UBE surgery is a widely performed minimally invasive spinal surgery with satisfactory clinical outcomes, such as reduced pain and rapid recovery(14). Generally, specific instruments are required during conventional percutaneous endoscopic lumbar discectomy surgery, as well as shallow learning curve and a high rate of complications when applied for the treatment of lumbar spinal stenosis(15). The endoscopic instruments used in UBE could also be used in other surgeries, such as knee arthroscopy(8), greatly reducing medical expenses. Furthermore, the use of two channels, the viewing portal and the working portal, which are similar to those used in an interlaminar approach, is more in line with the surgical habits of spinal surgeons and allows full exposure of the area requiring decompression. However, there are still some shortcomings of UBE under certain conditions. On the one hand, it requires muscle splitting and shaving of the working space, which may cause bleeding affecting the surgical field and prolong the operative duration. On the other hand, laminotomy and foraminoplasty are usually performed in UBE by piezosurgery, and the high-frequency ultrasonication of piezosurgery causes the surgical field to become turbid, increasing the difficulty of the procedure for the surgeon.
Considering these disadvantages of UBE surgery, we designed a simple device for establishing the surgical portals. This device is versatile, allows a sufficient range of motion for surgical instruments and continuous irrigation, and is both readily available and relatively inexpensive. Such a device could be easily regulated by assistants, enabling prompt changes in the water flow volume and operating space. If the surgeon needs a clearer visual field under endoscopy or a temporary space for instrument movement, the assistant can gently tighten the strap to complete the operation (Fig. 3). Obviously, the convenience of this design is that the surgical space can be temporarily regulated without excessive muscle tissue ablation and the consequent minor damage. Meanwhile, the Y-shaped drainage device applied in our method provides a temporary fulcrum for the working portal, which is conducive to stable operation by the spinal surgeon and reduces the risks associated with equipment slippage. In addition, unlike stainless steel or titanium alloy, our drainage device is made from a soft plastic suction tube (an inexpensive material that is easy to trim), which can yield to the moving instruments while providing the stiff support required during surgery, thus increasing the convenience of the operation (Fig. 2). In addition, such a device could be temporarily fixed to the skin by silk thread without requiring long-term support from a surgical assistant.
Our study demonstrated that this modified portal design for UBE surgery was a feasible and effective technique for use in the treatment of single-level lumbar degenerative disease, including stenosis and disc herniation. The clinical outcomes of biportal endoscopic decompression at 12 months after surgery confirmed the advantages of UBE. As mentioned above, there were significant improvements in the mean VAS scores for leg pain and back pain, as well as in the ODIs during the follow-up period compared with preoperatively (Table 3). Furthermore, the endoscopic operative duration was 71.04 minutes per level, with an average channel establishment time of only 5.20 minutes (Table 2). In fact, the time for establishing a surgical portal notably decreased as experience was gained. This result also means that surgeons could quickly grasp the essentials of channel establishment with short-term training and avoid excessive increases in the operative duration, thereby reducing unnecessary damage to patients.
In addition, UBE surgery with the modified portal technique also showed less postoperative drainage (data not shown). The drainage tube was once routinely inserted into the operative cavity in the first few patients. However, we found that the amount of postoperative drainage was very small, and the extubation time was only one day after the operation. Therefore, whether the drainage tube needed to be placed was only dependent on the situation during our surgery. This result is not consistent with that of a previous study, which claimed that saline used for irrigation during the operation would infiltrate into the surrounding muscle and leak into the drain after surgery, which might be the reason for the greater drainage volume(16). This difference may be due to our shorter operative duration, the use of high-definition imaging, and the application of a radiofrequency probe and piezosurgery during the operation, all of which minimized the risk of bleeding in small vessels and cancellous bone. More importantly, the Y-shaped drainage device was conducive to the discharge of saline, thus greatly decreasing the remaining irrigation fluid. We also believe that reducing the need for drainage tube placement would support patient activity in the early postoperative period and the concept of rapid recovery from minimally invasive surgery.
Despite the potential superiority of UBE surgery, signs of muscle oedema were still detected on postoperative magnetic resonance imaging. Nevertheless, the complications were limited to one case of dural tear (2.0%), one case of revision surgery (2.0%), and there were no cases of symptomatic haematoma, infection (Table 2).
Several limitations of the current study should be addressed. First, all surgeries was done by a single surgeon. The relatively small sample size is another limitation. Moreover, to facilitate a standardized operation, hydromechanical tests should be performed to confirm the specific changes in the surgical area during use of the modified operative channel. Furthermore, the effect of the irrigation fluid volume on muscle or nerve roots, especially via shear stress, needs to be further studied in detail.