With the development of surgical instruments and surgical techniques, PELD has gradually become one of the mainstream operations for the treatment of lumbar disc herniation. In patients with lumbar degenerative disease, the nerve root outlet is often narrowed due to reduced disc height, osteoarthritic changes in the facet joints, cephalad subluxation of the SAP. Therefore, most of these patients are associated with foraminal stenosis. In this study, foraminal stenosis was defined as “4mm or less for the posterior disc height and 15 mm or less for the foraminal height , and distance between posterior edge of the disc and ventral aspect of the facet joint was less than 8 mm ”. For patients with foraminal stenosis, the diameter of the foraminal is often smaller than that of the diameter of our surgical endoscope. If the cannula is inserted into the narrow orifice, the cannula may compress the existing nerve root and cause postoperative dysesthesia. To prevent this complication, foraminal plasty is a routine procedure.
Hoogland et al. [12, 21, 22] established the existing TESSYS system, which is a technique for enlarging foramen by using staged reamers. The PELD technique has a very steep learning curve , and likewise the TESSYS technique has a very steep learning curve [23, 24]. Different from the YESS technique proposed by Yeung in 2002 , the TESSYS technique follows an "outside-in" approach, in which the disc herniation into the spinal canal is removed directly under the endoscope through an enlarged foramen. The decompression process looks directly into the nerve root. However, foraminal plasty should not be performed in the same way for different foraminal sites, and the desired foraminal procedure should be performed for each patient. In addition, there are disadvantages such as instability in the direction of the reamer when using it, such as improper operation, and the risk that the reamers may touch the soft tissue, dura and nerve roots at the edge of the foramina and cause unnecessary injury.
The intervertebral foramen and its adjacent area are the main areas of our surgical operation. However, there are a large number of ligaments and vessels in this area. Surgeons usually pay attention to whether the nerve root is hurt during the operation, thus neglecting the protection of blood vessels and ligaments. An anatomical study shows that, a large number of ligaments exist inside and outside the intervertebral foramen . In these ligament spaces, there are many nerve branches and blood vessel branches. The traditional TESSTYS technology is to constantly adjust the angle and depth of the reamer under fluoroscopy. When the reamer reaches the desired position, the intervertebral foramoplasty is completed. But the whole process of this technique is blind, emphasizing the position of the bony and neglecting the protection of nerves, blood vessels and soft tissue. Some studies have shown that dysesthesia may occur after TESSYS surgery due to the irritation of nerve root associated with the approach . Meanwhile, some scholars found that TESSYS was associated with a high probability of nerve root injury . Wang et al. reported that 3 cases of nerve root injury in 207 cases of TF-PELD operation . Another scholar reported a case of destruction of the radicular artery accompanied by the right L4 exiting nerve root during foramen plasty, followed by bleeding .
TF-PELD is operated through Kambin triangle, which is considered to be a safe operation . This area is generally thought of as a blank area with no important organization. However, some scholars have found branches of ascending lumbar vein and intervertebral vein in Kambin triangle . Therefore, blind foraminoplasty is dangerous because the inside and outside of the intervertebral foramen are filled with nerves and blood vessels. For these reasons, we proposed a novel visualized foraminoplasty technique.
Like the traditional TESSYS technique, our proposed new visual foramoplasty technique is a more thorough "outside-in" principle. Our puncture site and first placement of the working cannula were completely outside the spinal canal. After the working cannula was placed, the external foraminal vessels, ligaments and other tissues were clearly visible (Fig. 4). Careful dissection of these ligaments and blood vessels during foraminal plasty can achieve further hemostasis and preserve maximum anatomical integrity. Although the PELD procedure itself has the advantage of low blood loss, our surgical approach further reduces blood loss. The exact amount of blood loss cannot be calculated due to the presence of continuous irrigation with normal saline during the operation. Our technique greatly avoids the injury of large blood vessels and minimizes the possibility of postoperative epidural hematoma. The traditional TESSYS technique neglected the protection of soft tissues and blood vessels inside and outside the foramina due to its emphasis on preventing the reamers from entering too deep into the spinal canal through fluoroscopy in the process of foramina, which may increase the possibility of postoperative wound exudation and delay wound healing.
In our study, intraoperative pain scores were significantly reduced, and radiation exposure was significantly reduced in the new technique group compared to the traditional TESSYS group technique, suggesting that this technique is a good option for patients. Ideally, our new visual foramoplasty technique requires only four fluorograms to achieve our desired puncture location. However, the traditional TESSYS technique not only requires a large number of fluoroscopic positioning to reach the appropriate position of the puncture needle during the puncture process, but also requires continuous fluoroscopy in the anteroposterior and lateral position during the process of the reamers expanding the foramina to ensure that the reamers will not enter the spinal canal too deep and damage the nerve root and dural sac. In addition, a significant reduction in pain during foramoplasty also contributed to increased patient compliance. In the process of foraminal plasty, patients may change their position due to pain, which will affect the smooth progress of puncture positioning and even increase the number of fluoroscopies. Previously, some scholars have pointed out that repeated puncture will increase the risk of radiation exposure of patients and medical staff . In order to reduce the number of fluoroscopy, some scholars have pointed out that the use of ultrasound-assisted needle insertion and foraminalplasty in TF-PELD can reduce the radiation exposure of medical personnel , while our technology can well reduce the radiation exposure without the assistance of external equipment.
Our technique allows individualized foraminalplasty according to the characteristics of the patient's foraminal stenosis, thereby reducing articular surface damage caused by excessive removal of bony tissue like the traditional TESSYS technique , and avoiding the failure to completely remove the herniated disc due to inadequate foraminalplasty. No nerve root or dural injury occurred in the 70 patients in our new technique group. Furthermore, none of the hundreds of patients who underwent the new technique but were not included in the study had any nerve root damage. In addition, our technique allows arbitrary adjustment of the position and orientation of the tip of the working cannula, using the surrounding skin and muscle tissue as elastic fulcrum, to perform foraminal shaping at the desired angle (Fig. 5). Therefore, for the high-grade migrated herniated discs and even contralateral herniated discs, the surgeon could lever the cannula to make it more horizontal, upward or downward tilting, even contralateral. In addition, one patient in the new technology group who had significant discomfort in the leg after the placement of the working cannula reported improved discomfort after changing the working cannula angle.
Our technology also has the following limitations. First, the new visualized foraminoplasty technique has a significantly longer foraminal shaping time than the traditional technique. Due to the continuous saline irrigation during the operation, too long operation time may have a certain impact on the intracranial pressure of the patients, and the patients may have symptoms of increased intracranial pressure such as headache after the operation. At the same time, prolonged placement of the working cannula increases the possibility of compression of the nerve root. Thirdly, in order to obtain a clearer field of vision, radiofrequency hemostasis will be performed on the bleeding bone surface during foraminoplasty, which will undoubtedly increase the risk of thermal injury in patients. Fourth, in the foraminal shaping process, we need an assistant to assist with the use of the dynamic system under the endoscope, which also has a certain test for the proficiency of the assistant. And finally, we have a very steep learning curve for this technique, which is very demanding for surgeons. However, the effects of both procedures on spinal stability still require many patients to be followed for a long time.