discs; removal of fragmented discs or sections of vertebrae, with anterior surgical decompression of the spinal canal; replacement of vertebral bodies with biologic or alloplastic materials for spinal fusion; and ventral stabilization procedures with implants designed for use in thoracoscopy.

The thoracolumbar junction is the section of the truncal spine most often affected by traumatic injuries and spinal fractures. In most cases, it is necessary to partially detach the diaphragm to provide access to the retroperitoneal section of this region. The thoracoscopic trans-diaphragmatic approach described in this chapter opens up the whole thoracolumbar junction in a minimally invasive surgery, allowing one to perform all the procedures needed for a full reconstruction of the anterior column.

Video-assisted thoracoscopic surgery decreases the morbidity associated with open thoracotomy such as significant pain and respiratory problems, substantial blood loss, poor cosmesis, and prolonged hospitalization. With an adequate learning curve of training, these procedures are safe and have low complication rates. Thoracoscopic surgery is in many cases an alternative to conventional open surgery.

Keywords: diaphragm, minimally invasive surgery, spinal fracture, spinal fusion, surgical decompression, thoracoscopic surgery, thoracoscopy, video-assisted thoracoscopic surgery

26.1 Introduction

Cord compression in the thoracic spine typically involves the anterior column and can potentially lead to neurologic deficits. These patients may benefit from decompression and reconstruction of the anterior weight-bearing column. However, traditional anterior approaches require extensive exposures that can cause significant morbidity and mortality including intercostal neuralgia and post-thoracotomy syndrome. Furthermore, those patients requiring diaphragmatic detachment to access pathology in the thoracolumbar region can develop visceral herniations into the chest.¹^,² Much of the morbidity associated with the standard thoracotomy is related to chest wall injury.¹^,²^,³

Thoracoscopic decompression with reconstruction and instrumentation provides a minimally invasive approach to reduce the iatrogenic injury to tissues seen with more traditional transthoracic approaches. Thoracoscopic techniques can be employed to gain access to the thoracic spine, including the thoracolumbar junction, by minimal thoracoscopic detachment of the diaphragm. This is made possible by an anatomic peculiarity of the pleural cavity and the diaphragmatic insertion whose lowest point, the costodiaphragmatic recess, is projected onto the spine perpendicularly just above the baseplate of the second lumbar vertebra.³^,⁴^,⁵ Thus, with a diaphragmatic opening of approximately 6 to 10 cm, the entire L2 vertebral body can be exposed, which is a much smaller opening than that required for conventional open techniques.

As with traditional thoracotomy approaches, thoracoscopic techniques are based on the classic spine surgery principles of neural decompression, restoration of spinal alignment, reconstruction, and short-segment stabilization. When performed by well-trained surgeons, thoracoscopic spine surgery has a low rate of complications comparable to the open approaches, with good clinical outcomes and similar deformity correction. Advantages of thoracoscopic spine surgery over open procedures include less morbidity with faster postoperative recovery, less analgesia, shorter hospital stay, and better cosmetic result. Although an anterior thoracoscopic technique alone can be used to perform sympathectomies and thoracic discectomy or to treat compression fractures, a combined open posterior approach may be needed in those patients with three column spinal injuries. These techniques are more difficult in morbidly obese patients. Another disadvantage of thoracoscopic techniques is increased difficulty in handling complex dural injuries.

26.2 Indications

With the advancement of the thoracoscopic spine surgery, the number of indications has also increased. These possible indications include the following:

• Anterior reconstruction of recent or old fractures or injuries of the thoracic and thoracolumbar regions that can present with instability, deformity, and/or stenosis.³

• Spinal canal stenosis with a lesion anatomy that favors the anterolateral approach.⁶

• Centrally located herniated thoracic disc.⁷

• Surgery for deformities and scoliosis.⁸

• Treatment of some tumors if spine stability is compromised after resection.

• Treatment of various infectious processes.⁹

• Revision surgery (i.e., infection of the surgical bed, failure or loss of implant purchase, etc.).

Good candidates for anterior thoracoscopic vertebral reconstruction and instrumentation are those with previous indications, whether or not the anatomy of the lesions is favored by the anterolateral approach. Thinner patients allow for easier surgeries. Obese patients, although more difficult to operate on, benefit the most from a thoracoscopic procedure. The procedure is essentially the same in obese patients as in thinner patients once the portals are set. Obesity therefore is not a contraindication. Adequate relaxation is required and preoperative purging is recommended. The patient should not have lung restriction or significant ventilatory problems because he or she must withstand selective ventilation in only one lung, which is aimed to collapse the other one.

26.3 Preoperative Planning

A complete neurological assessment has to be done prior to surgery. Depending on the type of surgery that we plan to do, it is usually necessary to have anteroposterior (AP) and lateral thoracic and lumbar X-rays. CT scan or MRI is necessary to evaluate the characteristics of the soft tissue and bone. Typically, the fractured or deformed vertebrae are easy to locate under fluoroscopy. If in doubt, surgeons can resort to visually apparent osteophytes previously identified on radiographs and CT to assist in localization. Pay attention to patients with an abnormal number of ribs or lumbar vertebrae. We typically order and evaluate a lumbar and thoracic AP and lateral plain radiograph as well as a chest X-ray prior to surgery to assist in identifying the proper level(s) for surgery. It is important to assess the location of the great vessels and possible anatomical variables for surgery planning. Size of the vertebrae is another parameter that must be taken into consideration in choosing the optimal instrumentation.

During the anesthetic assessment prior to surgery, pulmonary and respiratory functions should be checked. If there are any doubts, forced expiratory volume in 1 second (FEV₁) and diffusion capacity for carbon monoxide (DLCO) allow surgeons to determine preoperatively whether the patient can tolerate selective ventilation of one lung during surgery, as well as postoperatively.

26.3.1 Instrumentation

Standard video endoscopic and thoracoscopic instruments are used to perform the procedure. The image transmission system consists of a rigid endoscope angled at 30 degrees and linked to a three-chip camera. A xenon cold light source with high light-transmitting capacity is essential to illuminate the entire thoracic spine. Instruments required for thoracoscopic dissection include osteotomes, hooks for dissection, hook probes, sharp and blunt rongeurs, Kerrison rongeurs, curettes, and so on. Thoracoscopic instruments for bone and soft-tissue resection should be long with large handles to work safely and securely within the thoracic cavity. Instruments should preferably have a scale marked on both sides for bone and intervertebral disc resection to gauge the depth of instrument insertion during decompression. We had used the Z-Plate (Medtronic Sofamor Danek, Memphis, TN) until October 1999 for reconstruction purposes. Ever since then, we have used the MACS TL system (Aesculap, Tuttlingen, Germany) exclusively because it is specially designed for endoscopic application. This system greatly facilitates the procedure and is now available in a second generation.

26.4 Surgical Approach and Technique

26.4.1 Anesthesia and Patient Positioning

Thoracoscopic procedures are performed with the patient under general anesthesia with single-lung ventilation. The positioning of the double-lumen tube is controlled bronchoscopically. A Foley catheter, central venous line, and arterial line are placed in all cases.

The operating room setup is shown in Fig. 26.1. The patient is placed in a stable lateral position on the right side and fixed with a four-point support at the symphysis, sacrum, scapula, and arms. The proper use of padded brackets is very important to secure and stabilize the surgical posture⁴ ( Fig. 26.2a). Below the corresponding hemithorax, an inflatable air bag is placed for maximum physiological opening of the intercostal spaces. It is useful to use a cushion shaped as an “inverted U” between the legs, which slightly flexes the upper hip to relax the upper aspect of the iliac psoas muscle. The side of approach is mainly decided according to the location of the great vessels, for which CT is best suited. Normally, a right-sided approach is preferred for upper and middle thoracic pathology, and a left-sided approach is preferred for lower thoracic spine and thoracolumbar junction pathology. The arm on the approach side is abducted and elevated to facilitate endoscopic placement and manipulation during the procedure.

Fig. 26.1 Operating room setup for thoracoscopic spine surgery.

Fig. 26.2 (a) Surgical position in the lateral decubitus position. The level of injury is located using fluoroscopy. (b) The surgeon and the assistant holding the camera stand behind the patient. On the opposite side, another assistant surgeon manages the suction-irrigation and the retractor. (c,d) Location of different surgical portals: the black arrow indicates the working channel portal with exact projection on the level of injury, the white arrow indicates the portal for the endoscope, the black asterisk indicates the portal for suction-irrigation, and the white asterisk indicates the portal for the retractor. (Reproduced with permission from Elsevier Spain. Original source: Beisse R, Verdú-López F. Situación actual de la cirugía toracoscópica del raquis torácico y lumbar. Parte 1: Aspectos generales y tratamiento de las fracturas. Neurocirugía 2014;25(1):8–19. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L. All rights reserved.)

Before the operation is begun, the position and free tilt of the C-arm must be checked. Sterile draping extends posteriorly from the middle of the sternum anterior to the spinous processes as well as from the axilla down to approximately 8 cm caudal to the iliac crest. Both monitors are placed at the lower end of the operating table on opposite sides to allow the surgeon and the assistant an unrestricted view. The surgeon and the assistant holding the camera stand behind the patient. The C-arm intensifier is placed between the surgeon and the cameraman. The assistant and the C-arm monitor are placed on the opposite side ( Fig. 26.2b).

26.4.2 Port Placement

Port placement is critical and will affect the ease of accessing the pathology. With the assistance of fluoroscopy, the targeted vertebrae are marked on the skin. First, an AP fluoroscopic projection is done at 0 degrees to verify that the column is not rotated. The surgical table may be slightly rotated to adjust the position. Second, the lateral projection is performed at 90 degrees, making sure that all margins (anterior, posterior, and upper and lower plates) of the vertebral bodies are appraised on fluoroscopy without double contours, which in this case represent the actual situation of injury. For this task, it is very helpful to use, as a rule, a Kirschner wire (K-wire).

Fig. 26.3 (a) Introduction of trocars through the intercostal space under endoscopic control. (b) Using the left thoracoscopic approach to access the thoracolumbar junction, the spine, aorta, lung, and diaphragm are shown. (c) Thoracoscopic view showing the line of diaphragmatic insertion. (d) Diaphragmatic opening with hook diathermy electrode. (Reproduced with permission from Elsevier Spain. Original source: Beisse R, Verdú-López F. Situación actual de la cirugía toracoscópica del raquis torácico y lumbar. Parte 1: Aspectos generales y tratamiento de las fracturas. Neurocirugía 2014;25(1):8–19. Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España, S.L. All rights reserved.)

The working channel is centered exactly over the target vertebrae (12.5-mm diameter). The optical channel for the endoscope (10-mm diameter) is placed two or three intercostal spaces cranial to the target vertebrae for approaching the lower thoracic spine and thoracolumbar junction pathology. For pathology of the middle and upper thoracic spine, the optical channel is placed caudal to the target vertebrae. The ports for suction/irrigation (5-mm diameter) and the retractor (10-mm diameter) are placed approximately 5 to 10 cm anterior to the working port and optical channel ( Fig. 26.2c,d). The port for the diaphragm and/or lung retractors should be placed as far ventrally as possible to avoid instrument “fencing.” It is sometimes helpful to use two separate working ports directed above and below the segment to be instrumented.

The operation begins with the most cranial approach (optical channel). Through a 1.5-cm skin incision above the intercostal space, small Langenbeck hooks are inserted. Muscles of the thoracic wall are crossed in a blunt, muscle-splitting technique, and the intercostal space is opened by blunt dissection, thus exposing the pleura and creating an opening into the thoracic cavity. The 10-mm trocar is inserted, and single-lung ventilation is begun. The 30-degree scope is inserted at a flat angle in the direction of the second trocar. Under direct endoscopic visualization, perforation of the thoracic wall is performed to admit the second, third, and fourth trocars⁴ ( Fig. 26.3a). The second portal is usually done for the retractor, allowing an initial inspection of the surgical area before introducing the next ports. Once the four trocars are placed, the endoscopic view of the surgical site must remain constant to avoid spatial disorientation.

With the main surgeon and the camera assistant behind the patient (as we do), the aorta is arranged horizontally above. Below are the vertebral bodies and intervertebral discs located perpendicular to the aorta ( Fig. 26.3b). Further down is the spinal canal, which hides behind the pedicles, neural foramina, and the heads of the ribs in the thoracic region. The cranial side is on the right and the caudal side on the left.

26.4.3 Prevertebral Dissection and Access to Thoracolumbar Junction

The target area can now be exposed with the help of a fan retractor inserted through the anterior port. The retractor holds down the diaphragm and exposes the insertion of the diaphragm on the spine. The pathologic area is identified with a long spinal needle inserted through the thoracoscopic port under fluoroscopic guidance. The pleura is incised and mobilized over the proximal ribs of the involved vertebra and one level above and below the vertebra. The segmental vessels are ligated with an Endo-Clip ( Fig. 26.4a), coagulated with an endoscopic bipolar coagulator, and transected. As opposed to the traditional approach to the thoracolumbar junction, which requires extensive diaphragmatic detachment, the thoracoscopic approach requires minimal diaphragmatic detachment. Thus, with a diaphragmatic opening of approximately 6 to 10 cm, the entire L2 vertebral body can be exposed.

In order to appreciate the anatomic orientation, the anterior circumference of the motion segment and the location and course of the aorta are palpated with a blunt probe. The line of dissection for the diaphragm is “marked” with monopolar cauterization ( Fig. 26.3c,d). The diaphragm is then incised using endo-scissors. A rim of 1 cm is left on the spine to facilitate closure of the diaphragm at the end of the procedure. To facilitate diaphragmatic reconstruction, an incision is made that runs along the spine and the ribs parallel to the diaphragmatic insertion, which leaves a 1- to 2-cm cuff of diaphragmatic tissue for reapproximation. The diaphragm is thinner in this portion than at the bony insertion site and makes subsequent suturing easier. Retroperitoneal fat tissue is now exposed and mobilized from the anterior surface of the psoas muscle insertion. The psoas muscle is dissected very carefully from the vertebral bodies in order not to damage the segmental blood vessels “hidden” underneath. A retractor is then placed into the diaphragmatic gap.