The posterolateral approach for intradiscal access and percutaneous fusion is very similar to the classic endoscopic surgical approach [9, 10]. The patient should be positioned prone in an articulated table, with the hips flexed at the level of the great trochanter using four contact cushions: A for the pelvis, B for the chest, C for the head, and D for the legs (see Fig. 7.2). The hip flexion should be increased step by step until the lumbar lordosis disappears. The aim of this flexed position is to increase lumbar vertebral distraction in order to allow an easier approach through Kambin’s safety triangle [11]. The fluoroscope should be tested in anterior/posterior (A/P) and lateral views on the articulated table in order to obtain a proper image of the disk level of interest (see Fig. 7.3). In target-oriented endoscopic surgery, the exact location of the skin’s entry point depends on where the desired objective is placed (intradiscal up to intra-canal) [8]. For the intradiscal access used in percutaneous fusion surgery, the transforaminal posterolateral approach at 60° from the posterior spine process is usually the optimal choice (see Fig. 7.4). The end plates should be visualized in a parallel position using a Fergusson A/P projection. Now a line is drawn on the skin parallel to the superior end plate of the inferior vertebral body and 10 cm from the midline to the lateral are measured. However, the distance of 10 cm is patient dependent and should only be used as an approximation, as it could vary depending on the disk’s level and the vertebral size of every individual patient [7, 10, 12]. After selecting the optimal axial view of the disk to be punctured in magnetic resonance imaging (MRI) (see Fig. 7.5), the optimal entry point should be planned by following these steps:

If your trajectory hits on the vertebral facet (see green arrow in Fig. 7.5), a foraminoplasty will probably be required to optimally reach the intervertebral disk. The superior articular process (SAP) from the inferior vertebra can interfere with the entrance to the epidural space. In patients with a degenerated facet, the SAP could be an insurmountable obstacle even to access the intervertebral disk. In these cases, a foraminoplasty is mandatory to safely access the disk space. The caudal part of the neuroforamen is a safe region to access the canal and the epidural space [4, 5] without harming the neural structures like the exiting root or the dorsal root ganglion. Therefore, the foraminoplasty must be done using manual reamers aiming the caudal part of the neuroforamen as shown in Figs. 7.11 and 7.15.

After proper patient positioning, the skin entry point needs now to be drawn on the patient’s back (see Fig. 7.6):

After marking the entry point with the skin marker, presurgical skin cleaning and sterile draping of the surgical field should be performed. Under anteroposterior and lateral fluoroscopic control, an 18-G needle is inserted into the disk (Fig. 7.9) as described by Yeung and Tsou [10]. The skin is anesthetized with bupivacaine 2%, and the patient is kept conscious under light sedation during the surgical procedure when surgery time is expected to be less than 1 h. Otherwise full anesthesia and neuromonitoring are required.

Local anesthesia with sedation was used for a selected group of patients upon a patient’s explicit request only and if written permission was granted by the anesthesia team. Some patients were operated under local anesthesia (bupivacaine and 1% lidocaine) with intravenous sedation, analgesia, and cardiopulmonary monitoring by an independent anesthesiologist who was present during the whole surgical procedure.

In patients undergoing full anesthesia, intraoperative neuromonitoring was systematically performed by an independent neurophysiologist that routinely collaborates with our clinic. Somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) were employed during the whole surgical procedure to monitor all involved peripheral nerves. At specific situations during surgery (e.g., screw insertion, cage insertion, etc.), additional nerve stimulation was done to ensure that nerve roots were not compromised (nerve root distance was considered acceptable at signal intensities ≥10 mA).

A contrast discography with indigo carmine (Taylor Pharmaceuticals, Decatur, IL) diluted with iopamidol 300 1:10 can be performed to confirm the annulus’ containment and in the mentioned cases with local anesthesia and sedation also the segmental level of pain generation. The needle trajectory is anesthetized with lidocaine 1% and the annulus border as well. Through an 8-mm skin incision, progressive tissue dilatation is achieved by placing a beveled cannula 7.5-mm outer diameter, in immediate contact with the foraminal border of the annulus (Fig. 7.10). Bone reamers can be used to perform foraminoplasty [4, 5] under fluoroscopic vision allowing intradiscal access even to an extreme collapsed disk space (height ≤ 5 mm). Reamed foraminoplasty can be performed under fluoroscopic vision to undercut the superior facet and to enlarge the foramen without touching or harming the neural structures (Fig. 7.11).

The B-Twin interbody spacer ( Disc-O-Tech Medical Technologies Ltd., Herzliya, Israel) (see Fig. 7.1a), is a titanium expandable device with a jacking-up mechanism that provides additional stability to the end plates in the axial plane. This prevents rotation and allows a good bone integration. We employed this device in a series of 107 cases [17] with the described percutaneous posterolateral approach as a stand-alone device. No discectomy or partial discectomy was performed, preserving the natural annulus’ shape and stability.

In a first step, the procedure consists of bone reaming under direct endoscopic control to widen the foramen. Even for level L5–S1 the approach has been improved thanks to the evolution of endoscopic reaming techniques [3]. The transforaminal access can be visualized by use of an endoscope [15] similar to a transforaminal discectomy or foraminoplasty. The author used endoscopic visualization to show the exiting root and the epidural space (see Fig. 7.12). This proved to be important during the earlier cases for the confirmation of accessibility of the intervertebral disk space. In a second step, the B-Twin expandable device was used as a disk spacer to partially restore or to maintain the height of the collapsed disk. Finally, the endoscope can be used to confirm visually the decompression of the exiting nerve root. In addition, the exiting root can be mobilized under direct endoscopic vision with a flexible probe [3] (Ellman International, Hewlett, NY) (Fig. 7.11). After retrieving the endoscope, the implant can be inserted and expanded under fluoroscopic control. The skin is sutured, and the anteroposterior and lateral fluoroscopic controls were printed for case records.

To our best knowledge, this was the first reported experience with an expandable spacer being implanted by the endoscopic transforaminal approach in the lumbar spine. In this study, placing one or two B-Twin spacers into the same disk level was associated with a similar outcome. The intervertebral expansion of the spacer provided decompression of the neural structures and facet joints with a minimum invasiveness to the surrounding structures. Moreover, additional stability to the disk especially in case of slight instability or grade 1 spondylolisthesis was also achieved with the implant’s expansion. One of the technical difficulties was the irreversibility of the spacer once expanded, preventing its relocation when it had been improperly placed. In these cases, extraction of the device especially under local anesthesia was very problematic. Hence, a new implant with a modified design would be desirable. In addition, an expandable spacer with a higher bone-implant-bone contact surface would also be desirable.

The technical limitations of the B-Twin expandable implant inspired the design and production of a new expandable implant (Opticage™, Interventional Spine, Inc., Irvine, CA, USA) with a larger bone-implant contact surface and a relocation mechanism that allowed the repositioning and re-expansion of the cage until correct sagittal balance is achieved (Figs. 7.1 and 7.13).

The Opticage™ (Interventional Spine, Inc., Irvine, CA, USA), see Figs. 7.1c and d, is a titanium expandable cage that has an adjustable height from 9 to 14 mm by turning a handle with torque control. The cage automatically locks at the desired height and allows expansion/retraction and repositioning. The use of an expandable cage permits the instrumentation to be small, as the disk access can be done with a small annulotomy of just 7-mm diameter. The Opticage has an expansion strength of 1600N, and once expanded the graft can be directly injected into the implant. In comparison to the B-Twin cage, the Opticage has higher contact surface, and its convex surface allows an optimal adaptation to the end plate’s shape during the expansion process (see Fig. 7.13). The expandable interbody implant was not designed as a stand-alone fusion device and should be used with supplemental posterior spinal fixation [9, 15] (i.e., facet screw fixation systems, interspinous devices and posterior pedicle screw-and-rod systems) to achieve a 360° vertebral fusion (also see the following section for further details on posterior fixation devices).

Regarding the surgical technique, the patient is operated in a prone position and in forward flexion, as mentioned before. The patient’s position on the table should be adjusted to facilitate the approach to the disk, especially at level L5–S1, by increasing forward hip flexion but avoiding a kyphotic correction of the lumbar lordosis. The patient should be prepped and draped using a sterile technique. In a first step, the percutaneous posterolateral transforaminal approach is performed as mentioned in the prior section.

A special percutaneous insertion tool (Optiport™, Interventional Spine Inc., Irvine, CA, USA) was developed for the transforaminal disk access. Combining the percutaneous approach with an endoscopic view of the soft tissues helped to develop the design of the telescopic instruments. The use of an endoscope to visualize the exiting root and the epidural space was very important during the earlier cases [3, 6] in order to confirm the safety of the percutaneous surgical approach. Now, if the surgeon considers it appropriate, the Optiport instrumentation can be used separately under fluoroscopic control only or in combination with an endoscopic system. The ability to endoscopically visualize the neuroforaminal disk access may be of particular importance when the presence of conjoined nerve roots or furcal nerve in the neuroforamen is suspected [13] (see Fig. 7.12). The Optiport allows progressive tissue dilatation by inserting the three stages of this telescopic instrument of 12.5-mm outer diameter (Fig. 7.14) through a 15-mm skin incision. A foraminoplasty can optionally be performed to enlarge the caudal part of the foramen to insert the instrument without harming the exiting root (see Fig. 7.15). The foraminoplasty could also be performed with the sharp edges of the telescopic instrument (stages 1 and 2) (see Fig. 7.14), by rotating the instrument ±45° around the longitudinal axis. Care should be taken to ensure that the smooth side of the telescopic instrument remains always oriented toward the exiting nerve root (see Fig. 7.16). The beveled cannula (stage 3 of the telescopic instrument) is then inserted until reaching contact with the annular wall. The careful rotation of the bevel will protect the exiting root (Figs. 7.16 and 7.17). Afterward, stages 1 and 2 are removed by pulling back the instruments through the beveled cannula. A percutaneous working channel to the intervertebral disk has now been created such that surgical procedures can be performed through the Optiport. A standard discectomy should be performed through the Optiport to remove a minimum of 80% of the disk nucleus from the treatment level. Partial integrity of the annulus should be maintained to contain the interbody implant. The end plate cartilage and the remaining disk materials are removed with curettes and rasps (see Fig. 7.17). The percentage of end plate preparation is similar to that described for standard TLIF through the traditional posterolateral approach, as the telescopic access instrumentation can be moved around ±30° in a vertical-transversal plane and rotated 360°, allowing access to 60–80% of the disk. Once adequate discectomy has been achieved, demineralized bone matrix (DBM), beta-tricalcium phosphate (ß-TCP) mixed with stem growth factors, or autogenous bone graft should be placed into the anterior and lateral recesses of the intervertebral disk. Then, the interbody implant is filled with DBM, ß-TCP, or autogenous bone. The cage is then inserted through the beveled cannula and expanded under a C-arm fluoroscopic lateral control (Fig. 7.18). The most recent generation of Opticage (“G3 generation,” see Fig. 7.1d) allows injecting the graft material directly through the implant. Hence, this way a better graft distribution around the expanded cage can be achieved. Finally, A/P and lateral control X-rays are taken (Fig. 7.19), and the skin is sutured with reabsorbing Vicryl 00 (Figs. 7.20, 7.21, and 7.22).