Fig. 62.1
(a) Skin marking for spinal needle trajectory. (b) Spinal needle entry point 10 cm lateral to midline. (c). AP view fluoroscopy demonstrating spinal needle traversing neural foramen and terminating above caudal pedicle. (d) Lateral view fluoroscopy confirming depth of spinal needle, terminating at the intervertebral disc space. (e) K-wire replaces spinal needle with tube dilators in place. (f) Beveled cannula in place after tissue dilation. (g) Endoscope enters beveled cannula. (h) Grasping forceps in working channel of endoscope. (i) AP view fluoroscopy demonstrating grasping forcep removing intervertebral disc material. (j) Intervertebral disc material removed. (k) Skin incision closed with absorbable suture. (l) Dermabond placed over skin incision
Relevant Anatomy
Kambin’s triangle is a space created by the following borders [25]:
Medial edge of the exiting nerve root.
Lateral edge of the superior articular process of the caudal vertebra.
Superior edge of the caudal vertebral body.
This triangle is also called the “safety working zone,” and surgeons can safely access and remove herniated disc material in this region.
Anesthesia
The procedure is performed with conscious MAC sedation, consisting of midazolam and fentanyl.
Patient positioning
The patient can be positioned either prone, with chest and hip bolsters, or in the lateral decubitus position , based upon the surgeon’s preference. In the lateral position, pillows can be placed under the contralateral hip to flex the neural foramen open, while gravity causes the dura to retract away to the contralateral side. There is also less blood loss due to decreased abdominal pressure in the lateral decubitus position [26].
Skin Entry
The skin entry point is 10–14 cm lateral to midline, at the operative level, on the ipsilateral side of the disc herniation. The correct spinal level can be confirmed with fluoroscopy. The trajectory for levels below L3-4, however, is limited by the iliac crest. The entry point in this case, therefore, will be above the level of the iliac crest. After injecting the skin with local anesthetic, an 18-gauge spinal needle is advanced towards the neural foramen, and position is continuously confirmed with AP and lateral view fluoroscopy. The needle should traverse the neural foramen and dock into the disc space. At this point, the needle tip will be at the inferior border of the neural foramen and at the midpoint position of the caudal pedicle.
Discography
The surgeon can opt to inject indigo carmine dye into the disc space to assess for presence of a herniation, degree of opacification, epidural leak, and degree of disc degeneration [24].
Dilating Tubes and Foraminoplasty
The skin entry point is incised lengthwise to approximately 5 mm and to a depth just beyond the thoracodorsal fascia to allow adequate space for the dilating tubes. At this time, the spinal needle stylet is removed and replaced with a K wire, and this position is confirmed on fluoroscopy . A series of dilators help to expand the fascia to make space for the endoscope apparatus. The dilating tubes and reemers give the surgeon more easy access through the neural foramen and into the disc space by removing the medial portion of the superior articular facet of the caudal vertebral body. The position of each series of dilators and reemers is confirmed continuously with AP and lateral fluoroscopic imaging.
Endoscopic Discectomy
The dilators are now removed, and a beveled cannula is docked onto the inferior aspect of the neural foramen. The 30-degree-angled endoscope traverses through this cannula, and a single 2.7 mm working channel built into the scope apparatus allows the surgeon to use grasping forceps, bipolar cautery, and pedicle finders through the endoscope for constant visualization. The beveled cannula can be used to retract away critical structures, such as the exiting nerve root, allowing the surgeon to freely grasp disc material. Serial rotation of the cannula allows inspection of the thoroughness of the foraminal decompression.
Closure
Closure with an absorbable suture is performed on the skin only.
Complications
Complications of the transforaminal endoscopic approach for discectomies include recurrence of herniation, with a reported rate of 2.4% of patients during a 3-month postoperative period [27]. Gastambide et al. have reported a 3% disc re-herniation rate during a 2-year postoperative period [24]. Redo procedures can be performed once again with the endoscopic approach or via an open microdiscectomy.
Close proximity to the exiting nerve root can result in iatrogenic radiculopathy. Approximately 1 to 6.7% of patients experience postoperative radiculopathy, with resolution several months after surgery [14, 27]. Choi et al. demonstrated that increased operation time and shorter distance between the exiting nerve root and lower margin of the disc were the two factors that significantly increased the risk of nerve root injury [14]. Inferior displacement of the exiting nerve root creates a smaller “safety working zone,” leading to increased risk of nerve root injury and subsequent postoperative radiculopathy [14].
Vascular injury is another feared complication of the endoscopic approach. Retroperitoneal hematoma after an endoscopic procedure most commonly presents as sudden inguinal pain after a pain-free interval immediately postoperatively [28]. Arterial branches of the segmental lumbar artery have been postulated as sources for these hemorrhages. Yong et al. recommend using lateral fluoroscopic images when first advancing the spinal needle into the neural foramen. This step ensures that the needle does not advance deeper than the posterior vertebral line, also known as the line of Ahn [29]. Inspection of preoperative CT or MRI can also ensure that blood vessels do not cross the spinal needle trajectory.
Other Endoscopic Approaches to the Spine
The procedures described in this chapter describe a transforaminal approach, but endoscopic surgery continues to evolve to include more approaches. The transforaminal approach is not limited to the lumbar spine, but has also been applied to the thoracic spine [11, 32]. In the lumbar spine, interlaminar approaches are also used to access more central disc herniations . Endoscopic spine surgery is also performed in the cervical spine to address both anterior and posterior pathology. Hsu et al. performed an anterior cervical endoscopic approach to resect a recurrent cervical chordoma [30]. A recent comparison of anterior and posterior cervical endoscopic discectomies demonstrated no significant difference in functional outcomes [31].
Conclusion
Endoscopic spinal surgery is a less invasive mode to address spinal pathologies that would otherwise require more traditional approaches with larger incisions, intrusive muscle and soft tissue dissection, and longer recovery times. Through proper patient selection, this modality can be effective in addressing spinal disc disease.
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