Minimally Invasive Spinal Decompression and Stabilization Techniques I

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Chapter 126 Minimally Invasive Spinal Decompression and Stabilization Techniques I

Sait Naderi, Joseph Watson, Nevan G. Baldwin, Maurice M. Smith

Ideally, minimally invasive techniques should achieve the operative goal with minimal tissue disruption. In spinal stabilization surgery, particularly in the thoracic and lumbar regions, much of the associated morbidity is secondary to the extensive soft tissue dissection necessary to widely expose the spine for arthrodesis.

Percutaneous fixation of the thoracic and lumbar spine was used as an alternative to invasive surgery in the 1980s. At the same time, growing experience with percutaneous discectomy nurtured the development of fusion techniques to accompany decompression. The current widespread use of minimally invasive techniques in thoracic and abdominal surgery has been a catalyst for the development of less invasive ventral approaches to the spine.

The anatomic and biomechanical differences among the cervical, thoracic, and lumbar regions of the spine create completely different issues in the approach to decompression and stabilization of each region. Techniques for minimally invasive treatment are considered for each region separately; however, many of the principles of complication avoidance and management apply to all regions. There has been far more experience with techniques in the lumbar spine than in the thoracic region. Comparatively few data have yet been obtained on cervical spine approaches.

The evolution of minimally invasive spinal surgery for decompression of the neural structures began with the uniportal procedures, using the arthroscope for decompression of contained disc herniations. The first laparoscopic lumbar discectomy was reported by Obenheim in 1991.¹ The efficacy of different endoscopic surgical procedures has been documented, leading to the development of more complex and biportal arthroscopic procedures for treatment of noncontained herniations.

The use of minimally invasive surgery for fusion of motion segments of the spine was introduced at a later date. Magerl introduced this technique for percutaneous external transpedicular fixation of the thoracic and lumbar spine in the 1980s.² Percutaneous dorsolateral interbody fusion also was performed successfully by Leu and Schreiber, who reported on the procedure in 1991.³ Drawbacks of these procedures included the likelihood of screw tract infection and discomfort associated with externally placed implants.

Recent advances in the evolution of minimally invasive surgery for fusion and stabilization include: (1) percutaneous interbody fusion during arthroscopic disc surgery; (2) transperitoneal and thoracoscopic placement of the interbody cage implant in the lumbar spine and thoracic spine, as well as placement of the transpedicular screw, combined with temporary subcutaneous plates in the lumbar spine; (3) placement of the plates and screws in the thoracic spine; (4) percutaneous translaminar facet screw placement; (5) percutaneous odontoid screw placement; (6) image-guided upper cervical spine instrumentation; and (7) robotic transpedicular screw placement. Other researchers simultaneously were developing techniques for fusion with new approaches, including the extreme lateral approach for lumbar interbody fusion (XLIF), transforaminal lumbar interbody fusion (TLIF), and axial interbody fusion (AxiALIF, TranS1, Wilmington, NC) techniques.

Leu ⁴ was one of the first to use endoscopy for spinal fusion, both ventrally and dorsolaterally. Endoscopic spinal fusion was performed first in the lumbar spine. Interest in the use of minimally invasive surgery for thoracic spine disease has increased recently. The initial results, using video-assisted thoracoscopic surgery (VATS), are encouraging, because this procedure is characterized by less pain and shorter hospital stays.⁵^–⁷

Regan et al.⁸^–¹⁰ reported their results in thoracic spinal pathology using ventral and dorsal interbody grafting, with and without instrumentation. Rosenthal¹¹ reported the use of VATS for ventral decompression and stabilization in patients with metastatic tumors or scoliotic deformities of the thoracic spine. His technique involves endoscopic microsurgical decompression, combined with reconstructive techniques and instrumentation placed through thoracoscopic portals.

Advantages and Difficulties

The main advantages of endoscopic spine surgery are its lower morbidity, attributable to the minimally invasive approach, and cosmetic advantages. Significantly less postoperative pain is experienced by these patients because of the avoidance of extensive muscular incision and removal of ribs. There also is less impairment of pulmonary function after VATS. Dorsolateral endoscopic approaches for pedicular fixation result in less epidural bleeding, decreased incidence of perineural and intraneural fibrosis, and less venous stasis.

The most significant disadvantage of endoscopic stabilization is that it is time consuming. This aspect can be overcome, but there is a considerable learning curve. The technology and equipment costs for this approach also create a large “up front” investment requirement. All endoscopic approaches, especially thoracoscopic approaches, can be converted to open procedures, if necessary, to control bleeding or to deal with excessive adhesions.

Indications and Contraindications

Although the indications for endoscopic fusion and stabilization are similar to those for open procedures, the options are more limited. Endoscopic stabilization can be performed after decompression for burst fractures, spinal tumors, and spinal deformities (e.g., idiopathic scoliosis and Scheuermann disease), and for instability secondary to degenerative disease of one or two motion segments.

Contraindications to endoscopic dorsolateral lumbar spine fusion and stabilization include (1) considerable loss of intervertebral disc height, preventing decortication of the end plates; (2) severe spinal deformity associated with distorted neural and pedicular anatomy; (3) infection; (4) failed previous operation for interbody fusion; and (5) very large tumors requiring extensive resection.¹²

Contraindications to VATS include (1) inability to tolerate deflation of one lung, (2) significant respiratory disease, and (3) previous open thoracotomy.¹³

Contraindications to laparoscopic transperitoneal lumbar fusion and stabilization include (1) significant abdominal trauma, (2) previous transabdominal lumbar operation, and (3) previous lower abdominal laparoscopic procedure (e.g., hysterectomy).¹⁴

Approaches

The anatomic features of different regions of the spine dictate a variety of endoscopic approaches for fusion and stabilization. A thoracic spine endoscopic approach necessitates VATS, whereas a lumbar spine instability requires a ventral approach, a lateral approach, a dorsolateral approach, or a combined approach. The choice of endoscopic approach in the lumbar spine is guided largely by surgeon preference.

Thoracic Spine

The most important minimally invasive technique for decompression and stabilization of the thoracic spine is VATS. This technique has been applied to a variety of thoracic spine disorders, including tumor, infection, disc disease, and deformity. VATS is performed using a double-lumen tube for deflation of the ipsilateral lung with the patient under general anesthesia and in the lateral decubitus position (Fig. 126-1).

FIGURE 126-1 Thoracoscopic spinal surgery. Portal placement varies according to the level of the pathology. More portals also may be required for procedures with instrumentation to allow improved angles for hardware placement and access for retractors and other instruments.

Method

Instruments required for an open thoracotomy should be readily available for emergency use. A left- or right-sided approach may be used, depending on the pathology. Some authors prefer a right-sided approach if the pathology is not lateralized, because there is more space lateral to the azygos vein than the aorta. Consideration should be given to the position of the artery of Adamkiewicz if the intervention requires the sacrifice of one or more segmental arteries in the middle to lower thoracic region, especially T9-11 on the left.

The initial trocar should be inserted in the manner of a tube thoracostomy (over the top of the rib) in the anterior axillary line at the sixth or seventh intercostal space. Multiple working trocars may be used for instrument insertion as necessary. Soft trocars are preferred for the portals because they are less traumatic to the neurovascular bundle on the inferior rib undersurface. The size of the instrument is limited only by the intercostal distance.

The surgical levels are identified by counting ribs, preferably with fluoroscopy, and by marking in the disc space. Alternatively, ribs may be counted endoscopically from the first rib down. The rib number corresponds to the lower vertebral body at the disc space (e.g., sixth rib at T5-6). Adequate exposure of the disc space usually requires resection of the rib head, except in the lower thoracic region where the rib head may be well caudal to the disc space, permitting unobstructed access. Attention to the segmental vascular branches in the mid-bodies is advised. Stabilization across the vertebral body requires the careful division of these vascular structures. The sympathetic chain also may be identified in the surgical field through the parietal pleura. Varying anatomy of the regions of the thoracic spine dictates different exposure techniques. For the upper thoracic region, it may be necessary to elevate and support the ipsilateral arm to rotate the scapula away. In the lower thoracic region, it may be necessary to retract the diaphragm.

After exploratory thoracoscopy using a 30-degree-angle scope, a second trocar is inserted. If complete atelectasis is not achieved, a brief period of CO₂ insufflation may help to collapse the lung. As the thoracic spine is visualized through the parietal pleura, the correct level is identified by counting the ribs. Radiographic confirmation by fluoroscopy or a plain radiograph also can be obtained. The parietal pleura is then divided using monopolar cautery. After the fluoroscopic identification of the correct level, the third and fourth ports are inserted at the level of the pathology. A 0- or 30-degree-angle scope can be used. Generally, 2 to 3 cm of rib resection and partial resection of the pedicle are adequate. After using electrocautery to “clean up” the surrounding soft tissues, a discectomy with decompression is performed. Bleeding at this stage can be controlled by bipolar electrocautery, argon beam coagulation, or packing the area with hemostatic agents (e.g., Gelfoam or Surgicel).

Uncontrolled bleeding may necessitate conversion to an open procedure. Therefore, it is advisable to have an open thoracotomy setup available.

On completion of the decompression, fusion can be performed using bone chips obtained from a rib or harvested from the iliac crest. Regan et al.¹⁰ described the placement of an interbody cage into the disc space after decompression.

Rosenthal ¹¹ described reconstruction by homologous bone or by injection of semiliquid methylmethacrylate. He used a ventral plate and screw system (Z-plate, Sofamor-Danek, Memphis, TN) for fixation and special equipment for dilation of the skin incision during the insertion of the plate, and for insertion of instruments for handling the plates and screws in the chest cavity. These techniques allow the surgeon to address pathology resulting from degenerative disease, trauma, or metastatic disease, and then to stabilize the spine with methylmethacrylate struts, cages, or plates.^11,¹⁵^–¹⁷

After completion of the entire decompression and stabilization procedure, a tube thoracostomy is placed and the lung is reexpanded.

Complications

As with laparoscopic procedures, there is an entire complement of risks associated with the intrathoracic approach. Reported complications include prolonged atelectasis, pleural effusions, intercostal neuralgia, and diaphragmatic injury.¹⁵^–¹⁷ Time of lung collapse (i.e., length of operation) is related to the pulmonary morbidity associated with chest procedures. Therefore, until the operating surgeon has become familiar with the thoracoscopic spine procedures, he or she may expect longer operating times and some increased morbidity. In one series of thoracic endoscopic discectomies, the complication rate was 14%, which was compatible with the reported complication rate with open approaches.¹⁸ The use of flexible portals may reduce the incidence of intercostal neuralgia, although this still occurred in 2 of 17 patients in whom the flexible portals were used.¹⁵ Complications related to the decompression, in a series of 77 patients, were excessive epidural bleeding in one patient and transient paraparesis in another.¹⁶ In a comparative study, Mangione et al. reported less blood loss and a shorter hospital stay, as well as a similar rate of complication after VATS, when compared with open thoracoscopic thoracic spine decompression.¹⁹

Operating at the wrong level is always a concern in the thoracic spine. This may be avoided by ruling out variant anatomy (e.g., accessory ribs), using preoperative radiographs, and accepting only high-quality radiographic images intraoperatively.