Lumbar interbody fusion is a classic surgical procedure in the treatment of lumbar degenerative disease. Traditional open surgery mainly includes posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF). Since Cloward first proposed PLIF in 1953 , as a classic operation, it has a good curative effect in the treatment of lumbar degenerative diseases . However, traditional PLIF requires stripping and pulling of the paravertebral muscles, which is prone to causing postoperative chronic low back pain [15-17]. To overcome these limitations, TLIF was developed, which retains the intact ligament structure and thus maintains biomechanical stability .
Spinal endoscopic surgery has the advantages of minimal trauma, short hospitalization time and quick postoperative recovery  and is even better than traditional open surgery in the treatment of lumbar disc herniation [20,21]. However, limited discectomy under endoscopy may result in residual disc reherniation . Endo-TLIF combined with endoscopic surgery and lumbar fusion surgery, using spinal endoscopic instruments for TLIF operation, can combine the advantages of both and achieve effective lumbar fusion with less trauma.
Endo-TLIF transforms the traditional operation under direct vision into a magnified display image, which makes the vision clearer and wider and realizes lumbar decompression and fusion assisted by endoscopy. In this procedure, the articular process, the lower margin of the superior lamina, and the upper margin of the inferior lamina were excised with a trephine under the protection of a percutaneous sleeve. The bony decompression range of TLIF was replicated. Decompression can be performed according to requirements during open surgery, and surgical procedures can simulate open surgery to achieve endoscopic decompression and fusion.
In this study, the efficacy of Endo-TLIF in the treatment of lumbar degenerative diseases was analyzed, including the duration of surgery, blood loss, length of incision, time in bed and hospital stay. The clinical indicators were excellent, with the characteristics of minimal invasiveness and quick recovery. The ODI scores and low back pain and leg pain VAS scores of patients were significantly improved compared with those before surgery, indicating that this operation method has an obvious effect on the patients' waist function and pain symptoms. Postoperative X-ray results showed that ADH, PDH and FH changed significantly, and the change in LL was not obvious. MRI results showed that DSCA was significantly improved compared with preoperative results. This procedure is satisfactory in restoring lumbar stability and relieving spinal cord compression. In this study, all 21 patients were followed up for more than half a year, their symptoms were significantly improved, without any serious complications, and the early clinical efficacy was satisfactory.
For body surface localization, the transverse axis was marked along the target intervertebral space, the longitudinal axis was marked along the spinous process, and the upper and lower spinous processes and pedicles were marked simultaneously. Endo-TLIF requires smaller skin incisions and less muscle dilation. The dorsal facet joint on the affected side is used as the starting point of endoscopic operation, and bony markers are relatively safer. Compared with the intractable low back pain caused by multifidus injury in open surgery , Endo-TLIF can protect the multifidus muscle and the posterior column of the spine to the maximum extent, maintain the stability of the spine, and reduce the incidence of low back pain. The whole operation was performed under visualization, and the surgical field was magnified tens of times by a high-resolution lens, which could distinguish bleeding capillaries. Moreover, the water pressure generated by water medium can significantly reduce bleeding, make the visual field clearer, effectively avoid nerve damage, and achieve direct and precise decompression.
Endo-TLIF is a full-visual spinal endoscopic procedure that replicates the TLIF procedure. The range of decompression follows the TLIF procedure, with partial excision of the facet and lamina. During trephine decompression, part of the facet and the upper and lower lamina were removed, and the distal end could reach the starting and ending point of the ligamentum flavum. The proliferated ligamentum flavum was treated with forceps. Decompression range: the cephalic side can reach the lower edge of the superior pedicle, the lateral side can reach the outer opening of the intervertebral foramen, the caudal side can reach the upper edge of the inferior pedicle, and the contralateral side can reach the midline of the spinous process or even beyond the spinous process.
Under endoscopy, the disc and endplate were destroyed by the reamer and curette. The anterior longitudinal ligament can reach as far as possible and form a fan-shaped area, which is conducive to intervertebral bone grafting and cage implantation. We treated the endplate directly under the endoscope without destroying the endplate cortex. From a technical point of view, Endo-TLIF should be superior to traditional TLIF in terms of endplate preparation. Traditional TLIF cannot directly look at the internal structure during endplate preparation. Endo-TLIF has obvious advantages in both preparation quality and scope. Subchondral bone injury or incomplete endplate preparation may lead to cage subsidence or fusion failure after open TLIF [24,25]. Finally, endoscopic observation helps to reduce the risk of damage to large vessels, which sometimes occurs during blind endplate preparation .
The fusion operation was performed in the safe passage of the Kambin triangle. The large channel of the sleeve is placed through the Kambin triangle, and the axis of the sleeve is parallel to the intervertebral space. In this position, the sleeve can easily pass through the Kambin triangle and be inserted into the intervertebral space, and the cage is easier to place. During the insertion of the sleeve, attention should be given to rotation and observation, and the dura and nerve roots should be protected by the lingual end of the sleeve. The autogenous bone used for bone grafting was removed by trepanning, which was crushed by bone forceps and implanted into the intervertebral space. Due to the abundant cancellous bone, the procedure was more conducive to intervertebral fusion.
When the pedicle and translaminar facet screws were fixed, the operation could be guided by a C-arm machine according to the marked position on the body surface. The direction of the translaminar facet screw was "spinous process → lamina → articular process → pedicle". The screw enters through the junction of the superior spinous process and lamina, passes through the superior lamina, passes through the contralateral facet joint, and reaches the junction of the transverse process and pedicle. When the screw is inserted, it penetrates four layers of cortical bone and fixes the facet joint. Translaminar facet screw fixation as a minimally invasive technique has been reported [27-29]. The comparison of facet screw and pedicle screw fixation showed biomechanical equivalence [30-32]. Previous reports indicated that transplate screw fixation is a simple, safe and satisfactory method [33,34]. When we performed pedicle screw fixation, we used the original incision of spinal endoscopy, and the minimally invasive operation effectively reduced trauma. Translaminar facet screws combined with pedicle screws, similar to triangular stable structures, can achieve good fusion of anterior, middle and posterior columns so that stability can be guaranteed.
As recent reports summarizing clinical experience, clinical case series and cohort studies have pointed out, endoscopic surgery can achieve minimal invasion[35-38]. Endoscopic spinal surgery uses minimally invasive muscle dissection, does not require excessive bone excision, and minimizes the damage to surrounding tissues. Due to its minimally invasive characteristics, Endo-TLIF can reduce blood loss, reduce the risk of deep vein thrombosis and pulmonary embolism, restore lumbar and back function in the early stage, and reduce the risk of postoperative fibrosis scar formation. Through the transforaminal approach, the nerve root and dural sac can be found quickly, which is convenient for direct and safe decompression around the dural sac and nerve root under endoscopy. Endo-TLIF has more flexibility in anesthesia methods. Different from traditional TLIF, Endo-TLIF can be performed under local anesthesia. The use of conscious sedation reduces the risks associated with general anesthesia and promotes real-time neurofeedback from patients. Therefore, Endo-TLIF may be useful for elderly or special patients who are at high risk for open surgery under general anesthesia.
The main purpose of operation mode selection is to improve symptoms and benefit patients . The Endo-TLIF technique uses endoscopy as a tool to achieve the decompression and fusion effect of TLIF. At present, the Endo-TLIF three-screw technique is mainly used in the treatment of lumbar spinal stenosis, single segment instability, degeneration, lumbar disc herniation and grade I spondylolisthesis. For patients with grade II or above spondylolisthesis, severe lumbar instability and severe osteoporosis, two pairs of pedicle screws can be added. We do not have evidence or advocate the use of Endo-TLIF for the treatment of severe scoliosis above 20 degrees.
Endo-TLIF is an emerging endoscopic technique with promising prospects in terms of minimal tissue damage, low complication rate and cost effectiveness. However, there are few reports on endoscopic fusion, and the level of evidence is very low. In particular, no articles on endoscopic three-screw fusion have been reported. Therefore, well-designed randomized trials are needed to confirm the safety, efficacy and clinical relevance of Endo-TLIF. In addition, another limitation of Endo-TLIF is that it needs a long learning curve. To achieve good results with Endo-TLIF, it is necessary to be familiar with transforaminal endoscopic decompression, open unilateral laminectomy and bilateral decompression, and interbody fusion before attempting the procedure.