
==== Front
J Orthop Surg Res
J Orthop Surg Res
Journal of Orthopaedic Surgery and Research
1749-799X
BioMed Central London

39218990
5018
10.1186/s13018-024-05018-x
Research Article
Biportal endoscopic transforaminal lumbar interbody fusion with large cage: a technique without additional spacer portal
Xu Zhengyu
Zhuolin Zhong
Jing Xiaowei
Hu Qingfeng huqingfeng@zju.edu.cn

grid.13402.34 0000 0004 1759 700X Department of Orthopedics, the Fourth Affiliated Hospital of School of Medicine, and International School of Medicine, International Institutes of Medicine，Zhejiang University, N1, Shangcheng.st, Yiwu City, China
2 9 2024
2 9 2024
2024
19 53217 7 2024
20 8 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
Background

Large spacers offer numerous advantages such as higher fusion rates and lower subsidence rates. However, due to the anatomical constraints of the approach, the use of large spacers in biportal endoscopic transforaminal lumbar interbody fusion(BE-TLIF) necessitates an additional incision and special instruments for spacer implantation leading to less frequent use.

Methods

This study has refined several techniques within BE-TLIF. We insert the cage and impact the cage transverse with a special design instrument in the same working portal. This allows for the use of large spacers during BE-TLIF procedures without the need for an auxiliary cage-inserting incision.

Conclusion

The technique is a straightforward, safe, and minimally invasive method for inserting large cages in the treatment of lumbar instability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-024-05018-x.

Keywords

Biportal endoscopic
Transforaminal lumbar interbody fusion
Lumbar instability
issue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
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pmcBE-TLIF introduction

Transforaminal lumbar interbody fusion (TLIF) is considered a standard technique for posterior lumbar stabilization and fusion. It provides the surgeon a route by resecting the facet joint to insert an interbody cage filled with auto-/allograft bone and screw fixing the spine [1, 2]. Since its introduction by Harms and Jeszenszky, the conventional or open TLIF has evolved into a minimally invasive procedure (MIS-TLIF) which is associated with reduced damage to paraspinal tissues, satisfactory clinical outcomes, and an adequate fusion rate [3–5]. However, the evolution did not end there. Full-endoscopic TLIF has resulted in a transforaminal fusion with high image quality, providing TLIF with more safety, and specificity at the site of the pathology [6, 7]. Among them, biportal endoscopic TLIF (BE-TLIF) has advantages such as the ability to perform direct neural decompression as in open surgery, a lower incidence of neural injury, and endoscopic endplate preparation [8, 9]. Recently, a modified BE-TLIF technique that used a large cage called biportal endoscopic extreme transforaminal lumbar interbody fusion (BE-eXTLIF) was introduced. The large cage means a lower subsidence rate and a higher fusion rate. However, the insertion of the spacer in the BE-eXTLIF needs an additional portal because of the characteristics of the approach [10, 11]. In this study, we have used a modified method that uses a larger space in BE-TLIF without the additional portal thus achieving a better fusion rate and being less invasive.

Relevant surgical anatomy and large cage description

According to Hoshide`s anatomy study, the length of the basic Kambin`s triangle was measured to be 17 mm in the L3-4 region and 18 mm in the L4-5 region [12]. Hence, the length of the extended Kambin`s triangle (LEK) was measured by adding the space of the ipsilateral facet that was removed and the space of Kambin`s triangle (Fig. 1A). LEK can also be measured in the axial MR images (Fig. 1B). According to our experience, for most patients in L4-5 and L5-S1, the entrance is enough for the standard DLIF or OLIF spacer with a width of 18 mm and a length of 40–45 mm. The height of the spacer can be selected between 9 and 13 mm according to the patient’s specific conditions. A 6° angle spacer was applied to improve the segmental and lumbar lordosis (Fig. 2). The PEEK lumbar intervertebral fusion cage was produced by Canwell Medical Co., Ltd. (Jinghua, China).

Fig. 1 A. 3D scheme of the length of extended Kambin`s triangle (LEK). B. LEK can be measured as the distance from the dural sac to the exiting nerve root in the axial MR image

Fig. 2 Description of the large space in the biportal endoscopic transforaminal lumbar interbody fusion

Positioning and surgical portals establishment

The patient is positioned prone on a radiolucent table with general anesthesia. The approach will be performed on the patient’s symptomatic side. Generally, the vertical skin incisions (viewing portal 0.8 cm, working portal 1.0 cm in length) are placed at the projection of 0.5 cm lateral from the pedicle lateral edges. (Fig. 3A, B, C). The working portal can be extended to 1.8 cm when a large cage is inserted. We adopt a relatively medial surgical incision compared to the extraforaminal route [13] that facilitates the facetectomy and reduces the risk of exiting nerve root injury during the implantation of the fusion device. Different from the existing modified far lateral endoscopic TLIF, our novel working portal(0.5 cm lateral to the pedicles) is positioned between the previously described working portal(over the pedicles) and the large cage insertion portal(5 cm lateral to the pedicles) [14], allowing for the large cage insertion.

Fig. 3 Illustration of skin incision and portal establishment. The red circles line the pedicles. The yellow lines represent the entries for viewing and working portals

Unilateral laminotomy and facetectomy

The ipsilateral lamina and inferior articular process were removed by an ultrasonic osteotome (Fig. 4A). The tip of the superior articular process was partially removed until the foraminal area was completely exposed (Fig. 4B). Bone fragments from the lamina and facet joint were used as autologous graft material packed within the fusion cage. If the patient presents with symptoms of lumbar spinal canal stenosis and nerve root compression, adequate decompression should be performed. In patients without radicular symptoms, preserving the ligamentum flavum above the dura sac and around the exiting nerve root could reduce the risk of bleeding and nerve root injury.

Fig. 4 Endoscopic view of laminotomy and facetectomy

Intervertebral space processing

Annulotomy could be performed using a sharp scalpel (Fig. 5A). The nucleus pulposus was completely removed with the use of a curette and pituitary forceps (Fig. 5B). The cartilaginous endplate was separated from the osseous endplate under a magnified endoscopic view, and adequate endplate preparation could be performed. Endplate preparation could be achieved without injury to the osseous endplate. The space model was used to determine the depth and height of the intervertebral space (Fig. 5C).

Fig. 5 Discectomy and intervertebral space (IVS) processing. A. Annulotomy with a scalpel. B. intervertebral disc and cartilaginous endplate excision. C. A space model was inserted to the IVS to assure the height of IVS

Placement of a large cage

Upon verifying that the entrance of Kambin’s triangle could accommodate the large cage, the latter—packed with autologous bone material—was inserted into the intervertebral space through the working portal. During the cage insertion, a nerve retractor was gently used to retract the dural sac medially, thus expanding the length of extended Kambin’s triangle, while also serving a protective role in safeguarding the dural sac throughout the insertion process (Fig. 6A, E, J).

A designed angle impactor was anchored at the cage insertion hole, allowing for the transverse repositioning of the cage via the impactor (Fig. 6B, F). However, the angled impactor could not achieve complete transverse orientation of the large cage (Fig. 6G). We utilized a straight impactor to align the cage parallel to the posterior edge of the vertebral body (Fig. 6C, H). To ensure that the cage was fully transverse, a 90° angled hook was employed (Fig. 6I).

Fig. 6 large cage insertion procedures. A. Illustration cage insertion on the MR image. B. scheme of the impacting with an angled impactor on the MR image. C. Scheme of the impacting with a straight impactor on the MR image D. Confirmation of the LEK and the IVS under endoscopic view. E-I. Endoscopic view of the large cage insertion and impacting. J. Large cage insertion with a dural sac retraction to confirm the safety in the working portal. Red arrow: the exiting nerve root

Percutaneous pedicle screw fixation and wound closure

Ipsilateral pedicle fixation screws were placed through the working and viewing portals. The contralateral transpedicular screws require new incisions, as usual (Fig. 7A, B, C, D). The four incisions are all closed with a single suture. A drain is supposed to be inserted in the caudal, ipsilateral incision to evacuate residual irrigation fluid and potential bone bleeding (Fig. 7E).

Fig. 7 A-D fixation screws implanting under intraoperative fluoroscopic guidance. E. Incision closing with a drain tube. F. Appearance of the incision, 1 month after the surgery

Indications and radiologic results

Patients with degenerative lumbar spondylolisthesis and instability are indicated for the technique. We do not perform the technique in patients with high-grade lumber spondylolisthesis (grade ≥II, according to Meyerding classification), severe osteoporosis, trauma, or tumors. Typically, the cages we utilize are 18 mm wide and feature a 6° lordotic angle. Postoperative X-rays indicate a significant restoration of disc space height and lumbar lordosis compared to the preoperative status (Fig. 8C, D). Postoperative magnetic resonance imaging (MRI) demonstrates a larger contact area between the large fusion cage and the vertebral bodies, suggesting higher fusion rates and lower subsidence rates (Fig. 8G, H).

Fig. 8 A 56-year-old woman presented with low back pain and claudication received the procedures. A-B. The preoperative radiograph showed L4 listhesis with instability. C-D. The postoperative X-ray shows that the listhesis was corrected and the lordotic curve was restored; E-F. The preoperative MR images indicate lumbar spinal stenosis at the L4/5 level. G-H. The postoperative MR image shows an adequate contact area with the large cage insertion

Discussion

Although the large cages similar to OLIF/LLIF have many advantages, their application is limited in the posterior lumbar surgical approach. Some experts have modified surgical techniques to allow the use of large cages in BE-TLIF [10, 11, 15, 16]. Currently reported surgical techniques for BE-TLIF with large fusion cages require an additional spacer portal. The incision is usually made 3–5 cm lateral to the working portal. The relatively oblique insertion of the cage allows a straight impact to transversely reposition the large cage in the working portal and restore the Lumbar lordosis (Fig. 9A, B). However, this method has two drawbacks. Firstly, the implant`s more oblique insertion trajectory is close to the exiting nerve root, increasing the risk of nerve injury. Secondly, the additional spacer portal increases soft tissue damage. Similar to previously reported BE-TLIF procedures, we introduce a technique that employs large cages, yet without an additional portal for cage insertion. The large cage provides an extensive contact area between the endplates, not only facilitating fusion and reducing the risk of cage subsidence but also aiding in the restoration of lumbar lordosis. Through precise trajectory planning and gently retracting the dural sac medially, we accomplished the implantation of the fusion cage within the working portal under endoscopic visualization. This approach obviates the need for an additional cage inserting incision and direct exposure of the neural roots, thus simplifying the surgical procedure, minimizing tissue disruption, and lowering the risk of nerve injury. Moreover, the custom-designed angled impactor enabled the transverse repositioning of the large cage within the working channel, facilitating the restoration of lumbar lordosis.

Fig. 9 Scheme of the previously reported large cage insertion procedure. A. The insertion of the fusion cage through the lateral spacer portal. B. A straight impactor was used to reposition the cage transversely in the working portal. Red arrow: the exiting nerve root

Limitations

According to the characteristics of the lumbar anatomy, lumbar levels rostral to L4 have a narrower Kambin corridor. A large cage with the introduced dimension can injure the nerve root during the inserting procedure. A smaller cage with a length of 36 mm and a width of 14.5 mm could be selected in the upper lumbar intervertebral fusion procedure.

Impacting and repositioning the cage within the IVS is crucial for restoring lumbar lordosis, a process that may carry the risk of endplate disruption for elderly patients with osteoporosis. This particular concern, however, is not pertinent to OLIF and LLIF techniques.

How to avoid complications

In comparison to traditional bone chisels, our use of an ultrasonic osteotome for the resection of the facet joints reduces bleeding and minimizes the risk of nerve concussion.

Sufficient focus should be placed on the anterior longitudinal ligament. Preoperative assessment of the anterior longitudinal ligament integrity can be conducted using sagittal MR scans to evaluate its strength or deficiency. During the surgery, after the completion of intervertebral space and endplates procedures, a nerve dissector can be used to explore the integrity of the anterior longitudinal ligament in order to prevent anterior displacement of the cage during the cage impacting process and avoid injury to the anterior abdominal aorta.

Although the risk of nerve injury is relatively low in our procedures, there are several tips to avoid potential injury to the exiting nerve. Before surgery, LEK can be measured on the axial MR image. Patients with a LEK of at least 18 mm, along with moderate medial retraction of the dural sac, can ensure the safety of the insertion of an 18 mm wide fusion cage. Preoperative measurement of the vertebral body’s anteroposterior diameter should exceed 40 mm to ensure that a 40 mm long spacer can be fully inserted into the intervertebral space. These precautions guarantee that the nerve roots will not be disturbed during the transverse impacting process. Besides, preserving the ligamentum flavum around the exiting nerve root could reduce the risk of nerve root injury.

During the surgery, appropriate retraction of the dural sac is necessary to accommodate the insertion of the large cage. This surgical method is not recommended for patients with dural sac adhesions due to prior spine surgery.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Supplementary Material 1

Acknowledgements

Not applicable.

Author contributions

Zhengyu Xu wrote the main manuscript text. Qingfeng Hu and Xiaowei Jing complete surgeries. Zhuolin Zhong prepared Figs. 1 and 2. All authors reviewed the manuscript.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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