Background
Endoscopic surgery has demonstrated its effectiveness against disc herniations. However, there are limitations in its use in removing a highly up-migrated lumbar disc in hidden zone. This study aimed to introduce the biportal endoscopic approach for the treatment of a highly up-migrated lumbar disc and to report the preliminary surgical outcomes.
Methods
This study included 28 patients with a highly up-migrated lumbar disc who underwent biportal endoscopic surgery through one-level above contralateral corridor for disc removal. Patients were re-evaluated by postoperative MRI to confirm the successful removal of ruptured fragments. Simple X-ray was obtained for assessing the development of spinal instability. Back and leg pain were evaluated using Visual Analog Scale (VAS) scores. The satisfaction rate of clinical outcomes was assessed using the modified MacNab criteria.
Results
The mean age of patients was 62.3 years, and the mean follow-up period was 21.4 months. Compared to preoperative scores, VAS scores of back and leg pain significantly improved. At the final follow-up, two patients had unfavorable outcome due to the presence of residual leg pain. There was no new development of segmental instability or spondylolisthesis.
Conclusions
Biportal endoscopic approach with one-level above contralateral corridor may be an alternative treatment method for a highly up-migrated lumbar disc, with advantages including direct visualization of the hidden zone from the tail of ruptured fragment to the ruptured site, preservation of the facet joint and pars interarticularis.

Background
Endoscopic spinal surgery for lumbar foraminal lesions comes to be more popular recently. Bleedings around the foramen during extraforaminal endoscopic approach could make surgical filed turbid and more difficult to perform procedures safely. There were, however, few reports and insufficient information about vascular geometry around the foramen. Purpose: To report lumbar foraminal vascular geometry to help endoscopic spinal surgery underwent well and decrease technical complications by control of bleeding.
Materials and Methods
We reviewed operating record movie clips of extraforaminal approach using biportal endoscopic spine surgery (BESS). Several bleeding foci were matched with previously reported vascular anatomy and vascular geometry was modified to adapt to endoscopic view.
Results
There were four main arterial branches coming out from the lumbar segmental artery. Inferior articular artery, superior articular artery, inter-articular artery and radicular artery could be faced in order during extraforaminal approach using BESS. To escape heavy bleeding from the inferior articular artery and superior articular artery, the dorso-distal surface of transverse process (TP) should be exposed to make a working space without scratching the proximal area of the TP and dorsal surface of the facet. Inter-articular artery was hidden and covered under the capsule overlying superior articular process. Radicular artery was running along the midline of the root under the foraminal ligamentum flavum.
Conclusion
The information of the geometric location of the four arterial branches could help to escape heavy bleeding on extra-foraminal approach and control the bleeding foci to prevent postoperative hematoma.