Single transverse-orientation cage via MIS-TLIF approach for the treatment of degenerative lumbar disease: a technical note

Abstract

Background: Single transverse cage placed in the anterior vertebral column can better maintain lumbar lordosis and sagittal alignment and is frequently used via the lateral transpsoas approach. However, there is no clear description in the literature of the steps required to place the single transverse cage during the instrumented transforaminal lumbar interbody fusion (TLIF) procedure for the treatment of degenerative lumbar disease. The objective of this study is to describe the technique using single transverse-orientation cage when performing TLIF procedures. Materials and methods: We present 18 illustrative cases in which single transverse-orientation cage was placed according to a step-by-step technique that can be used during the TLIF procedure. Information acquired included procedure time, intraoperative blood loss and postoperative complications. The preoperative and postoperative Oswestry Disability Index (ODI) and the visual analogue scale (VAS) scores were recorded. Changes in disc height and segmental lordosis were measured at radiographs. Results: The single transverse-orientation cage was successfully placed in 18 patients in a stepwise technique to achieve lumbar fusion. Using this technique, the patients significantly improved clinically and radiographically at postoperative visits. Conclusions: This is the first report demonstrating the safety and efficacy of instrumented TLIF with single transverse-orientation cage for the treatment of degenerative lumbar disease. Single transverse-orientation cage via MIS-TLIF approach can maintain greater lumbar lordosis and avoid the unique complications of lateral transpsoas approach. Understanding the options for cage placement is important for surgeons considering the use of this technique.

Introduction

Transforaminal lumbar interbody fusion (TLIF) is a popular technique for treatment of degenerative lumbar diseases. The safety and efficacy of this technique have been demonstrated in many clinical studies [1-3]. TLIF results in less destruction of the posterior elements and less gross destabilization of the spine, which maximize fusion stability. Furthermore, it allows better access to the neuroforamen and reduces the need to manipulate spinal nerve roots [4,5]. Due to the simplified procedure and the unilateral technique, operative time, potential blood loss and the risk to neural structures is reduced [6].

Instrumented TLIF with the implantation of two interbody cages has been widely recommended as a standard procedure to restore segmental alignment and achieve successful fusion. This recommendation is based on the assumption that two cages provide adequate stability, but there are several practical problems with two cages. First, the use of two cages may place the posterior foramina at risk laterally, especially with a thick disc, when larger diameter cages are necessary. Second, incomplete disc excision may occur with reaming, especially if the endplates are biconcave, thus limiting the fusion environment. Third, it is difficult to achieve symmetric positioning with two cages. Fourth, a very wide lateral vascular mobilization and retraction is necessary with two cages. Fifth, the insertion of two cages could result in higher direct costs to the patient, as well as extending operative time. These drawbacks could be offset to some extent by the use of single cage.

Will implanting a single cage achieve acceptable balance, stability, and successful fusion? Previous in vitro biomechanical studies have shown that the stiffness with a single cage was statistically equivalent to two standard cages in all modes of testing (including compression, flexion, extension, left and right lateral bending, and left and right torsion) [7-9]. Several studies on TLIF with one oblique-orientation cage instead of two have already been reported [10-15]. Their results suggest that there are equivalent or even better outcomes with a single cage than for patients who received two cages supplemented with transpedicle screws.

There are few reports that focus on the direction of cage insertion during lumbar interbody fusion. Some authors favor the use of oblique insertion of the single cage with instrumented TLIF [12,16]. However, current studies [17,18] found that achieving sufficient lumbar lordosis and sagittal balance usually require an anterior lumbar cage through lateral transpsoas approach. We describe here the technical steps used to place single transverse-orientation cage via the MIS-TLIF procedure as an attempt to enhance lumbar lordosis restoration and an alternative method to avoid the unique complications of lateral transpsoas approach.

Surgical technique

All operations were performed by the same surgeon (Jun Tan). The MIS-TLIF procedure was performed essentially as reported in previous studies [10,16], with one cage packed with excised local bone. Briefly, after pedicle screws are inserted, a box cutter was used to open the entry into the disc space. Initial distraction of the disc space was necessary to access the disc for a thorough discectomy. Distraction was achieved by using dilators. After performing a complete discectomy and curettage of the endplate, copious irrigation was used. To achieve a solid interbody fusion, the disc space was filled with as much bone graft material as possible.

The cage (Concorde Bullet, Depuy Spine, MA, USA) size was determined by both preoperative templating and intraoperative evaluation, using a trial cage to confirm initial stability. An appropriate-sized cage filled with excised local bone was inserted into the disc space and positioned in the transverse orientation, assisted by an inserter guide rail. The step-by-step surgical procedure is illustrated in Figure 1.

Figure 1.

A-D. Summary of the technique steps (insertion and rotation) for placement of transverse-orientation cage.

A control intraoperative lateral fluoroscopic image was obtained and the correct position of the cage was checked. After the pre-lordosed rod was seated and compression applied, the contralateral facet and bilateral transverse processes were decorticated and packed with a locally excised bone graft. Brace support was recommended for 6-8 weeks after surgery.

Clinical and radiological assessment

The analysis included the following factors: feasibility of the procedure, blood loss, operative times, complications, re-operations, implant failures, neurological recovery and radiologic assessments. Follow-up consisted of evaluation during clinical visits and postoperative radiographs. Neurological outcomes were assessed by patients using the Oswestry Disability Index (ODI) and visual analog scale (VAS) questionnaires. Radiologic outcomes including segmental lordosis (SL) and disc height (DL) were analyzed at plain radiographs (Figure 2).

Figure 2.

Method of measuring anthropometric paramaters. A. DH (disc height): the average value of a (anterior disc height) and b (posterior disc height). B. SL (segmental lordosis): the angle between tangent lines to the inferior endplate and the superior endplate of two adjacent vertebrae.

Results

Cages were implanted successfully in all patients. No infections of the incisions or deep infections were found after surgery, and no patients exhibited postoperative aggravation of nerve damage.

Significant improvement in back or leg pain scores and Oswestry scores were observed. Radiologic data also revealed a significant difference in the segmental lordosis and disc height between the preoperative and postoperative periods (Table 1). Cage loosening or migrating was not observed during the follow-up period.

Table 1.

List of initial 18 cases of TLIF with transverse cage

Patient	Sex	Age	Pre diagnosis	Operative level	Operative time (min)	Blood loss (ml)	FU (mo)	ODI (%)	VAS (back)	VAS (leg)	CM	DH	SL
								Pre/Post	Pre/Post	Pre/Post		Pre/Post (mm)	Pre/Post (°)
1	M	53	HNP	L4/L5	109	220	8	68/26	8/1	8/2	No	10.5/12.9	5.9/9.3
2	M	60	SPNDY	L3/L4/L5	137	345	6	47/18	7/1	7/1	No	10.2/12.5	6.1/9.0
3	M	74	HNP	L4/L5/S1	148	360	4	71/25	8/2	8/3	No	9.8/11.6	5.4/7.5
4	M	54	HNP	L4/L5	132	335	5	52/20	7/1	8/3	No	10.8/13.2	6.4/9.6
5	F	36	SPNDY	L4/L5	97	190	7	41/18	6/2	7/2	No	9.7/11.5	6.9/9.7
6	F	54	SPNDY	L4/L5	127	310	6	63/21	7/3	8/1	No	8.5/10.8	5.0/8.2
7	M	72	HNP	L4/L5/S1	157	355	9	57/17	7/1	7/2	No	8.7/11.3	4.3/7.8
8	M	63	HNP	L4/L5	136	315	8	44/13	6/2	7/1	No	9.5/12.0	5.9/8.7
9	F	32	SPNDY	L3/L4/L5	150	350	10	50/11	7/1	8/2	No	9.9/12.2	6.6/10.4
10	F	55	HNP	L5/S1	112	210	7	57/19	8/3	9/4	No	9.0/11.9	4.6/7.9
11	F	61	SPNDY	L4/L5	148	330	4	71/24	5/1	7/2	No	8.1/11.2	4.4/8.1
12	M	52	SPNDY	L3/L4	139	270	6	60/19	8/4	7/3	No	10.1/13.0	5.6/8.7
13	F	68	SPNDY	L4/L5	142	290	7	48/17	6/2	8/1	No	8.9/11.7	4.2/7.8
14	M	63	HNP	L3/L4	92	165	8	55/16	7/2	7/2	No	9.2/12.6	5.7/8.6
15	M	76	SPNDY	L4/L5/S1	132	310	6	64/21	7/3	8/2	No	9.4/11.4	4.0/8.1
16	F	45	SPNDY	L5/S1	112	190	8	57/14	6/3	7/2	No	8.9/11.6	5.6/8.4
17	F	39	HNP	L3/4/5/S1	175	380	5	69/17	8/2	8/2	No	9.1/12.7	6.8/10.5
18	F	58	SPNDY	L4/L5	130	300	8	51/22	6/1	7/2	No	8.8/11.9	5.3/8.4
Mean	9M/9F	56.39±12.57	9HNP/10SPNDY	~~	131.94±21.26	290.28±67.00	6.78±1.66	57.50±12.24/19.28±7.00	6.89±0.90/1.94±0.94	7.56±0.62/2.06±0.80	~~	9.39±0.73/12.00±0.69	5.48±0.91/8.69±0.89
P								<0.001	<0.001	<0.001		<0.001	<0.001

F, female; M, male; SPNDY, spondylolisthesis; HNP, herniated nucleus pulposus; FU, follow-up; mo, months; Pre, preoperative; Post, postoperative, DH, disc height; SL, segmental lordosis CM, cage migration.

Illustrative case

A 74 year-old male presented with chronic low back pain, left leg pain and sciatica for 10 years. Magnetic resonance imaging (MRI) revealed a L4-5 left herniated nucleus pulposus with severe L4-5 spinal stenosis, disc collapse at L5-S1 (Figure 3A, 3B). We recommended L4-S1 instrumented fusion with single transverse cage which followed the same steps we have described above. Postoperative images showed that transverse-orientation cage via MIS-TLIF was placed successfully into the anterior vertebral region (Figure 3C-E).

Figure 3.

Illustrative case. A and B show the preoperative radiographs. C-E show the postoperative radiographs. The transverse-orientation cage (red arrow) was placed successfully into the anterior vertebral region.

Discussion

TLIF with one cage simplify the standard TLIF procedure, shorten operative times, and provide satisfactory clinical outcomes. Our results demonstrate that single transverse cage via instrumented MIS-TLIF is also a effective method to increase lumbar lordosis and avoid complications of the lateral transpsoas approach, which also known as extreme lateral interbody fusion (XLIF) or direct lateral interbody fusion (DLIF), for the treatment of lumbar degenerative diseases.

This method has some obvious advantages. It is an easier technique than the routine two-cage TLIF or one-cage DLIF. In treatment of patients with unilateral sciatica, the cage can be placed from the symptomatic side, which avoids retraction of the nerve root and dural sac of the asymptomatic side. As the application of the supplementary instrumentation can immediately provide adequate postoperative stability, an undersized cage can be used without concern about displacement. Regarding the surgical procedure, single-cage via MIS-TLIF also has the advantages of less blood loss, shorter surgery time, and a shorter hospital stay.

However, the surgical differences may favor the use of oblique insertion of the cage, as this requires less exposure, enables precise implantation, especially when used with supplementary instrumentation. Wang et al. [19] compared the stabilities imparted by cages placed using oblique and conventional posterior approaches, and found that for cages used alone, the stability differed as a function of cage orientation was different. With supplementary posterior fixation, the differences resulting from cage orientation were significantly reduced, both before and after cyclic tests [19]. Harris et al. [20] found that the position of the cage did not change the stiffness or stability. Heth et al. [21] demonstrated that transversely implanted threaded fusion cages allowed a greater range of motion in all directions immediately after implantation and after fatiguing.

Intervertebral height and lumbar lordosis reconstruction are important for achieving good surgical results [22]. Suh et al [17] found out that achieving sufficient lumbar lordosis and sagittal balance require an anterior lumbar cage. Kepler et al [22,23] reported that anterior cage placement results in greater lordosis while middle/posterior placement has a minimal effect on sagittal alignment and change in disc height was significantly associated with an anterior cage position. Most authors favor the use of oblique insertion of the single cage with instrumented TLIF [12,16]. The disadvantage to this technique is that this cage may also have the potential to decrease the amount of lordosis due to its placement in a back-to front position where it blocks the posterior third of the vertebral bodies from coming into closer apposition and consequently lordosis when pedicle screws are compressed [24]. In our study, cage was placed into the anterior aspect of the disc space and thus overcome this problem and increase segmental lordosis and disc space.

Indications for the use of single fusion cages in the lumbar spine have not yet been fully established or proven by long-term outcome studies. In this study, we only chose patients with degenerative spondylolisthesis and lumbar disc herniation accompanying severe back pain and unilateral sciatica.

In this study, a single cage was positioned in the transverse orientation to restore and maintain the sagittal balance of the motion segment. Although theoretically, a larger angle of declination of the oblique orientation of the cage is better for restoring the sagittal balance of the motion segment [25,26], the angle of the oblique orientation should be determined by the operative circumstances. In addition, limited visual access into the intervertebral space does not allow optimal positioning of the cage. In our experience, the transverse orientation of the cage should be considered and encouraged.

Because this is a technical note, we report mainly on the feasibility and safety of this procedure, and not long-term outcomes or fusion rates. The number of patients in this study was selected primarily to illustrate the technique, not to evaluate long-term outcomes. Further studies with larger patients numbers, longer follow-up periods, and comparison with standard TLIF will be needed to demonstrate the durability of the technique.

Conclusion

We performed MIS-TLIF using transverse orientation of single cage to increase lumbar lordosis and avoid the unique complications of DLIF or XLIF. Compared to routine TLIF, this technique is clinically safe, easy, and economical to treat lumbar degenerative disease. Understanding the options for cage placement is important for surgeons considering the use of this technique.

Disclosure of conflict of interest

None.