Chapter 28 Posterior Lumbar Foraminal Decompression

Since the first publication by Hijikata and colleagues [1] in 1975 on purely percutaneous intradiscal lumbar disc decompression, several developments have been made with this approach for different forms of lumbar, and later also cervical, disc pathologies. The original Hijikata technique, developed for Japanese patients, was adopted in Zurich after its presentation at the 1978 SICOT (Société Internationale de Chirurgie Orthopédique et de Traumatologie) meeting in Kyoto, where it was introduced as a unilateral posterolateral decompression technique for contained lumbar disc herniations. It became evident that the sizes of the original instruments would require adaptation to the larger dimensions of anatomical structures in European patients. Specifically, a stepwise modification of the diameter of the dilating cannulas was needed to reach a working channel of 6 mm. With the larger cannula, the introduction of arthroscopic control became possible in 1982. This arthroscopic control, when used with a biportal cannula approach [2], for the first time allowed simultaneous endoscopic control, or discoscopy [3], of intradiscal selective tissue removal in the posterior field of the intervertebral disc space. Through this process, the indirect decompression of subligamentarily contained lumbar disc herniation was standardized in its specific range of indications.

Other surgeons aimed for technical improvement of uniportal intradiscal disc decompression by higher abrasive activity, with new devices such as the automated nucleotome introduced in 1985 by Onik and associates [4]. Its ease of application made disc surgery available to a larger group, including nonsurgical physicians, explaining the somewhat uncontrolled boom of percutaneous disc decompression in the later 1980s. This overuse with unconvincing results contributed to a rapid decline in the reputation of percutaneous methods for disc decompression in general. Because the slim aspiration cannula vacuumed disc tissue from any direction, limited control of the direction of disc tissue removal was possible. The tissue removed was not necessarily aspirated from the posterior subanular zone. The same inherent problem existed with later centrodiscal ablative laser disc decompression, which clearly limited this application to indirect decompression of symptomatic contained protrusions and did not allow for calculable tissue removal in the posterior subligamentary zone. Such calculable removal was better achieved through biportal endoscopically controlled mechanical tissue extraction with pituitary forceps under endoscopic control. In this approach, direct visualization of tissue fragment removal became available and challenged conventional microdiscectomy in this range of indications. Owing to this experience, it became evident as early as the 1980s that intradiscal techniques could not be adapted for adequate removal of any transligamentary sequestrated herniation because of geometric constrictions. In these cases, conventional open techniques, such as minimal interlaminotomy or microdiscectomy [5], remained the “gold standards.”

Endoscopic applications in the area inside the anulus fibrosus were in clinical use with biportal percutaneous nucleotomy beginning in the mid-1980s, but by its nature the technique remained without direct therapeutic use for extradiscal tissue removal. In the United States, Kambin used his anuloscopy for medicolegal reasons from 1988 on for endoscopic documentation of the anular fibers before their trepanation with his trephine-cutter, which was then his standard method for uniportal entrance into the lumbar disc with decompressive forceps [13]. With this method he could avoid damage to the exiting roots during anular trepanation. His technique was further developed by Savitz [6] in the 1990s, in combination with laser-assisted fluoroscopic microdiscectomy. In our experience, the laser application did not offer convincing advantages over mechanical tissue removal with a biportal approach, but others found it advantageous for tissue shrinking in coaxial unilateral applications [7,8].

In 1990, on the basis of our experience with minimally invasive techniques such as intradiscal endoscopic control for pointed mechanical tissue removal, we tried to explore the anular and foraminal site locally at the end of our biportal interventions. However, with the 7.5-mm working cannula that was available at the time, such exploration was not successful. During the same period, we made the first pathoanatomical investigations into the use of rod-lens coaxial endoscopic devices derived from integrated cystoscopes for use in non-prefigured retroperitoneal compartments. These devices were the precursors of a 6-mm, open coaxial endoscopic technique for direct visualization of foraminal sequestrated herniations, introduced clinically for the first time worldwide in 1991 [9,10].

Development of similar methods followed in the United States in 1993 for lumbar decompressive applications. Later, the uniportal coaxial endoscopic procedure was adopted by others, such as Yeung and Chow [8], who developed a similar system with a slightly smaller working channel but a second channel for laser fiber application as an additional working tool for disc decompression and bony enlargement of the foraminal access (Fig. 28-1).

Figure 28–1 Foraminoscope as developed in cooperation with Karl Storz GmbH Tuttlingen, Germany. Straightforward 6-degree, telescope autoclavable, with a 3-mm instrument channel.

Anatomical and technical considerations

In a European of average height, the lower lumbar foraminal ports measure about 1.2 to 1.6 cm in craniocaudal height and 6 to 8 mm in dorsoventral diameter. The lumbosacral junction L5-S1 is slightly less wide, and owing to its location under the level of the iliac crests, it is difficult or even impossible to approach for any percutaneous lateral or transforaminal technique. If anatomical accessibility of the foraminal area seems questionable, a local transforaminal steroid injection under fluoroscopic control can help screen for this method of decompression.

The foraminal port is composed primarily of fat tissue, which surrounds the exiting and descending root with its sensory ganglion. The root then further descends lateroventrally into the fossa lumbalis and joins the plexus lumbalis. Other connecting venous vessels draining the peridural venous plexus pass the lower foraminal site and can cause local venous bleeding during surgical procedures. The lumbar segmental arteries, which are normally located somewhat cranial to the foramen and lateral to the pedicle, are usually not encountered during foraminoscopic surgical procedures.

For the clinical presentation of typical dysesthetic radicular pain (e.g., pretibial burning sensation in a L4-L5 foraminal compression), the compression of the sensory ganglion beyond the pedicle by ascending foraminal disc herniation is the typical anatomical correlation (Fig. 28-2). Affected patients, without additional herniation in the canal and therefore without compression of the lateral recess, hardly ever show root tension signs, such as positive response to Lasègue maneuver.

Figure 28–2 Intraforaminal herniation with an ascending sequestrated disc tissue that is compressing the exiting root with its ganglion in the subpedicular zone (arrow).

Because the posterior longitudinal ligament is covering only the medial part of the foraminal zone, we often see a combination of partially subligamentary contained (medial) and free (more lateral) sequestrated herniation. It is our experience that larger lateroforaminal fragments are more often seen patients older than 55 years who also have some twisting-instability and already visible facet changes.

Our first clinical experiences with posterolateral foraminoscopic exploration showed that because of fatty pads and venous bleeding, an efficient endoscopically controlled tissue removal would experience limited success without some temporary spacing in this anatomically not directly preconfigured “virtual optical chamber.” In experimental settings, it became evident that for other endoscopic applications, available gas media such as nitrogen and carbon dioxide were inappropriate because of their rapid dissipation into the surrounding tissue compartments in addition to their potential embolic complications. To avoid these complications, isotonic liquids such as saline and lactated Ringer solution were standardized for this purpose. In addition to providing some local spacing, the continuous flow of irrigation also keeps visibility clear. In cases with venous bleeding, the irrigation pressure can be raised above 40 cm H₂O column pressure, which will clear venous bleeding from the area. This slight hyperpressure could be optimized by introduction of posterior rubber valve-taps that allow tight penetration with fine 3-mm forceps through the working channel down to the working zone. Nevertheless, some dissipation of irrigation fluid into the retroperitoneal space, up to 600 mL during a 40-minute procedure, remains common. We have not seen any measurable intraoperative hemodynamic or postoperative clinical effect of this retroperitoneal volume load, which is reabsorbed within hours.

First using saline solution at room temperature, we found a specific positive effect for cooled irrigation (around 8° C). The use of cooled irrigation causes vasomotor contraction, by which fine arteriolar bleeding can also be markedly reduced, thereby reducing the necessary amount of irrigation volume from more than 4 L to around 2 L every 30 minutes. Consequently, the local hypothermia in the foraminal area, besides providing a more routine technical application, may have also contributed to a decrease in postoperative analgesic demands.

Indications

The target indication for foraminoscopic microdiscectomy since its introduction in 1991 has been lumbar foraminal and extraforaminal disc herniation with clinical root/ganglion compression syndrome that is resistant to conservative treatment or is rapidly evolving under conservative treatment. The incidence of this condition in our population is around 10% of all operative lumbar disc cases [11].

The diagnosis of this type of herniation is often delayed because it occurs outside the lumbar canal [5] and therefore often does not correspond to classic clinical signs, such as a positive response to Lasègue root tension maneuver, nighttime pain, and pain aggravated by lying on the side opposite the herniation site.