Keywords stand-alone LLIF - lateral lumbar interbody fusion - lumbar spine - dimension - lumbar
endplate diameter
Introduction
Minimally invasive spine surgery represents an increasingly favored method of addressing
spinal disorders. A prominent technique within this approach is the lateral lumbar
interbody fusion (LLIF), which has demonstrated efficacy in treating various spinal
pathologies, including low-to-moderate spinal canal stenosis, lateral recess and/or
foraminal canal stenosis, low-grade spondylolisthesis (grades I–II), degenerative
scoliosis, and degenerative disc disease.[1 ]
[2 ] Previously, the standard LLIF with supplemental fixation procedure typically utilized
an 18-mm anterior–posterior (A-P) cage, but there have been recent developments in
the form of 22- and 26-mm wide cages aimed at reducing the risk of subsidence, particularly
in osteoporotic patients.[3 ]
Stand-alone LLIF is the trans-psoas approach technique that offers the advantage of
maintaining segmental stability without supplemental fixation. However, previous studies
have indicated higher rates of cage subsidence when LLIF is performed without additional
instrumentation.[4 ]
[5 ] Recent literature suggests that using a 26-mm wide cage for stand-alone LLIF results
in a significantly reduced cage subsidence rate.[2 ]
[3 ] It is important to note that most of the existing literature is based on studies
conducted on Caucasian populations, which have a larger anatomical structure compared
with Asians. Therefore, further studies on the morphologic vertebral body in the Asian
population are warranted to determine the most suitable wide cage size for stand-alone
LLIF.
The purpose of this study is to establish a precise database concerning the width
of the vertebral endplate, A-P width of the vertebral endplate, and intervertebral
disc height of the lumbar spine in Asian populations.
Materials and Methods
A total of 91 digitized computed tomography (CT) images of the lumbosacral spine were
obtained from patients experiencing back pain, all of whom had negative findings in
their CT scans between 2017 and 2021. Approval for the study was obtained from the
Committee on Human Rights Related to Research Involving Human Subjects at Lerdsin
Hospital. The digitized CT images underwent measurement and analysis using the Picture
Archiving Communication System. The analysis encompassed the measurement of the superior
and inferior vertebral endplate width, superior and inferior vertebral endplate depth
(A-P width), and intervertebral disc height of the lumbar spine. The superior vertebral
endplate width is determined as the maximum distance of the superior endplate, measured
from a tangentially drawn line connecting the lateralmost edges of the superior endplate
([Fig. 1A ]). Similarly, the inferior vertebral endplate width is ascertained as the maximum
distance of the inferior endplate, measured from a tangentially drawn line connecting
the lateralmost edges of the inferior endplate. Moreover, the superior vertebral endplate
depth (A-P width) is defined as the maximum distance of the superior endplate, measured
from a perpendicular line drawn from the anteriormost edge of the superior endplate
to the posterior edge of the superior endplate ([Fig. 1A ]). Likewise, the inferior vertebral endplate depth (A-P width) is defined as the
maximum distance of the inferior endplate, measured from a perpendicular line drawn
from the anteriormost edge of the inferior endplate to the posterior edge of the inferior
endplate. Finally, the intervertebral disc height is defined as the maximum distance
of the intervertebral disc, measured from a vertical line drawn from the inferior
endplate of the cephalad vertebra to the superior endplate of the caudal vertebra
([Fig. 1B ]). The data will be reported using the mean and standard deviation (SD). An intraclass
correlation coefficient (ICC) was employed to assess the reliability of the measurements.
Given that a single observer (T.P. for blinding) conducted all the measurements, a
two-way random-effects model with absolute agreement analysis was utilized.
Fig. 1 (A, B) Measurement of superior vertebral endplate depth is defined as the maximum
distance of the superior endplate, measured from the perpendicular line drawn from
the anteriormost edge of the superior endplate (a) to the posterior edge of the superior
endplate (b). Measurement of superior vertebral endplate width is defined as the maximum
distance of the superior endplate, measured from the line drawn tangentially from
the lateralmost edge of the superior endplate (c) to another lateralmost edge of the
superior endplate (d). Measurement of the intervertebral disc height is defined as
the maximum distance of the intervertebral disc, measured from the vertical line drawn
from the inferior endplate of the cephalad vertebra (e) to the superior endplate of
the caudal vertebra (f).
Results
A total of 91 digitized CT images encompassing 455 lumbar spine vertebrae were subject
to measurement. The cohort comprised 52 males (57.1%) and 39 females (42.86%), with
a mean age of 46.0 years (SD = 13.7), ranging from 17 to 69 years. The reliability
analysis exhibited an ICC value of 1.00 across all measurements. [Table 1 ] succinctly presents the mean values, SDs, and range of data for the lumbar spine
(L1–L5) derived from measurements of axial and sagittal CT images of the 91 subjects.
Table 1
The mean measurements of various anatomical dimensions, encompassing SVEW, SVED, IVEW,
IVED, and IVDH derived from a cohort of 91 subjects
Parameters (mm)
Females
Males
t -test
Overall
L1
SVEW
39 ± 2.7 (33.7–45.2)
43.3 ± 3.3 (36.6–51.0)
p < 0.001
41.4 ± 3.7 (33.7–51.0)
SVED
28.8 ± 2.5 (24.1–33.8)
31.6 ± 3.0 (25.1–41.0)
p < 0.001
30.4 ± 3.1 (24.1–41.0)
IVEW
40.4 ± 2.6 (35.9–47.3)
45.3 ± 3.3 (40.0–51.9)
p < 0.001
43.2 ± 3.9 (35.9–51.9)
IVED
29.7 ± 2.2 (24.3–34.1)
32.4 ± 3.1 (23.1–41.0)
p < 0.001
31.3 ± 3.0 (23.1–41.0)
IVDH (T12/L1)
9.3 ± 1.6 (5.7–12.5)
9.0 ± 1.6 (5.0–13.0)
p = 0.33
9.1 ± 1.6 (5.0–13.0)
L2
SVEW
40.6 ± 2.5 (34.9–46.8)
45.8 ± 3.2 (38.9–52.9)
p < 0.001
43.6 ± 3.9 (34.9–52.9)
SVED
30.2 ± 2.5 (26.0–38.8)
33.1 ± 2.7 (26.6–41.3)
p < 0.001
31.8 ± 3.0 (26.0–41.3)
IVEW
42.7 ± 3.1 (36.0–50.0)
47.7 ± 3.5 (41.1–55.7)
p < 0.001
45.6 ± 4.1 (36.0–55.7)
IVED
31.9 ± 3.0 (26.0–41.3)
34.2 ± 2.7 (28.0–41.6)
p < 0.001
33.2 ± 3.0 (26.0–41.6)
IVDH (L1/L2)
10.1 ± 1.8 (6.6–13.7)
10.0 ± 1.7 (6.1–14.0)
p = 0.93
10.0 ± 1.7 (6.1–14.0)
L3
SVEW
43.1 ± 3.1 (35.4–48.4)
48.1 ± 3.7 (38.0–55.8)
p < 0.001
45.9 ± 4.2 (35.4–55.8)
SVED
31.8 ± 2.7 (22.5–37.4)
34.4 ± 2.3 (28.6–39.6)
p < 0.001
33.3 ± 2.8 (22.5–39.6)
IVEW
45.4 ± 3.3 (37.8–53.3)
50.5 ± 3.8 (42.2–58.4)
p < 0.001
48.3 ± 4.4 (37.8–58.4)
IVED
32.1 ± 2.2 (27.1–36.4)
35.0 ± 2.2 (30.0–40.2)
p < 0.001
33.7 ± 2.6 (27.1–40.2)
IVDH (L2/L3)
10.4 ± 2.0 (5.2–14.4)
11.8 ± 2.0 (6.7–16.6)
p = 0.001
11.2 ± 2.1 (5.2–16.6)
L4
SVEW
45.2 ± 3.4 (36.4–54.0)
49.6 ± 3.6 (40.7–57.7)
p < 0.001
47.7 ± 4.1 (36.4–57.7)
SVED
32.4 ± 2.2 (28.6–38.2)
35.0 ± 2.5 (29.0–42.2)
p < 0.001
33.9 ± 2.7 (28.6–42.2)
IVEW
46.6 ± 3.2 (37.9–53.5)
51.3 ± 3.4 (42.7–58.4)
p < 0.001
49.3 ± 4.0 (37.9–58.4)
IVED
32.9 ± 1.9 (29.0–37.5)
35.8 ± 3.1 (30.0–46.6)
p < 0.001
34.6 ± 3.0 (29.0–46.6)
IVDH (L3/L4)
11.5 ± 2.0 (6.7–16.1)
12.5 ± 2.1 (8.2–19.8)
p = 0.04
12.1 ± 2.1 (6.7–19.8)
L5
SVEW
46.1 ± 3.4 (39.3–54.0)
50.8 ± 3.6 (44.1–59.5)
p < 0.001
48.8 ± 4.2 (39.3–59.5)
SVED
32.9 ± 3.3 (23.2–43.6)
35.8 ± 3.2 (29.1–45.5)
p < 0.001
34.5 ± 3.5 (23.2–45.5)
IVEW
46.8 ± 3.0 (40.8–53.9)
50.2 ± 3.2 (41.9–58.3)
p < 0.001
48.7 ± 3.5 (40.8–58.3)
IVED
33.5 ± 2.6 (27.9–40.8)
35.7 ± 3.1 (29.3–44.6)
p < 0.001
34.8 ± 3.1 (27.9–44.6)
IVDH (L4/L5)
11.5 ± 2.1 (6.7–15.9)
13.0 ± 2.2 (8.4–19.4)
p = 0.001
12.4 ± 2.3 (6.7–19.4)
Abbreviations: IVDH, intervertebral disc height; IVED, inferior vertebral endplate
depth; IVEW, inferior vertebral endplate width; SVED, superior vertebral endplate
depth; SVEW, superior vertebral endplate width.
Superior Vertebral Endplate Width
The mean dimensions of the superior vertebral endplate width were as follows: at L1,
39 ± 2.7 mm for females, 43.3 ± 3.3 mm for males, and 41.4 ± 3.7 mm overall; at L2,
40.6 ± 2.5 mm for females, 45.8 ± 3.2 mm for males, and 43.6 ± 3.9 mm overall; at
L3, 43.1 ± 3.1 mm for females, 48.1 ± 3.7 mm for males, and 45.9 ± 4.2 mm overall;
at L4, 45.2 ± 3.4 mm for females, 49.6 ± 3.6 mm for males, and 47.7 ± 4.1 mm overall;
and at L5, 46.1 ± 3.4 mm for females, 50.8 ± 3.6 mm for males, and 48.8 ± 4.2 mm overall.
The average superior vertebral endplate width of females was consistently smaller
than that of males. Furthermore, there was a statistically significant increase in
superior vertebral endplate width from L1 to L5 (p < 0.05).
Inferior Vertebral Endplate Width
The mean dimensions of the inferior vertebral endplate width were as follows: at L1,
40.4 ± 2.6 mm for females, 45.3 ± 3.3 mm for males, and 43.2 ± 3.9 mm overall; at
L2, 42.7 ± 3.1 mm for females, 47.7 ± 3.5 mm for males, and 45.6 ± 4.1 mm overall;
at L3, 45.4 ± 3.3 mm for females, 50.5 ± 3.8 mm for males, and 48.3 ± 4.4 mm overall;
at L4, 46.6 ± 3.2 mm for females, 51.3 ± 3.4 mm for males, and 49.3 ± 4.0 mm overall;
and at L5, 46.8 ± 3.0 mm for females, 50.2 ± 3.2 mm for males, and 48.7 ± 3.5 mm overall.
The mean inferior vertebral endplate width of females was found to be generally smaller
than that of males. Additionally, there was a statistically significant increase in
the inferior vertebral endplate width from L1 to L5 (p < 0.05).
Superior Vertebral Endplate Depth (A-P Width)
The mean dimensions of the superior vertebral endplate depth at L1 were found to be
28.8 ± 2.5 mm in females and 31.6 ± 3.0 mm in males, with an overall measure of 30.4 ± 3.1 mm.
At L2, the measurements were 30.2 ± 2.5 mm in females, 33.1 ± 2.7 mm in males, and
31.8 ± 3.0 mm overall. For L3, the dimensions were 31.8 ± 2.7 mm in females, 34.4 ± 2.3 mm
in males, and 33.3 ± 2.8 mm overall. At L4, the measurements were 32.4 ± 2.2 mm in
females, 35.0 ± 2.5 mm in males, and 33.9 ± 2.7 mm overall. Finally, at L5, the dimensions
were 32.9 ± 3.3 mm in females, 35.8 ± 3.1 mm in males, and 34.5 ± 3.5 mm overall.
It was observed that the mean dimensions of the superior vertebral endplate depth
were smaller in females compared with males. Moreover, the data indicated a statistically
significant increase in the superior vertebral endplate depth from L1 to L5 (p < 0.05).
Inferior Vertebral Endplate Depth (A-P Width)
The mean dimensions of the inferior vertebral endplate depth at L1 were 29.7 ± 2.2 mm
for females, 32.4 ± 3.1 mm for males, and an overall of 31.3 ± 3.0 mm. At L2, the
dimensions were 31.9 ± 3.0 mm for females, 34.2 ± 2.7 mm for males, and an overall
of 33.2 ± 3.0 mm. At L3, the measurements were 32.1 ± 2.2 mm for females, 35.0 ± 2.2 mm
for males, and an overall of 33.7 ± 2.6 mm. Moving to L4, the dimensions were 32.9 ± 1.9 mm
for females, 35.8 ± 3.1 mm for males, and an overall of 34.6 ± 3.0 mm. Finally, at
L5, the measurements were 33.5 ± 2.6 mm for females, 35.7 ± 3.1 mm for males, and
an overall of 34.8 ± 3.1 mm. It was observed that the average inferior vertebral endplate
depth in females was smaller than that in males. Furthermore, there was a statistically
significant increase in the inferior vertebral endplate depth from L1 to L5 (p < 0.05).
Intervertebral Disc Height
The mean intervertebral disc height at T12/L1 was 9.3 ± 1.6 mm in females and 9.0 ± 1.6 mm
in males, with an overall average of 9.1 ± 1.6 mm. At L1/L2, the heights were 10.1 ± 1.8 mm
in females, 10.0 ± 1.7 mm in males, and 10.0 ± 1.7 mm overall. Moving to L2/L3, the
respective values increased to 10.4 ± 2.0 mm in females and 11.8 ± 2.0 mm in males,
with an overall average of 11.2 ± 2.1 mm. Continuing to L3/L4, the values rose further
to 11.5 ± 2.0 mm in females, 12.5 ± 2.1 mm in males, and an overall average of 12.1 ± 2.1 mm.
Finally, at L4/L5, the heights were 11.5 ± 2.1 mm in females, 13.0 ± 2.2 mm in males,
and an overall average of 12.4 ± 2.3 mm. Overall, there was a consistent increase
in intervertebral disc height from T12/L1 to L4/L5. Statistical analysis indicated
no significant differences in intervertebral disc heights at the T12/L1, L1/L2, and
L3/L4 levels (p > 0.05). However, significant differences were observed at L2/L3 and L4/L5 (p < 0.05).
Discussion
Over the past few decades, LLIF has emerged as a widely favored minimally invasive
spinal procedure for addressing various spinal disorders. Initially introduced by
Ozgur[6 ] in 2001, the primary goal of LLIF is to achieve indirect decompression of the neural
elements, restore intervertebral disc height, and increase the central and foraminal
canal diameter, while avoiding the significant complications associated with anterior
lumbar interbody fusion, such as bowel or great vessel injuries, retrograde ejaculation,
and arterial thromboembolism.[7 ]
[8 ]
[9 ]
[10 ]
[11 ] Additionally, to minimize operative time, intraoperative blood loss, and rates of
muscular structure damage, stand-alone LLIF, a relatively trans-psoas approach of
cage placement without supplemental fixation, may be employed. Nevertheless, a significant
concern with this procedure is determining the appropriate cage size and location
of cage placement, as improper placement can lead to several complications, including
neural structure impingement or damage, cage migration, or cage subsidence.[12 ]
[13 ]
Regev et al[14 ] observed a higher incidence of cage overhang when the insertion site is located
in the anterior one-third of the disc space, potentially resulting in serious complications,
such as impingement of the retroperitoneal vessels, retroperitoneal seromas, hematomas,
and radiculitis of adjacent nerve roots. Conversely, undersized cage placement can
lead to postoperative cage subsidence, resulting in potential loss of indirect decompression
due to bony structure collapse and condensation around the interbody cage.[15 ]
[16 ]
[17 ] Furthermore, the rate of subsidence depends on the cage width, with Le et al[18 ] reporting a 14.1% subsidence rate using an 18-mm wide cage compared with only 1.9%
when using a 22-mm wide cage. It is widely agreed that proper cage placement involves
using a large cage length and lateral placement to maximize contact with cortical
bone, ensuring that the implant spans the lateral borders of the ring apophysis.[5 ] There is also a consensus that the cage center should lie within the middle 20%
of the vertebral body, based on available semiquantitative data in the literature.[19 ]
[20 ]
[21 ] However, consensus on the proper size of the cage width in stand-alone LLIF has
not been reached.
To reduce subsidence in LLIF, one of the major concerns for this issue is the cage
dimensions.[22 ] According to Le et al,[18 ] the appropriate cage length is contingent on the distance of the periphery of the
end plates. It becomes pertinent only if the implant does not fully reach the peripheral
endplate. Hence, the width of the cage holds greater significance than the length,
as the increased width provides enhanced biomechanical advantages, unlike the increased
length. Prior literature has indicated that subsidence is linked to a low footplate-to-vertebral
body endplate ratio (<0.5), low bone mineral density, and nonsupplemented fusion.[2 ]
[23 ]
[24 ]
[25 ]
[26 ] Currently, there are three standard wide cage sizes—18, 22, and 26 mm—for the LLIF
procedure. Custom-made width cages are not widely adopted and pose challenges in production
([Fig. 2 ]). Lang et al[2 ] conducted an analysis on the implementation of a 26-mm wide cage in nine Caucasian
patients for stand-alone LLIF, comparing the outcomes with previous cases using 18
and 22-mm wide cages. Their study established that using a 26-mm wide cage significantly
reduced the incidence of cage subsidence compared with the 18- and 22-mm wide cages.
Fig. 2 (A. B) An axial computed tomographic image showed an 18-mm wide cage position following
the LLIF procedure performed on a Thai patient (A). Measurement of intervertebral
endplate depth (a–b) was 30.4 mm, intervertebral endplate width (c–d) was 45.2 mm,
and calculating of footplate-to-vertebral body endplate ratio was 0.6 (B). LLIF, lateral
lumbar interbody fusion.
The morphological parameters of the lumbar spine have been described previously, but
most of the studies have been conducted on Caucasian subjects.[27 ]
[28 ]
[29 ]
[30 ]
[31 ]
[32 ]
[33 ]
[34 ]
[35 ]
[36 ]
[37 ]
[38 ] Only a few studies were evaluated in Mongolian subjects.[39 ]
[40 ]
[41 ]
Our study demonstrated that the width of the superior vertebral endplate is consistently
smaller than that of the inferior vertebral endplate within the same vertebra. Additionally,
the width of the vertebral endplate generally exhibits an increasing trend toward
the lower vertebral levels. In this examination, the range of vertebral endplate depth
varied from 22.5 to 46.6 mm. Overall, the inferior vertebral endplate exhibited a
greater depth compared with the superior vertebral endplate within the same vertebra.
Nevertheless, the average depth of the superior and inferior vertebral endplates was
found to be similar within the same disc space level.
Based on the geometrical features of lumbar vertebrae documented in previous literature,
[Table 2 ] presents a comparison of the various parameters measured in our study with those
from previous studies. Our findings reveal similarities in the morphometric characteristics
of lumbar vertebrae between Caucasian subjects and our research cohort. Consequently,
it is suggested that a 26-mm wide cage may be appropriate for stand-alone LLIF in
the Asian population.
Table 2
A comparative analysis of the average measurements of the SVEW, SVED, IVEW, IVED,
and IVDH
Parameters (mm)
Panjabi et al[27 ]
Berry et al[28 ]
Wang et al[29 ]
Tan et al[39 ]
Current study
L1
SVEW
41.2 ± 1.0
45.2 ± 4.6
45.3 ± 3.7
42.7 ± 0.4
41.4 ± 3.7
SVED
34.1 ± 1.3
31.9 ± 3.7
34.8 ± 3.2
32.3 ± 0.5
30.4 ± 3.1
IVEW
43.3 ± 0.8
49.1 ± 3.7
47.6 ± 4.0
46.2 ± 0.6
43.2 ± 3.9
IVED
35.3 ± 1.3
32.3 ± 3.5
33.5 ± 2.9
33.6 ± 0.6
31.3 ± 3.0
IVDH (T12/L1)
N/A
N/A
N/A
N/A
9.1 ± 1.6
L2
SVEW
42.6 ± 0.7
47.7 ± 4.7
47.0 ± 3.5
44.9 ± 0.5
43.6 ± 3.9
SVED
34.6 ± 1.1
33.3 ± 3.7
35.7 ± 2.3
33.3 ± 0.6
31.8 ± 3.0
IVEW
45.5 ± 1.1
54.8 ± 4.8
50.3 ± 3.6
48.6 ± 0.4
45.6 ± 4.1
IVED
34.9 ± 0.7
33.4 ± 3.4
36.2 ± 2.8
34.4 ± 0.6
33.2 ± 3.0
IVDH (L1/L2)
N/A
N/A
N/A
N/A
10.0 ± 1.7
L3
SVEW
44.1 ± 0.9
49.6 ± 3.2
48.0 ± 3.1
47.0 ± 0.4
45.9 ± 4.2
SVED
35.2 ± 1.1
33.9 ± 3.3
35.7 ± 3.1
35.2 ± 0.3
33.3 ± 2.8
IVEW
48.0 ± 1.2
53.8 ± 3.7
51.5 ± 3.4
51.2 ± 0.4
48.3 ± 4.4
IVED
34.8 ± 1.2
34.2 ± 3.3
35.6 ± 2.8
35.6 ± 0.7
33.7 ± 2.6
IVDH (L2/L3)
N/A
N/A
N/A
N/A
11.2 ± 2.1
L4
SVEW
46.6 ± 1.2
51.2 ± 5.6
51.3 ± 3.7
49.4 ± 0.2
47.7 ± 4.1
SVED
35.5 ± 0.9
34.9 ± 3.4
35.8 ± 2.8
36.3 ± 0.6
33.9 ± 2.7
IVEW
49.5 ± 1.4
50.9 ± 4.6
53.6 ± 3.7
53.3 ± 0.6
49.3 ± 4.0
IVED
33.9 ± 0.9
35.6 ± 3.1
36.1 ± 2.8
35.6 ± 0.7
34.6 ± 3.0
IVDH (L3/L4)
N/A
N/A
N/A
N/A
12.1 ± 2.1
L5
SVEW
47.3 ± 1.2
53.4 ± 4.4
53.0 ± 4.1
48.9 ± 0.4
48.8 ± 4.2
SVED
34.7 ± 1.2
35.1 ± 2.8
35.5 ± 2.9
35.8 ± 0.6
34.5 ± 3.5
IVEW
49.4 ± 1.4
52.7 ± 4.3
52.3 ± 4.7
51.4 ± 0.5
48.7 ± 3.5
IVED
33.2 ± 0.9
34.5 ± 3.0
34.7 ± 3.2
33.8 ± 0.5
34.8 ± 3.1
IVDH (L4/L5)
N/A
N/A
N/A
N/A
12.4 ± 2.3
Abbreviations: IVDH, intervertebral disc height; IVED, inferior vertebral endplate
depth; IVEW, inferior vertebral endplate width; N/A, not available; SVED, superior
vertebral endplate depth; SVEW, superior vertebral endplate width.
Our study has some limitations. Primarily, the data were derived from individuals
visiting a single institution, which may result in variances in morphometric parameters
between our demographic and patients from diverse geographic regions. Additionally,
potential measurement errors exist; however, we mitigated this concern by averaging
three measurements and conducting ICC analysis, which demonstrated strong correlations
across all parameters. Finally, our study solely focuses on the morphometrics of the
vertebral body without clinical application, underscoring the necessity for further
clinical investigations.
Conclusion
This study has compiled a dataset detailing the morphometric characteristics of lumbar
vertebrae within the Asian population. Results indicate that the dimensions of lumbar
vertebrae in this study align closely with those observed in previous studies on the
Caucasian population. This data could potentially inform surgical strategizing and
aid in the selection of appropriately sized wide cages for stand-alone LLIF procedures
within the Asian demographic.
