Degenerative lumbar foraminal stenosis is relatively common condition in which the circumferential narrowing of the space available for the nerve root leads to back pain and radicular symptoms. The preferred surgical treatment to relieve the compression of the nerve root has not been established yet. Recently, several reports have shown good clinical outcomes in patients who underwent biportal endoscopic decompression for the treatment of degenerative lumbar foraminal stenosis. The floating-type biportal endoscopic technique could be used with various surgical instruments without docking in the narrowed foramen, unlike the full-endoscopic technique. Multiple sites can be accessed with more freedom in the approaching angle through triangulation and portal switching. We reviewed articles to understand putative outcome factors and discuss the appropriate indications for biportal endoscopic foraminal decompression. Lumbar lordosis, degenerative lumbar scoliosis, height of the posterior intervertebral disc and level of procedure were all related to clinical outcomes. The best indications and contraindications to the endoscopic foraminal decompression still depends on the surgeon’s skill level and evolving experience. However, we could suggest that biportal endoscopic spinal surgery is supposed to be an alternative treatment for foraminal decompression preserving motion and stability, and decreasing the need for fusion surgery in various lumbar degenerative disease.
Among, degenerative lumbar spinal disorders, degenerative foraminal stenosis is a relatively common condition in which a nerve root is entrapped in a narrowed foramen, with a reported incidence of ~8-11% [
Contemporary studies on the degeneration of the lumbar spine have determined that age-related degeneration of the intervertebral disc eventually results in instability of the spinal segment. The ensuing hypermobility is associated with thickening of soft tissues in the foramen, followed by hypertrophy of the facet joints, particularly at the superior articular process (SAP) [
Several different surgical techniques for degenerative lumbar foraminal stenosis have been used, including foraminotomy, facetectomy, partial pediculectomy, fusion, and distraction instrumentation. Spinal fusion has been the standard treatment for patients with degenerative lumbar foraminal stenosis associated with preoperative instability or deformity. However, facetpreserving decompression is a more desirable primary treatment for patients with degenerative lumbar foraminal stenosis in the absence of gross instability. With the advancements in minimally invasive surgery, many surgeons have reported good results with facet-preserving decompression and endoscopic partial facetectomy in the treatment of degenerative lumbar foraminal stenosis [
Conventional surgical methods for the treatment of lumbar foraminal or far lateral stenosis can be categorized as total facectectomy with or without fusion and facet-preserving foraminotomy. Total facetectomy offers sufficient decompression through the nerve root course. However, this often leads to segmental instability and back pain [
Hijikata and Kambin separately introduced percutaneous nucleotomy and Kambin further described the safe triangular zone (Kambin’s triangular zone) for docking and working on the transforaminal region [
Instruments including standard spine instruments, 0° and 30° 4 mm diameter endoscopes, radiofrequency probe, and endoscopic drills were used. Endoscopes with different viewing angles were used alternately, depending on the operative field. The procedures were operated under epidural or general anesthesia, and the patients were positioned prone, with the abdomen free. Level confirmation was conducted under intraoperative fluoroscopy. Under anteroposterior C-arm fluoroscopic imaging parallel to the upper endplate of the proximal vertebral body at the operative level, the upper and lower pedicles and their transverse process were marked. One-centimeter incisions were made 2 cm lateral to the lateral margin of the pedicle line on the mid-line of each of the two transverse processes (
In order to perform biportal endoscopic spine surgery, two portals must be created. Spinal needles were temporarily introduced through the skin incision to confirm triangulation of the viewing portal and working portal under C-arm fluoroscope. Initially, a 0 degree scope was inserted through viewing portal, and a saline irrigation pump was connected to the endoscope, set to a pressure of 25-30 mmHg during the procedure, and controlled within this range depending on the condition of the surgical view. Keeping the sheath for the working portal is helpful to maintain stable continuous saline flow. Soft tissues was gently detached from the lateral edge of the isthmus of the lamina, facet joint and transverse process of the targeted intervertebral foramen with a small periosteal elevator or radiofrequency probe. After exposing the lateral edge of the isthmus, facet joint, and transverse process, soft-tissue remnants and bleeding were effectively managed by a pituitary rongeur and radiofrequency probes (
The tip of the superior articular process (SAP) of the facet joint was resected and removed using a curved chisel, pituitary rongeur, and Kerrison punch. It is difficult to remove the resected tip of the SAP at once under the endoscope due to its large size; therefore, removing the tip of the SAP is a time-consuming process. After resection of the tip of the SAP, the ligamentum flavum was detached and removed from the undersurface of the isthmus of the lamina (the entrance of foramen) using a specially designed angled curette, upward-curved Kerrison punch, and upward-curved pituitary rongeur. After flavectomy, the exiting nerve was exposed and the decompression procedure around the nerve was performed using the Kerrison punch and curettes (
The end point of decompression is the free mobilization of the exiting nerve root and the dural sac containing the traversing nerve root. Additional discectomy was performed in the case of disc protrusion or extrusion contributing to the foraminal stenosis. If an annulotomy was required, it could be performed using a Penfield dissector or micro-knife. After adequate hemostasis with a radiofrequency probe, a drain was inserted through the working portal and the endoscope and instruments were extracted. The skin was repaired with a skin bond after a 1-point subcutaneous suture.
In case of lumbar spinal stenosis, patients usually have several types of stenosis with (1) hypertrophic ligamentum flavum and disc protrusion leading to lateral recess stenosis, (2) foraminal compression with foraminal disc protrusion, syndesmophytes, and facet hypertrophy decreasing the anteroposterior diameter or overriding the superior articular facet, decreasing foraminal height with pedicle impingement, and (3) extraforaminal decompression. Sometimes, two separate approaches to decompress both lateral recess and foraminal/extraforaminal nerve root compression are required [
By manipulating and tilting the endoscope, the undercutting of the central and contralateral lamina can be achieved, while the deep layer of the contra-lateral ligamentum flavum (LF) is prevented from expanding the dural sac. After removing the deep layer of the contra-lateral LF with rongeurs, pituitary forceps, and SAP resection with a curved chisel, the whole ventral dural sac is visualized. The lateral margin of the contralateral dura is followed by a dural retractor, and the shoulder of the contralateral traversing nerve root is visualized. This area is further decompressed using a curved Kerrison rongeur and angled curettes. The lateral margin of the dura of the traversing nerve root is visualized without constriction when it is easily retracted using a ball-tipped nerve hook. The endoscope is angled cranially to decompress the exiting nerve root on the contralateral side of the foraminal region. The contralateral lower lamina of the cranial vertebra is drilled off further with the burr, until the exiting nerve root at the foraminal region is visible. At this point, the foraminal area is decompressed with an angled bone curette and curved foraminotomy rongeurs until the exiting nerve root is visualized free of constrictions; it is also retractable with a ball-tipped nerve hook.
Lee’s foraminal stenosis classification was commonly used to define the location of the offending pathology within the foramen by dividing it from medial to lateral into the entry (dural to pedicle; zone 1), middle (medial pedicle wall to center pedicle; zone 2) and exit (center pedicle to the lateral border of the facet joint; zone 3) zones [
Spinal stability after conventional spinal surgery has always been an issue. Many surgeries have been performed due to spinal instability yet, there is no clear definition of spinal instability. It is most widely believed that the loss of the normal spinal pattern of motion causes pain or neurologic dysfunction [
Instability after resection of the SAP may be of concern. Biomechanical studies have reported that graded facetectomy greater than 50% markedly affect the translational and rotational stabilities of the movable segment [
Decompression Over Full Endoscopic Procedure The primary advantages of endoscopy-assisted spinal surgery have been reported in several papers [
Secondly, far lateral stenosis caused by L5-S1 level of the hypertrophied sacral ala is limited by the full endoscopic technique, whereas the biportal endoscopic technique is able to solve the body decompression by instruments such as the osteotome and the endoscopic drill via another portal. Third, as a condition for successful decompression, the SAP in the foramen must be completely removed until the ligamentum flavum is exposed, and the exiting root must be fully decompressed from the entrance of the foramen to the extraforaminal area. However, in the case of open microscopic decompression or full endoscopic decompression, access to the inside of the L5-S1 foramen is not easy due to the iliac crest. With biportal endoscopic spine surgery, multiple sites can be accessed with more freedom of approaching angle through triangulation and portal switching. When using a 30° endoscopy, various views can be obtained through rotation.
Open decompression surgery using the Wilte approach is a conventional decompression surgery for extraforaminal or foraminal stenosis. Open microscopic foraminotomy reports a success rate of 72-83%, though it has a lower success rate compared to other spinal surgeries [
Several authors have serendipitously found that actual symptoms do not always correspond to the imaging degree of foraminal stenosis [
It is well known that sagittal spinal balance is significantly associated with the postoperative quality of life of patients with spinal deformities [
Yamada et al. [
The heights of the posterior intervertebral disc could be one of the factors that affect clinical outcomes because disc space narrowing is likely to cause root compression. Lewandrowski et al. [
There must be several technical pitfalls and complications in the learning curve of biportal endoscopic foraminal decompression. Muscle edema, hydro-peritoneum, incomplete decompression, blurred surgical view, and injury of the radicular artery due to unfamiliar or misunderstanding of the anatomic structure were present. Muscle edema occurred due to a poor saline output; inserting a cannula through the portal could be helpful. If orientation were lost without touching the transverse process, the psoas muscle layer could become penetrated, and infused saline could make a hydro-peritoneum. If it is difficult to determine the exact location of the structure, the positioning of the endoscope should be rechecked using a fluoroscope.
Controlling small bleeds from the vessels and radicular artery was very important to make a clear surgical field and not to injure the root. A blurred surgical field due to small bleedings interrupted the procedure frequently. Small vascular bleeding could be controlled using 1.5 mm radiofrequency coagulation under the very lowest setting of energy. The hypertrophied tip of the SAP should be removed sufficiently to decompress the root and prevent dynamic stenosis at the foramen [
Careful analysis of CT and MRI images is vital to planning the amount of foraminal decompression with consideration of the anteroposterior and superior-inferior diameter of the foramen. Such planning avoids unnecessary endoscopic foraminal exploration. When intraforaminal lesions are treated, it is important to use a 30° endoscope with a specially designed angled curette, an upward-curved Kerrison punch, and an upwardcurved pituitary rongeur. Clinical findings with concordant imaging are key in patient selection. Preoperative clinical and radiological assessments for gross anteroposterior and lateral instability are essential. We need further research to predict poor progression factors after endoscopic foraminal decompression.
It is not clear yet which indication is best for biportal endoscopic foraminal decompression. The best indications and contraindications to the endoscopic foraminal decompression still depends on the surgeon’s skill level and evolving experience. Also, several papers suggested less durable outcomes in patients with complex foraminal stenotic lesion and combined severe central stenosis. Stratifying patients based on the underlying compressive pathology and appropriate skill level of the endoscopic spine surgeon attempting the decompression may facilitate achieving the goals of the endoscopic surgery [
Through the studies about endoscopic partial facetectomy for foraminal stenosis, the results revealed that endoscopic facectectomy seems not to alter spinal stability when compared with conventional surgeries. We hypothesize that this is due to the reduced tissue destruction similar to that seen with tissue sparing conventional facetectomy. Thus, the ligament structure of the spine is held mainly intact which has been shown to be important for the structural integrity of the spine. Biportal endoscopic spinal surgery is supposed to be an alternative treatment for foraminal decompression in various foraminal stenosis conditions while preserving motion and stability and decreasing the need for fusion surgery to relieve various lumbar degenerative diseases.
No potential conflict of interest relevant to this article.
Ⓐ: C-arm fluoroscopic image A-P view. Black line: Endoscopic portal incision. White line: instrumental portal incision. Black circle: pedicles. Ⓑ : C-arm fluoroscopic image lateral view.
Ⓐ : Left-side approach endoscopic foraminal view. After making initial working space, physician can identify the foraminal anatomy. Ⓑ : After partial resection of SAP tip.
Left-side approach. The radicular artery located laterally of superior articular process (SAP). Black arrow shows radicular artery before coagulation Ⓐ and after coagulated state Ⓑ by RF probe.
Ⓐ: Left-side approach endoscopic foraminal view. Exposure of the tip of superior articular process(SAP) is first step for entering the foramen. Ⓑ: After resection of the tip of SAP, the ligamentum flavum covering the exiting root was identified. Ⓒ: Under the LF, the exiting root was located. Ⓓ: After removal of LF, all foraminal anatomy was identified.
Ⓐ: Left-side approach endoscopic foraminal view. Discectomy using Kerrison punch. Ⓑ : Bony spur can be easily resected by endoscopic burr. Ⓒ: Identify the cranial surface of root using hook. Ⓓ: Decompression procedure around the root was done.
Ⓐ: Right-side approach and Left–side contralateral decompression. Sub-laminotomy is important to make working space. Ⓑ: After contralateral flavectomy, contralateral traversing root is easily identified. Superior articular process (SAP) and inferior articular process (IAP) were seen. Ⓒ: The herniated disc should be removed to decompress the traversing root. Ⓓ: After partial removal of the tip of superior articular process SAP, contralateral exiting root and medial wall of pedicle are identified.