Minimally Invasive Spinal Decompression and Stabilization Techniques I

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Chapter 126 Minimally Invasive Spinal Decompression and Stabilization Techniques I

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.

Leu4 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.57

Regan et al.810 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.

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).

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.

Rosenthal11 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.11,1517

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.1517 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.

Lumbar Spine

A variety of laparoscopic, endoscopic, minimally invasive, and robotic techniques currently are used to stabilize and/or decompress the lumbar spine.

Fusion and Instrumentation

Laparoscopic Transperitoneal Surgery for the Lumbar Spine

The ventral endoscopic approach is limited primarily to the L4-5 and L5-S1 disc spaces because of the relation of the aorta and vena cava to the spine. The increased use of minimally invasive abdominal and retroperitoneal procedures with the laparoscope has paved the way for its use as an approach to the spine.

Despite limited enthusiasm for laparoscopic ventral discectomy for the treatment of simple disc disease,10 interbody fusion techniques have received a warm welcome, as evidenced by the number of meeting presentations and papers on the topic.16,2026 The procedure has evolved from the placement of bone graft in the interspace to the use of titanium interbody distraction cages.

Technique

The ventral exposure of the lumbar spine from the peritoneal cavity is limited to L5-S1 and variably to L4-5. Laparoscopic exposure is performed in the routine manner, similar to an intra-abdominal procedure. This includes a bowel preparation, insertion of a Foley catheter and a nasogastric tube, and preincisional prophylactic antibiotics. The patient is supine in the Trendelenburg position, with the back extended using large rolls under the lumbosacral junction (Fig. 126-2). Insufflation techniques are standard, but a gasless technique also is described, which does not require specially designed instruments.27 Assistance from a general surgeon comfortable with laparoscopy is advised.

Exposure of the L5-S1 space requires incision of the parietal peritoneum over the disc in the midline. Fluoroscopy is used to identify the disc properly. The midline sacral artery and vein must be divided. The parietal peritoneum is mobilized using blunt dissection, with bleeding controlled by bipolar electrocautery (rather than unipolar cautery), for fear of injuring the closely related autonomic plexus. At the L4-5 space the exposure can be more difficult, because the disc space often sits at the crotch of the bifurcation of the great vessels. Gentle retraction of the common iliac vein and artery is required, and it may be necessary to sacrifice segmental branches. Exposure may be facilitated by inserting Steinmann pins into the L4 vertebral body to give static retraction of the vessels.

Discectomy is performed by sharp incision of the ventral anulus fibrosus and by radical removal of disc material with curets and pituitary forceps. Fusion proceeds by distraction of the disc space and insertion of bone graft under compression. Currently popular is the use of a threaded titanium cage, which has been cleared by the U.S. Food and Drug Administration and is commercially available for open procedures. It also is cleared for endoscopic placement from the ventral approach. With the endoscopic placement, the procedure is outlined as follows: an estimate of graft size is made on the basis of the preoperative radiographs and specific templates provided by the manufacturer of the device. The sizes are checked in situ to confirm that adequate exposure is available. Next, a disc space distractor is placed on one side of the midline. On the other side, a circular hole is drilled (under fluoroscopic guidance to ensure a trajectory parallel to the vertebral end plates) to a depth of approximately two thirds of the diameter of the disc space. The hole is then tapped, and the titanium implant, filled with autologous bone chips, is screwed into the disc space. The distractor is then removed, and the tapping/implant procedure is repeated at the site previously occupied by the distractor. The implants should be sufficiently countersunk so that no aspect comes into contact with the overlying vascular structures. The peritoneum is then reapproximated over the site. The exposure and anatomy may dictate that only one graft be placed. However, this is not as biomechanically sound as two cages, placed side by side, especially in lateral flexion.20 Currently, other materials such as threaded allograft dowels also are available for transperitoneal endoscopic fusion operations.

A retroperitoneal approach to the ventral aspect of the spine at levels L4-5 and L5-S1 with interbody fusion also is technically feasible. This reduces the chance of postoperative adynamic ileus and intra-abdominal adhesions. This approach also provides access to the lateral aspects of level L1-4, although the great vessels prevent midline access at these levels. Previous abdominal surgery is a relative contraindication for the transperitoneal exposure. This is not an issue with the retroperitoneal approach. An experience with 20 cases has been reported.24

Complications

Complications associated with transperitoneal exposure are uncommon. However, they require immediate management by experienced abdominal surgeons. An experience with 17 cases included significant ileus in four patients, which required, in two patients, an open laparotomy for bleeding. In addition, there were two graft donor site infections.26 In another series of 22 cases, 1 iliac vein laceration was encountered, as well as 2 bone donor site infections.16 In the small series of ventral retroperitoneal fusions, no significant complications were reported.24 Sexual dysfunction is a dreaded complication of this approach, resulting from disruption of the sacral autonomic plexus. Several cases of transient (3 weeks) retrograde ejaculation were reported in a series using an open anterior lumbar interbody fusion technique.20 It is recommended that, in men, reflection of the parietal peritoneum over the ventral disc space be performed with the aid of bipolar rather than monopolar electrocautery to prevent the spread of current and reduce the risk of damage to the autonomic plexus.20,27 If Steinmann pins are used, care must be taken during removal, as well as insertion, so that the sharp tip does not lacerate a vessel, particularly the iliac vein. The hazards of the approach and drilling the disc space adjacent to the iliac vessels are ameliorated with special instruments to protect the vessels during drilling. Familiarity with these instruments is imperative.

Results

Although the total experience with minimally invasive techniques in spine surgery is small in comparison with the vast experience with open procedures, the early results are encouraging (Table 126-1). Follow-up of these patients, to date, has been relatively short. Mathews et al.21 reported successful fusion in all of their first five cases. McAfee et al.,28 reporting the complications in the first 50 endoscopic procedures in a multicenter study, did not observe any great vessel complications. The complications reported by other authors include cage extrusion, inferior vena cava laceration, dorsal disc extrusion, prolonged ileus, and atelectasis. Zucherman and Zdeblick29 and Novotny et al.23 reported that 2 of 23 (9%) and 2 of 8 (25%) operated cases, respectively, were converted to open surgery.

TABLE 126-1 Recently Reported Series of Patients Undergoing Fusion and Stabilization via Endoscopic Procedures

Author No. of Patients Procedure
Mathews et al. (1991)39 4 ALIF
Novotny et al. (1994)23 8 TP-ALIF with cage or femoral allograft
McAfee et al. (1994)22 10 TP fusion
Mathews et al. (1994)21 5 TP with iliac crest
Kambin and Schaffer (1996)12 25 Lumbar posterolateral
Zuckerman et al. (1996)14 23 TP with cage implant
Rosenthal et al. (1996)17 12 Thoracoscopic with ventral plate
Regan (1996)18 7 Thoracoscopic with anterior instrumentation
Dickman et al. (1996)5 1 Thoracoscopic fusion

ALIF, anterior lumbar interbody fusion; TP, transperitoneal.

Note that cases involving decompression only are excluded from the table.

The first results of minimally invasive surgery for spine decompression and stabilization are encouraging. However, some problems persist, including long operation time, the requirement for expensive equipment, and the steep learning curve.30 With increased experience, the rate of complications should decrease. Technologic advances should improve the safety of these operations and also may broaden the indications for the application of these techniques.

Percutaneous Translaminar Facet Screw Fixation

Percutaneous translaminar facet screw fixation using fluoroscopy was performed successfully.31,32 Shim et al.32 reported that this technique was a safe and useful minimally invasive dorsal augmentation method following ALIF or axiALIF.

Lumbar Discectomy

With or without laser nucleotomy, lumbar discectomy is the most commonly used minimally invasive technique.39 Three major pathways are used to perform lumbar discectomy: dorsolateral uni- or biportal discectomy, transforaminal endoscopic discectomy, and dorsal midline endoscopic discectomy.4042 Dorsolateral uni- or biportal discectomy is the earliest technique, using a small incision 8 cm lateral to the midline and almost 45 degrees of working canal. A midline approach is similar to the microdiscectomy technique, whereas the transforaminal technique approaches the neural foramen first. Endoscopic discectomy provides better pain relief, shorter hospitalization stays, earlier return to work, and less paraspinal muscle atrophy.43,44 Ruetten at al.,40 using a transforaminal technique, reported that patients had a lower rate of low back pain after the endoscopic procedure when compared with microdiscectomy.

Complications of Endoscopic Discectomy

Complications associated with percutaneous lumbar discectomy are few, but include a 1% to 2% risk of discitis and a 1% to 2% risk of a symptomatic psoas muscle hematoma. Anecdotal evidence indicates that there is a risk of injury to the nerve roots or surrounding vascular structures.41,4547 As is emphasized elsewhere in this textbook, careful placement of the guidewire is crucial for the avoidance of complications with this approach. Theoretically, the risks of infection and injury to the great vessels are increased by the manipulations of bone grafting. However, this has not been demonstrated clinically.

Cervical Spine Decompression

Despite advances in available technology and interest in minimally invasive stabilization procedures in the thoracic and lumbar spine, relatively few reports on the use of these methods in the cervical spine have been published. Percutaneous discectomy and chemonucleolysis of the cervical spine reportedly have been effective in selected patients in uncontrolled trials.48,49 Percutaneous disc access requires a ventrolateral approach. The needle entry is at the medial border of the sternocleidomastoid muscle. With the fingers of one hand acting to separate the carotid sheath and esophagus, the needle is passed under fluoroscopic control into the desired disc space. Although percutaneous decompression has been described, concomitant fusion has not been reported to date.

Microendoscopic technique has been popularized during recent years. Using a small incision for a mini-keyhole foraminotomy, nerve root can be exposed and decompression for both spondylotic changes and disc herniation can be performed.50,51 Fessler and Khoo50 reported less blood loss, shorter hospitalization stays, less use of narcotics, and better pain relief after cervical microendoscopic foraminotomy when compared with the open technique.

Percutaneous surgical techniques have been recently popularized in craniovertebral junction surgery. The first results after percutaneous odontoid screw fixation and C1-2 fixation are encouraging.52,53

References

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