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.

The foramen of L5-S1 can develop several degenerative diseases such as extraforaminal lumbar disc herniation, foraminal stenosis with disc height collapse, degenerative or spondylolytic spondylolisthesis, and far-out syndrome. The floating technique in biportal endoscopic spine surgery (BESS) keeps a certain distance between instruments and spinal structures. 1) This key point makes the floating technique different from conventional endoscopic surgery, which uses the Kambin’s safe triangle as a work zone. The floating view can enable the surgeon to see the structures panoramically, under high magnification: consequently, fine discrimination of their margin and safe manipulation of neural structures can be guaranteed. A certain gap between the floating scope and lesion can permit various instruments, generally used in open spine surgery, to be inserted from the sides with fewer limitations. Extraforaminal or foraminal lesions under the lamina can be reached by avoiding the iliac crest, and total facetectomy, which has the potential of iatrogenic instability, is not required to explore the foraminal structures. However, the floating view can be obstructed by small bleeds from laminectomized bone and/or surrounding vessels. This present article describes the technique and provides tips on how to perform BESS with floating technique safely and successfully for various lesions at the L5-S1 foramen.

Background
Owing to its new introduction, there are few documents on pit-falls of biportal endoscopic spine surgery (BESS) clinically. The authors reported etiologies in need of early exploration after BESS for lumbar degenerative diseases and strategies to overcome them.
Methods
BESS were performed for lumbar spine diseases (LSDs) by two spine surgeons from December 2013 to March 2016. Postoperative MRI was checked for all cases and following-up MRIs in the case in need of revision surgery within six months after the first surgery due to pain intolerable, sustained or recurred. The complicated cases were reviewed and classified as radiographic and operative findings to reveal the main reasons for early explorations.
Results
The 562 cases (M:295, F:267, Age 58.5±14.1 yrs, 20~88 yrs) included lumbar disc herniation (LDH) (255 cases), extraforaminal disc herniation (22 cases), spinal stenosis (218 cases), degenerative spondylolisthesis (27 cases), revision surgery after recurred disc herniation or restenosis after open surgery (24 cases), juxtafacet cyst (11 cases), adjacent segment stenosis with fusion surgery (3 cases), and spondylolytic spondylolisthesis (2 cases). Early explorations were needed in 43 cases (7.7%) at 26.1±31.5 days after the initial operations. Causative etiologies were listed as recurred LDH (12 cases, 27.9%), remnant stenosis (7 cases, 16.3%), remained ruptured disc fragment (6 cases, 14.0%), root edema (5 cases, 11.6%), synovitis (4 cases, 9.3%), hematoma (3 cases, 7.0%), dura tear (2 cases, 4.7%), recurred stenosis (2 cases. 4.7%), wrong level (1 case, 2.3%) and postoperative fungal infection (1 case, 2.3%). Thirty-one cases (72.1%) were revised within 4 weeks and most conditions (40 cases, 93.0%) were improved after early exploration using BESS. Two cases of dura tear were conversed to open repair. One case of fungal infection was suspected to related with the patient’s medical illness including long-term steroid use for chronic lung disease with pulmonary fibrosis and Diabetes mellitus.
Conclusions
Preoperative planning should be prepared carefully to decrease early exploration. It was helpful to comparing MRIs immediately postoperative and early following-up to find the reasons. Don’t hesitate to explore the operated site again using BESS, because most etiologies are supposed to be controlled by early exploration without need of converting to open surgery except in the case of dura tear in need of dural repair.