Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy

25 Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy


Hyun-Chul Shin, Jonathan B. Lesser, Robert E. Isaacs, and Noel I. Perin


Abstract


In patients with symptomatic, large, centrally located and calcified thoracic disc herniations with significant spinal cord compression, thoracoscopic surgery (video-assisted thoracoscopic surgery) is a viable minimally invasive alternative to open thoracotomy. Both thoracoscopic discectomy and tubular retractor–guided discectomy, while achieving the same results as an open thoracotomy, reduces postoperative pain and shoulder girdle dysfunction and provides better cosmetic results, shorter hospital stay, and earlier return to normal activity.


Keywords: thoracoscopy, video-assisted thoracoscopic surgery, mean arterial blood pressure


25.1 Introduction


Thoracic disc herniation is an uncommon but clinically important cause of incapacitating axial and/or radicular pain with or without neurologic deficits. The incidence of clinically significant thoracic disc herniation has been estimated to be approximately 1 patient per 1 million people (0.25–0.75% of all disc ruptures). The incidence of asymptomatic disc herniations in thoracic spines imaged with magnetic resonance imaging (MRI) is between 11.1 and 14.5% of the general population. Thoracoscopic discectomy can be performed on disc herniations from T2–T3 through T12–L1.


A number of surgical approaches have been proposed for the treatment of symptomatic thoracic disc herniation. Posterior approaches include transpedicular and pedicle-sparing approaches. These approaches are most suitable for lateral and foraminal disc herniations. The costotransversectomy and lateral extracavitary approaches allow for posterolateral access to the more central and paracentral disc herniations, although anterior access is somewhat limited. Transthoracic and thoracoscopic approaches are most suitable for large central and calcified disc herniations with spinal cord compression and afford better unrestricted access to the anterior thecal sac than do posterior and posterolateral approaches.


The transthoracic approach to thoracic disc herniation was first reported by several investigators in 1969.1


The transthoracic approach allows better visualization of the disc–dural interface, reducing the extent of spinal cord manipulation and its resultant complications. The major advantage of this approach is the improved visualization of the thecal sac and the relationship between the disc herniation and the dura. This is particularly helpful in the management of calcified midline disc herniations, especially when there is significant spinal cord compression and adherence to the dura. It is, however, an approach to the thoracic spine that is associated with significant postoperative morbidity and pain. The morbidity is related to extensive rib retraction and rib resection, and division of chest wall muscles, shoulder girdle muscles, and the diaphragm.


The thoracoscopic approach to thoracic disc herniation derives the same benefits as the transthoracic approach, with a reduction in postoperative pain and morbidity related to muscle dissection. The first reported application of the video-assisted thoracoscopic approach to thoracic disc herniation was in 1994.2 The advantages of the thoracoscopic approach include a substantial reduction in tissue trauma and thus a reduction in the postoperative pain and shoulder girdle dysfunction associated with an open thoracotomy. In addition, thoracic disc herniations in the lower thoracic spine (T8–L1) can be performed thoracoscopically without the need to take down the diaphragm, thus significantly reducing the morbidity. After thoracoscopic discectomy, the intensive care unit (ICU) stay and the hospital stay are shorter because patients can be mobilized much faster.


Thoracoscopic surgery has a steep learning curve because of the lack of tactile feedback. Surgeons also need to familiarize themselves with working with long instruments through small openings in a two-dimensional videoscopic environment, and perfect the hand–eye coordination required as well. Although three-dimensional scope technology is available, it is expensive and cumbersome and may not afford a significant advantage. Operative times will be reduced with experience and become comparable to those associated with the open thoracotomy.


To help reduce the learning curve associated with thoracoscopic approaches, the minimally invasive tubular retractor–guided transthoracic approaches are being utilized. This approach reduces the morbidity of the thoracotomy approach and overcomes the steep learning curve of thoracoscopy. We have combined thoracoscopy with the tubular retractor system and use of the operating microscope for excellent three-dimensional visualization.


25.2 Preoperative Assessment


MRI scans are the mainstay in the preoperative work-up of patients with thoracic disc herniation. In the presence of a good MRI showing a thoracic disc herniation with neural compression, a myelogram is unnecessary. We usually obtain a computed tomography (CT) scan to assess the extent of calcification of the thoracic disc herniation. All patients undergo chest radiography with sufficient penetration to count ribs, and they undergo anteroposterior and lateral lumbar radiography as well. Particular note should be taken of the number of ribs on the chest radiographs, especially the presence of a cervical rib and if only 11 ribs are present. These radiographs and the location of the thoracic disc herniation on MRI must be closely correlated with the intraoperative localizing radiographs to avoid operating at the wrong level. Additionally, patients undergoing an anterior transthoracic approach can be admitted on the day before surgery so that a radiologist can place a metallic marker into the head of the rib at the appropriate level.


All patients must have a preoperative medical evaluation with particular attention paid to pulmonary function; patients with severe emphysema and impaired lung function may not tolerate single-lung ventilation; patients with a prior history of empyema and/or pleurodesis are also not candidates for thoracoscopic discectomy.


25.3 Preoperative and Intraoperative Anesthetic Considerations


After induction of general anesthesia, a double-lumen endobronchial tube is placed, and the correct position is verified with a fiberoptic bronchoscope. A 20-gauge radial artery catheter is usually inserted on the dependent side. Because motor and somatosensory evoked potentials are continuously evaluated during the surgical procedure, nondepolarizing muscle relaxants are allowed to completely wear off, and a total intravenous anesthetic, consisting of remifentanil and propofol, plus an air-oxygen mixture is administered to maintain anesthesia. Muscle relaxants are not used for the remainder of the surgical procedure. A phenylephrine infusion is used as needed to maintain adequate mean arterial pressure (above 80 mm Hg)


25.4 Surgical Technique


25.4.1 Patient Positioning


The patient is positioned in the lateral decubitus position as for an open thoracotomy. The side selected for the approach depends largely on the side of the disc protrusion. However, if the disc is more or less in the midline, in the upper (T2–T5) or midthoracic (T5–T8) spinal area, a right-sided approach is selected. In the lower thoracic spine (T9–L1), a left-sided approach is preferable because the diaphragm may be up to the fifth intercostal space and retraction of the diaphragm with the underlying liver may be somewhat more difficult. An axillary roll is placed under the dependent chest to keep the axilla free. The lateral popliteal nerve area on the dependent leg is padded, a pillow is placed between the legs, and a rolled-up blanket is placed against the anterior abdominal wall. The patient’s hips are taped firmly to the table; tape is applied loosely around the knees and ankles to keep the legs from falling over when the table is rotated during surgery. The down arm is flexed at the elbow, padded, and positioned in front of the patient’s face on the operating table. This avoids an arm board, which might interfere with the surgeon’s ability to move freely, and allows adequate radiographs to be obtained. This is especially true when dealing with middle and upper thoracic herniations. The upper arm is supported on an elevated arm board with the arm abducted slightly more than 90 degrees and flexed over the patient’s head. The table is placed in steep reverse Trendelenburg position to allow the lung to fall away from the spine and the diaphragm and abdominal contents to fall caudally. In addition, the table is rotated toward the abdominal side of the patient allowing the lung to fall away from the spine.


25.4.2 Thoracoscopic Port Placement


It is important to plan the location of the ports so that the retractor and the endoscope do not interfere with the instruments being placed at the working ports. The anterior, middle, and posterior axillary lines are drawn on the patient. We obtain an anteroposterior plain radiograph of the thoracic spine with metallic markers on a strip of paper tape placed over the patient’s thoracic spine posteriorly in the midline. This allows the surgeon to roughly mark the level of the disc herniation and plan initial port placement. Contrary to most reports, the working port is not placed in the anterior axillary line. Instead, the initial port position is marked on the patient’s flank at and slightly posterior to the posterior axillary line, in line with the level of the herniated disc. The initial port serves as the working port. In individuals with large, rounded chests, port placement is even more critical. If the working port is too anterior, the direction of access is more posterior at the spine, instead of looking down at the pedicle. In both large and obese patients, a port placed more anteriorly will adversely change the angle of approach to the disc space. This will lead to a more horizontal approach to the disc, making it difficult to look down at the pedicle, instead looking directly back toward the rib, transverse process, and facet joint.


The port site selected is marked with a marking pen, and the patient’s entire chest is prepared and draped as for a thoracotomy. Electrodes are placed for somatosensory and motor evoked potential monitoring prior to positioning, and baseline recordings are obtained after positioning is complete.


As the chlorhexidine or Betadine preparation of the surgical site is initiated, the anesthesiologist collapses the lung on the ipsilateral side and applies suction to that lung. A 2-cm incision is made in the skin, and the incision is carried down to the chest wall muscles. A Kelly clamp is used to separate the chest wall muscles in the direction of the fibers toward the selected intercostal space. The clamp is directed along the upper border of the lower rib to avoid injuring the neurovascular bundle. By necessity, the initial entry into the chest cavity is blind. The Kelly clamp is pushed in a controlled fashion through the parietal pleura into the chest cavity; the anesthesiologist will hold the breathing for a few seconds during this maneuver. The clamp is opened along the length of the intercostal space to enlarge the entry port. A forefinger is inserted into the chest cavity and swept around the chest wall to release any adhesions. A soft, pliable Thoracoport (U.S. Surgical), 15 mm in diameter, is introduced into the pleural cavity. The length of the Thoracoport depends on the thickness of the chest wall as measured by placing the operator’s finger into the chest cavity. If the port extends too far into the chest cavity, it will impede visualization and interfere with the range of motion of the working instruments introduced via that port. If the port is cut too short, it will slip back into the chest wall muscles and interfere with the introduction of the working instruments.


A 10-mm, 0-degree-angled endoscope is placed via this port, and an initial exploratory thoracoscopy undertaken. The second working port for suction/irrigation is placed in line with the first port, rostral or caudal to the first port depending on the level of the disc herniation. All ports after the initial working port are guided into the pleural cavity with continuous endoscopic visualization.


A third port is placed in the anterior axillary line away from the working ports or in line with the working ports, for retraction of the lung and/or diaphragm. The third port is placed such that the long shaft of the fan retractor outside the chest is not in the path of the working instruments. A fan retractor is placed via this port to retract the lung and/or diaphragm away from the spine, and the retractor is held in position using a table-mounted retractor holder.


Finally, an endoscopic port is placed posterior to the posterior axillary line to and away from the working ports, either rostral or caudal to the working ports depending on the level of the disc herniation. A 10-mm, 30-degree-angled endoscope is introduced via this port and held in position using a table-mounted scope holder (image Fig. 25.1).


25.4.3 Identification of the Disc Space


The ribs are counted from the apex of the chest cavity downward. The highest rib visualized thoracoscopically is the second rib. The ribs are counted from the second rib to the rib corresponding to the appropriate disc space. The 1st and 2nd ribs articulate with the first and second vertebral bodies only; likewise, the 11th and 12th ribs articulate with their respective bodies only. All other ribs straddle the disc space, the 3rd rib with the T2–T3 disc, and the 10th rib with the T9–T10 disc space, respectively. It is important to count down to the appropriate rib corresponding to the disc to be operated on and mark the disc with the Bovie or Harmonic scalpel (Ethicon Endo-Surgery, Inc., Cincinnati, OH). A Steinmann pin is placed through one of the ports or directly through the chest wall into the identified disc space, and a cross-table radiograph of the thoracic spine is obtained to reconfirm the level. With very obese patients when we anticipate difficulty with identification, we have had the radiologist place a metallic marker into the head of the appropriate rib with fluoroscopic guidance the day before surgery. The marker is then readily identified in the operating room with a cross-table radiograph.


25.4.4 Exposure and Preparation of the Surgical Field


Once the disc space and the overlying rib have been identified, the parietal pleura over the proximal 2 to 3 cm of the rib is opened to expose the corresponding rib and rib head at that level. The Harmonic scalpel with ultrasonic cutting and coagulating capabilities is used to open the pleura. The pleural opening is extended down the rib to the disc space and then at right angles along the vertebral body above and below the disc (inverted T). The use of the Harmonic scalpel instead of the cautery avoids charring locally, which can obscure tissue landmarks. The radicular artery and vein will be encountered over the middle of the vertebral bodies. Using right-angled dissectors, the artery and vein are freed from the vertebral body, and after an endoscopic clip applier (5-mm clips) is used to clip the vessels proximally and distally, these vessels are divided. This will prevent tearing of these vessels during the drilling phase of the operation that could lead to uncontrollable bleeding.


25.4.5 Resection of the Rib


The head and neck of the rib with 2 cm of the shaft of the rib should be removed. The parietal pleura over the rib is divided as described above in an inverted T shape. Using angled curettes, the soft tissues along the upper and lower borders of the rib are dissected free. Care should be exercised to avoid injuring the neurovascular bundle along the lower border of the rib. If bleeding does occur, this is controlled with bipolar coagulation. The head of the rib is disarticulated at the costovertebral articulation. A Cobb elevator is insinuated into the joint space on all sides and rocked from side to side to release the costovertebral articulation (image Fig. 25.2a). The R attachment of the Midas Rex drill (Medtronic Sofamor Danek) with an adjustable sheath is used to drill the distal end of the rib. A trough is created in the shaft of the rib, drilling from rostral to caudal and deep to superficial.


Oct 17, 2019 | Posted by in NEUROSURGERY | Comments Off on Thoracoscopic Discectomy and Thoracoscopy-Assisted Tubular Retractor Discectomy

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