Video-assisted endoscopic spinal surgery: Thoracoscopic discectomy

-Acta

Acta Neurochir (Wien) (1995) 134:196-199

Ncurochirurgica 9 Springer-Verlag 1995 Printed in Austria

Video-Assisted Endoscopic Spinal Surgery: Thoracoscopic Discectomy A. Caputy 1, J. Starr 2, and C. Riedel 1 Departments of INeurosurgery and 2Orthopaedic Surgery, George Washington University Medical Center, Washington, DC, U.S.A.

Summary The use of new endoscopic techniques to conduct a thoracic discectomy is presented. The development of these endoscopic techniques through live porcine and cadaver models are outlined. It is concluded that the use of multiple ports for the endoscopic approach to the thoracic spine provides an exposure to the anterior and lateral spinal theca that is equal to the exposure afforded by the more extensive thoracotomy. Current techniques are being developed for transperitoneal and retroperitoneal endoscopic lumbar spine surgery. Keywords: Discectomy; thoracoscopic.

Introduction The use of endoscopic surgical techniques to diagnose and treat diseases of the abdomen and thorax has expanded to include conditions which in the past had required larger more extensive open surgical procedures. Although thoracoscopy has been used to evaluate diseases of the chest for m a n y years, it was primarily a diagnostic tool for lesions of the pleura or mediastinum [2, 10]. Recent advances in video-assisted endoscopic technology have broadened thoracoscopic capabilities beyond the realm of diagnosis alone and into the treatment armamentarium for a broad spectrum of chest disease [5]. Thoracic disk herniation is a rare cause of spinal cord compression. Prior to the 1960s the variability and lack of specificity of the symptoms of thoracic disk herniation often resulted in a delay in the diagnosis. With the advent of magnetic resonance and other advanced imaging techniques the diagnosis is now more easily confirmed. Surgical treatment was confined initially to a decompressive laminectomy with disappointing results and high complication rates. As surgical techniques have been developed that allow decompression of the spinal canal without manipula-

tion of the spinal cord, the surgical outcome has improved [6, 8, 12-14, 16]. Most surgeons now approach thoracic disc herniations through a posterolateral extracavitary or an anterior transthoracic route. These decompressive surgical techniques require large surgical incisions; the surgical morbidity associated with these extensive procedures may be significant. The use of endoscopic techniques to provide access to the anterolateral thoracic spine would minimize the extent of the surgical incisions while providing a wide surgical field with a high degree of illumination and magnification [7, 11, 15]. The current report presents the use of endoscopic techniques to conduct a thoracic discectomy and spinal cord decompression. The technique employs multiple endoscopic ports to provide more flexibility in the surgical dissection and greater visualization from multiple angles.

Material and Methods Live Porcine Model

Three 70-kg pigs were used. Operations were carried out under general endotracheal anesthesia using double lumen endotracheal tubes to allow deflation of the ipsilateral lung. Five to seven open rigid or soft thoracic ports were used to allow maximum flexibility in endoscope and instrument placement and to test different working angles. Although not required for discectomy, the segmental vessels had to be taken for vertebral body resection. These vessels were exposed using laparoscopic scissors and dissectors, then divided between clips or after bipolar cauterization. Discectomy and vertebrectomy were carried out using standard spinal instruments. Cadaver Model

Cadavers were placed in the lateral decubitus position. Removal of the ipsilateral lung through a contralateral thoracotomy

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obviated the need for lung retraction. Multiple ports were evaluated for visualization, working distances and angles, and specific instrument combinations to facilitate dissection and avoid crowding. Five disectomies and a partial vertebrectomy were carried out. Standard instruments were again used with emphasis on drilling techniques. Open review of the operated levels was then performed to determine the extent of disc resection. Case Report

The patient is a 30 year old man with intractable interscapular mechanical back pain. His pain developed following a motor vehicle accident. It is occasionally accompanied by muscle spasms. His symptoms are exacerbated by bending, pulling and reaching out or overhead. He failed to respond to extensive non-operative therapies including anti-inflammatory medications, muscle-relaxants, and physiotherapy. Physical examination demonstrated local tenderness but no evidence of myelopathy. Radiographic evaluations include standard radiographs, CT myelography and MRI (Fig. 1). These demonstrated degenerative changes with loss of disc height and end-plate sclerosis at T6-7. At T7-8 there was a right sided herniated nucleus pulposus with remodeling of the right ventral spinal cord. After extensive discussions of the various options the patient elected to undergo thoracoscopic discectomy. The surgical procedure is performed with the patient under general endotracheal anesthesia using a double-lumen tube that allows collapse of the ipsilateral lung. Deflation clears the lung from the operative field and provides excellent visualization of the anterior longitudinal ligament and great vessels with minimal, intermittent retraction of the lung. Unlike thoracotomy in which the expanded lung can be retracted relatively easily, this is difficult and cumbersome to accomplish in a thoracoscopic procedure. The patient is positioned in the lateral decubitus position. In this instance a right sided approach was used because the disc was posterolateral to the right and because, at the T7-8 level, the vessels are readily avoided from the right side. The patient is prepared for thoracotomy in the event that this is required to handle a complication or if the anatomical objective cannot be accomplished endoscopically. After the anesthesiologists deflate the lung a small incision is made in the anterior axillary line in a mid thoracic intercostal space, usually T5-6, T6-7 or T7-8. In this case the T7-8 space was chosen as this also provides a primary working port directly opposite the level of the disc to be excised. Using a Kelly clamp the pleural cavity is entered and a 12 mm thoracic trocar placed. The thoracoscope is then introduced and the pleural cavity inspected. The remaining trocars are then placed under direct vision with the thoracoscope. Four to five ports are employed, to allow for the scope itself, suction, two working instruments (such as rongeurs, graspers and scissors) and a retractor if needed. Ports are placed in the anterior and mid axillary lines for the best working angle and visibility. They are placed at the level of the disc (two), and at intervals above and below of 1-3 interspaces. This number and type of part placement assures maximum flexibility in coordinating visualization and comfortable, efficient instrument use without crowding. Care must be taken that the lower port(s) is not placed through the diaphragm. The diaphragm may be higher in position after deflation of the lung than anticipated. A pre-operative chest X-ray should be checked for pathological elevation of the diaphragm. Insufflation is not required and only open trocars are used. Flexible trocars are helpful. Use of certain instruments is facilitated if the trocar is removed and the instrument placed through the chest wall.

Fig. 1. Axial MR image showing a T7-8 disc herniation

Fig. 2. Intra-operative photograph showing a thorascopic discectomy. The rongeur is in the intervertebral disc space. The suction device shows the neural foraminae. The arrow marks a segmental vessel Following the placement of all ports, the pleural cavity and spine are then inspected and the ribs counted from the apex. A marker is then placed and the proper level confirmed radiographically. Using monopolar cautery the pleura is then incised beginning along the rib corresponding to the lower vertebral body of interest

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198 (the T8 rib for a T7-8 disc) crossing the rib head and then continuing both superiorly and inferiorly parallel to the spine. For most discectomies the segmental vessels can be preserved, however, if wider bone removal is anticipated the vessels should be dissected free, clipped and/or cauterized and divided. The proximal 3 cm of the rib and rib head are then freed from the surrounding soft tissue with curettes and elevators and then the rib and rib head removed with rongeurs. The underlying disc is identified and overlying soft tissues removed with dissectors and monopolar cautery to better delineate the disc and adjacent vertebral bodies. Tracing the disc posteriorly the T8 pedicle and foramen are then identified. After carefully freeing the margin of the pedicle with a curette, a small Kerrison is used to resect the cephalad portion of the inferior (here T8) pedicle to broaden exposure. A knife is then introduced, fully visualized throughout, and the annulus incised. Discectomy is then carried out with curettes and rongeurs (Fig. 2). Portions of the adjacent vertebral bodies are also removed and a cavity excavated to allow downward displacement of the disc encroaching the canal away from the thecal sac and into the cavity from whence it is removed. Initial disc removal is relatively simple; assuring adequate decompression is more difficult. Removal of the dorsal corners of the adjacent vertebral bodies greatly enhances visualization of the spinal canal and ventral aspect of the thecal sac. Freely changing ports for instruments and endoscope is a must. After decompression Gelfoam and bone wax may be used for hemostasis. The chest cavity and lung are reinspected. A 32 french chest tube is then placed into the apex with thoracoscopic visualization. The wounds are closed with muscle layer and subcuticular sutures.

Results

Porcine disc spaces are very narrow and partial resection of the adjacent vertebral bodies was mandatory to adequately visualize the thecal sac intraoperatively. Vertebrectomy allowed wide visualization of the thecal sac. Six discectomies and two vertebrectomies were completed. There were no intra-operative complications and no cerebrospinal fluid leaks. Five discectomies and a partial vertebrectomy were performed on cadaveric specimens. Although the human disc space is considerably wider than the porcine, drilling the adjacent bone greatly facilitated disc resection and assured better visualization of the thecal sac. In our initial discectomy little bone was removed and discectomy did not extend across the spinal canal. Subsequent resections included removal of the dorsal aspect of the endplate and body above and below the disc space and adequate disc removal occurred in all cases. Our patient had no operative complications. No pulmonary injury occurred, there was no air leak and his chest tube was removed at 36 hours. His symptoms were improved immediately post-op but long term follow-up will determine the success of the pro-

cedure. He was discharged home four days postoperatively. Discussion

Thoracic disc herniation is an uncommon clinical syndrome with a variable presentation which accounts for 0.15-1.0% of intervertebral disc surgery [17]. The early surgical treatment of herniated thoracic discs with a decompressive laminectomy yielded an unsatisfactory clinical outcome which was thought to be secondary to the attendant spinal cord manipulation necessary to complete the discectomy [1,3, 6, 8, 9, 12, 17]. Approaches to the thoracic spine that minimize the manipulation of the cord were developed. A posterolateral approach to the thoracic spine has been described by a number of authors. The surgical technique involves a varying amount of costotransversectomy and can often be extrapleural [3, 8, 9]. A transpedicular approach was described by Patterson and Arbit [13] which involved a paramedian incision and a modified laminectomy with a lateral resection of the facets and pedicle. It did not include the extensive rib resection of the posterior lateral approach. Others have modified these approaches to provide a greater posterolateral exposure. The lateral extra cavitary approach provides full lateral exposure to allow complete anterior decompression and removal of pathologic compression across the spinal canal [12]. Extended costotransversectomies also provide a wider exposure with an unencumbered visualization of the anterior and lateral spinal canal and dura [4, 6]. However, the surgical exposure is large and often a spinal fusion is required [6]. The transthoracic anterior approach as developed by Perot and Munro [14] and Ransohoff et al. [16] and Bohlman and Zdeblick [1] has been found to be successful at the decompression of the anterior spinal canal [1, 14, 16, 17]. However, this surgical approach involved an extensive thoracotomy incision, transpleural collapse of the lung and mobilization of the aorta. The surgical morbidity is often significant. Patients undergoing endoscopic thoracic surgery for pulmonary resections have been found to have less post-operative pain, and improved pulmonary function, and less surgical morbidity when compared to an equivalent patient population undergoing a thoracotomy [11, 15]. The application of video assisted endoscopy for spinal disorders seems particularly well suited to the thoracic spine. Endoscopic thoracic

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spine surgery provides excellent exposure of the spinal canal and allows the decompression of the spinal cord. Disc material and osteophyte spurs can be removed. The exposure allows for an interbody fusion. The exposure is adequate to provide decompression and drainage of spinal abscesses, to biopsy vertebral body tumors and to provide vertebral body decompression. The pleural cavity allows for excellent endoscopic visualization, freedom for manipulation of instruments and does not require insufflation so that standard spinal instruments familiar to the spinal surgeon may be used. Minimal soft tissue dissection is required for exposure, unlike lumbar approaches. The use of multiple ports for this endoscopic approach to the thoracic spine provides an exposure ~:o the anterior lateral spinal canal and spinal theca that is equal to the exposure afforded by the more extensive thoracotomy. There are, however, many 1imitations currently, most related to inadequate instrumentation. In our experience safe removal of thoracic discs with complete decompression of the spinal cord often requires removal of a portion of the adjacent vertebral bodies. Rongeurs can be used but we prefer high speed drills. Available drills do not meet the requirements of thoracoscopic procedures. Long fine drills with guards over most of the bit shaft are mandatory to avoid pulmonary injury. Also there is a long lever arm from the level of the port that tends to diminish the surgeon's control over "kicking" movements of the drill. We are developing a drill with a distal control device that is brought in through a separate port. Manufacturers are currently designing extended spinal instruments for endoscopic use, including round-barreled instruments for abdominal approaches where insufflation requires as gas-tight seal between instrument and trocar. As more patients undergo endoscopic thoracic spinal procedures the morbidity and operative outcome can be compared to traditional procedures. Clearly the potential for endoscopic spine techniques holds great promise. Instrumentation will evolve, further broadening the role of endoscopic spinal surgery. Surgical techniques are currently being developed for transperitoneal and retropcritoneal endoscopic lum-

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