The concept of posterolateral percutaneous discectomy was firstly introduced in 1973. Parvis Kambin conducted percutaneous indirect spinal canal decompression by nucleotomy using Craig’s cannula in a nonvisualized posterolateral approach [1]. Hijikata firstly published the technique of nonvisualized posterolateral percutaneous discectomy in 1975, which was a standalone procedure [2]. In the mid-1980s, Onik introduced a motorized aspiration shaver to the percutaneous discectomy technique [3] and then, Onik and Maroon reported the clinical outcome of ‘automated percutaneous discectomy’ using the nucleotome [4,5].

After the percutaneous discectomy age, an endoscope called “discoscope” was applied to the percutaneous discectomy technique for direct visualization. Hausmann and Forst [6] introduced a nucleoscope for viewing the intervertebral disc space. In 1990, Kambin also described an important illustration in the transforaminal approach, so called ‘triangular working zone’ in which there are neither vessel nor nerve [1]. The safe zone is bordered anteriorly by the exiting nerve root, inferiorly by the end plate of the lower vertebra, posteriorly by the superior articular process of the inferior vertebra, and medially by the traversing nerve root. The definitive description of the triangular working zone enabled the introduction of larger endoscope with larger instruments and more sophisticated decompression without exiting nerve root damage. Mayer and Brock described the technique of percutaneous endoscopic lumbar discectomy (PELD) for contained disc herniation using an angled lens scope allowing dorsal vision around the annular tear [7]. This was similar to Schreiber’s biportal approach. They removed the herniated nucleus with rigid or flexible forceps, as well as with automated shaver system under intermittent endoscopic control (discoscopy). Since then, so called ‘PELD’ is one of the representative terms of endoscopic lumbar discectomy techniques.

Mathews 1996 [8] and Ditsworth 1998 [9] opened the era of real transforaminal approach. Ditsworth described the technique in which a working channel endoscopy passes completely through the foramen into the spinal canal and the surgeon directly removes free fragments and decompresses the nerve root and dural sac [9]. Since then, a truly transforaminal approach, as opposed to just going through part of the foramen and into the disc, has been developed and the target disc pathology is broaden from contained disc herniation to non-contained disc herniation.

The basic concept of the percutaneous endoscopic surgery has been evolved from an indirect intradiscal decompression to a direct epidural or selective neural decompression. The working space has been extended from central nucleus to peri-annular and finally, epidural space [10]. In the new millennium, various advanced endoscopic techniques have been developed. Selective endoscopic discectomy was named by Kambin [11] and Yeung [12] independently. Yeung et al. used the Yeung Endoscopic Spine System (YESSTM) which has a rigid rod-lens, integrated, multichannel, wide-angled endoscope [13]. They described the selective endoscopic discectomy technique for extruded lumbar disc herniation. They also introduced a foraminoplastic approach at the L5-S1 level. In 2003, the endoscopic surgical system became more contemporary as launching YESS designed around the transforaminalendoscopic approach for intradiscal and epiduroscopic procedures. Yeung et al. also described the utility of provocative intraoperative discography, thermal discoplasty and annuloplasty, and annular resection for creation of an annular window to perform foraminoplasty using abrasive drills, burrs, and lasers [14]. Some authors reported the endoscopic technique for various situations such as recurrent disc herniation, disc herniation at L5-S1 level, migrated disc herniation or upper lumbar disc herniation. Ahn and Lee described the endoscopic technique for recurrent disc herniation and upper lumbar disc herniation [15,16]. Sometimes the standard posterolateral approach might be associated with problems in reaching the epidural space due to anatomical peculiarities. This problem of poor visualization of the epidural space was solved with an extreme lateral approach described by Reutten et al. [17]. They pointed out that the usual transforaminal access is posterolateral and associated with problems in reaching the epidural space directly with unhindered vision, and then they described an extreme lateral access into the spinal canal using the full-endoscopic uniportal transforaminal approach. At the same time, Schubert and Hoogland described a foraminoplastic approach with bone reamer to remove the migrated and sequestrated disc herniation [18]. They used a bone reamer to undercut the part of superior facet to reach the epidurally extruded disc fragment. Lee applied a classification system for the migrated disc herniation and demonstrated the clinical outcomes according to the disc migration zone [19].

Although various foraminoplastic approaches were introduced, most of the techniques were not for real foraminal decompression, but for approach to the intracanal pathologies. Therefore, the history of foraminal endoscopic decompression started in the late 1990s. Knight et al. introduced endoscopic laser foraminoplasty for various foraminal nerve root entrapment syndromes [20]. The basic concept of foraminoplasty is reshaping foramen by ablating soft tissues such as foraminal ligaments and osteophyte using side-firing laser under endoscopic visualization. Ahn et al. described a percutaneous endoscopic lumbar foraminotomy technique using bone reamer and laser [21]. Schubert and Hoogland also reported the use of a bone reamer for foraminoplasty in case of migrated disc herniation [18]. However, the previous techniques have limitations for definite foraminal decompression. The use of laser is effective for only neural entrapment caused by soft tissue or fragile osteophyte. However, it may be less effective for severe bony foraminal stenosis. Blind use of bone reamer also has inherent limitations such as bone bleeding and neural injury because it is a blind technique without any direct vision control. Nowadays, some authors reported more advanced endoscopic foraminal decompression techniques that can be performed for severe foraminal stenosis cases. The use of endoscopic burr and endo-punches enables a safer and more effective full-scale foraminal decompression [10,22].

The hypertrophy of the superior articular process is the most common cause of the lumbar lateral recess and foraminal stenosis. As a result, the traversing nerve root is opted to be compressed in the lateral recess zone. The transforaminal approach may be suitable for the treatment of the lateral recess stenosis. The approach angle is more efficient while preserving the facet joint with the transforaminal approach. The working sheath is usually engaged in the foramen, especially in the caudal surface of the superior articular process, not in the disc space [18,21,23]. The tip of the superior articular process can be resected by a bone trephine or endoscopic burrs in an outside-to-inside manner. After bony resection, the thickened ligamentum flavum can be subsequently resected by endoscopic forceps and micropunches. Then the compressed traversing nerve root can be identified, and a sophisticated soft tissue decompression can be performed. An additional partial pediculectomy at the caudal part of the foramen may enhance the decompression effect. The essential technical point is the precise landing of the working sheath and sufficient decompression of the critical point, which is usually located around the hypertrophic superior articular process and ligamentum flavum. Technical obstacles against the complete decompression are the safe placement of the working sheath in the foramen, epidural bleeding, blurring of the endoscopic visual field, and confusion in the endoscopic anatomical discrimination. Thus, this technique is more challenging than the standard percutaneous endoscopic discectomy. However, an advanced and pracical techniques have been published with reliable outcomes [24].

For a definitive endoscopic decompression for central lumbar stenosis, the size of the working channel endoscope and the related instruments have become bigger and stronger.

The surgical technique can be performed using the standard method described in previous studies [25,26]. The patient was placed in a prone position under general or epidural anesthesia. The initial landing point is the lateral edge of the interlaminar space. After serial dilation, the final working sheath was placed on the lamina. Then a percutaneous endoscopic laminotomy was performed from the medial border of the superior facet using the endoscopic burr and punches. Decompression under endoscopic control can be performed including cranial and caudal laminotomy, medial facetectomy, and removal of the ligamentum flavum. In the case of bilateral decompression, further decompression of the contralateral side is needed after ipsilateral decompression. The working channel endoscope and the working sheath were directed toward the contralateral side, dorsal to the dural sac. It is essential to leave the ligamentum flavum intact to protect the dural sac during the contralateral laminotomy. The bone resection over the ligamentum flavum should be conducted until the medial aspect of the contralateral facet can be reached. The remaining ligamentum flavum was then completely removed using the endoscopic punches and other supplementary instruments.