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Unilateral Biportal Percutaneous Transforaminal Endoscopic Lumbar Foraminal Decompression and Discectomy: A Technical Note
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.344669
Keywords: Biportal endoscopic spine surgery, lumbar canal stenosis, pars interarticularis, superior articular process
Minimal invasive spine surgery (MISS) using the percutaneous transforaminal endoscopic discectomy/decompression (PTED) is commonly performed and is found to be safe and effective in experienced hands.[1],[2] This can be performed by either a uniportal or biportal endoscopic technique. This article describes in detail the technique of PTED using a biportal endoscopic spine surgery technique.
The video in the article describes the technique of unilateral biportal endoscopic spine surgery for lumbar foraminal stenosis. The video describes the relevant surgical anatomy required to perform this surgery. Using this technique the left L4-5 foramen was decompressed and discectomy was done. Case description: A 70-year-old man presented with progressive neurogenic claudication and with numbness in the left L4 dermatome for six months. His claudication distance was 200 m. He had decreased sensation in the left L4 dermatome to all modalities of sensation by 50%. His MRI showed severe canal stenosis of left L4-5 foramen secondary to disc prolapse. X-ray showed degenerative changes at L4-5 level. There was no listhesis. This is depicted in [Figure 1].
To effectively perform PTED one should be familiar with the surgical anatomy of the neural foramen and its contents. The neural foramina is occupied by the exiting nerve root, radicular artery, and venous plexus. The radicular arteries are the direct branches from the abdominal aorta. They are frequently paired and well seen from L1 to L4 levels and infrequent at L5 level. The radicular artery is located superior to the exiting nerve root.[3] The exiting nerve root and the dorsal root ganglion occupy the superior aspect of the neural foramina. Kambin's triangle an empty zone (E) described by Parviz Kambin in 1980 is the safe surgical corridor for the paraspinal approach to the disc space. The triangle's hypotenuse is formed by the exiting nerve root. The inferior border is formed by the inferior end plate of the target disc space. The posterior or the vertical part of the triangle is formed by the lateral edge of the superior articular process (SAP). The superior articular process of the lower vertebrae is the key anatomical landmark for the foraminal approach.[4] This is depicted in [Figure 2].
Indications and contraindications PTED technique can be safely applied in treating paracentral lumbar disc herniations (LDH) and is very effective in dealing with far lateral LDH and foraminal LDH. It is also effective in treating lateral recess and foraminal stenosis.[1],[2] PTED is contraindicated in patients with spondylolisthesis, discitis and bleeding diathesis.[2]
Anesthesia: All PTED surgeries are performed under Propofol sedation with erector spinae regional block. Under ultrasound guidance, a 20-G epidural needle is inserted along the plane of the transducer until the tip hits the transverse process of L1. A volume of 30 ml of 0.5% ropivacaine along with 2.5 mg of dexamethasone and 0.1 mg epinephrine is injected selectively at the L1 transverse process, erector spinae, muscle, and fascia. This is repeated on the other side. This is ideal for surgeries being performed from L1 to L5 levels. There are no hemodynamic changes associated with this block. This paraspinal block also provides good postoperative analgesia.[5],[6] Position Patient is positioned prone on Wilson's frame. Care is taken to protect the eyes and the abdomen and to avoid pressure at bony prominences. The area is cleaned and prepped using standard surgical principles. Equipments The procedure requires a 3.5-mm spherical bur (Conmed Linvatec), 0°(Zero degree arthroscope) 4-mm-diameter endoscope (Conmed Linvatec), bipolar flexible radiofrequency probe (Ellman Trigger-Flex probe, Ellman International), 3.5 mm VAPR radiofrequency (RF) electrode (DePuy Mitec), Working cannula (designed by senior author Eum), serial dilators (size 1, 2, 3) a specially designed T shaped soft tissue dissector, standard laminectomy instruments, such as hook dissectors, Kerrison punches, straight and curved curettes and pituitary forceps [Figure 3].
Placement of portals Under C arm fluoroscopic guidance, the upper and lower pedicles at the required disc space, and the upper and lower endplates along with the transverse processes are marked. Using a spinal needle (22G) the isthmus or the pars interarticularis (P) is identified and marked. Since identification of the superior articular process (SAP) is difficult on an AP and lateral fluoroscopic imaging it is emphasized that identification of pars interarticularis helps in correct placement of the portals. After confirming the level of pars interarticularis, the skin incisions are made 1 cm above and below to facilitate the working portal and the scopy portal. Usually skin incision is made 2-3 cm from the midline. For a right-handed surgeon approaching from a left side the working portal is below and scopy portal is above [Figure 4] and [Figure 5]. It is vice versa if approached from the right side. This arrangement of the working and scopy portal is interchangeable.
Triangulation This is the most important step of a biportal endoscopic spine surgery (UBESS). After confirming the foramen of interest, the thoracolumbar fascia is infiltrated with local anesthesia (lidocaine). Then the first dilator is used to identify the pars, followed by creating the working space with the second and third dilator. The working cannula specially designed by the senior author (Eum) is used to facilitate easy passage of instruments. The scopy portal is made 2 cm above the distal portal. The T shaped dissector helps in detaching the muscles and soft tissues attached to the bony boundaries of the neural foramen. Triangulation between the scope and the RF probe is the key step before the foraminal dissection. Once the triangulation is complete it is ensured that there is adequate and free egress of normal saline used for irrigation [Figure 6].
Creation of surgical corridor RF probe is used to achieve hemostasis and to coagulate the muscle and fascia. Saline irrigation facilitates a clear visual field at the area of interest. The first step of surgery is to identify the pars-interarticularis (P) which is followed by identification of the superior articular process (SAP). The tip of the superior articular process (SAP) is excised using a drill and the empty zone (E) is reached by dissection. The attachments of the ligamentum flavum is identified and is excised. This will expose the fat and the exiting nerve root. Any bleeding during the dissection is controlled by the RF probe. Dissection is carried up to the pars interarticularis and by partially drilling the pars interarticularis the foraminal surgical corridor is created. This can be summarized as Pars interarticularis – Superior articular process—Empty zone–UP (dissection). (PSE-UP) [Figure 7].
Decompression is complete when we see the pulsations of the exiting nerve root and the thecal sac. If there is disc bulge or disc prolapse annulotomy is performed using a penfield dissector and the sequestered disc is removed. [Figure 8] At each level, C arm is used to confirm the position of the disc space.
Closure Hemostasis is achieved and after making sure the surgical corridor is clean the working portal is removed. Excess saline retained in the working space is drained by manual squeezing and suction aspiration. A suction drain (Hemovac, 50 ml) is placed and anchored with a stitch. The portals are closed with a subcutaneous stitch/ethilon and tissue adhesive is used to approximate the skin edges. Adequate sterile dressings are applied. [Figure 9]
Video link https://youtu.be/mMW9Bdw73T4 QR Code:
Video timeline with audio transcript:
After surgery patient had significant improvement in his symptoms. His postoperative period was uneventful. Postoperative MRI of the lumbosacral spine showed adequate decompression at the left L4-5 foramen, the root was free. There was no evidence of muscle damage. [Figure 10]
The most crucial step in the surgery is early identification of pars interarticularis (P), followed by identification of superior articular process (SAP), dissection in the empty zone of the Kambin's triangle. This can be summarized as P-S-E.[5] In contrast to open microsurgery, PTED has a steep learning curve. PTED is associated with complications related to the neural and arterial structures around the neural foramen. The incidence of nerve root injury and postoperative dysesthesias reported in the literature is close to 5% following a uniportal transforaminal endoscopic technique. The incidence of dural tear is less than 5%. Inadequate separation of the ligamentum flavum, due to incomplete sectioning of epidural ligaments which connects the flavum to the dura can lead to dural tear. This can be managed with tachycomb.[5],[7],[8] If the dural tear is over 1 cm endoscopic suturing can be done, if this is not successful, we need to convert to open surgery. In author's experience conversion of endoscopic surgery to open surgery to manage a CSF leak was required in only 1% of his case series. Epidural bleeding can be controlled with radiofrequency probe. Surgiflow helps in controlling the epidural bleeding.
Unilateral biportal endoscopic spine surgery (UBESS) provides a wider and clearer view of the surgical field, obviates the need for special endoscopic instruments, facilitates greater freedom of movement, is versatile, and enables better surgical manipulation and effective decompression, discectomy as compared to the uniportal technique and open surgeries.[5],[6],[9] UBESS is performed under sedation and regional anesthesia thereby reducing the chances of nerve injury as the patient can perceive pain and warn the surgeon if there is any inadvertent nerve handling.[5],[6] UBESS can be safely applied for degenerative pathologies from L1-S1. Iliac crest at L5-S1 level does not pose any surgical challenge as the approach is always medial to the iliac crest. UBESS offers many advantages with minimal pain at the operative site, reduced hospital stay, early rehabilitation, and less tissue damage at the site of surgery. It has a steep learning curve and offers excellent results in experienced hands.
UBESS is an ideal alternative to the uniportal endoscopic and minimal invasive microsurgery for foraminal, paracentral disc herniations, lateral recess, and foraminal stenosis. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
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