Minimally invasive spine surgery (MIS) has been introduced to our surgical armamentarium as a means to improve clinical outcomes by achieving a complete decompression [1] while minimizing soft tissue trauma and enabling a more rapid recovery. Endoscopic surgery has uniquely gained significant traction worldwide and has become the most promising MIS technique. The major benefits of endoscopic surgery include the mobility of the endoscope during the procedure, adjustable magnification by manipulating the endoscope depth in the operating field, and constant irrigation of debris and blood to attain clear vision by saline irrigation. With the endoscope and working instruments docked via serial dilation directly at anatomical region of interest, surgeons experience minimal soft tissue trauma and reduced blood loss. Two popular approaches have been described: uniportal surgery utilizes one channel for both endoscopic and surgical components, while biportal surgery uses 2 separate channels for both components [2].
For uniportal lumbar endoscopy, the 2 most popular approaches to lumbar discectomy are the transforaminal approach and the interlaminar approach [3,4]. For unilateral biportal endoscopic (UBE) surgery, a paraspinal approach is usually adopted for foraminal decompression and far-lateral disc herniations. Interlaminar decompression is commonly reserved for central or paracentral disc herniations. While the interlaminar approach is the standard for the lower lumbar spine, it has specific risks and drawbacks for upper lumbar segments. Anatomically, upper lumbar segments have narrower lamina and more vertically oriented facet joints, leading to potential isthmus fractures during laminectomy. In addition, the conus medullaris may be near, and with densely packed nerve roots in a narrow space for cerebrospinal fluid, there is limited margin for safe dural retraction. Hence, transforaminal approaches may be preferred to avoid these complications. Percutaneous endoscopic lumbar discectomy (PELD) has been reported [5] to be successful in management of upper lumbar disc herniations. This approach has yet been established for biportal users.
The authors in this article [6] introduce a far-lateral transforaminal UBE technique for lumbar discectomy, which is especially indicated for upper lumbar cases. A similar far-lateral trajectory to PELD is utilized via the UBE approach to safely manage central or paracentral disc herniations. No laminectomy is performed, hence there should be a low risk of segmental instability. Similar to other UBE surgeries, one endoscopic portal and one instrument portal are needed. Due to the length towards the structures of interest, a long semi-tubular retractor is required to ensure water flow at the instrument portal. The skin incisions are made 5–6 cm from the midline to adopt a very steep trajectory and to reach the neuroforamen.
In this retrospective study [6], 27 patients with L1–2, L2–3 or L3–4 central or paracentral disc herniation were treated via far-lateral transforaminal UBE lumbar discectomy. Various clinical outcome scores such as the Oswestry Disability Index and the visual analogue scale all improved for patients after successful discectomy. Interestingly patients required a longer postoperative hospital day than expected (average 3.6 days) despite a short operation time. It may be difficult to discern any reason for this, as there are too many external factors, including cultural reasons for postoperative stay. Fortunately, only one complication of postoperative discal cyst was described which required a revision decompression.
The surgeries were overall successful despite tackling several migrated herniations superiorly or inferiorly. These are expected to be challenging especially if they extend beyond the pedicle level due to limited visualization by the endoscope. In the authors’ experience, the 2 cases with high superior migration were removed because the herniated fragment was removed in one single fragment. This begs the questions: “how does the surgeon determine if the fragment is completely removed?” and “what is the fallback approach to deal with these retained discs?” Although the authors suggest that the disc fragments can be removed blindly using hook instruments, it creates uncertainty during the surgery. Without intraoperative imaging such as MRI, it may not be a completely safe indication. Despite the successful results presented, any migrated disc beyond the superior or inferior pedicle level should be considered as a contraindication for this approach especially in more inexperienced hands.
The authors suggest that upper lumbar segments have wider neural foramens. This is true in most situations. I commonly manage degenerative deformities, and in neglected idiopathic curves, the apical vertebra is often found at L1 or L2. Reaching the concavity of the curve may be challenging in such scenarios and may also be regarded as a relative contraindication. The authors rightly noted several factors that may preclude this approach specifically those that obstruct access, such as large superior articular processes. The surgical trajectory may also be obstructed for higher lumbar levels like L1–2. Skin incisions 5–6 cm from the midline may overlap with the lower rib, and this gap may be even smaller in deformity cases. A left-sided UBE approach may be easier with the endoscopy portal placed at the cranial incision since 30° endoscopes are available for better visualization. However, on the right-sided approach, the instrument portal may be hindered by the rib leading to more difficult bony and soft tissue work.
Despite the nuances that are noted above, the UBE approach provides a very clear visualization of the ventral aspect of the thecal sac. The biportal approach allows for constant irrigation inflow with a separate outflow portal to improve debris and blood clearance. This approach also provides direct visualization without thecal sac retraction for central and paracentral disc herniations. This avoids inadvertent neuropraxia as well as confirmation of complete disc removal which is potentially a risk for interlaminar approaches.
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