After the percutaneous diskectomy age, an endoscope termed the diskoscope was applied to the percutaneous diskectomy technique for direct visualization. Hausmann and Forst introduced a nucleoscope for viewing the intervertebral disk space [7]. Schreiber and Suezawa firstly reported a transdiskoscopic nucleotomy technique [8]. In the study, some of the patients underwent percutaneous diskectomy performed under the diskoscopic visualization. In 1988, Kambin et al. reported the first intraoperative diskoscopic views of herniated nucleus pulposus and he suggested that the visualization of the epidural space would be very important in his later articles [9]. In 1989, Schreiber et al. used a biportal approach with a diskoscope and injected indigocarmine dye into the disk to discriminate abnormal nucleus pulposus and annular fissure [10].

In 1990, Kambin also described an important anatomical feature regarding the transforaminal approach – the so-called triangular working zone in which there is 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 diskectomy (PELD) for contained disk herniation using an angled lens scope allowing dorsal vision around the annular tear [11]. 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 (diskoscopy). Since then, the so-called PELD is one of the representative terms of endoscopic lumbar diskectomy techniques.

Mathews 1996 [12] and Ditsworth 1998 [13] 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 [13]. Since then, a truly transforaminal approach, as opposed to just going through part of the foramen and into the disk, has been developed and the target disk pathology is broaden from contained disk herniation to noncontained disk herniation.

In 1996, Kambin and Zhou published a technique of endoscopic decompression for the treatment of lateral recess syndrome. They decompressed the nerve roots, compromised by lateral recess stenosis, by annulectomy and osteophytectomy with forceps and trephines in using angled endoscopes (0- and 30-degree endoscopes) [14].

They described that in the case of large central disk herniation at the level of L5–S1, sequestered disk herniation, or migrated disk herniation, open surgery was required [14, 15].

The basic concept of the percutaneous endoscopic surgery has been evolved from an indirect intradiskal decompression to a direct epidural or selective neural decompression. The working space has been extended from central nucleus to periannular and finally epidural space [16]. In the new millennium, various advanced endoscopic techniques have been developed. Selective endoscopic diskectomy was named by Kambin et al. [17] and Yeung [18] independently. Yeung used the Yeung Endoscopic Spine System (YESS^TM) which has a rigid rod lens and integrated, multichannel, wide-angled endoscope [19]. They described the selective endoscopic diskectomy technique for extruded lumbar disk 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 transforaminal endoscopic approach for intradiskal and epiduroscopic procedures. Yeung and Yeung also described the utility of provocative intraoperative diskography, thermal diskoplasty and annuloplasty, and annular resection for creation of an annular window to perform foraminoplasty using abrasive drills, burrs, and lasers [20]. Some authors reported the endoscopic technique for various situations such as recurrent disk herniation, disk herniation at L5–S1 level, migrated disk herniation, or upper lumbar disk herniation. Ahn and Lee described the endoscopic technique for recurrent disk herniation and upper lumbar disk herniation [21, 22]. 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. [23]. 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 disk herniation [24]. They used a bone reamer to undercut the part of superior facet to reach the epidurally extruded disk fragment. Choi and Lee introduced a technique of interlaminar approach to L5–S1 level or migrated disk herniation from L4 to 5 level [25, 26]. Lee et al. applied a classification system for the migrated disk herniation and demonstrated the clinical outcomes according to the disk migration zone [27].

In 2006, Lee et al. studied the limitation of endoscopic diskectomy in the aspect of the size and location of disk herniation [28]. They concluded that open surgery may be considered for herniations with high-canal compromise and high-grade migration. Lee et al. also described percutaneous endoscopic intraannular subligamentous herniotomy [29]. The concept of herniotomy is removal of whole iceberg, not just the tip of the iceberg. It is important to prevent recurrent disk herniation or incomplete removal which is one of the main concerns about minimally invasive endoscopic surgery [16].

Although various foraminoplastic approaches were introduced, most of the techniques were not for true 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 [30–32]. 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 [33]. Schubert and Hoogland also reported the use of a bone reamer for foraminoplasty in the case of migrated disk herniation [24]. 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 [16, 34].

Most previous studies on percutaneous endoscopic surgeries have mainly described the technique which treats the lumbar radiculopathy caused by nerve root compromise. Several pioneers tried to treat diskogenic back pain with percutaneous endoscopic techniques. In 2004, the surgical technique of minimal access posterolateral transforaminal selective endoscopic diskectomy and bipolar radiofrequency thermal annuloplasty to interrupt the purported annular defect pain sensitization process was introduced to treat the patients with chronic lumbar diskogenic pain [35]. In this study, a total of 113 patients were recruited; however, the results showed lack of clinical benefit from this procedure. In 2010, Ahn and Lee reported the outcome predictors of percutaneous endoscopic lumbar diskectomy and thermal annuloplasty (PELDTA) for diskogenic low back pain, in which 83.5 % patients showed symptomatic improvement and the success rate was 70.9 % [36]. In their conclusion, PELDTA could be effective for the patients with chronic diskogenic low back pain. Lee and Kang used laser-assisted spinal endoscopy (LASE) kit for the percutaneous intradiskal decompression to evaporate and shrink the posterior and central nucleus for improvement of lumbar pain [37]. Percutaneous endoscopic laser annuloplasty, a new minimally invasive technique, used LASE for direct coagulation of the painful inflamed granulation tissue with new vessels and nerves in 30 patients with diskogenic low back pain. They reported favorable outcomes for carefully selected groups of patients with diskogenic low back pain. Although the theoretical background is fascinating, the clinical application of this technique is not, as of yet, established. The patient selection and surgical technique should be more standardized to produce a reliable clinical result in the future.

The application of the laser to minimally invasive or percutaneous lumbar surgery is very attractive to spine surgeons because of the ability to deliver a large amount of energy through a small fiber to a focused spot area. The laser tissue interaction can be classified into three types: photochemical effects, photothermal effects, and photomechanical and photoionizing effects [38]. Until now, for percutaneous laser disk decompression (PLDD), lasers in the near-infrared region (Nd:YAG, Ho:YAG, and diode lasers) and with visible green radiation (frequency doubled Nd:YAG, called “KTP laser”) were reported to be effective [38]. The basic technique of PLDD is similar for all trials. The procedure is conducted under local anesthesia of the skin and underlying muscles. After assessment of the correct disk level by using fluoroscopy, a hollow needle is inserted 10 cm from the midline, pointing toward the center of the disk. A laser fiber (0.4 mm) is inserted through the needle into the center of the nucleus pulposus. Laser energy is then delivered into the nucleus pulposus to vaporize its content and reduce intradiskal pressure [39].

In the mid-1980s, Ascher and Choy developed percutaneous laser diskectomy technique [40, 41]. Ascher firstly applied laser into the disk surgery using a neodymium:yttrium-alluminum-garnet (Nd:YAG) laser [40]. The procedure included fluoroscopically guided insertion of an 18-gauge needle into the disk space through which 400-nm laser fiber was advanced into the disk space. Approximately 1200 J of energy in short bursts to avoid heating the adjacent tissues was delivered to ablate a small intradiskal tissue. Through the spinal needle, the vaporized tissue was escaped. Finally, an adhesive bandage covered the needle site and patient was discharged. In 1990, Davis performed laser diskectomy with the potassium titanyl-phosphate (KTP) 532-nm laser in 40 patients and reported 85 % success rates [42]. Choy et al. introduced the new technique of percutaneous laser disk decompression (PLDD) in 1992 [43]. They reported the clinical outcomes of 333 patients with 78.4 % of good to fair results. Subsequently, Mayer and Brock suggested a combined technique between laser ablation and endoscopy in order to keep observing the amount of removing disk tissues during surgery [11]. There was a report on comparison study between Ho:YAG laser diskectomy and conservative treatment in 1993 [44]. Even though they could not identify a significant difference in terms of complications, they concluded that the laser diskectomy was a safe procedure to be effective in relieving symptoms in some patients. There was also a comparison study between the Ho:YAG and ND:YAG laser in 1994 [45]. They demonstrated that Ho:YAG laser was the best for compromising between efficacy of absorption and convenience of fiber-optic delivery. In 1995, Casper et al. reported an 84 % success rate at 1-year follow-up in the patients treated by the side-firing Ho:YAG laser [46]. In 1998, Knight et al. reported endoscopic laser foraminoplasty using a side-firing Ho:YAG laser for chronic low back pain and sciatica [30]. Then, Hellinger started to use the Ascher technique for Nd:YAG laser ablation in 1999, who had treated more than 2500 patients for 13 years and his overall success rate was approximately 80 % [47]. In 2000, Yeung reported an 84 % success rate in his experiences with more than 1000 patients whose herniated lumbar disks were treated by KTP laser [48]. Nowadays, the laser can be used as a supplementary role in ablation of bone and soft tissue. It can be also used for thermal laser annuloplasty in the treatment of diskogenic back pain.