Minimally Invasive Anterior Approaches Thoracoscopy And Anterior Lumbar Interbody Fusion Alif

Thoracoscopy

Thoracoscopic surgery is a standard tool in thoracic surgery for a variety of indications (43,44) owing to the lower rates of morbidity compared with open thoracotomy. In the early 1950s, spinal indications for thoracoscopy were limited to accessing the spine in cases of Potts disease (45). However, improvements in thoracoscopy have permitted improved access to the disc space, vertebral bodies, spinal cord, nerve roots, and sympathetic chain, allowing neurosurgeons to utilize endoscopic approaches to the thoracic spine with increasing frequency and for varied indications.

Unique features of this rapidly evolving technology include the type of anesthesia employed and the equipment used. In most cases, patients undergoing thoracoscopic surgery are ventilated by single-lung ventilation to allow manipulation of the other lung for access to the spine. Patients need thorough pre-operative evaluations to ascertain whether their cardiorespiratory systems can handle a potentially lengthy operation under single-lung ventilation. The equipment used in thoracoscopy is also radically different from the standard operative set. The components of a thorascopic imaging system include a telescope, light source, video camera, and projection system. Standard telescopes for endoscopic procedures are 5-10 mm rigid scopes that transmit an image to a video camera on the opposite end. The camera contains one to three chargecoupled devices (CCDs), which convert photons to electrical signals that are then processed into a video image. Endoscopes may also be angled so that the angle of view varies from a perpendicular axis; both the 0- and 30-degree scopes are commonly employed in spine surgery. Trocars are key elements of the endoscopy set and are the access devices to the thoracic cavity through which the endoscope and surgical instruments are introduced. Unlike in laparoscopy, the thoracic cavity does not require carbon dioxide insufflation; thus trocars need not be "closed" to retain the insufflated gas. Lastly, a wide range of surgical instruments designed specifically for endoscopic use are available, including fan retractors, suction-irrigators, clip appliers, needle holders, electrocautery, and standard tools for bony decompression engineered for use through a trocar.

Sympathectomy

Exposure and ligation of the sympathetic chain is exceedingly amenable to thoracoscopic intervention. The most common clinical indication for the procedure is palmar hyperhidrosis but can also include axillary sweating, facial sweating (blushing), and upper extremity pain syndromes (46-51). Although the lateral decubitus position is favored for a unilateral sympathectomy, some have advocated a supine approach if bilateral sympathectomies are contemplated (46). A biportal approach is most commonly used with trocars introduced in the third and fifth intercostal spaces as the ipsilateral lung is collapsed by the anesthesiologist. The lung is carefully retracted, and the pleura overlying the vertebra is divided to expose the T2 and T3 ganglia, which supply the sympathetic innervation to the lower trunk of the brachial plexus and ipsilateral upper extremity. Great care is taken to avoid the stellate ganglion and azygos vein located just cephalad to the second rib. Once exposed, the T2 ganglion, as well as its eponymous ventral ramus—the nerve of Kuntz—and the T3 ganglion are cauterized. Once hemostasis is achieved, an

18- or 20-Fr chest tube is placed through one of the portals, and trocars are removed. The lung can then be reinflated and a Valsalva maneuver applied during incisional closure to prevent pneumothorax. Chest tubes are removed either the same or the following day. Reported rates of symptomatic alleviation are nearing 100% with minimal lengths of stay and infrequent complications, which have included Horner's syndrome, intercostal neuralgia, and compensatory hyperhidrosis (46,47,52-58).

Discectomy

Anterior approaches to the thoracic spinal column are recommended for ventral disc herniations, with thoracotomy remaining the standard open procedure that provides optimal exposure to the anterior spinal canal. Although costotransversectomy and transpedicular techniques avoid opening the chest, direct visualization of the ventral spinal cord is compromised, making mid-line calcified discs particularly difficult to address owing to poor ventral visualization. The thoracoscopic discectomy is an alternative to open surgical approaches in the treatment of thoracic disc herniation. Thoracoscopic discec-tomy allows adequate ventral exposure and is advantageous over the open techniques because of decreased postoperative pain, less shoulder girdle dysfunction, reduced blood loss and morbidity, and decreased hospital stays (59-61).

For thorascopic discectomy, patients are placed in the left or right lateral decubitus position depending on the laterality of the disc extrusion. Bilateral herniations are usually approached from the right to avoid the ascending thoracic aorta (62-64). The appropriate level is scouted with C-arm fluoroscopy, and up to four portals are placed in the anterior and posterior axillary lines after the lung is deflated. The ipsilateral lung is mobilized off the anterior surface of the spine, and the level is definitively determined by counting ribs, beginning caudally. The pleura overlying the associated rib and disc space is mobilized, and costotransvese and costovertebral ligaments are detached to facilitate removal of the proximal 2-3 cm of rib and superior pedicle. This allows visualization of the anterolateral aspect of the dura, to expose the disc space. At this point, further decompression requires the creation of a trough in the dorsal aspect of the disc space and vertebral bodies above and below the disc space to facilitate maximal removal of disc material. Disc material is then removed in standard fashion with a pituitary rongeur and angled curets (Fig. 6). Chest tubes are placed through existing portals before closing and are usually left in for no longer than 24 h, depending on output. Indications include myelopathy and thoracic radicular pain. Results from thorascopic discectomy are encouraging, with symptomatic improvement in 70-89% of patients and more than 85% of patients reporting satisfaction with the procedure. Operative time was shorter in a series comparing thoracoscopy with thoracotomy; reported complications included durotomy, hemothorax, pleural effusion, misidentified level, and retained disc fragment. Practitioners have emphasized the technically demanding nature of thoracoscopic discec-tomy (59-67).

Fig. 6. (A) Four portals are placed in the anterior and posterior axillary lines of a patient in the lateral decubitus position after the lung is deflated. (B) The ipsilateral lung is mobilized off the anterior surface of the spine, fluoroscopy is utilized to confirm the appropriate level, and the pleura overlying the associated rib and disc space is mobilized to facilitate removal of the proximal 2-3 cm of rib and superior pedicle. (C) The superior portion of the pedicle is removed using a diamond burr and a Kerrison rongeur. The dura can then be visualized.

Fig. 6. (A) Four portals are placed in the anterior and posterior axillary lines of a patient in the lateral decubitus position after the lung is deflated. (B) The ipsilateral lung is mobilized off the anterior surface of the spine, fluoroscopy is utilized to confirm the appropriate level, and the pleura overlying the associated rib and disc space is mobilized to facilitate removal of the proximal 2-3 cm of rib and superior pedicle. (C) The superior portion of the pedicle is removed using a diamond burr and a Kerrison rongeur. The dura can then be visualized.

Corpectomy/Vertebrectomy and Fusion

Operative techniques in thoracoscopic spine surgery have broadened as technical aspects of the procedure have advanced. Present indications include not only discectomy and sympathectomy but also corpectomy, vertebrectomy, anterior instrumentation, and corrective procedures for adult and pediatric scolio-

sis. Vertebrectomy and corpectomy have been performed with identical indications as open surgery including myelopathy or radiculopathy from infection, tumor, vertebral body fractures, and large transdural heavily calcified discs (68-70). Port placement and patient positioning are similar to discectomy. The proximal 3 cm of rib head above and below the involved vertebral body are resected to expose the pedicles, and dura and disc spaces above and below the level(s) of pathology are prepared. This is followed by the fashioning of a large cavity in the vertebral body with a combination of an osteotome, drill, curet, and rongeur. The posterior longitudinal ligament (PLL) is taken, and the endplates of the vertebral bodies above and below are decorticated in preparation for graft placement. Candidate grafts have included autologous iliac crest, allo-graft humerus, distractible titanium mesh cages, and methylmethacrylate introduced through Silastic tubing telescoped into the superior and inferior endplates spanning the vertebrectomy (68-71). Grafts are brought through the portal end and positioned in standard fashion with a combination of Babcocks, impactors, and tamps. Anterior plate stabilization after grafting to prevent excessive movement of the spine and graft displacement may be accomplished with the Z-plate (Sofamor-Danek) or with the more recently described MACS-TL plate (Aesculap, Tuttlingen, Germany) (71).

Proponents of the techniques cite less blood loss, less chest tube drainage, less pain medication usage, and shorter intensive care unit and hospital stays compared with the patients who undergo thoracotomy as reasons to favor the thoracoscopy (48,68-71). Furthermore, anterior and anterolateral reconstruction with grafting and plate stabilization offers the biomechanical advantage of anterior and middle column restoration. However, disadvantages include poor exposure of the posterior elements and potential complications including pneumothorax, hemothorax, chylothorax, atelectasis, pneumonia, injury to any thoracic or mediastinal vascular and visceral structures, spinal instability, cardiac arrhythmias, and spinal cord injury.

ALIF/Laparoscopic ALIF

Minimally invasive posterior approaches to the lumbar spine have previously been discussed. Anterior lumbar interbody fusion (ALIF) has emerged as an alternative approach to the surgical treatment of degenerative disc disease and spondylolisthesis (reviewed in refs. 72 and 73). ALIF results in decreased operative time, reduced blood loss, and decreased postoperative pain and hospital stays compared with conventional posterior fusion techniques (73-75). Additionally, ALIF proponents maintain that anterior column reconstruction is bio-mechanically superior to posterior column reconstruction and avoids paraspinal muscle trauma and denervation compared with posterior techniques.

There are currently two minimally invasive ALIF techniques that have improved on the traditional open laparotomy: the mini-open ALIF and the laparoscopic ALIF. The mini-open technique, first described by Mayer in 1997, reduces postoperative morbidity by using a smaller incision combined with a muscle-splitting exposure (76,77). Access to the lumbar interspaces is obtained by making a 4-cm transverse paramedian incision in the supine or left lateral

Alif Surgery Pictures
Fig. 7. Positioning and incisions for a mini-open ALIF at the L4-5 level.

decubitus patient at the appropriate level (Fig. 7). This is followed by a muscle-splitting dissection through external obliques, internal obliques, transverse abdominus, and traversalis fascia to the retroperitoneal space. For the psoas muscle, genitofemoral nerve, iliac vessel bifurcation, and lumbar interspace, any of a number of retractor systems (we use the Syn retractor from Synthes) may be introduced to retract the peritoneal contents to enlarge the surgical corridor. At the L4-5 level, care must be taken to avoid avulsing the iliolumbar vein. The iliac vessels should also be handled carefully; often only the right iliacs require mobilization. Complete disc space exposure at L5-S1 requires mobilization of the hypogastric nerve plexus, which if injured may lead to retrograde ejaculation in men. As such, dissecting tools like the Kittner should be used instead of electrocautery once the disc space is visualized. Once the disc space and neighboring endplates are appropriately exposed, an annulotomy and discectomy are performed followed by preparation of the neighboring endplates by removal of the remaining cartilaginous attachments. Candidate grafts include autograft, femoral ring allograft, titanium cages, and carbon fiber cages. The particular interbody graft employed often depends on the surgeon's predilections. Fusion rates at 6 mo are approx 90-95%, and reported complications include visceral injury, vascular injury, retrograde ejaculation, and, more commonly, postoperative ileus (73-76,78,79).

The overall safety and efficacy of the laparoscopic ALIF, first described by Obenchian and Zucherman (80,81), has been reported (82-86). However, a growing list of comparative studies indicates that the laparoscopic approach does not confer any particular advantage to the surgeon performing a mini-

Visceral Autograft
Fig. 8. AP and lateral diagrams showing a laparoscopic L5-S1 ALIF.

open ALIF (74,78,79). A report by Zdeblick and David on mini-open vs laparoscopic ALIF at the L4-5 level noted a statistically significant increase in complications in the laparoscopic group compared with the open group (20% vs 4%) and overall found no convincing reasons to support a laparoscopic ALIF at the L4-5 level (Fig. 8). More recently, Kaiser et al. (78) performed a retrospective analysis on their experiences using the mini-open ALIF and the laparoscopic ALIF. They reported an increase in mean operative time for the laparoscopic ALIF at the L5-S1 level and also a striking increase in the incidence of retrograde ejaculation in patients undergoing the laparoscopic approach compared with the mini-open procedure (45% vs 6%). They theorized that mobilization of the hypograstric plexus with laparoscopic tools was somehow more traumatic than sweeping the plexus off the disc space with cot-tonoids under direct visualization. Other authors have also reported increased complication rates in patients undergoing laparoscopic ALIF instead of mini-open ALIF. The authors noted not only an increased number of complications during the laparoscopic approach but also a 20-35% necessity to convert the laparoscopic approach to an open one to enhance exposure (74,87). Interbody graft choice is also limited by the laparoscopic approach. Moreover, length of hospital stay, blood loss, and postoperative discomfort—parameters that make minimally invasive procedures more attractive than conventional open approaches—are similar between the two approaches.

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