In recent years, unilateral biportal spinal endoscopic surgery has gradually revived. South Korean scholars have especially made great contributions to this field [24–26], elevating the procedure from pure decompression to endoscopic fusion, and accelerating the development of this technology worldwide.
At present, biportal endoscopic spinal interbody fusion reported in the literature mostly represents transforaminal lumbar interbody fusion (TLIF) [27–29], while some authors also adopt posterior lumbar interbody fusion (PLIF).
During BLIF in this study, unilateral or bilateral spinal canal decompression could be performed through the interlaminar approach under full endoscopic view: one facet joint was removed to preserve the lateral bone wall of the superior facet to protect the nerve root outlet from injury: and the resected bone was collected for subsequent autologous bone grafting. The space between the traversing root and the exiting roots could be noticed clearly, and the ligamentum flavum was cut laterally from the center to expose the dural sac, nerve roots, and other tissues in the spinal canal. Nucleus pulposus forceps, curettes, and reamers were used to remove the nucleus pulposus and strip the cartilage endplate tissue. Further, the endoscope could be extended into the intervertebral space for exploration to ensure that the cartilage endplate was fully scraped and the bone endplate was exposed.
Notably, a special channel could be placed for intervertebral bone grafting and a specially-designed retractor was used to fully expose the incision and protect the nerve root(Fig. 5). Thus, the cage could be implanted into the intervertebral space with the assistance of endoscopy and fluoroscopy, which is undoubtedly an advantage over uniportal endoscopy . The internal fixation method is similar to that of minimally invasive TLIF (MIS-TLIF), and is done using a percutaneous pedicle screw system with fluorocopy-guided screw placement. In BLIF, percutaneous screws can be placed using the original channel.
In the realm of uniportal endoscopic fusion, Chinese peers have put in great efforts. Wu, et al.  in a conducted a retrospective study compared open TLIF and endoscopic TLIF (Endo-TLIF) for VAS and ODI. They concluded that full-endoscopic TLIF is feasible for the treatment of single-segment lumbar degenerative diseases, and is characterized by less trauma, quick recovery, and low cost.
A meta-analysis  compared Endo-LIF and MIS-TLIF. Based on the evidence generated by their study, there was no significant difference in the clinical efficacy and safety between Endo-LIF and MIS-TLIF for the treatment of lumbar degenerative diseases. Although Endo-LIF had a longer operative time, it had the advantages of lesser tissue trauma and rapid recovery after operation.
At present, Endo-LIF and MIS-TLIF are the mainstream and classic techniques of lumbar endoscopic fusion surgery. However, comparisons between biportal endoscopic lumbar interbody fusion and uniportal endoscopic lumbar interbody fusion have rarely been reported.
In this study, a retrospective analysis was conducted to compare the operative time, complications, VAS, ODI, and radiological outcomes between biportal endoscopic fusion and uniportal endoscopic fusion. There was no significant difference in VAS and ODI between the two procedures. Compared with uniportal endoscopic fusion surgery, biportal endoscopic fusion surgery takes lesser time and has a higher fusion rate. In the author's opinion, this could be mainly attributed to the fact that in the biportal endoscopic technique, 30° endoscopy enables a wider surgical field of vision, greater maneuverability of instruments, and thus a broader, more thorough, and more efficient decompression range. In addition, compared with the uniportal alternative, the cage can be placed and transversely under biportal endoscopic visualization, which makes the placement of the cage more consistent with the mechanical effect. This is perhaps the reason for the higher fusion rate. At the same time, we also believe that biportal endoscopic fusion surgery, which does not rely on specialized instruments but uses traditional open surgical ones, is associated with a better learning curve than the uniportal endoscopic technique.