Introduction
Lumbar disc herniation (LDH), with the disc material extruded outside the normal intervertebral space, is the main cause of low back and lower extremity pain (1). Although conservative care remains the main strategy for treatment, discectomy is required when clinical symptoms cannot be resolved via nonsurgical treatment (2, 3).
With advances in medical technology, open discectomy has been gradually replaced by minimally invasive spine surgery, and microdiscectomy has become an important part of the treatment of LDH (4). Facilitated by the development of endoscopic equipment and techniques, a variety of modified minimally invasive lumbar surgical techniques have been developed (5).
To protect the normal spinal structure, percutaneous transforaminal endoscopic discectomy (PTED) for LDH was developed after it was proposed by Yeung in 1997 and Hoogland in 2003 (6, 7). Based on the safety area of the lumbar posterolateral zone, PTED could remove the herniated disc effectively under local anesthesia (8). With favorable clinical results and good perioperative quality of life, PTED is appreciated by many spinal surgeons and patients (9). However, in addition to its steep learning curve, this technique requires specialized equipment, and discectomy is limited by the working channel (10).
In recent years, unilateral biportal endoscopic discectomy (UBE) with an arthroscopy system has become increasingly popular, especially in Asia (11). UBE decompression is performed on the ipsilateral side via two small separated surgical portals. Compared to PTED, UBE is not limited by the uniportal tube (12). The surgeons could perform discectomy and annulus fibrosus suture in a magnified surgical field with a high-definition arthroscope and a clear surgical field with saline irrigation (13). Previous reports have also shown satisfactory clinical outcomes of UBE for cervical and thoracic spinal disease (14, 15).
Few studies have directly compared PTED and UBE for the treatment of LDH (16). Therefore, to explore the differences between the two surgical techniques, this study compared the clinical efficacy of UBE and PTED for treating single level LDH.
Discussion
The significant improvements in the VAS score, ODI score and modified MacNab criteria revealed acceptable patient satisfaction in both groups, indicating that both PTED and UBE were effective in treating LDH. However, apartfrom times of x-ray, PTED is advantageous regarding the operative time, estimated blood loss, incision length, length of postoperative hospital stay, and short-term postoperative back pain relief.
For the surgical treatment of LDH, the most classic decompression is open laminectomy with or without fusion (19). However, open laminectomy destroys the paraspinal muscles and the posterior stabilizing structures. Therefore, a less invasive approach is needed to reduce injury and minimize surgical wounds during the treatment of lumbar disease (20).
As a microinvasive technique, PTED is widely applied for treating LDH with faster postoperative rehabilitation and less surgical injury. Compared to conventional open discectomy, PTED has the advantage of protecting the posterior ligament structures, facet joint and lamina. It avoids the need for nerve-root retraction and has a shorter hospitalization, reduced intraoperative bleeding, and faster recovery (21).
PTED can be completed under local anesthesia (22). After lidocaine combined with epinephrine hydrochloride solution is administered, the surgical field is clearer without obvious drug-related complications. The pressure of irrigation can also be appropriately reduced, theoretically reducing the incidence of spinal hypertension reactions (23). In addition, if the surgical equipment stimulates the nerve root during the operation, the awake patient will experience an abnormal sensation, and the surgeon can stop the process in a timely manner. The patient can be asked whether they subjectively feel their symptoms being alleviated, and the straight-leg test can be performed; these responses can be used to determine whether the operation should be terminated. Local anesthesia also reduces complications related to general anesthesia in elderly patients.
However, most hospitals in developing countries cannot afford to purchase these types of equipment and cannot master the technology quickly due to its steep learning curve. In addition, it is not easy to place the tube at the target point of the lateral approach if the iliac crest is high. In addition, the working places and visual field are limited to a single rigid working cannula.
Since first reported by De Antoni in 1996, UBE with arthroscopy has achieved good clinical effects (24). However, the development of UBE was limited due to the lack of power motor drills and the radiofrequency used to remove the lamina and achieve hemostasis. In recent years, with the emergence of endoscopic surgical instruments, UBE has been widely used in the treatment of LDH and lumbar spinal stenosis (25, 26).
Soliman proposed the application of this minimally invasive technology for the treatment of LDH in 2013 (27). He concluded that the surgical field of vision was expanded with different channels, and vascular bleeding was less under irrigation. The decompression process and instruments of UBE are similar to those used for open posterior discectomy, and thus this procedure can be carried out after only a short training period (28). Therefore, the learning curve of UBE is relatively flat and short. Xu demonstrated that the learning curve for mastering UBE is 54 cases (29).
The operating instruments and observation port are in different channels. The working port does not restrict the operating instruments of UBE. The working efficiency can be greatly improved with the use of conventional, large-sized surgical instruments, such as an osteotome, rongeur, forceps, and nerve retractor (30). In addition, surgeons in developing countries can complete the procedure without purchasing specialized supporting surgical instruments and other endoscopic systems. Moreover, unlike PTED, the UBE approach is not affected by a high iliac crest (31).
In our research, the operative time of UBE is longer than PTED. For one reason, the operative time for UBE is from the beginning of general anesthesia until a drainage tube is placed after hemostasis; the operative time for PTED is from the insertion of a local anesthetic to a drainage tube placed. For another, before laminotomy, the water pressure is 35 cm–40 cm H2O (32). But when performing the discectomy, to avoid potential neurological complications caused by the increased epidural and intracranial pressure and muscle edema caused by the high pressure of irrigation fluid, we lower the water pressure to 25 cm H2O (33). The time of hemostasis may be longer. So, the total operative time of UBE is longer than PTED in our research. But this does not mean that the efficiency of UBE is inferior to PTED in the progress of discectomy.
As for times of x-ray, the UBE group is superior to PTED in this research(6.13 ± 1.28 vs. 11.16 ± 3.71). Among the procedure of PTED, the times of x-ray was higher and mainly included: the process of local anesthesia, sequential dilators and bone drills insertion to expand the soft and osseous tissues by resecting the ventral osteophytes on the superior articular process, and the working cannula placement. In the UBE, the purpose of fluoroscopy is to find the junction of the inferior lamina and the spinous process and prevent mismaking of the target lumbar segment. So in terms of times of x-ray, the UBE group is superior to PTED.
However, the trauma of UBE is relatively larger than that of PTED (34). Due to the lack of a rigid cannula to dilate the soft tissue, the longissimus pectoralis and multifidus muscle need to be bluntly dissected to create a working space before decompression. The artificial creation of the operation spaces may damage the muscle attached to the lamina and the other anatomical structures. Therefore, theoretically, UBE would result in greater blood loss and worse postoperative back pain than PTED. The probability of cerebrospinal fluid leakage caused by dural injury when retraction of the nerve root is relatively high under general anesthesia (35).
In this research, three patients in the UBE group underwent dural tears when the anatomical structure was retracted to expose the disc. One of them experienced cerebrospinal fluid leakage and postoperative headache. The first dural tear occurred during the removal of the ligament flavum by the forceps with the low water pressure and the bleeding vision. The othe two dural tears were caused when the traversing roots was pushed by the assistant in a medial direction to expose the disc. We suggest that vigorous force cannot be used while pulling on the dura and an experienced assistant is needed. Besides, thorough hemostasis is needed when bleeding occurs before the next steps.
Additionally, one patient complained of weakness of the tibialis anterior in the PTED group. The working channel compresses the nerve root when the bone drill graves the upper articular of L5, which results in radicular symptoms. Another patient had a dural tear during the procedure but without cerebrospinal fluid leakage after the surgery. To avoid these complications, the surgeon should be careful when performing the foraminoplasty with a bone drill.
This study has some limitations. First, it was a retrospective study with a relatively short follow-up period and a small sample size. Second, the operation choices were limited. To confirm the long-term outcomes, a prospective and multicenter study with different surgical procedures and a larger sample size is necessary in future research.