Minimally Invasive L5–S1 Anterior TLIF Cage Placement in Lateral ALIF Exposure as a Bailout Option for Low Iliocaval Junctions: Report of Four Cases

Abstract

The aim of this study was to demonstrate that anteriorly placed transforaminal lumbar interbody fusion (TLIF) footprint bullet cage is a safe and effective bailout option if difficult left common iliac vein (LCIV) anatomy is unexpectedly encountered during the L5–S1 lateral anterior lumbar interbody fusion (L-ALIF). This retrospective case series includes four patients who received anteriorly placed TLIF cages at L5–S1 during L-ALIF surgery. Demographics, complications, and clinical/radiographic results were collected. The analysis included four female patients with a mean age of 59.0 years and mean body mass index (BMI) of 23.9. Three patients had degenerative conditions and one patient had a deformity. All the patients had an LCIV obstructing the center of the L5–S1 disk space, and titanium TLIF bullet cages were placed and secured with washers and screws. The L5–S1 segmental lordosis increased by 8.3 ± 6.1 degrees with a final mean lordosis of 23.5 ± 8.4 degrees; the L5–S1 intradiskal angle increased by 12.0 ± 7.0 degrees with a final mean disk angle of 18.8 ± 7.0 degrees; the posterior disk height increased by 4.4 ± 2.7 mm with a final mean disk height of 8.0 ± 2.1 mm. The mean numerical rating scale (NRS) for back pain improved by 5.3 ± 2.5 and the mean NRS leg pain improved by 7.7 ± 2.5 over a mean follow-up of 14 months (range: 6–20). There have been no perioperative complications or implant failure to date. If challenging vascular anatomy is encountered during L-ALIF exposure that prevents ALIF footprint cage placement, proceeding with smaller TLIF bullet cage placement anteriorly rather than abandoning the surgical approach is a safe and effective option.

Keywords

L5–S1 spine - degenerative spondylosis - lateral ALIF - TLIF - single position surgery

Introduction

Lumbar interbody fusion is an indicated surgical option for patients who have exhausted conservative management and require spondylosis stabilization, deformity correction, lumbar lordosis restoration, or nerve decompression.[1] For patients with degenerative lumbar disease that require fusion at L5–S1, there are various approaches that allow for placement of the interbody, including anterior, posterior, and posterolateral. Posterior and posterolateral interbody fusions historically were the most common techniques, but anterior approaches may be advantageous in their increased interbody size that can better restore lumbar lordosis and decrease the likelihood of adjacent segment disease.[2]

Anterior lumbar interbody fusion (ALIF) approaches often are through a retroperitoneal approach that require an access surgeon, most commonly a general or vascular surgeon, to reduce the risk of injury to surrounding vasculature, the ureters, or bowels.[3] Because this is most commonly done in the supine position, this would require additional time and logistics to flip the patient in the prone position in order to place posterior fixation with pedicle screws. This approach, however, can also be performed with the patient in the lateral decubitus position through a lateral ALIF (L-ALIF) technique. This approach allows for single position surgery that can allow for placement of the same large anterior interbody and posterior pedicle screws simultaneously.[4] The L-ALIF technique can also be performed through smaller incisions due to the patient's body habitus falling away from the surgeon than in a traditional supine ALIF.[5] To this end, it has been demonstrated that both ALIF and L-ALIF can be safely performed by spine surgeons, without overall increased risk of complications.[6] [7]

However, when considering the L-ALIF approach at L5–S1, it is imperative for the surgeon to carefully study the patient's imaging and evaluate the vasculature anterior to the spine to determine the feasibility of the approach including X-ray and MRI. While the L5–S1 disk space is accessed between the bifurcations of the iliac vessels in a supine position for the traditional anterior approach, the disk space is accessed via a slightly more lateral approach over the left common iliac vein (LCIV) for the L-ALIF.[4] The LCIV is the most commonly injured vascular structure in the ALIF and L-ALIF approaches for the L5–S1 disk given its often medial location and can sometimes obstruct the disk space.[8] [9] [10] Previous work by Chung et al categorized three LCIV types based on morphology and risks of subsequent injury during dissection and mobilization, with type 1 representing a widely split and lateralized LCIV, and types II and III representing LCIV anatomy obstructing the disk space due to low iliocaval junctions.[11] Here we present four cases in which patients undergoing L-ALIF had LCIV types II or III with low iliocaval junctions that precluded placement of a large ALIF-type interbody cage, and had transforaminal lumbar interbody fusion (TLIF) type interbody cages placed through the available anterior annulotomy corridor instead as a bailout option. Clinical and radiographic results are discussed.

Materials and Methods

Clinical Data

This is a retrospective single-center report of four consecutive patients who underwent minimally invasive L5–S1 lateral ALIF surgery at an academic medical center with TLIF footprint cages placed through the lateral anterior approach. Demographic data, perioperative complications, and clinical and radiographic results were collected. This research was approved by the medical center's institutional review board.

Surgical Technique

Details of this surgical approach have been described previously and it was performed in a similar fashion.[5] [12] Once all retractor blades are placed and the annulus of the L5–S1 disk is confirmed, the mobility or lack thereof of the LCIV is identified. Endokittners are used to explore and dissect the medial border of the LCIV to determine how much the vein can be retracted or rolled laterally. If the vein is observed to flatten or lose its dark blue color on retraction, this generally indicates that its retraction limit has been reached. In LCIV types II and III, the low iliocaval junction can often be seen in this surgical corridor and precludes placement of the usual upside LCIV retractor blade, which instead retracts the soft tissue only just superficial to the LCIV for continued visualization.

An annulotomy is made in the visualized space available and the anterior longitudinal ligament (ALL) is released. Disk preparation is performed in the usual fashion, taking great care not to injure the LCIV, which is near all the diskectomy tools in the surgical field of view. Upgoing curets and other angle instruments are helpful to remove the disk material underneath the remaining annulus behind the LCIV, similar to a standard TLIF diskectomy technique. Once the endplates are prepared, the disk space is packed with bone graft, and a TLIF footprint bullet cage is then placed through the available annulotomy using the available TLIF cage inserter ([Fig. 1]). Because the cage is being placed in “reverse” orientation, the lowest degree of lordosis is chosen (generally 0 or 5 degrees) while still sizing to an appropriately desired height. One or two separate retention screw and washers are then placed carefully to avoid injuring the nearby LCIV. Intraoperative imaging is used to confirm satisfactory placement and closure then proceeds in the usual fashion.

Fig. 1 (A) Lateral and (B) anteroposterior (AP) fluoroscopic views of the bullet transforaminal lumbar interbody fusion (TLIF) cage being placed through the lateral anterior surgical access.

Results

A total of four patients (all females) underwent surgical intervention ([Table 1]). The mean age was 59.0 (range: 32–73) years, the mean body mass index (BMI) was 23.9 (range; 19.6–28.6), and the mean follow-up period was 14 (range: 6–20) months. The diagnosis was degenerative in three patients and deformity in one patient. Patients 1 and 2 were noted to have their LCIV unexpectedly obstructing the L5–S1 disk space intraoperatively, whereas patients 3 and 4 were suspected preoperatively to this difficult anatomy. All patients subsequently had titanium TLIF bullet cages placed and secured with washers and screws ([Fig. 2]). Patients 1 to 3 completed their single position surgery with pedicle screws placed in the same setting while still in the lateral decubitus position, while patient 4 underwent her staged placement of pedicle screws for her minimally invasive deformity correction on another day as planned. There was no direct decompression performed at the L5–S1 level for any of these patients.

Table 1 Patient clinical and radiographic data

Pt	Age/sex	BMI	Procedure	Preoperative L5–S1			Postoperative L5–S1			Preoperative NRS		Postoperative NRS
				SL (degrees)	IDA (degrees)	PDH (mm)	SL (degrees)	IDA (degrees)	PDH (mm)	Back pain	Leg pain	Back pain	Leg pain
1	70F	23.6	SPS L4–L5 OLIF, L5–S1 L-ALIF	10	1	0	17	16	5.8	10	10	2	0
2	61F	23.8	SPS L4–L5 OLIF, L5–S1 L-ALIF	15	6	3.5	18	10	9.6	6	5	1	0
3	32F	19.6	SPS L5–S1 L-ALIF	17	7	8.0	32	24	9.2	8	9	5	1
4	73F	28.6	L1–L5 OLIF, L5–S1 L-ALIF	17	11	5.5	27	25	7.2	8	0	7	0

Abbreviations: BMI, body mass index; IDA, intradiskal angle; L-ALIF, lateral anterior lumbar interbody fusion; NRS, numerical rating scale; OLIF, oblique lumber interbody fusion; PDH, posterior disk height; Pt, patient; SL, segmental lordosis; SPS, single position surgery.

Fig. 2 Preoperative and postoperative standing lumbosacral films showing the single position lateral anterior lumbar interbody fusion (L-ALIF) surgery utilizing the anterior transforaminal lumbar interbody fusion (TLIF) cage placement.

The L5–S1 segmental lordosis increased by 8.3 ± 6.1 degrees with a final mean lordosis of 23.5 ± 8.4 degrees; the L5–S1 intradiskal angle increased by 12.0 ± 7.0 degrees with a final mean disk angle of 18.8 ± 7.0 degrees; and the posterior disk height increased by 4.4 ± 2.7 mm with a final mean disk height of 8.0 ± 2.1 mm. All patients experienced clinical resolution of radicular pain associated with the L5–S1 level through indirect decompression alone. The mean numerical rating scale (NRS) for back pain improved by 5.3 ± 2.5 and the mean NRS for leg pain improved by 7.7 ± 2.5 with all patients expressing improvement or complete resolution of any preoperative leg pain. There were no perioperative complications or reoperations and no implant failure, haloing, or subsidence.

Discussion

The traditional supine ALIF at L5–S1 is a powerful approach that provides regional correction, indirect decompression, realignment, and fusion.[13] [14] Another one of the most commonly used approaches for L5–S1 interbody fusion involves the TLIF. Since this is a posterior approach, it is often a more familiar approach for spine surgeons and allows for placement of pedicle screws and rods in the same position. However, studies have shown that the ALIF approach continues to have its advantages, which include high fusion rates, good restoration of disk height and lordosis, and a reduced risk of dural injuries compared to the TLIF approach.[14] [15]

The minimally invasive L-ALIF offers the same benefits as the traditional supine ALIF, while also providing spine surgeons the additional benefits of a more minimally invasive incision and single position surgery with posterior pedicle screw fixation without repositioning the patient.[5] Similar to the supine ALIF, the L-ALIF approach requires special consideration of vascular anatomy, particularly the LCIV. Given the positioning of the patient for an L-ALIF at L5–S1, the LCIV is commonly encountered and must be carefully handled. Chung et al outlined three types of LCIV that can be seen on MRI.[11] In type I, the LCIV runs laterally more than two-thirds the length of the left L5–S1 disk. In type II, the LCIV obstructs the L5–S1 disk space, but perivascular adipose tissue is present, and it can be easily mobilized. In type III, the LCIV obstructs the disk space and no perivascular adipose tissue is present. Additionally, the diskectomy corridor is quite narrow, and there is difficult LCIV mobilization. Both type II and III LCIV anatomy represents low iliocaval junctions and studies have demonstrated that vessel injury rates were higher in these settings due to the retraction of these vessel types for ALIF footprint cages.

Because MRI is performed supine, the dynamic nature of tissue includes the possibility that the vasculature may shift slightly in the lateral decubitus position. The large cut slices or gantry of an MR image may not necessarily always demonstrate the exact anatomy of the LCIV at the disk space. Finally, if the LCIV is stretched across the disk space or if the patient is dehydrated, the vein may not be fully appreciated ([Fig. 3]). In these four cases, the LCIV was noted intraoperatively to be at the midline with a low iliocaval junction, and could not be mobilized laterally enough for even the smallest ALIF interbody cage geometries, which typically are 30 to 32 mm wide ([Fig. 4]). Instead of aborting the case and converting to a completely posterior TLIF approach, the anterior surgical exposure was taken advantage of, and a smaller TLIF footprint cage was placed anteriorly. Given the release of the ALL and anterior annulus, this technique still allowed for greater lordosis correction and realignment than would be possible from a completely posterior TLIF approach.[16] [17] Despite flat cages being used, we believe that lordosis was still achieved due to release of the ALL and the direct anterior distraction of the disk space and restoration of its height, while still providing anterior load sharing. This was reflected in radiographic improvements similar to and consistent with prior L-ALIF literature,[5] and all patients experienced clinical improvements from their preoperative symptoms with an average reduction of 5.3 on NRS for back pain and reduction of 7.7 on NRS leg scores. From a workflow perspective, this bailout option also allowed for the surgical procedures to proceed as planned with single position lateral surgery for patients 1 to 3, and a circumferentially minimally invasive deformity correction for patient 4, avoiding unanticipated disruptions that would have been encountered with repositioning and changes in the surgical plan or further rescheduling for another day.

Fig. 3 (A) Axial T2 MRI view of the L5–S1 disk space in patient 1 demonstrating a thin inferior border of the LCIV as noted by the arrow. (B) Intraoperative view demonstrating the very low iliocaval junction and inability to retract a window for a larger footprint anterior lumbar interbody fusion (ALIF) cage. Noted is the titanium transforaminal lumbar interbody fusion (TLIF) cage already placed in between the left common iliac vein (LCIV) and right common iliac vein (RCIV) between the available space of the iliocaval junction.

Fig. 4 (A) Axial T2 MRI view of the L5–S1 disk space in patient 2 demonstrating what initially was believed to be a widely split left common iliac vein (LCIV) without any intervening venous structures at the middle of the disk space as noted by the arrow. (B) Intraoperative view of a large LCIV, which in retrospect was flattened on MRI in front of the disk space. The asterisk denotes the center of the disk space; while attempts were made to retract this vein, which had already been dissected and freed, the proximal low iliocaval junction prevented this from being mobilized wide enough for a 32-mm-wide anterior lumbar interbody fusion (ALIF) footprint cage.

Patients 3 and 4 had preoperative imaging demonstrating type II LCIV anatomy, so there was an understanding that there was an increased likelihood that a large ALIF interbody would not be able to be used. After careful consideration of the patients' symptoms, anatomy, and other surgical approaches and discussion with the patients, it was determined that proceeding with an L-ALIF was the best option. Given the success in patient outcome and radiographic improvements seen in the first two patients despite conversion to placement of an anterior TLIF cage, the surgeon was comfortable proceeding with the intention of an L-ALIF knowing that the procedure may have to be converted to an anterior TLIF. Given these findings, surgeons who are experienced with the L-ALIF approach may even be able to offer L-ALIF approaches for patients with type II LCIV if they feel comfortable converting to an anterior TLIF.

Nevertheless, there are significant limitations to this case series. Because the TLIF bullet cages are being implanted in reverse orientation from the front, it remains unknown whether there will be any longer-term effects on subsidence, implant loosening, or fusion rates even though there have been no noted implant-related failures across our mean follow-up period thus far. We provide this report to demonstrate that while not ideal, placement of smaller TLIF bullet cages was feasible and both clinically and radiographically successful. To this end, this option can still serve as a bailout option and alternative to aborting the L-ALIF approach altogether if difficult LCIV anatomy is encountered concomitant with an interbody window too small for a standard ALIF footprint cage.

Conclusion

Although preoperative imaging can demonstrate favorable vascular anatomy in the supine position and in a sequence of pictures, unexpected anatomical vascular challenges can present themselves intraoperatively when performing an L-ALIF at L5–S1. Here we present four cases in which placing a TLIF bullet cage from the L-ALIF approach is a feasible, safe, and effective bailout option for surgeons who encounter anatomical challenges that prevent the ability to place a larger ALIF footprint interbody cage.

Conflict of Interest

M.H.P. reports receiving consulting fees from Medtronic, Globus, Carlsmed, and NovApproach.

Authors' Contributions

T.Y.K. contributed to acquisition of data and drafting of the article and gave final approval of submitted version. M.H.P. contributed to the conception and design of the study, analysis and interpretation of data, and revising the article, and gave final approval of the submitted version.

Ethical Approval

This research was approved by the medical center's institutional review board, the patients consented to the procedure, and the participants and any identifiable individuals consented to publication of his or her image.

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Publication History

Article published online:
20 March 2025