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JCMC/ Vol 11/ No. 1/ Issue 35/ Jan- Mar, 2021
ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
ABSTRACT
Background: Pedicle screw instrumentaon has revoluonized spine surgery on account of its
superiority over other stabilizaon systems. It is safe when properly placed and versale for a
range of procedure from fracture xaon to complex deformity correcon. Sound anatomical
knowledge of the pedicle may also be helpful during surgical approach to lumbar foramina disc
herniaon and epidural steroid injecon as well as in the diagnosis of some lumbar degenera-
ve diseases and chronic back pain. In this study we aimed to provide locoregional data on
lumbar pedicle morphometry of Nepalese populaon.
Methods: A descripve observaonal study was conducted on 50 dry adult human lumbar vertebrae
of unknown sex at Chitwan Medical College from August 2020 to December 2020. Pedicular width,
height and the interpedicular distance were measured. All the data were numerally coded in excel
and analysis was done in Stascal Package for Social Sciences (SPSS) version 20.
Results: The mean width of the pedicles of le side gradually increased as we moved down the
vertebrae and measured 7.43 ±0.84 mm in L1 and 12.18±1.71 mm in L5 vertebrae. The mean width
of the pedicles on the right side, however, showed an increasing trend with a lower value at L3 level
and was measured as 7.91± 1.17 mm. The mean height of the pedicles alternavely decreased and
increased down the vertebrae for both the sides. The mean interpedicular distance gradually in-
creased craniocaudally and was found to be 20.35±0.95 for L1 and 25.97±3.58 mm for L5 vertebrae.
Conclusions: This study conrmed the measurement of lumbar pedicles’ dimensions and provides
its regional data on Nepalese populaon. These data may be crical for clinicians working near the
vicinity of the lumbar pedicles.
Journal of Chitwan Medical College 2021;11(35):46-51
Available online at: www.jcmc.com.np
ORIGINAL RESEARCH ARTICLE
234
¹Department of Anatomy, Chitwan Medical College, Bharatpur-10, Chitwan, Nepal
²Department of Surgical Oncology, Plasc and Reconstrucve Surgery Unit, B. P. Koirala Memorial Cancer Hospital, Bharatpur-7, Chitwan, Nepal
³Department of Anatomy, Lumbini Medical College and Teaching Hospital, Palpa, Nepal
⁴Department of Anatomy, Kathmandu Medical College Teaching Hospital, Duwakot, Bhaktapur, Nepal
⁵Department of Anatomy, Maharajgunj Medical Campus, Kathmandu, Nepal
ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
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Received: 12 Jan, 2021
Accepted: 25 Feb, 2021
Published: 25 Mar, 2021
Key words: Instrumentaon; Lumbar vertebrae;
Pedicle screws; Spinal manipulaon; Spine; Verte-
bral pedicles.
*Correspondence to: Sushma Khawada, Department
of Anatomy, Chitwan Medical College, Kailashnagar,
Bharatpur-13, Chitwan, Nepal.
Email:
Khawada S, Sudhin BN, Pandey N, Shrestha I,
Dhungel D. Morphometric study of lumbar ver-
tebral pedicles. Journal of Chitwan Medical Col-
lege.2021;11(35):46-51 .
JCMC
INTRODUCTION
Lumbar vertebra bridges axial skeleton with the appendicular
skeleton and help support the weight of the upper body and
permit movement. Short but strong paired pedicles arise
posterolaterally from each vertebral body near its upper
border. 1 Spine and orthopedic surgeons take advantage of
the robust nature and unique anatomy of lumbar pedicles
for transpedicular screw xaon. Lumbar canal stenosis as
suggested by decreased interpedicular distance is one of the
important cause of low backache. Transpedicular approaches
are also being increasingly used in many surgeries such as bone
biopsy, bone graing, vertebroplasty and kyphoplasty as well
for the access of the spinal canal by anesthesiologist for lumbar
epidural anesthesia.2
The variability in width, height, orientaon and interpedicular
distance makes pedicle screw inseron very challenging. 3 For
a successful surgery and appropriate implant design, sucient
knowledge of lumbar vertebral pedicle morphometry and
anatomical data is crical in order to avoid inadvertent
penetraon of the pedicle wall. 4 The anatomy of the lumbar
pedicle has been extensively studied previously using cadavers,
dry bones and dierent imaging techniques; however, wide
regional variaons has been noted.2,5,6
The aim of this anatomical study was to quanfy pedicle
dimensions on dry adult lumbar vertebra by using direct caliper
measurement.
METHODS
A descripve observaonal study was conducted on dry
adult human lumbar vertebrae aer geng approval from
instuonal review commiee (CMC-IRC/077/078-020) of
Chitwan Medical College. The study period was from August
2020 to December 2020.
All the lumbar vertebrae collected at the Department of
Anatomy, Chitwan Medical College comprised the sample
frame in our study. Samples were selected using simple
random sampling technique. Sample size was calculated to be
50 using the formula n = Z² × σ² /d², where, n = sample size,
Z = 1.96 for 95% condence level, σ = 1.48 from populaon
standard deviaon taken from Choubisa et al2 and d = margin
of error as 0.41.
JCMC/ Vol 11/ No. 1/ Issue 35/ Jan- Mar, 2021
ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
Fiy clean and dried lumbar vertebrae, ten from each
segments were included in the study. Deformed vertebra and
vertebra with broken fragments were excluded from the study.
The vertebra were serially numbered from one to y using
blue marker pen. The instruments needed for the study were
150 mm digital vernier caliper product of china accurate up-to
0.01mm, marking pen etc.
The following parameters were observed by the measurement:
Width of the pedicle (Horizontal) in mm: The width was taken
as the distance between the medial and lateral surfaces of the
pedicle.
Height of the pedicle (Vercal) in mm: The height was taken
as the distance between the superior and inferior margins of
the pedicle.
Interpedicular distance in mm: The measurement was done
at the medial surfaces of right and le pedicle of the same
vertebra.
The measurement of the Pedicle width, height and
interpedicular distance were done as shown in the Figures 1,
2 and 3 respecvely.
All the data were numerically coded in excel and analysis was
done in Stascal Package for Social Sciences (SPSS) version
20. The mean and standard deviaon of width and height of
pedicle as well as interpedicular distance were calculated and
tabulated.
RESULTS
The study evaluated pedicle morphometry of 50 lumbar ver-
tebrae (L1–L5) of unknown sex. The results of the width and
height of both sides are shown below in Tables 1 and 2, while
the interpedicular distance are presented in Table 3.
Lumbar Vertebra Maximum Minimum Maximum Minimum
L1 7.32±0.83 8.41 6.07 7.43±0.84 8.7 5.94
L2 8.13±1.37 11.28 6.65 7.90±1.64 11.2 5.38
L3 7.91±1.17 9.01 5.78 8.46±1.19 9.86 6.49
L4 11.30±1.55 13.5 8.77 10.79±1.72 14.18 7.86
L5 12.28±1.45 13.8 9.81 12.18±1.71 15.04 9.38
Lumbar Vertebra Maximum Minimum Maximum Minimum
L1 14.76±1.40 18.2 13.29 14.12±1.36 17.47 12.9
L2 13.62±1.24 15.32 10.82 13.53±0.83 14.85 12.32
L3 14.58±1.16 15.89 12.47 14.11±1.23 15.93 11.68
L4 12.83±0.59 13.72 11.9 12.48±0.54 13.44 11.52
L5 13.24±2.16 16.64 10.06 13.37±1.60 16.93 11.19
JCMC/ Vol 11/ No. 1/ Issue 35/ Jan- Mar, 2021
ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
Lumbar vertebra Maximum Minimum
L1 20.35±0.95 21.23 19.43
L2 21.43±1.16 22.37 20.84
L3 21.77±1.72 23.17 20.32
L4 23.41±1.61 24.39 22.32
L5 25.97±3.58 28.34 25.09
The largest pedicle width (PW) was seen on both sides at L5 with
a mean of 12.28 ± 1.45 mm on the right side and 12.18 ± 1.71 mm
on the le side. The smallest pedicle width was seen at L3 level
on the right side and L2 level on the le side. Of the 50 evaluated
vertebrae, only 5 vertebrae had width less than 5 mm. Pedicles
having width less than 5, 6 or 7 mm may pose diculty while
inserng screws; their frequency are tabulated in the Table 4. As
shown in Table 4, 40% and 30% of L3 vertebrae on the right and
le side respecvely had sub 8 mm pedicle width; 30% right sid-
ed and 20% le sided lumbar vertebrae had PW less than 7 mm.
While no L5 or right sided L4 vertebral pedicles had sub 8 mm
width, only 10% of le sided pedicles were less than 8 mm wide.
Levels
L1 0341 1 5
L2 02 3 1 1 2
L3 1 2 1 02 1
L4 0 0 0 0 0 1
L5 0 0 0 0 0 0
There was an increase of PW from cephalic to caudal vertebral
level on the le side as shown in Figure 4. On the right side,
however, a small notch was noted at the L2-L3 level as shown
in Figure 5. It was found that the width of the pedicles on the
right and le side are signicantly dierent from each other (p
value < 0.00001).
The mean PH alternavely decreased and increased down
the vertebrae for both the sides and was noted to be 14.12
± 1.36, 13.53 ± 0.83, 14.11 ± 1.23, 12.48 ± 0.54 and 13.37
± 1.60 mm for the le side and 14.76 ± 1.40, 13.62 ±1.24,
14.58 ±1.16, 12.83 ± 0.59 and 13.24 ± 2.16 mm for the right
side respecvely. This ‘staircase like’ descent of the mean PH
seemed more symmetric on the right side as compared to
the le side as shown in Figure 6 and 7. Signicant dierence
between the pedicle heights was noted between the two sides
(p value = 0.047).
At vertebral levels L1 to L3, PH was always greater than the PW;
the gap, however, gradually decreased as we moved caudally.
Although 20% of L4 vertebrae on the right side and 10%on the
JCMC/ Vol 11/ No. 1/ Issue 35/ Jan- Mar, 2021
ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
le side had larger PW as compared to PH,30% on the right and
20% on the le side had such paern at L5 level.
The mean IPD in our study increased steadily from L1 to L5
vertebral level with a relavely steeper climb caudally as
shown in Figure 8.
DISCUSSION
The lumbar vertebra, being the mobile region of the vertebral
column, is oen involved during accidents, degenerave
changes, congenital defects and metastasis. Advances in
medical technology has enabled spine surgeons maneuver a
screw to x it for regaining acvity.7 Posterior approach into the
lumbar pedicle is a preferred method for a screw placement
as it has been proven to be the strongest part of the vertebra
even in osteoporoc bone.8 A mistakenly placed pedicle screw
can, however, impinge nerve root, leak cerebrospinal uid,
fracture pedicle and cause screw loosening.
Screw placement in praccable posion requires in-depth
anatomical knowledge of the lumbar pedicles. Individual
variability as well as age, gender and ethnic dierences
would make its accurate placement challenging.6,9 Although
intraoperave use of modern radiological techniques such
as navigaon with CT, uoroscopy or O-arm decreases the
inadvertent risk of injury to the surrounding structures, it sll
carries some risk of a screw misplacement; nkering the screw
for intraoperave adjustment would increase the risk further.10
We used direct caliper measurements for lumbar pedicles. It
has advantage over radiological methods as it provides the
most accurate account of pedicle morphometry.8
Pedicle width (PW) is the most important limitaon in relaon
to pedicle screw xaon due to its smaller size compared
to the pedicle height (PH). In our study, PW progressively
increased from L1 to L5 on the le side. The width on the right
side, however, increased from L1 to L2, slightly decreased at
L3, and again increased at L5 which is unlike any other study.
Most authors, however, have noted the width to gradually
increase from L1 to L5.11-14 Alam et al noted that, although,
the pedicle diameter in their study of 49 CT images gradually
increased from L1 to L5; the mean values for the L3 and L4
vertebrae were idencal. 15 The width of the pedicle is smallest
at L1 and largest at L5 level which suggests that pedicle screw
xaon is relavely unsafe at upper lumbar vertebra. The
values of the PW in our study are comparable to some studies;
2,6,12 however, few studies have documented smaller values11,16
while many studies have shown higher values as compared to
ours.8,13,17 Some authors have noted a much smaller values in
some of their specimens at L111,14 and a much higher value at
L5 level.13,16,18 L2 and L5 vertebra on the le side had the lowest
(5.38 mm) and highest (15.04 mm) value of pedicle width in our
study. Shorter stature of Nepalese populaon on addion to
genec, environmental and dietary factors could have played a
role in the overall smaller pedicle dimension in our populaon.
Yu et al noced that pedicle width at level L1 to L3 was more
in African Americans as compared to Caucasians while reverse
was true at levels L4 and L5.8 Dzierżanowski et al noted that
most morphometric lumbar similaries concern the L1 and L2
vertebra bodies; whereas it varied the most in the caudal part
of lumbar spine, irrespecve of the race.10
Due to a smaller number of sub-8 mm PW at the lower
vertebral pedicles (Table 4), it seems reasonable to use a
5 mm pedicle screw diameter for lower lumbar xaon in
Nepalese populaon but we support the exisng literature
recommending pre-operave use of imaging and liming the
screw diameter to less than 80% of the measured width for its
safe placement.19
Many studies have shown that PH values decreases from L1
to L5. 4,12,15 In our study, however, we noted that PH slightly
increased at L3 level, decreased at L4 and increased again at L5.
These ndings are in accordance to few other studies.20-22 Some
authors noted that the PH increased from L1 up-to L2 and then
gradually decreased.2,6,16 Dzierżanowski et al observed that
the PH decreased steadily on the right side; on the le side,
however, it decreased up-to L4 and then increased. 10 Mitra
et al as well as Kim et al noted that the mean PH gradually
decreased from L1 to L4 but it again increased at L4 and L5.
11,18 Seema et al noted a minimum vercal diameter at L5 level
while the maximum value was seen at L2 level in their study of
100 plain X-ray lms.17 In our study, the mean PH ranged from
12.83 to 14.76 mm on the right side and from 12.48 to 14.12
mm on the le side. L1 on both sides had the highest mean P
values; the largest PH value being 19.47 mm on the le side
and 18.20 mm on the right side.
Interpedicular distance is a reliable index for the assessment
of the size of the lumbar canal and its measurement may be a
preliminary, but useful aid in the diagnosis of the lumbar canal
stenosis syndrome. 23
We report a progressively increasing mean interpedicular
distance from 20.35 ± 0.95 mm at L1 to 25.97 ± 3.58 mm at
L5. This is in agreement with several other studies showing
interpedicular distance to increase gradually from L1 to
L5.17,23,24 Al-Rakhawy et al and Banik et al encountered a dip in
IPD at L3 level while Aar et al found the mean IPD increase to
halt at L2 level.23,25,26
Some studies have reported much larger values of IPD at L5
level.5,24,25 The remarkably higher value at L5 was probably
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ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
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ference in morphologic features of the lumbar vertebrae between Cau-
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caused by the dierent conguraon of the vertebra, in which
the pedicles were more lateroventrally implanted on the body
and were fused with the transverse processes.27
Mansur et al noted that the transverse diameter of the spinal
canal of any lumbar vertebra is proporonal to the size of the
vertebral body at that level and that its rao with the body
would be more helpful for idenfyng spinal canal stenosis.5
Choubisa et al from India compared their ndings with the
study by Marasini et al from Nepal and noted that lumbar IPD
of their populaon was 5 to 6 mm less while PH and PW were
1 mm more.2,6
Although the dierence in pedicle size between gender, age
and race has been well documented in literature, we are
unable to report such a nding as the present study was
conducted in dry adult lumbar vertebrae of unknown sex.20.24.28
Further studies are warranted on lumbar morphometry on a
larger populaon in both genders and in various ethnic groups
for generalizability.
The study was carried out in preserved human lumbar
vertebrae. No comparison was made with clinical or radiological
data. Low sample size and specimen of unknown sex may have
introduced some inaccuracies in our measurements.
CONCLUSION
The present study noted that the mean width of the le sided
pedicles gradually increased down the vertebrae whereas the
right side showed an increasing trend with a lower value at L3
level. The mean pedicle height alternavely decreased and
increased down the vertebrae for both the sides. IPD gradually
increased as we moved down the vertebral level. Regional data
from the present data forms a baseline of adult lumbar vertebral
morphology and would be useful for anatomists, radiologists,
surgeons and physicians. It may also be helpful for the screw
and implant manufacturers. Larger study with sex and ethnic
consideraon can generate forensic and anthropological data
of the Nepalese populaon.
ACKNOWLEDGEMENT
The author would like to thank Mr Naresh Khawada for his
help in stascal analysis of the raw data.
None
None
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ISSN 2091-2889 (Online) ISSN 2091-2412 (Print)
21. Azu OO, Komolafe OA, Ofusori DA, Ajayi SA, Naidu ECS, Abiodun AA. Mor-
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22. Engelberg RB, Roguski M, Riesenburger RI, Do-Dai D, Jea A, Hwang SW.
Morphometric analysis of lumbar pedicles in paents with spinal dysra-
phism. Pediatr Neurosurg. 2015;50:1-6. [DOI]
23. Al-Rakhawy M, El-Shahat AE-R, Labib I, Abdulaziz E. Lumbar vertebral
canal stenosis: concept of morphometric and radiometric study of the
human lumbar vertebral canal. J Exp Clin Anat. 2010;4:51-62. [DOI]
24. Jadhav AS, Ka AS, Hereker NG, Jadhav SB. Osteological study of lum-
bar vertebrae in Western Maharashtra populaon. J Anat Soc India.
2013;62:10-6. [DOI]
25. Banik S, Rajkumari A. Morphometric analysis of lumbar vertebrae and
its applied clinical importance. Int J Anat Res. 2019;7(2.1):6381-6. [DOI]
26. Aar A, Ugur HC, Uz A, Tekdemir I, Egemen N, Genc Y. Lumbar pedicle: sur-
gical anatomic evaluaon and relaonships. Eur Spine J. 2001;10(1):10-5.
[DOI]
27. van Schaik JJ, Verbiest H, van Schaik FD. Morphometry of lower lumbar
vertebrae as seen on CT scans: newly recognized characteriscs. Am J
Roentgenol. 1985;145: 327-35. [DOI]
28. Abbas J, Peled N, Hershkovitz I, Hamoud K. Pedicle morphometry varia-
ons in individuals with degenerave lumbar spinal stenosis. Biomed Res
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