The indication for surgery must be determined according to today’s standards on the basis of radicular symptoms, neurogenic claudication, and existing neurological deficits [37, 38]. Isolated back pain cannot usually be improved by decompressing operations. Existing secondary pathologies, such as instabilities, may have to be treated at the same time using other procedures. The following anatomical indications are currently unequivocal:

In disk herniations within the spinal canal, the following inclusion criteria need to be taken into account due to the limited mobility:

In the case of lateral spinal canal stenosis, only foraminal stenosis caused by intraforaminal/extraforaminal cysts of the zygapophyseal joints is regarded as an indication for the transforaminal/extraforaminal approach.

Conventional open surgical procedures are indispensable today and will remain so in the future. The possible complications and consequential damage entailed by such procedures are familiar. New techniques must guarantee sufficient possibilities of attaining the surgical goal which are equal to those of established procedures [39].

Full-endoscopic operation, such as a truly minimally invasive procedure, offer advantages. These correspond largely to the advantages of microscope-assisted surgery, cited in each case, over the conventional open procedure. Full-endoscopic operations may thus be classified as the next step for technical advances in surgical techniques.

The following are cited as specific disadvantages:

As with all microsurgical techniques, the intraoperative procedure must be planned preoperatively based on imaging and clinical findings. The goal is to perform the resection of spinal canal structures as sparingly as possible depending on the pathology and provide adequate neurological decompression. Conventional X-rays of the lumbar spine and MR imaging are obligatory. In applying the lateral transforaminal approach, the access pathway may not be shifted by abdominal structures. Particular attention must be paid to this in the levels cranial to L4–L5. If the findings are not entirely clear, a single abdominal CT scan should be made through the disk level for evaluation and preoperative planning.

Patients must be informed about their disease, its possible long-term course, and consequences and, despite the minimal invasiveness and attendant advantages of the surgical procedure, all known side effects, complications, and therapeutic possibilities must be explained, as for conventional procedures. With reference to the full-endoscopic procedure, it is important to highlight that even with minimally invasive interventions, scarring may not be completely avoided. It is also important to emphasize that a switch to an open procedure may be required during the operation or subsequently in an additional procedure should unforeseen complications arise.

The preoperative preparation of the patients is the same as in microsurgical techniques. A single-shot antibiotic is applied for infection prophylaxis.

Full-endoscopic operations can usually be performed under local or general anesthesia. General anesthesia has advantages because it is more convenient for both the patient and the surgeon, permits positioning as required, and also facilitates complex work within the spinal canal. In cases of local anesthesia in the interlaminar approach, anesthesia for the route of access and also of the neural structures is necessary. Due to inflammatory processes, epidural anesthesia alone is frequently not sufficient, and therefore, intrathecal administration of local anesthetic must be carried out. In addition, systemic sedation is necessary for immobilization. Positioning entails costly control of vital parameters and correction of anesthesiological problems can be difficult.

In transforaminal approach, there is a risk of damaging the exiting nerve route passing the foramen. Theoretically, the risk can be reduced with the possibility of communicating with the patient. Thus, the operation under local anesthesia is also prevalent.

The operation is performed with the patient in prone position on a radiolucent table, under two-plane radiological control. The patient lies on a hip and thoracic rolls to relieve the abdominal and thoracic organs. The operating table is lordotically or kyphotically adjustable intraoperatively at lumbar level depending on the anatomy and pathology.

A radiolucent, electrically adjustable operation table and a C-arc are necessary. In addition to the surgical instruments and endoscopes, general equipments for endoscopic operations under fluid flow are needed, such as monitor, camera unit, light source, documentation system, fluid pump, shaver system, or radiofrequency generator. Equipment available for arthroscopy or endoscopy can be used. Depending on indication, the rod-lens endoscope has an outer diameter of 6.9 or 9.9 mm. The endoscope contains an intraendoscopic, eccentric working channel with diameter of 4.1 or 6.5 mm. The angle of vision is 25°. The working sheaths used have a beveled opening which enables creation of visual and working fields in an area without clear anatomically preformed cavity (Fig. 34.3a, b).

First, the skin incision is localized. The goal is to reach the spinal canal as tangentially as possible. At levels L4–L5 and L3–L4, in lateral X-ray path, the posterior line of the descending facet usually serves as the boundary which should not be crossed toward the ventral direction (Fig. 34.4a). To avoid injury to abdominal organs, a single abdominal CT scan through the individual disk should be made for evaluation and preoperative planning, especially at the cranial levels when findings are not unequivocal. Depending on the scan, an individual, less lateral approach should be selected.

An atraumatic spinal needle is inserted through the skin incision parallel running to the disk space in the target area. A practicable end point is the contact of the dorsal annulus in the medial pedicle line. After a target wire is inserted and the cannula removed, the cannulated dilator is inserted. It is absolutely essential to ensure that the dilator is located for all work steps at the level of the intervertebral disks and not displaced cranially as this can lead to damage of the emerging spinal nerves. The target wire is removed and the operation sheath with beveled opening is pushed through the dilator. When an appropriate position is attained, the site of the sheath opening is located at the medial pedicle line and the opening itself in the lateral ray path is positioned half in the ventral epidural space and in the dorsal annulus (Fig. 34.4b, c). From this point on, decompression is performed under visualization and continuous irrigation with isotonic saline without any special additives. The entire system is left open as standard so that the irrigation fluid can flow out. Further entry into the epidural space which may be required is made under visual control.

Annulus fragments are resected for dissection medially, until the disk herniation is localized and exposed. A rongeur is used to remove the disk herniation entirely or in parts. After complete resection, an unobstructed view is provided of the decompressed area. Depending on previous dissection, the dorsal longitudinal ligament can still be seen, which can be opened as necessary. The intervertebral space can then be cleared until the free intradiskal fragments are resected (Fig. 34.5a–c). The operation is implemented in the same way even if previous operations have been carried out in the operating area. After the operation has been completed, the instrument set is removed and the stab incision is closed. Drainage is not necessary.

The extraforaminal approach can be used for intraforaminal/extraforaminal pathologies or for anatomical/pathological conditions which preclude a harmless, direct passage of the foramen due to the restricted diameter or the position of the emerging spinal nerves.

The spinal cannula is pushed forward to the caudal pedicle under X-ray control. This is a safe zone in which the emerging spinal nerve is not damaged. Dilator and operating sheath are then inserted (Fig. 34.6a). From this point on, the operation is carried out under visualization and continuous irrigation with isotonic saline. The entire system is left open as standard so that the irrigation fluid can drain away.

Pedicle, ascending facet, and disk are dissected and the foramen is exposed. The operating sheath is used as an instrument to hold the emerging spinal nerves cranially and ventrally. The extraforaminal port should also be selected maximally lateral so that it passes under the nerve cranially without significant manipulation.

The operation then continues from this position, such as direct decompression in the foramen, entry into the spinal canal through the foramen, or prior bone resection.

In the case of intraforaminal/extraforaminal disk herniation, the approach is determined by the location of the herniation, which is generally sequestrated rostrally. The exiting spinal nerve is moved further rostrally with the operating sheath and identified. The herniation is localized, dissected, and resected. In order to gain access further cranially under the spinal nerve, it can be lifted with the movable shaft of the rongeur. In the same way, additional parts sequestrated cranially in the spinal canal can be resected. The intervertebral space can then be cleared (Fig. 34.6b, c).

In the case of intraforaminal/extraforaminal cysts of the zygapophyseal joints, dissection and precise identification of spinal nerve and cysts are important. The cysts are then opened, the material inside is removed, and the cyst walls are resected as far as possible.

Bone resection can be carried out in order to generally enlarge the foramen if it is constricted and to create a passage, but most frequently in order to achieve more mobility dorsally or caudally (Fig. 34.6d). Depending on the pathology, bone is resected in the ventral area of the ascending facet or in the cranial area of the caudal pedicle.

The extraforaminal approach at L5–S1 or in the last level presents a special situation, since the pelvis and the transverse process exert a particular influence on the approach. The caudal pedicle (S1) is the target for the spinal cannula. On account of the pelvis, the spinal cannula generally has a steep to a virtually posterior pathway after reaching the end position. After inserting the dilator, operating sheath, and endoscope, subsequent dissection is equivalent to the process for the standard extraforaminal approach but differs in implementation as the passage selected becomes steeper. This can result in the emerging spinal nerve being dissected and exposed directly from a dorsal position after the bony structures have been exposed, similar to the interlaminar technique. The operating sheath must also be used in a similar way. The precise performance of decompression depends on the findings of each case. Drainage is not necessary.

The skin incision is made as medially as possible through the interlaminar window. The craniocaudal localization depends on the findings of the pathology.

The dilator is inserted bluntly on the lateral edge of the ligamentum flavum or on the descending facet of the zygapophyseal joint under radiographic posterior-anterior control. From this point onward, the operation is performed under radiographic lateral control. The operation sheath with beveled opening is inserted via the dilator in the direction of the ligament. The subsequent procedure is then performed under visualization and continuous irrigation with isotonic saline solution. The entire system is left open as standard so that the irrigation fluid can drain away.

In order to reach the spinal canal, the ligamentum flavum is incised laterally to approx. 3–5 mm. The subsequent procedure is enabled by the elasticity of the ligament. By rotating, the operation sheath with beveled opening can be used as a second instrument and serves, for example, as a nerve hook in shifting the neural structures in the medial direction.

The neural structures are identified prior to operating on the primary disk herniation, in particular the lateral boundary. If the recess cannot be visualized laterally to the traversing spinal nerve, medial portions of the ascending facet can be resected with the punch. If adequate space is available in the recess, the operating sheath can be introduced with the opening aligned medially on the floor of the spinal canal in order to shift the neural structures in a medial direction. The sheath is rotated with continuous contact to the base of the spinal canal. If the operating sheath cannot be introduced directly in the recess, the maneuver can be carried out with the aid of the dissector. A partial decompression through the axilla must be carried out prior to the maneuver involving sheath rotation. At the same time, this prevents parts of the disk herniation from being displaced medially together with the neural structures. The protruding disk herniation material is dissected and resected. The intervertebral space can be cleared (Fig. 34.7a–c).

If the bony diameter of the interlaminar window does not permit passage or for large sequestered herniations, the window is enlarged using a burr and instruments. The descending facet joint is dissected and the medial edge and caudal pole are exposed. An incision is made on the surface leaf of the ligamentum flavum along its process at the medial edge of the descending joint facet. Bone resection begins at the caudal pole of the descending facet and continues along the medial part of the descending facet and toward the cranial lamina. Since the ligamentum flavum is inserted caudally, directly at the bony edge of the lamina, burrs are used to thin the lamina here and the intervention is then continued with resection using a punch.

When revision operations are performed, no assessment on the implication of the ligamentum flavum can be made in advance of the operation – so that the dilator and operating sheath are introduced directly at the descending facet joint. The ongoing approach varies with each individual and depends on the degree of scarring and the type of operation carried out previously. If there is significant scarring, dissection directly along the edge of the bone and the descending facet in a ventral direction has proved effective. If direct entry to the recess is not possible, the medial edge of the ascending facet joint is dissected and the approach is carried out strictly at the bone in the direction of the spinal canal. Once the recess has been adequately dissected, the operating sheath is introduced. Depending on the degree of scarring, the maneuver involving rotation of the operating sheath displaces all the tissue en bloc medially. The neural structures may be fixed depending on the scarring. There may be an increased risk of damage as a result of manipulation. The force applied when displacing the neural structures therefore needs to be carefully moderated. If it is not possible to enter the recess, bone resection described above has to be carried out in advance.

As described above, bone resection has to be performed for operating on a recess stenosis. The medial portion of the descending facet joint or parts of the cranial lamina have to be resected as part of the standard procedure until the cranial tip of the ascending facet is reached. Experience indicates that bone resection caudally is adequate if it extends to the middle of the caudal pedicle. The ligamentum flavum is frequently involved in the pathology and then has to be resected in the lateral area over the entire craniocaudal extension. Depending on the characteristics of the pathology, the medial bony edge of the ascending facet is resected using a punch or burr until the recess has been exposed. The maneuver involving rotation of the sheath is used to shift the neural structures medially. If compression is caused by a protruding annulus or ventral osteophytes, they must be resected.

If a single-sided port is used for the central spinal canal stenosis, the approach used in the lateral stenosis of the ligamentum flavum has to be expanded by resecting medially up to the midline. In the case of contralateral decompression in the over-the-top technique with a single-sided approach, bone is already removed medially up to the spinous process during dissection of the caudal lamina depending on the characteristics of the pathology. After ipsilateral decompression has been completed, the operating sheath is inserted contralaterally and the contralateral ligamentum flavum, the contralateral bone of the lamina, and the descending facet and the medial edge of the ascending facet are resected until the spinal canal and the recess are exposed (Fig. 34.7d). As in microsurgical interventions, the central spinal canal stenosis can also be sufficiently decompressed contralaterally in the over-the-top technique. The detailed decompression of the recess in the cranial and caudal area is frequently subject to ipsilateral decompression. A bilateral approach with independent ports on both sides should therefore be considered in cases of bilateral recess stenosis with radicular symptoms. This enables the complete median area of the spinal canal and its structures to be retained, which is not involved with the pathology in recess stenosis.