Among studies evaluating minimally invasive surgical (MIS) decompression of the L5 root, techniques involving transtubular endoscopic decompression under O-arm navigation are rare. We present the case of a 68-yearold woman with left leg pain, muscle weakness and gait disturbance of one month duration. The patient underwent transtubular endoscopic decompression under O-arm navigation. There is no radiation hazard to the operating room staff with this procedure. After surgery, the patient had significant pain relief and her left lower limb motor function had improved by follow-up at one year. C-arm-free endoscopic L5 root decompression is a safe and effective procedure

Arataki, Shinya

Fujiwara, Yoshihiro

Mehta, Rahul

Oda, Yoshiaki

Tanaka, Masato

Uotani, Koji

Yamauchi, Taro

English

Okayama University Scientific Achievement Repository

L 5 radicular symptoms are caused primarily by L4-5 pathology,  but may also occur due to foram-inal or extraforaminal L5-S1 lesions.  Extraforaminal lesions may be discogenic,  ligamentous or bony [1 , 2].  Of all symptomatic lumbar disc herniations,  L5-S1 extraforaminal herniations account for approximately 2-4% [3 , 4].  Because of the very narrow surgical pas-sage at this level,  approach is difficult and often requires resection of part of the L5-S1 articular facet,  which can lead to instability.  The above reasons limit the surgeon’s exposure to and familiarity with extraforaminal L5 root decompression.  A microendoscopic procedure in com-bination with navigation can help the surgeon to decompress the L5 root with precision.  Additionally,  the use of the O-arm system provides intraoperative 3D imaging and presents no risk of radiation exposure to operating room staff and surgeons.  To the best of our knowledge,  there have been very few studies to date on the use of O-arm navigation for L5 root decompression.  This study was approved by the institutional ethics com-mittee of Okayama Rosai Hospital.Surgical TechniqueThis procedure is performed under general anesthe-sia and neuromonitoring.  The patient is positioned prone.  A navigation reference frame (RF) is placed percutaneously into the contralateral sacroiliac joint,  and O-arm (Medtronic,  Inc.,  Minneapolis,  MN,  USA) images are obtained and transferred to a Medtronic Stealth Station S7 Navigation system (Medtronic).  With the help of a navigated probe,  the L5-S1 foraminal level is confirmed and the entry point for the skin incision is marked.  The subcutaneous tissue and muscles are dis-sected,  and the navigated first dilator is docked at the base of the L5 transverse process.  Sequential dilators are inserted over the first dilator,  and the final tube is inserted and fixed to the frame held firm by the table (Fig. 1).  The level is reconfirmed with the navigated Acta Med.  Okayama,  2021Vol.  75,  No.  5,  pp.  637-640CopyrightⒸ 2021 by Okayama University Medical School.http ://escholarship.lib.okayama-u.ac.jp/amo/Case ReportTranstubular Endoscopic Posterolateral Decompression of the L5 Root under Navigation and O-arm: A Technical NoteRahul Mehta,  Masato Tanaka＊,  Yoshiaki Oda,  Yoshihiro Fujiwara,   Koji Uotani,  Shinya Arataki,  and Taro YamauchiDepartment of Orthopaedic Surgery,  Okayama Rosai Hospital,  Okayama 702-8055,  JapanAmong studies evaluating minimally invasive surgical (MIS) decompression of the L5 root,  techniques involv-ing transtubular endoscopic decompression under O-arm navigation are rare.  We present the case of a 68-year-old woman with left leg pain,  muscle weakness and gait disturbance of one month duration.  The patient under-went transtubular endoscopic decompression under O-arm navigation.  There is no radiation hazard to the operating room staff with this procedure.  After surgery,  the patient had significant pain relief and her left lower limb motor function had improved by follow-up at one year.  C-arm-free endoscopic L5 root decompression is a safe and effective procedure.Key words:  C-arm-free,  navigation,  O-arm navigation,  endoscopic surgery,  L5 root decompressionReceived January 29, 2021 ; accepted March 30, 2021.＊Corresponding author. Phone : +81-86-262-0131; Fax : +81-86-262-3391E-mail : tanaka0896@gmail.com (M. Tanaka)Conflict of Interest Disclosures: No potential conflict of interest relevant to this article was reported.probe (Fig. 2).  The bone at the base of transverse pro-cess and the adjoining lamina are removed with a navi-gated burr.  Further surgical steps are planned according to the pathology.  For a ruptured disc,  the root is iden-tified and retracted gently,  and the disc fragment is removed.  In the case of foraminal stenosis,  the fora-men is widened using a burr.  Any compressing soft tissue is removed and the L5 root is identified by its surrounding perineural fat and vessels (Fig. 3).  Postoperatively,  the drain is removed after 48 hours.  The patient is mobilized as per his or her pain tolerance and discharged with instructions to avoiding lifting weight heavier than 5 pounds and bending forward for 6 weeks.Case PresentationA 68-year-old woman presented to us with left lower limb radicular pain which had progressed over 1 month and was not relieved with oral medication.  It was asso-ciated with L5 dermatomal paresthesia,  a straight leg raising test was negative,  and gluteus medius power was grade 4/5,  the tendoachilles was 4/5 and the extensor hallucis longus was 4/5 on the left side.  Deep tendon reflexes were normal,  and there were no signs of upper motor neuron lesions.  The patient had a Trendelenburg gait.  Magnetic resonance imaging (MRI) demonstrated left L5-S1 foraminal and extraforaminal stenosis with-out L4/5 central stenosis (Fig. 4A , B).  A computed tomography (CT) scan showed osteophytes at the supe-rior articular process and the posterior aspect of the end plates of L5 and S1 (Fig. 5A , B).  A diagnostic left L5 root block was performed,  which relieved pain.  The patient underwent left L5-S1 transtubular endoscopic posterolateral decompression under O-arm navigation.  A postoperative CT scan showed adequate decompression of the foramen and extraforaminal stenosis (Fig. 6A , B).There was significant immediate postoperative pain 638 Mehta et al. Acta Med.  Okayama　Vol.  75,  No.  5Fig. 1　 Placement of the percutaneous reference frame,  sequen-tial docking of tubes,  and fixture of the final frame.Fig. 2　 The level is reconfirmed with the navigated probe.Fig. 3　 Identifying the L5 root (white arrow).A BFig. 4　 A,  A preoperative magnetic resonance imaging (MRI) sagittal section shows no central stenosis; B,  A preoperative MRI axial section demonstrates left L5-S1 foraminal and extraforaminal stenosis (white arrow).relief and by the patient’s one-year follow-up,  her motor function had improved to grade 5/5.DiscussionThe diagnosis and surgical management of foram-inal/extraforaminal stenosis and extraforaminal disc herniation at the L5-S1 level is a challenge to every spine surgeon [5].  The broad L5 transverse process,  the small space between the sacral ala and the L5 transverse process,  the iliac crest,  and degenerative changes make the operating window very narrow.  Using the conven-tional open approach for foraminal/extraforaminal decompression requires significant removal of the facet joint,  which leads to instability and may further accel-erate the rate of degeneration [6].  However,  limiting bony removal to prevent instability may lead to inade-quate decompression.  The literature reports good results with minimally invasive surgery (MIS) tech-niques (microscopic/endoscopic),  provided that ade-quate decompression of the root is achieved [7-9].  The use of navigation for extraforaminal decompression of October 2021 Navigated Endoscopic Decompression 639A BFig. 5　 A,  A preoperative computed tomography (CT) scan sagittal section shows osteophytes at the L5-S1 foramen on the left side (white arrow); B,  A preoperative CT scan axial section demonstrates osteophytes at the L5-S1 foramen on the left side (white arrow).A BFig. 6　 A,  A postoperative CT scan sagittal section shows adequate decompression of the foramen and extraforaminal stenosis (white arrow); B,  A postoperative CT scan axial section demonstrates adequate decompression of the foramen and extraforaminal stenosis (white arrow).the L5 root has been recently studied with good surgical outcomes [10].Adding O-arm navigation to these procedures pro-vides 3D image guidance and thus helps with accurate placement of the tube.  Other benefits are safe decom-pression of the root,  the adequacy of the decompres-sion,  and precision in the degree of facet resection,  thus avoiding additional instability.  The use of a navi-gated burr during the procedure reduces the surgical time and ensures safety during the decompression.  An L5-S1 bony spur that compress the L5 nerve from the ventral aspect can be removed with a navigated burr accurately and safely.  Navigation accuracy may decrease if the RF is attached to the operation table instead of to the patient as the distance between the navigated instruments and the RF is greater and there may be movement [11].  If the RF is attached to the spi-nous process away from the target disc space,  naviga-tion accuracy may be hampered.  Guha reports in a quantitative study that working within 2 levels to the RF minimizes the risk of navigational error [12].  In our procedure,  the RF is placed percutaneously into the contralateral iliac bone through the sacroiliac joint,  so it is very stable and close to the L5-S1 disc space.  A small stab incision is sufficient for RF placement.  With this technique,  we can reduce radiation exposure for the surgeon and the operating room staff at centers where a large number of MIS procedures are performed.  There might be concern about radiation exposure to the patient.  We usually use a small field of view (FOV) and the low-dose mode of the O-arm 3D scan,  so one scan takes 24 sec.  The radiation/second of O-arm 3D scan-ning is 4 times that of fluoroscopy,  so one O-arm scan is the equivalent of approximately 1.5 min of fluoros-copy in terms of radiation measurement [13].Although there are many advantages,  there are also certain drawbacks to the procedure,  such as the need for infrastructure and instruments,  and an additional stab incision for the navigation reference frame.  Additionally,  the accuracy of navigation may be com-promised due to movement of the RF,  and a new scan may be needed in such a situation.ConclusionO-arm and navigation-guided C-arm-free endo-scopic L5 root decompression is a safe and effective procedure.  There is no radiation hazard to the surgeon or operating room staff.References 1. Wiltse LL,  Guyer RD,  Spencer CW,  Glenn WV and Porter IS: Alar transverse process impingement of the L5spinal nerve: the far-out syndrome.  Spine (Phila Pa1976) (1984) 9: 31-41. 2. Matsumoto M,  Chiba K,  Nojiri K,  Ishikawa M,  Toyama Y and Nishikawa Y: Extraforaminal entrapment of the fifth lumbar spinal nerve by osteophytes of thelumbosacral spine: anatomic study and a report off our cases.  Spine (Phila Pa 1976) (2002) 27: E169-173. 3. Kotil K,  Akcetin M and Bilge T: A minimally invasive transmuscu-lar approach to far-lateral L5-S1 level disc herniations: a prospec-tive study.  J Spinal Disord Tech (2007) 20: 132-138. 4. Lee S,  Kang JH,  Srikantha U,  Jang IT and Oh SH: Extraforaminal compression of the L-5 nerve root at the lumbosacral junction:  clinical analysis,  decompression technique,  and outcome.  J Neurosurg Spine (2014) 20: 371-379. 5. Abdelgawaad A ,  Babic D,  Siam A and Ezzati A: Extra-foraminal microscopic assisted percutaneous nucleotomy for foraminal and extraforaminal lumbar disc herniations.  Spine J (2018) 18: 620-625. 6. Haher TR,  Oʼbrien M,  Dryer JW,  Nucci R,  Zipnick R and Leone DJ:  The role of the lumbar facet joints in spinal stability: identifcation of alternative paths of loading,  Spine (Phila Pa 1976) (1994) 19:  2667–2671. 7. Kotil K,  Akcetin M and Bilge T: A minimally invasive transmuscu-lar approach to far-lateral L5-S1 level disc herniations: a prospec-tive study.  J Spinal Disord Tech (2007) 20: 132–138. 8. Pirris SM,  Dhall S,  Mummaneni PV and Kanter AS,  Minimally invasive approach to extraforaminal disc herniations at the lumbo-sacral junction using an operating microscope: case series and review of the literature,  Neurosurgical Focus (2008) 25: E10. 9. Zhou Y,  Zheng WJ,  Wang,  Chu JTW,  Li CQ,  Zhang ZF and Wang WD: The clinical features of,  and microendoscopic decom-pression for,  extraforaminal entrapment of the L5 spinal nerve,  Orthop Surg (2009) 1: 74–77.10. Stavrinou R,  Härtl B,  Krischek C,  Kabbasch A and Mpotsarisand R:  Goldbrunner,  Navigated Transtubular Extraforaminal Decompression of the L5 Nerve Root at the Lumbosacral Junction: Clinical Data,  Radiographic Features,  and Outcome Analysis,  Biomed Res Int (2016) 5: 1-6.  11. Fujiwara Y,  Tan Y,  Kadiri V,  Uotani K,  Yamauchi T and Tanaka M:  Intraoperative O-arm navigation guided anterior cervical corpec-tomy and fusion with minimally invasive cervical pedicle screw fix-ation (MICEPS) for severe ossification of the cervical posterior lon-gitudinal ligament (OPLL): A technical note.  Interdicip Neurosurg (2021) 23: May (in press).  12. Guha D,  Jakubovic R,  Gupta S,  Fehlings MG,  Mainprize TG,  Yee A and Yang V: Intraoperative Error Propagation in 3-Dimensional Spinal Navigation From Nonsegmental Registration: A Prospective Cadaveric and Clinical Study.  Global Spine J (2019) 9: 512-520.  13. Prodʼhomme M,  Sans-Merce M,  Pitteloud N,  Damet J and Lascombes P: Intraoperative 2D C-arm and 3D O-arm in children:  a comparative phantom study.  J Child Orthop (2018) 12: 550-557.640 Mehta et al. Acta Med.  Okayama　Vol.  75,  No.  5

Transtubular Endoscopic Posterolateral Decompression of the L5 Root under Navigation and O-arm: A Technical Note

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Transtubular Endoscopic Posterolateral Decompression of the L5 Root under Navigation and O-arm: A Technical Note

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