Thoracoscopic Corpectomy and Reconstruction

Published on 02/04/2015 by admin

Last modified 02/04/2015

Print this page

This article have been viewed 1500 times

Chapter 61 Thoracoscopic Corpectomy and Reconstruction

Thoracoscopic spine surgery, also known as endoscopic-assisted or video-assisted thoracoscopic surgery, is a minimally invasive, closed endoscopic approach to the ventral thoracolumbar spine for decompression and stabilization. It offers an alternative to open thoracotomy for thoracolumbar vertebral body resection from T5 through L2, ventral spinal cord decompression, and spine reconstruction with interbody and ventrolateral plate instrumentation for restoration of biomechanical stability.

Spinal instability caused by trauma or destructive disease has historically been treated through a dorsal approach. Purely dorsal techniques, however, often fail adequately to address ventrally located pathology. Dorsal decompression with thoracic laminectomy of ventral epidural masses has been associated with increased risk of injury to the spinal cord. Ventral spinal canal decompression through dorsal and even posterolateral approaches can be challenging and ineffective.¹^–³ Furthermore, dorsal instrumentation may not sufficiently stabilize a significantly disrupted ventral load-bearing spinal column.^4,⁵

To more effectively and directly decompress and stabilize the ventral spine, ventral thoracotomy and thoracoabdominal techniques were developed.^6,⁷ Although these approaches demonstrated improved outcomes and are an acceptable treatment modality for ventral thoracolumbar disease, the high access morbidity of these open procedures often results in post-thoracotomy pain syndromes, postoperative pneumothorax or pleural effusion, shoulder dysfunction, abdominal wall relaxation, and significant scarring of the chest wall.⁸

Spine surgeons have more recently adapted the minimally invasive thoracoscopic techniques that have been applied by thoracic surgeons for many years. Thoracoscopic spine surgery was first used for the treatment of thoracic disc herniations and traumatic fractures. With advances in thoracoscopic video technology, instrumentation, and instrument systems, thoracoscopic spine surgery has improved significantly, and its use has been expanded to include the treatment of most ventral thoracolumbar disorders, including trauma, tumor, and degenerative disease, as well as deformity correction in select cases.^4,⁹^–¹⁵

Specialized tools for endoscopic spine surgery are used to access the thoracic cavity through small chest incisions, and the surgery is performed under two-dimensional video guidance. Minimizing chest wall dissection and retraction through the use of small thoracoscopic incisions has significantly improved outcomes and reduced postoperative morbidity without compromising long-term successful fusion rates.9–11,16–18 The minimally invasive thoracoscopic approach can now be safely and effectively performed to treat disease that had previously required an open thoracotomy.

Advantages and Disadvantages

Several advantages are offered by the minimally invasive ventrolateral thoracoscopic approach over an open thoracotomy. Multiple vertebral levels and the ventral spinal canal can be visualized and treated without increasing surgical exposure when access ports are properly placed. The surgical field can be imaged with excellent resolution using modern high-definition endoscopic technology. The small intercostal incisions negate the need for rib resection and retraction, unlike open thoracotomy approaches, which necessitate large incisions, extensive dissection of intercostal muscles, rib resection, and retraction of the chest wall. The thoracoscopic approach is associated with reduced blood loss, need for blood transfusion,¹⁹ days of mechanical ventilation, perioperative wound pain, incidence of pulmonary and shoulder dysfunction, length of hospital stay, and days to rehabilitation.¹⁶^–¹⁸

For most spine surgeons, the major disadvantage of the thoracoscopic approach is unfamiliarity with the technique and high technical demand. The operation is performed distant from the surgical site in two dimensions based solely on thoracoscopic image guidance, which requires most spine surgeons to acquire a new set of skills. Before operating on a patient, the surgeon must gain familiarity with the new technique in practical and didactic training sessions. The surgeon and operating room staff must overcome a steep learning curve while gaining familiarity with the approach, and this can initially increase operative times by several hours. Anesthesia monitoring and double-lumen ventilation may also increase operative times. Conversion to an open thoracotomy may be required with difficult cases or when intraoperative complications cannot be resolved with the thoracoscopic technique. Finally, extensive intrathoracic disease, whether pulmonary or spinal, may be difficult to address with the thoracoscopic approach.

Indications and Contraindications

The thoracoscopic approach is best suited for patients with thoracolumbar disease limited to one vertebral body and the ventral spinal canal between T3 and L3, although multiple levels may be treated. The most common indication for thoracoscopic spinal surgery is in the setting of trauma. Among patients with traumatic spinal injury, ventral spinal reconstruction for biomechanical instability is the most common surgical indication. Traumatic spinal instability may be secondary to fracture, injury to the intervertebral discs, or significant ligamentous disruption. The mainstay of treatment for thoracolumbar fractures is rigid fixation with transpedicular screw and rod constructs. The decision to add ventral column reconstruction is based on the load-bearing capacity of the injured spinal segment. The load-sharing classification system developed by McCormack et al.⁵ established a correlation between failure of dorsal short segment fixation and the characteristics of the most significantly injured vertebrae. Fractures with a high degree of vertebral body comminution, fragment apposition, and postoperative deformity correction were found to be at high risk for dorsal instrumentation failure. Thoracoscopic surgery for reconstruction of the ventral load-bearing elements is indicated in these patients. Although patients with neurologic deficits from fracture intrusion into the ventral spinal canal comprise a minor subgroup of patients with traumatic spine injury, they are also indicated for spinal canal decompression and ventral stabilization.

In cases of spinal tumor, thoracolumbar surgery is indicated for treatment of spinal instability, radiation treatment failures, most cases of spinal stenosis secondary to epidural tumor causing neural compression, and pain intractable to conservative measures or to obtain a histologic diagnosis.^3,²⁰^–²³ The thoracoscopic approach is indicated for resection of vertebral body tumors with or without ventral spinal canal involvement and for ventral column reconstruction with interbody placement and ventrolateral instrumentation.

The thoracoscopic approach is contraindicated in patients unable to tolerate single-lung ventilation because of severe cardiopulmonary disease such as acute posttraumatic lung failure, significant pulmonary contusions, advanced chronic obstructive pulmonary disease or asthma, or hemodynamic instability. This approach is also contraindicated in patients with significant medical diseases, disturbances in hemostasis, or terminal illnesses precluding surgical treatment. The surgery may be technically challenging in patients with a history of trauma, prior surgery, or infection because of the development of dense pleural adhesions. In cases with substantial dorsal column disruption or involvement, stand-alone ventral surgery may be insufficient to achieve spinal stability, and supplemental dorsal fixation should be considered.

Preoperative Assessment and Planning

Radiographic and Diagnostic Evaluation

As with other spine surgeries, careful preoperative review and understanding of the radiographic studies are essential to identify the most appropriate treatment method and to plan the surgery. The presence or extent of vertebral body disease and bony destruction, instability of the load-bearing spinal column, spinal cord compression and canal stenosis, and anatomic malalignment are noted for surgical planning. Plain radiography can be used as an initial evaluation to localize the levels of involvement; however, CT must be obtained to further assess the anatomy and involvement of the osseous spine, which is important for precise surgical planning of the dimensions of the reconstruction. The spinal cord and neural elements, intervertebral discs, epidural contents, paraspinous anatomy, and soft tissues, including abnormalities such as tumors, are evaluated primarily with MRI. The detail and orthogonal views displayed with CT and MRI allow the best assessment for local anatomy and disease morphology. When necessary, other imaging modalities, such as angiography for vascular spinal tumors, may be used to obtain further information on the disease process.

The preoperative evaluation for thoracoscopic surgery also includes assessing the patient’s ability to tolerate surgery under general anesthesia with single-lung ventilation. The patient’s overall medical condition, including cardiovascular and hemodynamic stability, is assessed, and laboratory studies, including a complete blood count and coagulation panel, are reviewed. The patient’s pulmonary status is also thoroughly assessed before surgery, which may require an evaluation by a pulmonologist, anesthesiologist, or qualified internist. An evaluation by or discussion with a cardiothoracic surgeon may also be warranted in cases of pulmonary disease, previous lung injury, or infection to decide whether the patient is suited for thoracoscopic surgery or open thoracotomy. A cardiothoracic surgeon should be available at the time of surgery, with advance knowledge of the case when possible, in the event that immediate conversion to an open exposure is needed.

Planning of Approach

The patient’s imaging studies are examined in detail to develop a thorough understanding of the individual patient anatomy, particularly the relative locations of the chest wall and thorax, thoracolumbar spine and spinal cord, and mediastinal structures. The side of surgery is chosen based on disease lateralization and location with respect to the surrounding anatomy. The locations of the aorta and vena cava are noted in relation to plate placement and the lesion being treated. A left-sided approach is generally preferred at the thoracolumbar junction (T11-L2) and for disease lateralization to the left. For lesions of the upper to midthoracic spine (T3-10), a right-sided approach is typically chosen.

Planning of Resection and Reconstruction

Detailed preoperative examination of the patient’s bony anatomy is important for planning the reconstruction. The appropriate lengths of the vertebral body screws are determined by measuring the widths of the vertebrae on the preoperative images. The height of the interbody is approximated by measuring the distance between the inferior end plate of the cranial level and the superior end plate of the caudal level. The plate dimensions can also be approximated preoperatively by measuring the distance between the lower third of the cranial vertebral body and the upper third of the caudal vertebral body. The extent of pathologic canal intrusion is also measured to determine the amount of bony resection needed for sufficient ventral spinal canal decompression.

Operative Technique

Thoracoscopic Instruments and Instrumentation Systems

Minimally invasive thoracoscopic instruments have been specifically developed for this application and are highly specialized. They are designed with adequate length for safe and effective intrathoracic maneuvering, have large handles for improved grip and ease of use, and are made with nonreflective surfaces to decrease glare on the endoscopic view. For illumination and optimal visualization, a high-quality endoscopic camera is essential. A high-definition, 0- to 30-degree angled rigid endoscope with a high-output xenon light source provides the best digital resolution.

The room is set up with the surgeon standing directly behind the patient and operative site. A video monitor with the projected endoscopic image is placed in front of the patient, directly across from the main surgeon, and a monitor displaying the fluoroscopic image is placed beside the endoscopic video monitor. The assistant operating the endoscope stands to the right of the surgeon. The third assistant, when available, stands across from the main surgeon in front of the patient and operates the retractor and suction/irrigation devices.

In addition to specialized instruments, the MACS-TL ventrolateral thoracolumbar spinal implant (Aesculap, Tuttlingen, Germany) was specifically designed for thoracoscopic use (Fig. 61-1). It consists of a rigid plate that is secured to the ventrolateral vertebral body with two pairs of triangulated fixation screws for increased strength: two dorsal polyaxial screws and two ventral stabilizing screws. The screws are implanted into the normal vertebrae adjacent to the diseased vertebra(e). The fixation plate is then rigidly secured to the screws. The biomechanical properties of the MACS-TL plating system have been characterized in monosegmental and bisegmental partial and full corpectomy models both with and without dorsal ligamentous injury. Case series have also demonstrated its clinical efficacy.^10,^13,^15,²⁴^–²⁶