The oblique interbody fusion (OLIF), as a new type of minimally invasive technique, has good applicability at L2-L5. It has a wide range of indications including lumbar degenerative disease, spinal deformities, trauma, infections, and neoplasms [
There were a few cases using OLIF of L5-S1 in recent literatures; however, it is still quite difficult to perform OLIF51 because of the risks associated with stretch of the iliac vessels and the presence of the iliac wing disturbing insertion of the cage. Silvestre et al. [
Several studies have evaluated the size of OLIF51 surgical corridor. Capellades et al. [
The purpose of this study is to simulate the OLIF operation process at the L5-S1 level and then obtain anatomical data through CT image analysis, thus providing a way to evaluate the feasibility of OLIF51 and to minimize vascular complications in the preoperative planning stage.
120 consecutive patients undergoing lumbar CT examination at our hospital’s Department of Radiology from 1 October 2019 to 31 December 2019 were reviewed. All subjects had a clear thin-slice CT scan. Patients who had abdominal vascular abnormalities or diseases (i.e., abdominal aortic aneurysms, Budd-Chiari syndrome, abdominal aortic dissection, and iliac artery occlusion), spinal deformity from any cause, lumbar spondylolisthesis, transitional anatomy (i.e., sacralisation of L5, or lumbarisation of S1), lumbar fracture, or a surgical history on lumbar or retroperitoneum were excluded. The CT images were obtained via PACS (Picture Archiving and Communication System) with the patient in supine position. All the radiological measurements were measured and recorded by two independent researchers, and the average value was taken as the final result. This study was approved by the institutional review board following the declaration of Helsinki principles, and informed consent was obtained from all individual participants. The whole research is being reported in line with the STROCSS criteria [
The width of the OLIF cage is 18 mm (Medtronic, Inc, Minneapolis, Minnesota). As the actual operative window for OLIF is not less than the width of a cage, the author adopts 18 mm as the width of surgical corridor to simulate the operation process. The midline of surgical corridor is at the center of the L5-S1 disc, and the dorsal margin of surgical corridor is close to the left iliac crest. We assumed that the cage is inserted obliquely with the midline going through the center of the L5-S1 disc (Figure
Illustration showing the simulated surgical corridor. The midline of surgical corridor is at the center of the L5-S1 disc and the dorsal margin of surgical corridor is close to left iliac crest. Distance
On the axial plane of the L5-S1 disc, the area between the median line and the left edge of the intervertebral disc was equally divided into three zones. Patients were classified into three groups according to their right edge of the left iliac vein: lateral, intermediate, and medial (Figure
Diagram showing the anteroposterior diameter, the left-right diameter of L5-S1 disk, and the proposed classification for left common iliac vein positions. As shown in the figure, the left common iliac vein is classified into intermediate group.
We used the classification established by Capellades et al. [
Diagram showing the proposed classification for iliocaval junction positions.
In the present study, we proposed a new index that can evaluate the traction distance of iliac vessels. We named this index the V-line. The “V” stands for “vessel” or “vein.” We defined V-line as a straight line dividing equally the surgical corridor which we simulated before. According to the V-line, all cases were divided into 2 groups: V-line (+) group and V-line (-) group. In the V-line (+) group, more than half of the left iliac vein region is located in the ventral part of V-line, so the corridor external to the left iliac vessels leads to less traction. In the V-line (-) group, more than half of the left iliac vein region is located in the dorsal part of V-line, which indicates that a surgical corridor between the bifurcations of the iliac vessels is more optimal (Figure
The diameter of the OLIF surgical corridor is 18 mm. The midline of the surgical corridor is at the center of the L5-S1 disc. Left, the V-line (-) group, more than half of the left iliac vein region is located in the dorsal part of V-line. In this situation, we could retract the LCIV dorsally. Right, the V-line (+) group, more than half of the left iliac vein region is located in ventral part of V-line. In this situation, we could retract the LCIV ventrally.
All the following parameters were analyzed and recorded in an axial plane of the center of the L5-S1 disc.
The anteroposterior diameter is defined as the maximal distance of the anterior and posterior border of the intervertebral disk; the left-right diameter is defined as the maximal distance of the left and right border of the intervertebral disk (Figure
It is defined as the angle between the surgical corridor and the horizontal line. This parameter simulated the cage implantation angle when a patient was placed in the right lateral decubitus position (Figure
It is defined as the minimum distance to retract the iliac vein out of the surgical corridor (Figure
It is defined as the minimum distance to retract psoas major out of the surgical corridor. In all cases, psoas major was retracted dorsally (Figure
Continuous variables were presented as
We accessed 93 CT data in this paper, consisting of 49 men and 44 women with a mean age of
Univariate analysis of risk factors for V-line (+) during OLIF51.
Risk factors | Patients with V-line (+), | Patients with V-line (-), | ||
---|---|---|---|---|
Sex | ||||
Female | 14 | 30 | 1.672 | 0.196 |
Male | 22 | 27 | ||
Age | -0.764 | 0.447 | ||
L5-S1 disk AP diameter | -0.229 | 0.820 | ||
L5-S1 disk left-right diameter | -1.564 | 0.121 | ||
Tilt angle of surgical corridor | 3.595 | 0.001 | ||
Sacral slope | 3.269 | 0.002 | ||
Low iliac crest# | ||||
High iliac crest | ||||
The left iliac vein position (VP) | ||||
Medial | 22 | 3 | 44.570 | <0.001 |
Intermediate | 13 | 20 | ||
Lateral | 1 | 34 | ||
The iliocaval junction position (JP) | ||||
Very high | 8 | 31 | 23.263 | <0.001 |
High | 16 | 22 | ||
Low | 0 | 3 | ||
Very low | 12 | 1 |
According to the VP classification, 35 patients (37.6%) were grouped in the lateral group, 33 patients (35.5%) in the intermediate group, and 25 patients (26.9%) in the medial group. Statistically significant difference was found between gender and the left iliac vein position. Males displayed a more medial position of LCIV.
According to the JP classification, 3 patients (3.2%) were grouped in the very high group, 39 patients (41.9%) in the high group, 38 patients (40.9%) in the low group, and 13 patients (14.0%) in the very low group. No statistically significant differences were found between gender and the iliocaval junction position (Table
Gender differences of the left iliac vein position (VP) and the iliocaval junction position (JP).
The left iliac vein position (VP) | Female | Male | ||
---|---|---|---|---|
Medial | 25 (26.9%) | 5 (5.4%) | 20 (21.5%) | 0.001 |
Intermediate | 33 (35.5%) | 15 (16.1%) | 18 (19.4%) | |
Lateral | 35 (37.6%) | 24 (25.8%) | 11 (11.8%) | |
The iliocaval junction position (JP) | ||||
Very high | 3 (3.2%) | 2 (2.2%) | 1 (1.1%) | 0.449 |
High | 39 (41.9%) | 21 (22.6%) | 18 (19.4%) | |
Low | 38 (40.9%) | 17 (18.3%) | 21 (22.6%) | |
Very low | 13 (14.0%) | 4 (4.3%) | 9 (9.7%) |
To evaluate precisely the ease of surgical exposure of OLIF51, the study population was classified into 4 configurations by combining traction distance of LCIV and psoas major. According to the four-configuration classification, 47 patients (50.5%) were included in P (-) V (-) group, 18 (19.4%) in P (-) V (+) group, 13 (14.0%) in P (+) V (-) group, and 15 (16.1%) in P (+) V (+) group. The P (+) V (+) group is considered not suitable for OLIF51 due to hard exposure. There were 61.3% (57/93) of the subjects that were defined as V-line (-) and 38.7% (36/93) as V-line (+) (Table
V-line and four-configuration classification system.
P (-) V (-) | P (-) V (+) | P (+) V (-) | P (+) V (+) | Total | |
---|---|---|---|---|---|
V-line (-) | 25 (26.9%) | 8 (8.6%) | 9 (9.7%) | 15 (16.1%) | 57 (61.3%) |
V-line (+) | 22 (23.7%) | 10 (10.8%) | 4 (4.3%) | 0 (0.0%) | 36 (38.7%) |
Total | 47 (50.5%) | 18 (19.4%) | 13 (14.0%) | 15 (16.1%) | 93 (100.0%) |
Chi-square analysis or Student
The multivariate analysis identified gender of male (
Multivariate analysis of risk factors for V-line (+) during OLIF51.
Risk factor | Odds ratio | 95% confidence interval | |
---|---|---|---|
Sex | 12.152 | 1.208-122.276 | 0.034 |
The left iliac vein position (VP) | 265.085 | 16.629-4225.839 | <0.001 |
Tilt angle of surgical corridor | 0.750 | 0.632-0.890 | 0.001 |
Age | — | — | 0.112 |
L5-S1 disk AP diameter | — | — | 0.712 |
L5-S1 disk left-right diameter | — | — | 0.970 |
Sacral slope | — | — | 0.696 |
The iliocaval junction position (JP) | — | — | 0.364 |
OLIF51 is considered as minimally invasive ALIF through the oblique corridor in the lateral position [
Many literatures have proved the practicability of OLIF51 [
Similar to ALIF L5-S1, OLIF51 typically involves the corridor under the bifurcation of the great abdominal vessels [
In our study, the author adopted 18 mm as the width of surgical corridor to simulate the operation process. We had reason to believe that traction-difficultly structure will obstruct the OLIF working corridor, and there will be excessive stretch of these structures during the procedure. More than 1/3 of the subjects (33/93, 35.5%) were grouped into traction-difficultly LCIV and nearly three in 10 (28/93, 30.1%) were grouped into traction-difficultly PM. Further analysis revealed that about one-sixth of the subjects (15/93, 16.1%) processed traction-difficultly LCIV and traction-difficultly PM at the same time. Because left common iliac vein and psoas major account for more than half of OLIF working corridor, causing difficulty in operating channel placement and increased injury risk of these structures. Therefore, we consider these subjects not suitable for OLIF51, while the P (-) V (-) group is obviously the most ideal situation. And as for the other two groups, namely, the P (-) V (+) group and P (+) V (-) group, the former gives us a large operation space for psoas major and the latter for vessel. This classification could help spine surgeons make preoperative planning and guide the surgical management.
The anatomical structure of the lumbosacral segment is complex and adjacent to the important structure. Damage to LCIV is the most threatening complication associated with OLIF51 which can be very difficult to control once injured, and mobilization of these vascular structures is often a technically demanding procedure [
In 2017, Chung et al. [
During the surgery, surgeons have to mobilize LCIV for surgical exposure when it obstructs the operative window on the L5-S1 disc. We could mobilize LCIV laterally choosing the central disk space between the bifurcations or stretch it medially choosing lateral disk space external to the left iliac vessels. However, which approach might reduce the risk of mobilization has not been comprehensively studied. Previous work on the morphological characteristics of the LCIV cannot solve the problem properly. In this thesis, a new concept, V-line, is proposed for assessing the mobilization risk of these two approaches. By introducing the concept of V-line, we could qualitatively evaluate the extent of vascular traction of two approaches to guide surgical treatment.
In our work, there were 61.3% (57/93) of the subjects were defined as V-line (-). In this group, a surgical corridor between the bifurcations of the iliac vessels is more favorable which is exactly the mainstream approach in the world. One important concern with this approach is the injury to the SHP (superior hypogastric plexus), which overlies the L5-S1 disk between the bifurcations and supplies the sympathetic function for the urogenital system [
Naturally, the rest of the subjects (36/93, 38.7%) were defined as V-line (+), in which the corridor external to the left iliac vessels is superior for less stretch of the LCIV. On this condition, particular attention should be paid to the identification and handling of the iliolumbar vein (ILV) [
Recently, many studies analyzing the venous anatomy in the lumbosacral area have been reported. Whether they are useful for predicting the surgical approach of OLIF51? Multiple variables regressive analysis demonstrated that gender of male, medial position of LCIV, and high iliac crest were predictive factors of V-line, while age of the patient, L5-S1 disk size, sacral slope, and iliocaval junction position (JP) were not. As to the left iliac vein position (VP), it is found that almost all subjects of the medial group were classified into the V-line (+) group and they accounted for nearly 2/3 of the V-line (+) group. In addition, the height of iliac crest is also crucial for the preoperative evaluation, there were more than half of low iliac crest group could choose an external corridor to decrease the stretch of the LCIV. However, the iliocaval junction position (JP) was not a crucial factor. A possible explanation for this is that although lower junction positions have more medial LCIV, it is not the only factor, the junction angle will affect the distribution pattern of iliac vein as well. Therefore, in the clinical practice of OLIF51, a comprehensive, detailed analysis and conventional CT examination is important to minimize the vascular injury. For patients who are V-line (+), mainly among males having the LCIV near the midline or the iliac crest relatively low, a surgical corridor external to the LCIV should be taken into consideration, and vice versa. Finally, it is worth noting that all the subjects in P (+) V (+) group were divided into V-line (-) taking almost a quarter of the V-line (-) group, indicating potential difficulties in operating procedure.
The present research has several limitations. First, the study object of this article is patients undergoing lumbar CT examination, whose regional anatomical character in the lumbosacral area are different from those with lumbar degeneration disease. In addition, we did not include the disc height in the measurement which might change in different pathologies and impact the result of the iliocaval junction position. The second limitation concerns the patient’s position, as CT images are obtained in the supine position, whereas OLIF is performed in the right lateral decubitus position, the location and configuration of LCIV and psoas major may vary [
This study demonstrated that the majority of the patients were suitable for OLIF51 without excessive traction of the LCIV and the psoas major. There was a relatively high incidence of V-line (+) in the Asian population. Among male patients having the LCIV near the midline or the iliac crest relatively low, a surgical corridor external to the LCIV should be taken into consideration to minimize the risk of vascular injury.
The study had been registered in chictr.org.cn (UIN =
Left common iliac vein
Oblique lumbar interbody fusion
Anterior lumbar interbody fusion
Lateral lumbar interbody fusion
Left iliac vein position
Iliocaval junction position.
The datasets used to support the findings of this study are available from the corresponding author upon request.
This study was approved by the institutional review board following the declaration of Helsinki principles.
Informed consent was obtained from all individual participants. The whole research is being reported in line with the STROCSS criteria.
The authors declare that they have no competing interests.
This article has been presented as preprint according to the following link: