A novel technique for posterior lumbar interbody fusion to obtain a good local lordosis angle: anterior-release posterior lumbar interbody fusion

Article information

Asian Spine J. 2024;18(5):706-711

Publication date (electronic) : 2024 August 21

doi : https://doi.org/10.31616/asj.2024.0131

Daisuke Inoue¹, Hiroaki Matsumori¹, Hideki Shigematsu², Yurito Ueda¹, Toshiya Morita³, Sachiko Kawasaki², Masaki Ikejiri², Yasuhito Tanaka²

¹Department of Orthopaedic Surgery, Kashiba Asahigaoka Hospital, Kashiba, Japan

²Department of Orthopaedic Surgery, Nara Medical University Hospital, Kashihara, Japan

³Department of Orthopaedic Surgery, Ishinkai Yao General Hospital, Yao, Japan

Corresponding author: Daisuke Inoue, Department of Orthopaedic Surgery, Kashiba Asahigaoka Hospital, 839 Kaminaka, Kashiba City, Nara, Japan, Tel: +81-745-77-8101, Fax: +81-745-78-5090, E-mail: ddaiten@yahoo.co.jp

Received 2024 March 29; Revised 2024 June 4; Accepted 2024 July 2.

Abstract

Introduction

Posterior lumbar interbody fusion (PLIF) is commonly performed in lumbar spine surgery to achieve optimal local lordosis, often including a high-angle cage and total facetectomy, and placing the cage anteriorly aids local lordosis formation [1–4].

In a previous case, we performed PLIF combining posterior column osteotomy (PCO) and a high-angle cage, emphasizing bone union and local alignment correction [5]. A recently introduced expandable cage (Catalyft PL; Medtronic Inc., Memphis, TN, USA) offers a variable angle expandable to 22°. However, intraoperative and postoperative cage subsidence and postoperative correction loss may occur because of excessive cage expansion to achieve the desired local lordosis, resulting in suboptimal postoperative results (Fig. 1) [6].

Fig. 1

Preoperative/postoperative radiograph of conventional posterior lumbar interbody fusion. (A) Preoperative images show 6.2° segmental lumbar lordosis (SLL) and 2.3° segmental intervertebral angle (SIA). (B) Postoperative images show 9.5° SLL and 6.4° SIA. Cage subsidence is observed at the L4 endplate.

In a previous PLIF case, we performed PCO and loosened the posterior component. We believed that loosening the anterior tissues would achieve greater intervertebral mobility than conventional PLIF, maximize the characteristics of the Catalyft PL cage, and achieve larger local lordosis without cage subsidence.

Some studies have reported cutting off the anterior longitudinal ligament (ALL) to correct spinal deformity [7–9]. However, ALL amputation causes excessive instability, leading to nerve palsy after posterior fixation [10], increased anterior large-vessel injury risk, and decreased the bone union rate [11]. The annulus fibrosus (AF) also contributes to vertebral body stability [12]. We developed a PLIF technique that involves circumferential peeling off the AF at the endplate without cutting the AF or ALL and uses high-angle variable-angle expandable cages (termed anterior-release PLIF [ARPLIF]).

The indications for ARPLIF are the same as those for conventional PLIF, such as spondylolisthesis and foraminal stenosis. Among these, L3–S level cases are particularly suitable for cases where lordosis formation is considered important. Furthermore, the local alignment improvement is greater than that using conventional methods; thus, the range of indications can be expanded beyond conventional PLIF. For example, ARPLIF is considered a good indication for L5/S level in deformity correction surgery for spinal malalignment. In addition, in some cases, it can be applied to deformity correction surgery for kyphotic deformity, such as after osteoporotic vertebral fractures.

Technical Notes

This study was approved by the Ethics Committee of Kashiba Asahigaoka Hospital (approval code: 12-1-017). Informed consent for publication was obtained by opting out.

The patient was initially placed in the prone position. The steps until nerve decompression were performed as described previously [5].

ARPLIF requires complete resection of the left and right inferior articular processes. Because lateral AF release (AFR) at the intervertebral disc level is necessary, total facetectomy is performed through superior articular process resection beyond the lateral half of the pedicle. The identified intervertebral disc is incised. If the disc is incised to the lateral side of half the pedicle, lateral AFR and cage installation on the outer side at the intervertebral space is easier. Dilators are sequentially inserted to widen the intervertebral space. If resistance is encountered and turning the dilator becomes difficult, the procedure is paused and performed on the other side to prevent endplate injury during dilator operation. To maintain a wide intervertebral space, the dilator is kept on the contralateral side. Curettages are used to scrape the disc without fluoroscopic guidance. Before removing the remaining tissue, the procedure is repeated on the contralateral side.

AFR is the most important part of this procedure. Using cup curettages and a raspatory, the AF is peeled away from the lateral edge of the vertebral body to the anterior edge under fluoroscopic guidance without cutting the AF or ALL. Generally, the AF is thick and circled the vertebral body [12], and imageless manipulation often fails to scrape down the anterior edge of the vertebral body (Fig. 2). Excessive force may cause unexpected punctures of the anterior tissue, causing potential blood vessel injury. AFR only needs to be performed on one of the cephalad or caudal endplates, and the side facilitating comfortable device insertion for AF scraping along the endplate to avoid interference with the remaining vertebral arches should be selected because the device must be tilted according to the degree of lumbar lordosis. Peeling off should be performed while checking the lateral and anterior edges on frontal and lateral fluoroscopy (Fig. 3). Because the anterior tissue is not cut, the resistance of the anterior tissue, such as the ALL, must be perceived during AFR. In out AFR technique, we only use straight sharp spoons and curved knobs, not special tools (Fig. 4).

Fig. 2

Intervertebral disc scraping before annulus fibrosus release. Even if the intervertebral disc is scraped using hand sensation, the peeler cannot reach the anterior edge of the vertebral body.

Fig. 3

Annulus fibrosus release (AFR). (A) The peeler is advanced to the front edge of the vertebral body at the anterior AFR. (B) The peeler is advanced to the edge of the lateral side of the vertebral body at the lateral AFR. The peeler should be rotated slightly to check whether intervertebral space mobility has increased.

Fig. 4

Tools used during annulus fibrosus release. Only straight or curved sharp spoons and curved knobs are required, without special tools.

The intervertebral space demonstrates better mobility than that in the initial stages of intervertebral manipulation, allowing for the insertion of a larger dilator. If an 11-mm dilator can be easily rotated, the AFR is considered adequate.

After AFR, the disc space should be thoroughly cleaned to ensure complete soft tissue removal. Before inserting the expandable cages, a large bone graft should be taken. For bone grafting, we used only local bone in all cases. In ARPLIF, a sufficient volume of bone graft can be obtained because of the thorough posterior osteotomy; therefore, allograft or artificial bone other than the local bone is not needed. Although other sizes may be useful where a large intervertebral height remains, a 7-mm Catalyft PL cage is generally used. The cage should be placed hard lateral and anterior to the endplates [13]. External cage placement prevents the cage device from pinching and compressing the dural canal (Fig. 5). Adequate AFR in this step facilitates maximum possible expansion without a strong force. After maximum cage expansion, the intervertebral angle also improves along the cage (Fig. 6). To expand the disc space, we use two expandable cages. If only one expandable cage is used, it will be placed in the midline of the intervertebral space, and the cage will be expanded where the endplates are less hard [13]. Moreover, because the contact area between the cage and the endplate is smaller than that when the two cages are used, the risk of endplate injury during cage expansion is higher. Therefore, the use of two expandable cages is deemed necessary. At this time, ensuring that the cage does not move even on rotational force application is essential. Thus, if the cages are stable, the AF and ALL will not be severed. Subsequently, percutaneous pedicle screws should be inserted. In the case of slippage, a reduction force should be applied to the screws to correct it. Finally, the degree of intervertebral angle correction by cages should be checked, and a compression force should be applied to the screws (Fig. 7).

Fig. 5

Intraoperative photographs. (A) When the cage is inserted outside the intervertebral space, both cage inserters do not compress the spinal canal. (B) The left and right expansion devices will not interfere with each other, and both cages can be expanded simultaneously.

Fig. 6

Intraoperative images. (A) The segmental intervertebral angle (SIA) is 8.2° at the time of insertion. (B) By expanding the cages to the maximum, we could achieve 13.4° SIA, with no cage subsidence.

Fig. 7

Intraoperative images. (A) Image obtained after screw insertion. (B) Slippage has been corrected using a reduction force with screws. During this step, the segmental lumbar lordosis (SLL) is 18.2° and segmental intervertebral angle (SIA) is 14.7°. (C) Lordosis formation is performed by applying a compression force with screws. SLL has been corrected to 24.6° and SIA to 20.0°.

Since November 2023, ARPLIF was performed. Twenty cases have been followed up for >3 months postoperatively, and of these, six cases have been followed up for >6 months postoperatively. Table 1 shows the mean measurements of local lumbar alignment preoperatively and 3 months postoperatively. On lumbar spine lateral X-ray images, no instability in any of the cases was observed 3 months postoperatively, and no obvious screw loosening or cage subsidence was noted. In the six cases that were followed up for >6 months postoperatively, bone union was confirmed in all cases by computed tomography, and no cage subsidence was observed. Fig. 8 shows representative images.

Table 1

Alignment changes before and after anterior release posterior lumbar interbody fusion

Fig. 8

Preoperative/postoperative images. Findings from an 84-year-old man with L3/4 degenerative spondylolisthesis, lumbar spinal canal stenosis, right lower limb pain, and intermittent claudication. The patient was previously treated conservatively unsuccessfully before undergoing surgical correction at our department. Laminoplasty was performed at L1/2/3 and anterior release posterior lumbar interbody fusion was performed at L3/4. (A) Preoperative radiograph. At L3/4, segmental lumbar lordosis (SLL) is 4.3° and segmental intervertebral angle (SIA) is 1.1°. (B) Postoperative radiograph. SLL at L3/4 has improved to 24.4° and the SIA to 19.2°. (C) Postoperative lateral-view computed tomography image. There is no anterior leakage of the bone graft.

Discussion

In ARPLIF, PCO and AFR increase intervertebral mobility, whereas simultaneous expansion of both cages reduces the excessive load on the endplates, and by maximizing the potential of the Catalyft PL cages, the desired intervertebral angle is obtained without cage subsidence.

In cases of severe disc degeneration that has disappeared, or where preoperative local lumbar lordosis is poor, achieving a good lumbar lordosis may be challenging with conventional PLIF, resulting in iatrogenic lumbar kyphosis. Inadequate anatomical correction is considered one of the causes of postoperative adjacent segmental disorders and flatback syndrome, which worsen postoperative clinical outcomes [14]. Therefore, performing a surgical technique that focuses on local lumbar lordosis, even for a single PLIF, is necessary. This ARPLIF surgical technique was therefore devised. In addition, this technique does not involve removing the ALL and can be performed with fluoroscopy; thus, we do not consider it a high-risk surgery. In fact, no complications occurred in these cases.

With the efficient achievement of local lordosis, this technique proves valuable in deformity correction. In some cases of kyphotic deformity, such as flexible kyphotic deformity, it may be considered a useful alternative to more invasive procedures such as pedicle subtraction osteotomy. Compared with conventional PLIF, ARPLIF offers superior lordosis outcomes.

This study is limited by the small number of cases and the need for further follow-up to determine the long-term postoperative clinical outcomes of bone union and cage subsidence rate.

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