Endoscopic Surgical Approaches to the Lumbar Spine

Transforaminal Discectomy

The patient is positioned prone on a Wilson frame, and it is the authors’ preference to perform the procedure under local anesthesia so that the patient can provide live feedback whenever the nerve is irritated ( Video 129.1 ). This surgery can also be performed under general anesthesia, but neuromonitoring will have to be present so as to minimize the risk of iatrogenic nerve injury. For an endoscopic discectomy, the skin entry point is approximately 8 to 13 cm from the midline, and it becomes more medial as the more cephalad levels are being addressed. The skin entry point is highly variable and is influenced by the size of the patient, the orientation of the facet joints, and the location of the disc herniation. After infiltrating the skin with local anesthetic, an 18G needle is inserted. The needle is first inserted using anteroposterior (AP) imaging. The cephalocaudal trajectory of the needle is approximately 30 degrees. The facet joint will be encountered first, and the needle is then “walked” ventrally and laterally until it reaches the disc space. The needle should be gently advanced until a “give” is felt. Once the needle tip reaches the middle of the pedicle line on AP imaging, a lateral radiograph should be performed, and the image should show that the needle tip is at the posterior aspect of the superior end plate of the inferior vertebral body ( Fig. 129.1A ). The needle should advance toward the more caudal and dorsal portion of Kambin’s triangle to prevent injuring the dorsal root ganglion (DRG) of the exiting nerve root (see Fig. 129.1B ). The spinal needle is then exchanged for a guidewire. An obturator, followed by a working cannula, is inserted over the guidewire. The obturator is exchanged for an endoscope, and the discectomy is performed using micro pituitary rongeurs and bipolar electrocautery. After the initial decompression, the thecal sac, annulus, and disc material can be visualized. It is crucial that the fibrotic annular attachment of the herniated disc fragment is loosened before its removal is attempted using the micro pituitary rongeur (see Fig. 129.1C ). The decompression is deemed adequate when the thecal sac can be mobilized freely with a probe and the pulsation of the thecal sac is visualized. Annuloplasty is then performed using bipolar electrocautery to prevent further recurrence of the disc herniation (see Fig. 129.1D ).

Video 129.1 Transforaminal endoscopic discectomy

Interlaminar Discectomy

The patient is positioned prone on a Wilson frame in flexion to open the interlaminar space ( Video 129.2 ). The procedure is performed under general anesthesia, as retraction of the traversing nerve root can lead to patient movement and increase surgical risk. The midline of the target level is localized using fluoroscopy, and an 18G spinal needle is inserted 1 cm off the midline. The incision is placed so that the angle of approach is from caudal to cranial. This allows for an easier access through the interlaminar space, given the shingling of the laminae. The target point is the lateral edge of the interlaminar space, as confirmed on fluoroscopy. The needle is then exchanged for a guidewire, along which a series of dilators are placed. The working channel for the endoscope is established, and its final position is confirmed by fluoroscopy ( Figs. 129.2A and B ). The initial dissection of the ligamentum flavum is accomplished by a series of instruments specifically designed for endoscopic use (see Fig. 129.2C ). These include bipolar electrocautery, micro pituitary rongeurs, micro Kerrison rongeurs, and a specialized micro endoscopic drill. This drill is used to take down small portions of the lamina and facet joint complex. After further dissection into the interlaminar space, bipolar electrocautery is again used to coagulate any small capillaries in the area and to prepare deeper portions of the ligamentum flavum for resection. Continuous positive pressure irrigation helps push away the thecal sac as it is gradually exposed. A small blunt dissector is used to mobilize the thecal sac and remove any adherence between the dura and local tissue. Extended dissection releases the nearby fat, which is then resected to further expose the dura. A blunt dissector is again used to confirm the mobilization and decompression of the thecal sac. The traversing nerve root is identified and retracted medially. Given the angulation of the working cannula and the optics of the endoscope, nerve root retraction is achieved by rotating the port so that the side opening is lateral and the medially positioned traversing nerve root is protected and retracted. After preparation by bipolar electrocautery, a micro Kerrison rongeur is used to widen the dissection area of the annulus, facilitating access to the space. Having removed several major disc fragments, the blunt dissector is used to mobilize the nerve root and to reduce adherence to local tissue. This technique can also expose further disc fragments for resection. Bipolar electrocautery is then applied to stiffen the remaining annulus and to ensure good hemostasis.

Video 129.2 Endoscopic hemilaminotomy and resection of synovial cyst. (Courtesy of Gregory W. Basil and Michael Y. Wang, University of Miami Hospital, Miami, FL.)

Patient Selection

Inadequate neural decompression and intraoperative complications are the commonest causes for failed minimally invasive or endoscopic spine surgery. ^, Patients with a complete occlusion of the spinal canal, such as those who present with cauda equina syndrome or those with concomitant severe spinal stenosis or high-grade spondylolisthesis, will likely benefit from a more conventional open decompression surgery over a posterior endoscopic lumbar discectomy. A thorough evaluation of the patient’s preoperative magnetic resonance imaging scans should be performed to better assess the patient’s spinal pathology. In patients with conjoined nerve root, a transforaminal approach should be avoided for fear of neural injury. In patients with calcified disc herniation or significant migration of the disc herniation, the surgeon should be aware of his or her technical limitations and decide if such patients are suitable to undergo endoscopic spine surgery.

Technical Considerations

In the transforaminal approach, it is crucial that the starting point of the discectomy be as near to herniated disc and as far away from the exiting nerve as possible. The different anatomical layers (annulus, posterior longitudinal ligament, epidural fat, and thecal sac) should be clearly visualized on the endoscope. Lastly, the fibrous annular attachments of the herniated disc fragment should be adequately released before removing the herniated disc fragment whole using a micro pituitary rongeur in a twisting motion. Annuloplasty is then performed with a bipolar electrocautery to close up the annular defect and to prevent recurrence of a disc herniation.

In the interlaminar approach, dural tear is the commonest complication. To prevent this, the surgeon will have to decide whether the discectomy is directed toward the shoulder or the axilla of the nerve root; this is dependent on the location of the disc herniation. Once the thecal sac, deviated nerve root, and herniated disc fragment are clearly identified, the discectomy can be performed safely.