www.e-neurospine.org S17 Inside-Out and Outside-In Techniques in Endoscopic Spine Surgery: Are These Techniques Efficient Even for Pathology Irrelevant to the Intervertebral Foramen? “Inside-out (I-O)”—this simple phrase, which Yeung introduced in the 1990s, has be- come one of the standard terms used by endoscopic spine surgeons.1 Furthermore, the I-O technique has become a fundamental and popular technique in endoscopic transforaminal discectomy and decompression (ETD). The I-O technique enables better visualization of intradiscal conditions that cause pain, enabling the surgeon to perform intradiscal therapy. A comparative study2 in foraminal stenosis demonstrated that I-O had better long-term re- sults at a 5-year follow-up than the outside-in (O-I) technique. Yeung and Lewandrowski2 argued that the better outcomes of I-O were brought about by additional intradiscal thera- py during the early stage of an operation. However, the therapeutic effect of intradiscal treatment on backache when the I-O technique is used exceeds the scope of the current discussion. These techniques are mainly designated for the endoscopic management of pathology through the intervertebral foramen. There is no accessible route other than the through the foramen to approach pathology in the vertebral canal without laminectomy. Both techniques use a posterior and lateral incision from the midline of the back for skin access. The I-O technique is started by placing an endoscope in the disc, while the first step in the O-I tech- nique is localizing the foramen for foraminoplasty. In the final stage, the I-O technique leads to a widened foramen by successive decompressions.2 In contrast, the O-I technique results in free nerve roots by decompression in the last endoscopic view.3 According to these de- scriptions, I-O and O-I are surgical techniques for pathologies that are only accessible through the intervertebral foramen. I read 2 articles dealing with I-O and O-I in the management of endoscopic decompres- sion that were published in this special issue.4,5 These cases seemed to emulate Yeung’s con- cept when describing their endoscopic approach to a lesion. However, I did not find any critically different points, especially in the techniques used for the approach, between the 2 groups. They might not have a significant enough difference from each other for it to be appropriate to use different terminology. If pressed to find a difference between the tech- niques in these manuscripts, I might point out that they differ in terms of how to remove the ligamentum flavum (as a whole or piecemeal). In the article using the O-I technique,4 the author indicated that the O-I technique per- formed in their study was similar to “the over-the-top” technique.6 Using scientific termi- Neurospine 2020;17(Suppl 1):S17-19. https://doi.org/10.14245/ns.2040326.163 Neurospine eISSN 2586-6591 pISSN 2586-6583 Editorial Corresponding Author Chun-Kun Park https://orcid.org/0000-0003-4705-8034 Good Doctor Tn-Tn Hospital, 775 Kyeongsu-daero, Dongan-gu, Anyanag 14041, Korea E-mail: ckpmd@catholic.ac.kr See the article “Lumbar Endoscopic Unilateral Laminotomy for Bilateral Decompression Outside-In Approach: A Proctorship Guideline With 12 Steps of Effectiveness and Safety” via https://doi. org/10.14245/ns.2040078.039. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecom- mons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright © 2020 by the Korean Spinal Neurosurgery Society http://crossmark.crossref.org/dialog/?doi=10.14245/ns.2040326.163&domain=pdf&date_stamp=2020-07-31 Inside-Out and Outside-In Techniques in Degenerative Lumbar SpinePark CK Neurospine 2020;17(Suppl 1):S17-19.S18 www.e-neurospine.org nology, this technique can be referred to as unilateral laminoto- my with bilateral spinal canal decompression (ULBD), and an- other synonym in endoscopic surgery is “cross-over.” The origi- nal application of this technique was in open surgery.6 This technique, which is mainly used to decompress the contralater- al side of the canal, might have been carried out through ipsi- lateral single-incision skin access. In other words, although there are certain similarities between O-I and ULBD, O-I stands for a full series of endoscopic transforaminal techniques. There- fore a surgeon could divide the entire endoscopic procedure into several stages by time, whereas the “over-the-top” tech- nique is a specific way to handle a particular part of the entire endoscopic process.7 Consequently, It was improper to present the “over-the-top” technique as a similar procedure as the O-I technique, as each of these techniques plays a different role in the sequence of steps performed in an endoscopic procedure. In recent years, endoscopic decompression surgery has been used to treat central canal stenosis7 and other kinds of lumbar degenerative stenosis using newly designed endoscopes, with shorter and wider working channels, and surgical tools.8 The route approaching down from the skin via the lamina to the epidural space is anatomically more familiar to most spine sur- geons than the I-O technique in ETD. However, not a few en- doscopic spine surgeons, including Yeung, still place a high val- ue on I-O taking the foraminal route and insist that the ETD might be used for most lumbar spine pathologies, except for those that are unreachable. Accordingly, ETD cannot remain at the forefront in the field of endoscopic spine surgery, even if certain limited and specific pathologies may be managed better by ETD. The O-I and I-O techniques (mainly I-O), which are supposed to belong to ETD, should be appropriately applied in pathologies reachable by the transforaminal route. REFERENCES 1. Yeung AT, Tsou PM. Posterolateral endoscopic excision for lumbar disc herniation: Surgical technique, outcome, and complications in 307 consecutive cases. Spine (Phila Pa 1976) 2002;27:722-31 2. Yeung AT, Lewandrowski KU. Five-year clinical outcomes with endoscopic transforaminal foraminoplasty for symp- tomatic degenerative conditions of the spine: a comparative study of inside-out versus outside-in techniques J Spine Surg 2020;6(Suppl 1):S66-83. 3. Hoogland T, van den Brekel-Dijkstra K, Schubert M, et al. Endoscopic transforaminal discectomy for recurrent lumbar disc herniation: a prospective, cohort evaluation of 262 con- secutive cases. Spine 2008;33:973-8. 4. Kim HS, Wu PH, Jang IT. Lumbar endoscopic unilateral laminotomy for bilateral decompression (LE-ULBD) out- side-in approach: a proctorship guideline with 12 steps of effectiveness and safety. Neurospine 2020;17(Suppl 1):S98- 108. 5. Lim KT, Meceda EJA, Park CK. Inside-out approach of lum- bar endoscopic unilateral laminotomy for bilateral decom- pression: a detailed technical description, rationale and out- comes. Neurospine 2020;17(Suppl 1):S87-97. 6. Ulrich NH, Burgstaller JM, Gravestock I, et al. Outcome of unilateral versus standard open midline approach for bilat- eral decompression in lumbar spinal stenosis: is “over the top” really better? A Swiss prospective multicenter cohort study. J Neurosurg Spine 2019;31:236-45. 7. Siepe CJ, Sauer D. Mayer D. Full endoscopic, bilateral over- the-top decompression for lumbar spinal stenosis. Eur Spine J 2018;27(Suppl 4):S563-5. 8. Lim KT, Nam HGW, Kim SB, et al. Therapeutic feasibility of full endoscopic decompression in one- to three-level lumbar canal stenosis via a single skin port using a new endoscopic system, percutaneous stenoscopic lumbar decompression. Asian Spine J 2019;13:272-82. Inside-Out and Outside-In Techniques in Degenerative Lumbar SpinePark CK Neurospine 2020;17(Suppl 1):S17-19. www.e-neurospine.org S19 Title: Child with a Dove Artist: Pablo Picasso Year: 1901 Child with a Dove is one of Picasso’s earliest works: he was twenty-one, or even less, but his own style is already apparent. He probably painted it in Paris during his second visit, when he was staying with Spanish friends. By that time he had seen, studied, and assimilated contemporary French painting: he had taken Toulouse-Lautrec’s way of rendering a visual impression rapidly with a few forceful lines and shrill spots of color, and made it his own. Also, he had learned from Degas how to observe a figure sharply and with detachment. In Child with a Dove, we see a new thoughtfulness, a poetic sympathy with the subject, qualities that were to dominate his work in the years that followed. More information: https://www.pablopicasso.org/child-with-a-dove.jsp © 2020 - Succession Pablo Picasso - SACK (Korea)