Exploring cortical trajectory of the lumbar vertebrae: a morphometric study in dry skeletons: a retrospective study in Thailand

Parika Hanarwut; Sitthichai Iamsaard; Permsak Paholpak; Taweechok Wisanuyotin; Yuichi Kasai; Laphatrada Yurasakpong; Athikhun Suwannakhan; Arada Chaiyamoon

doi:10.31616/asj.2024.0223

Asian Spine J > Volume 18(5); 2024 > Article

Hanarwut, Iamsaard, Paholpak, Wisanuyotin, Kasai, Yurasakpong, Suwannakhan, and Chaiyamoon: Exploring cortical trajectory of the lumbar vertebrae: a morphometric study in dry skeletons: a retrospective study in Thailand

Clinical Study

Asian Spine Journal 2024;18(5):654-662.

Online first: October 22, 2024

DOI: https://doi.org/10.31616/asj.2024.0223

Exploring cortical trajectory of the lumbar vertebrae: a morphometric study in dry skeletons: a retrospective study in Thailand

Parika Hanarwut¹

, Sitthichai Iamsaard¹

, Permsak Paholpak²

, Taweechok Wisanuyotin²

, Yuichi Kasai²

, Laphatrada Yurasakpong^3,⁴

, Athikhun Suwannakhan^3,⁴

, Arada Chaiyamoon¹

¹Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand

²Department of Orthopaedics, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand

³Department of Anatomy, Faculty of Science, Mahidol University, Bangkok, Thailand

⁴In Silico and Clinical Anatomy Research Group, Bangkok, Thailand

Corresponding author: Arada Chaiyamoon, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand,
Tel: +66-4336-3173, Fax: +66-802942459, E-mail: aradch@kku.ac.th

Received June 11, 2024 Revised July 3, 2024 Accepted July 22, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Study Design

Retrospective cohort study.

Purpose

This study aimed to explore the morphometry of the Thai lumbar vertebrae.

Overview of Literature

The cortical bone trajectory (CBT) is a novel approach for vertebral screw fixation aimed at addressing spinal instability associated with spinal disorders. The morphometry of the lumbar vertebrae is crucial in tailoring screw design for each CBT application, given the significant variations in optimal screw sizes, lengths, and angles among populations.

Methods

A total of 300 dried lumbar columns were used to measure the pedicle height (PH) and width (PW), length for cortical bone trajectory (LCT), cephalad screw angle (CSA), axial cortical bone trajectory angle (ACA), and possible cortical zones for the CBT.

Results

The following average values were calculated: PH in L1, 15.09±1.44 mm; PW in L5, 16.96±2.42 mm; LCT in L3, 35.75±2.61 mm; CSA in L1, 20.85°±2.30°; and ACA in L5, 21.83°±2.49°. Women generally had shorter PH and PW than men, with significant differences across lumbar levels. The LCT was significantly shorter in women and was notably different between the left and right sides. The CSA and ACA varied significantly between sexes and sides, with specific lumbar levels showing wider angles in one sex over the other. The most common cortical zones for screw tips were Z3 and Z10, with high incidences across all lumbar levels.

Conclusions

This study presents detailed lumbar vertebral morphometry data specific to the Thai population. The results are essential for CBT application in screw fixation procedures. This information will contribute to the production of optimally designed screws for Thai patients in the future.

Keywords: Lumbar vertebrae; Lumbar vertebrae; Lumbosacral region; Spine

Introduction

The human lumbar spine is important for supporting the body weight, maintaining stability, facilitating trunk movements, and protecting the spinal cord, nerves, and vessels. Lumbar spine abnormalities can cause various spinal problems, such as lumbar stenosis, spondylosis, spondylolisthesis, lordosis, scoliosis, and fractures [1]. Two standard techniques are generally used to fix spinal instability and maintain stability in spinal disorders, namely, pedicle screw (PS) and cortical bone trajectory (CBT) fixations [1–3]. Although PS fixation is widely used for the treatment of spinal disorders, it is associated with screw malpositioning, leading to complications such as spinal dural tearing, cerebrospinal fluid leakage, and neurovascular injury [4]. Moreover, PS fixation results in screw loosening from the lumbar vertebral body, particularly in patients with osteoporosis [5].

Because PS fixation has some weak points and limitations for lumbar spinal stabilization, Santoni et al. [6] proposed a new technique called CBT fixation, which is considered a more rigid fixation. This technique reduces screw loosening, failure in osteoporosis, and stabilize and avoid complications caused by trajectory insertion in PS fixation [6]. CBT fixation increases or enhances the pulling-out strength and insertion torque compared with PS fixation [3,6]. Moreover, CBT fixation could reduce the estimated blood loss, incision length, and surgical dissection compared with the PS method [7].

The lumbar morphological information also refers to preoperative assessment before CBT screw fixation [2,8]. In addition, lumbar morphometry has been documented in various populations [3,9–13]. In the Thai population, only the morphology of dried lumbar vertebrae was used as basic information about PS fixation in North Thai bone samples.

Therefore, this study aimed to investigate all morphometric aspects of the lumbar vertebrae in Northeastern Thais, including pedicle height (PH), pelvic width (PW), length, cortical screw ending zone, and angles for the clinical application of CBT screw fixation. This study might provide basic information about Northeastern Thai lumbar vertebrae when considering the accurate position of the CBT screw fixation and preventing complications after screw fixation.

Materials and Methods

Bone collection

This study used dried lumbar vertebrae (L1–L5) of skeletons collected in the Unit of Human Bone Warehouse for Research (UHBWR), Department of Anatomy, Faculty of Medicine, Khon Kaen University, Thailand. This study was approved by the Khon Kaen University Ethics Committee for Human Research (approval no., HE641512). Skeletons from donors with diseases that could affect the skeletal system were excluded.

Measurements of lumbar parameters

The lumbar PH was measured at both sides using a digital Vernier caliper to measure between the narrowest points (or called isthmus) on the lumbar pedicle, as demonstrated in Fig. 1. The distance of PH is located between the superior border (SB) and the inferior border (IB) of the pedicle isthmus on the lumbar pedicle (Fig. 1A). The lumbar PW was also measured at both sides of the narrowest point (isthmus), distancing from the medial border to the lateral border of the pedicle isthmus, as shown in Fig. 1B. The hypothetical starting point (SP) on the lumbar lamina for applying in the CBT was marked as previously described [3,6]. The SP was determined using a drawing line from the vertical midline of the superior articular facet to a point that was measured at 1 mm lower from the IB of the transverse process. The possible endpoint (PE) of the screw tip in CBT was marked with a mechanical pencil (0.5 mm) on the cortical rim of the lumbar body on both sides. To mark this point, a stainless needle was used as a guide by placing it on the superior surface of the vertebrae through the hypothetical SP and middle pedicle. Then, the PE was spotted at the end tip of such needle on the center of the lumbar cortex as shown on the right side. The length for the cortical bone trajectory (LCT) was measured from the SP to the PE using a digital Vernier caliper, as shown in Fig. 1C. After marking the PE points on both sides, each point was further observed for the PE zones using a modified full-circle protractor that was divided into 12 zones (Z1–12) in the clockwise direction (Fig. 1D). Z1–Z6 were located on the right side, whereas Z7–Z12 belonged to the left side. After taking photographs and processing in ImageJ (https://imagej.net/ij/), the axial CBT angle (ACA) of the left and right sides on the superior lumbar view was performed by drawing two lines (Fig. 1E). The ACA of each side was angled between the vertical line dragged from a half of the lumbar body cortex through the spinous process, and the second line dragged from the PE to the midpoint of the spinous process on the axial plane, as shown in Fig. 1E. The cephalad screw angle (CSA) of the left and right sides on the lumbar level was identified by taking photos of the lateral vertebrae. Before loading into the ImageJ program and before taking images, a stainless needle was placed to identify an SP landmark (Fig. 1F). After visualizing under ImageJ, the CSAs of both sides were angled between a transverse line drawn continuously from the SP and in parallel to the superior endplate of the lumbar vertebral body and a line drawn from the SP to the PE, as shown in Fig. 1F. To investigate the PE on the lateral aspect, a mechanical pencil was used to drag down from the PE on the cortical rim.

Statistical analysis

Statistical analyses were performed using IBM SPSS Statistics ver. 28.0 (IBM Corp., Armonk, NY, USA). The independent t-test was used to compare differences in each parameter between sexes or sides, whereas the Mann-Whitney U test was used for nonparametric data. Significance was analyzed at a 95% confidence interval (p<0.05). Data were presented as means±standard deviations.

Results

Overall morphometry

The highest values of the PH, PW, LCT, CSA, and ACA were found in L1 (15.09±1.44 mm), L5 (16.96±2.42 mm), L3 (35.75±2.61 mm), L1 (20.85°±2.30°), and L5 (21.83°±2.49°), respectively. In contrast, the lowest values of such parameters were registered in L4 (13.38±1.30 mm), L1 (7.09±1.72 mm), L5 (34.71±2.71 mm), L5 (19.43°±2.30°), and L2 (18.47°±1.89°), respectively (Table 1).

PH and PW

The morphological data of the PH and PW on L1–L5 were compared between sexes and sides (Table 2). The results showed that the PH and PW of L1–L3 on both sides were significantly shorter in women than in men (p<0.001). In L4, only the right PH and PW on both sides in men were significantly longer than that in women (p<0.001). Although the PH of L5 was significantly shorter in men, the PWs on both sides were not significantly different between sexes. The total PH was significantly shorter in the left L1 but longer in the left L5 (p<0.05). Individually, in women, the PH was significantly longer in the right L1 but shorter in the right L4 (Table 2). For the PW of L1–L5, no differences were found between the left and right sides in each sex (p>0.05). However, the general data of the PW in L5 were significant on both sides (p=0.013).

LCT

The LCTs on L1–L5 on both sides were significantly shorter in women than in men (p<0.001) (Table 3). Both sexes demonstrated significantly longer left LCT (L1–L5) than the right LCT (p<0.001). Individually, in women, only the LCTs on all lumbar levels on the left side were significantly longer than those on the right side (p<0.001). In contrast, in men, the LCT was not significantly different between sides in all lumbar levels (p>0.05), as shown in Table 3.

CSA and ACA

Table 4 shows the CSA and ACA, which were compared between sexes and sides. The average right CSA in L1–L5 was significantly narrower than that of the left side (p<0.05). Particularly, at L2 and L5, the CSA and ACA in women were significantly wider in the right side (p<0.05). In L4, in women, only the CSA in the right side was significantly wider than that on the left side (p=0.020). Although the CSA of the L3 and L4 on left side in men were significantly narrower, the ACA was wider than the left side (p<0.05). In men, the CSA of L5 was significantly wider on the right side (p<0.001). In addition, the left CSA in L3–L5 was significantly wider; however, its ACA was narrower in women than in men (p<0.05). Individually, the CSA of L3 in men was significantly wider on the right side but was shorter on the left L5 (Table 4). Moreover, the ACAs of L1 and L2 in men were significantly wider on the left side (p<0.05). In contrast, the ACA of L3 in women was significantly wider on the right side (p=0.025). At L2, the ACA in men was significantly wider on the left side but was narrower in women on the right side (p<0.05), as shown in Table 4.

Incidences of the cortical zones for the cortical screw trajectory

Overall data of the cortical zones (Z1–12) on L1–L5 for the cortical screw trajectory are presented in Fig. 2. Z3, Z4, Z9, and Z10 are nearly the most endings of the screw tip at in all lumbar levels. Notably, right and left zones of L1–L5 were with the highest incidences were Z3 (L1 [77%], L2 [81%], L3 [69%], L4 [95%], and L5 [95%]) and Z10 (L1 [81%], L2 [86%], L3 [89%], L4 [94%], and L5 [97%]), respectively (Fig. 2). Z3 and Z10 were more prevalent on the right and left cortical zones in both men and women. L1–L3 was noted in approximately 80%–90% (Table 5). Interestingly, in both sexes, approximately 95% of the ending zones were found on L4 and L5 (Table 5).

Discussion

In this study of the Northeast Thais population, the PH on all lumbar levels (L1–L5) was between 9.53 mm and 27.34 mm. Compared with other populations, the height of L1 (15.09 mm) was close to that of New Zealander (15.10 mm) [14], North Indian (15.11 mm) [15], Nepalese (15.00 mm) [16], and Israeli (15.10 mm) populations [17]. L2 height (14.45 mm) was similar to that in North Thais (14.35 mm) [18], and Turkish (14.35 mm) [19]. In addition, L3 height (14.16 mm) was similar to that in North Thais (14.25 mm) [18]. The PH of L4 (13.38 mm) was also close to that in Nepalese (13.44 mm) [16]. Moreover, the PH in L5 in the examined Thai population (14.10 mm) was similar to that in Chinese (14.17 mm) [20], Turkish (14.20 mm) [21], Korean (14.20 mm) [22], and American (14.00 mm) populations [23]. However, the PH was shorter than those reported in previous studies. In the present study, the PH at all levels was longer than that in Central Indian, North Indian, Nepalese, Pakistani, Taiwanese, Turkish, Chinese, and Chinese Singaporean populations [9,12,13,19,24,25].

In the examined Northeast Thai population, the PW of the lumbar vertebrae was between 3.20 mm and 25.62 mm. The PW of L1 (7.09 mm) was similar to those in other ethnicities including Nepalese (7.02 mm and 7.17 mm) [16], Chinese (7.00 mm) [20], and Korean (7.10 mm) [22]. The PW of L2 (7.34 mm) of Thais was close to the central Indian (7.37 mm) [9] and Chinese (7.40 mm) [20]. For L3 (9.06 mm), the PW was similar to that in North Thais (9.10 mm) reported by the Chiang Mai University research group [18] and Taiwanese (9.15 mm) [12]. The PW of L4 (11.39 mm) was comparable to that of Japanese (11.30 mm) [26]. The highest PW at the L5 level (16.96 mm) in this study was similar to that of Chinese (17.00 mm) population [20]. Interestingly, our PW measurements were narrower than that of various populations including Indian [9,15], Chinese [20], Japanese [5], Korean [22], Taiwanese [12], Turkish [19], Bangladeshi [19], American [23], and North Thais [18]. Despite some differences among populations, these findings indicate that the optimal screw diameter in designing the CBT is commonly similar among populations, and the screw diameter appears to be still suitable under the commercially available sizes, i.e., 4.5–5.5 mm and 25–35 mm of screw lengths [27].

The LCT on all lumbar levels of the Northeast Thais population examined in this study was between 26.18 mm and 44.80 mm. Given the importance of the LCT, surgeons must consider this parameter when screwing because it can overprotrude into other soft tissues surrounding the vertebral body at each level. The CSA on lumbar levels (L1–L5, 13.30°–31.42°) of the Northeast Thais population examined has been demonstrated for the first time in this study, which were narrower than that of Chinese [10,20] and Japanese [3,26].

For the ACA on L1–L5, which was also first reported in the Northeast Thais population (12.48°–30.87°). Compared with the other population, the ACA of Thais was wider than that of Chinese [20] and Japanese [3]. The CSA and ACA are also very important to consider before the surgeons insert the screw to the lumbar vertebral cortex.

For the first time, this study attempted to investigate the possible safe zone for CBT in the Northeast Thais population. Z3 and Z10 on right and left cortical zones are the relatively correct safe zone for the CBT, as shown in Fig. 2. The cortical ending zones observed in this study on each lumbar level can be used in surgical mapping and awareness of injuries in surrounding structures from unsuitable screws.

For L1, an unsuitable screw length can damage the psoas major muscle or crus of the diaphragm as shown in Fig. 2A. Fig. 2B–D demonstrates that the psoas major muscle and sympathetic trunk should be monitored for possible damage if surgeons use unsuitable screw lengths for the CBT. For L5, not only the psoas major muscle but also the inferior vena cava and ureters must be monitored when using unsuitable screw lengths for the CBT (Fig. 2E).

However, this study has a few limitations. The ages of the donors were unknown, which made it impossible to establish age-related correlations. In addition, the pars interarticularis, another important area that could fracture if large screws are used, were not examined.

Conclusions

This study provides the optimal screw size for CBT screws in Northeastern Thais, which is 7.09–16.96 mm in diameter and 34.71–35.75 mm in length. In addition, the optimal CBT angle is approximately 19.43°–20.85°. Hopefully, these basic data of lumbar morphometric anatomy are beneficial for orthopedic and spine surgeons when performing cortical screw insertion for the CBT. For Thai populations, data obtained from this study can be used as basic data for research and development in screw production.

Key Points

Most cortical screw trajectory zones were located in specific lumbar levels, with high incidences at L1–L3 and L4–L5.
Sex and side differences in the measurements were noted.
This study provides critical morphometric data for the Thai population to aid in designing optimal screws for cortical bone trajectory applications in Thai patients.

Acknowledgments

The authors sincerely thank those who donated their bodies to science, enabling anatomical research to be conducted. Results from such research can potentially increase mankind’s overall knowledge, which can then improve patient care. Therefore, these donors and their families deserve our deepest gratitude.

Notes

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Author Contributions

Conceptualization: PH, AC. Methodology: PH, SI, AC. Investigation: PH, SI, AC. Formal analysis: PH, SI, PP, TW, YK, AC. Writing–original draft: PH, AC. Writing–review & editing: PP, TW, YK, LY, AS. Supervision: LY, AS. Final approval of the manuscript: all authors.

Fig. 1

All measurements of the lumbar vertebrae. (A) The lumbar pedicle height was measured at the lumbar pedicle between the superior border (SB) and the inferior border (IB). (B) The lumbar pedicle width was measured from the medial border (MB) to the lateral border (LB) of the pedicle isthmus. (C) The length for the cortical bone trajectory was measured from the starting point (SP) to the possible endpoint (PE). (D) The PE zones using a modified full-circle protractor were divided into 12 zones (Z1–Z12) based on the clockwise direction to record the possible safe zone. (E) The axial cortical bone trajectory angle (ACA) was angled between the vertical line drawn from the midpoint of the lumbar body cortex through the spinous process and the second line drawn from the PE to the midpoint of the spinous process (MSP) on the axial plane. (F) The cephalad screw angle (CSA) was measured between a transverse line drawn continuously from the SP and parallel to the superior endplate (SE) of the lumbar vertebral body and a line drawn from the SP to the PE.

Fig. 2

Possible safe zone for the cortical bone trajectory and surrounding structures at L1–L5. (A) The psoas major muscle and crus of the diaphragm are monitored when using an unsuitable screw length at L1. (B–D) The psoas major muscle and sympathetic trunk are monitored when using an unsuitable screw length at L2–L4. (E) The psoas major muscle, inferior vena cava, and ureters are monitored when using unsuitable screw lengths at L5. (F) The percentage of the ending points at the cortical zones observed in the lumbar vertebrae (L1–L5). A, abdominal aorta; IVC, inferior vena cava; SC, sympathetic chain; LSN, lumbar spinal nerve; QL, quadratus lumborum; MF, multifidus; LG, longissimus; IC, iliocostalis; SN, spinal nerve; PM, psoas major; LP, lumbar plexus; ES, erector spinae; CIA, common iliac artery; U, ureter; CD, crus of diaphragm; CG, celiac ganglion.

Table 1

Ranges and average values of lumbar parameters measured in this study (number of lumbar columns=300)

Lumbar levels	Morphometric lumbar parameters
Lumbar levels	PH (mm)	PW (mm)	LCT (mm)	CSA (º)	ACA (º)
L1	10.71–19.18 (15.09±1.44)	3.20–15.90 (7.09±1.72)	26.92–43.16 (34.72±2.67)	15.71–29.45 (20.85±2.30)	13.14–24.59 (18.85±1.89)
L2	10.23–19.34 (14.45±1.38)	3.49–12.54 (7.34±1.54)	27.42–43.50 (35.27±2.60)	15.31–30.70 (20.17±2.26)	12.48–24.40 (18.47±1.89)
L3	10.48–18.81 (14.16±1.31)	4.34–15.51 (9.06±1.74)	26.18–44.02 (35.75±2.61)	14.62–31.42 (20.65±2.28)	13.14–26.13 (18.86±1.99)
L4	9.53–18.43 (13.38±1.30)	6.23–19.17 (11.39±1.94)	28.32–44.14 (35.62±2.54)	14.06–27.90 (20.37±2.30)	14.86–25.76 (20.03±2.00)
L5	9.61–27.34 (14.10±2.41)	8.96–25.62 (16.96±2.42)	27.19–44.80 (34.71±2.71)	13.30–25.46 (19.43±2.30)	15.60–30.87 (21.83±2.49)

Values are presented as min–max (mean±standard deviation).

PH, pedicle height; PW, pedicle width; LCT, length for cortical bone trajectory; CSA, cephalad screw angle; ACA, axial cortical bone trajectory angle.

Table 2

Comparisons of the pedicle height and width from different lumbar levels (L1–5) between females (n=150) and males (n=150)

Lumbar levels	Gender	Pedicle height (mm)			Pedicle width (mm)

		Left	Right	p-value	Left	Right	p-value
L1	Female	14.30±1.42	14.65±1.43^a)	0.037	6.53±1.60	6.45±1.52	0.690

	Male	15.58±1.14^b)	15.83±1.18^b)	0.066	7.73±1.69^b)	7.66±1.64^b)	0.719

	Total	14.94±1.43	15.24±1.44^a)	0.012	7.13±1.75	7.06±1.69	0.615

	p-value	<0.001	<0.001		<0.001	<0.001

L2	Female	13.88±1.33	13.93±1.28	0.752	6.67±1.35	6.64±1.28	0.793

	Male	14.92±1.19^b)	15.08±1.27^b)	0.242	8.13±1.42^b)	7.93±1.45^b)	0.236

	Total	14.40±1.37	14.51±1.40	0.342	7.40±1.56	7.28±1.51	0.347

	p-value	<0.001	<0.001		<0.001	<0.001

L3	Female	13.66±1.20	13.62±1.23	0.778	8.44±1.59	8.25±1.51	0.291

	Male	14.64±1.22^b)	14.71±1.17^b)	0.620	9.78±1.68^b)	9.77±1.57^b)	0.954

	Total	14.15±1.30	14.16±1.31	0.893	9.11±1.77	9.01±1.71	0.482

	p-value	<0.001	<0.001		<0.001	<0.001

L4	Female	13.41±1.31	13.07±1.33^a)	0.028	10.64±1.77	10.93±2.03	0.189

	Male	13.43±1.25	13.60±1.27^b)	0.231	11.89±1.81^b)	12.09±1.73^b)	0.324

	Total	13.42±1.28	13.34±1.33	0.441	11.27±1.90	11.51±1.97	0.120

	p-value	0.876	<0.001		<0.001	<0.001

L5	Female	15.22±2.78	14.34±2.70^a)	0.006	16.50±2.59	17.04±2.67	0.079

	Male	13.53±1.80^b)	13.32±1.69^b)	0.300	16.92±2.18	17.37±2.13	0.072

	Total	14.37±2.49	13.83±2.31^a)	0.006	16.71±2.40	17.21±2.42^a)	0.013

	p-value	<0.001	<0.001		0.127	0.229

Values are presented as mean±standard deviation unless otherwise stated.

n, number of lumbar columns.

^a) Statistically significant difference (p<0.05) compared between left and right sides.

^b) Statistically significant difference (p<0.05) compared between females and males.

Table 3

Comparisons of the length for cortical bone trajectory from different lumbar levels (L1–5) between females (n=150) and males (n=150)

Lumbar levels	Gender	Length for cortical bone trajectory (mm)		p-value
Lumbar levels	Gender	Left	Right	p-value
L1	Female	34.07±2.07 (27.90–40.21)	32.75±2.07^a) (26.92–38.92)	<0.001
	Male	36.09±2.50^b) (30.00–41.56)	35.93±2.49^b) (29.89–43.16)	0.522
	Total	35.09±2.50 (27.90–41.56)	34.34±2.79^a) (26.92–43.16)	0.001
	p-value	<0.001	<0.001
L2	Female	34.62±1.77 (29.88–41.16)	33.34±2.04^a) (27.42–40.60)	<0.001
	Male	36.49±2.44^b) (30.28–41.37)	36.63±2.53^b) (28.64–43.50)	0.629
	Total	35.56±2.32 (29.88–41.37)	34.99±2.83^a) (27.42–43.50)	0.007
	p-value	<0.001	<0.001
L3	Female	35.17±2.16 (26.18–41.53)	33.76±2.15^a) (28.73–40.26)	<0.001
	Male	37.12±2.26^b) (31.83–42.56)	36.97±2.31^b) (29.40–44.02)	0.561
	Total	36.14±2.41 (26.18–42.56)	35.36±2.75^a) (28.73–44.02)	<0.001
	p-value	<0.001	<0.001
L4	Female	35.00±2.18 (29.36–39.61)	33.83±2.16^a) (28.32–39.60)	<0.001
	Male	36.95±2.18^b) (31.07–42.39)	36.71±2.27^b) (31.17–44.14)	0.347
	Total	35.98±2.39 (29.36–42.39)	35.27±2.64^a) (28.32–44.14)	<0.001
	p-value	<0.001	<0.001
L5	Female	34.43±2.19 (29.06–42.71)	32.80±2.40^a) (27.19–40.28)	<0.001
	Male	36.07±2.41^b) (29.12–44.80)	35.53±2.60^b) (28.22–41.10)	0.063
	Total	35.25±2.44 (29.06–44.80)	34.17±2.85^a) (27.19–41.10)	<0.001
	p-value	<0.001	<0.001

Values are presented as mean±standard deviation (min–max) unless otherwise stated.

n, number of lumbar columns.

^a) Statistically significant difference (p<0.05) compared between left and right sides.

^b) Statistically significant difference (p<0.05) compared between females and males.

Table 4

Comparisons of the CSA and the ACA from different lumbar levels (L1–5) between sexes (total=300: females=150 and males=150)

Lumbar levels	Gender	CSA (°)			ACA (°)

		Left	Right	p-value	Left	Right	p-value
L1	Female	20.80±2.44	21.23±2.13	0.105	18.80±1.84	18.95±1.70	0.464

	Male	20.49±2.47	20.86±2.08	0.168	19.07±1.95	18.58±2.02^a)	0.034

	Total	20.65±2.46	21.04±2.11^a)	0.034	18.94±1.90	18.77±1.87	0.270

	p-value	0.273	0.121		0.216	0.089

L2	Female	20.04±2.23	20.60±2.10^a)	0.026	18.19±1.80	18.60±1.64^a)	0.041

	Male	19.85±2.33	20.18±2.33	0.217	18.91±1.99^b)	18.18±2.01^a,b)	0.002

	Total	19.94±2.28	20.39±2.22^a)	0.016	18.55±1.93	18.39±1.84	0.287

	p-value	0.480	0.109		0.001	0.048

L3	Female	20.59±2.10	20.99±2.13	0.102	18.52±1.88	19.01±1.90^a)	0.025

	Male	20.01±2.40^b)	21.02±2.35^a)	<0.001	19.24±2.08^b)	18.66±2.04^a)	0.014

	Total	20.30±2.27	21.00±2.24^a)	<0.001	18.88±2.01	18.83±1.98	0.774

	p-value	0.026	0.927		0.002	0.123

L4	Female	20.38±2.31	20.99±2.21^a)	0.020	19.71±2.04	19.98±1.78	0.208

	Male	19.40±2.32^b)	20.72±2.02^a)	<0.001	20.45±2.05^b)	19.97±2.08^a)	0.046

	Total	19.89±2.37	20.86±2.12^a)	<0.001	20.08±2.07	19.98±1.93	0.546

	p-value	<0.001	0.266		0.002	0.951

L5	Female	19.24±1.90	20.34±2.02^a)	<0.001	21.16±2.36	22.09±2.30^a)	0.001

	Male	18.00±2.22^b)	20.13±2.30^a)	<0.001	22.13±2.36^b)	21.95±2.81	0.553

	Total	18.62±2.16	20.24±2.16^a)	<0.001	21.64±2.41	22.02±2.56	0.066

	p-value	<0.001	0.405		<0.001	0.643

Values are presented as mean±standard deviation unless otherwise stated.

CSA, cephalad screw angle; ACA, the axial cortical bone trajectory angle.

^a) Statistically significant difference (p<0.05) compared between left and right sides.

^b) Statistically significant difference (p<0.05) compared between females and males.

Table 5

Incidences of cortical ending zones for cortical screw trajectory in different lumbar levels compared between sexes (N=300 lumbar columns: 150 females and 150 males)

Lumbar levels	Gender	Right zones						Left zones

		Z1	Z2	Z3	Z4	Z5	Z6	Z7	Z8	Z9	Z10	Z11	Z12
L1	Female	0	0	112 (75)	38 (25)	0	0	0	0	23 (15)	127 (85)	0	0

	Male	0	0	119 (79)	31 (21)	0	0	0	0	34 (23)	116 (77)	0	0

L2	Female	0	0	133 (89)	17 (11)	0	0	0	0	11 (7)	139 (93)	0	0

	Male	0	0	131 (87)	19 (13)	0	0	0	0	31 (21)	119 (79)	0	0

L3	Female	0	0	138 (92)	12 (8)	0	0	0	0	13 (9)	137 (91)	0	0

	Male	0	0	130 (87)	20 (13)	0	0	0	0	20 (13)	130 (91)	0	0

L4	Female	0	0	143 (95)	7 (5)	0	0	0	0	8 (5)	142 (95)	0	0

	Male	0	0	142 (95)	8 (5)	0	0	0	0	11 (7)	139 (93)	0	0

L5	Female	0	0	145 (97)	5 (3)	0	0	0	0	5 (3)	145 (97)	0	0

	Male	0	0	139 (93)	11 (7)	0	0	0	0	4 (3)	146 (97)	0	0

Values are presented as number of lumbar columns (% of cortical ending zones on lumbar levels L1–5).

References

1. Kim KT, Song MG, Park YJ, Lee DY, Kim DH. Cortical trajectory screw fixation in lumbar spine surgery: a review of the existing literature. Asian Spine J 2022;16:127–40.

2. Delgado-Fernandez J, Garcia-Pallero MA, Blasco G, Pulido-Rivas P, Sola RG. Review of cortical bone trajectory: evidence of a new technique. Asian Spine J 2017;11:817–31.

3. Matsukawa K, Yato Y, Nemoto O, Imabayashi H, Asazuma T, Nemoto K. Morphometric measurement of cortical bone trajectory for lumbar pedicle screw insertion using computed tomography. J Spinal Disord Tech 2013;26:E248–53.

4. Laine T, Lund T, Ylikoski M, Lohikoski J, Schlenzka D. Accuracy of pedicle screw insertion with and without computer assistance: a randomised controlled clinical study in 100 consecutive patients. Eur Spine J 2000;9:235–40.

5. El Saman A, Meier S, Sander A, Kelm A, Marzi I, Laurer H. Reduced loosening rate and loss of correction following posterior stabilization with or without PMMA augmentation of pedicle screws in vertebral fractures in the elderly. Eur J Trauma Emerg Surg 2013;39:455–60.

6. Santoni BG, Hynes RA, McGilvray KC, et al. Cortical bone trajectory for lumbar pedicle screws. Spine J 2009;9:366–73.

7. Sakaura H, Miwa T, Yamashita T, Kuroda Y, Ohwada T. Posterior lumbar interbody fusion with cortical bone trajectory screw fixation versus posterior lumbar interbody fusion using traditional pedicle screw fixation for degenerative lumbar spondylolisthesis: a comparative study. J Neurosurg Spine 2016;25:591–5.

8. Senoglu M, Karadag A, Kinali B, Bozkurt B, Middlebrooks EH, Grande AW. Cortical bone trajectory screw for lumbar fixation: a quantitative anatomic and morphometric evaluation. World Neurosurg 2017;103:694–701.

9. Verma V, Agrawal U Sr. Lumbar pedicle morphometry of dry vertebral columns in relation to transpedicular fixation: a cross-sectional study from Central India. Cureus 2023;15:e38108.

10. Zhao YH, Ma YL, Wang L, et al. Anatomical study of the ideal cortical bone trajectory in the lumbar spine. Medicine (Baltimore) 2021;100:e24099.

11. Morita K, Ohashi H, Kawamura D, Tani S, Karagiozov K, Murayama Y. Thoracic and lumbar spine pedicle morphology in Japanese patients. Surg Radiol Anat 2021;43:833–42.

12. Lien SB, Liou NH, Wu SS. Analysis of anatomic morphometry of the pedicles and the safe zone for through-pedicle procedures in the thoracic and lumbar spine. Eur Spine J 2007;16:1215–22.

13. Alam MM, Waqas M, Shallwani H, Javed G. Lumbar morphometry: a study of lumbar vertebrae from a Pakistani population using computed tomography scans. Asian Spine J 2014;8:421–6.

14. Cook WH, Baker JF. Comparative analysis of lumbar spine vertebral morphology between Maori and New Zealand Europeans: a computed tomography study. Int J Spine Surg 2021;15:1072–81.

15. Choubisa L, Babel H. Morphometric study of pedicles of dried adult human lumbar vertebrae in Udaipur zone. Int J Anat Res 2018;6:5660–6.

16. Marasini RP, Gautam P, Sherchan B, Gurung G, KCBR . A morphometric study of lumbar spine pedicles in Nepalese population. J Coll Med Sci Nepal 2014;10:12–7.

17. Wolf A, Shoham M, Michael S, Moshe R. Morphometric study of the human lumbar spine for operation-workspace specifications. Spine (Phila Pa 1976) 2001;26:2472–7.

18. Jariyapong P, Mahakkanukrauh P. Pedicle morphology of the lumbar vertebra in Thais. Srinagarind Med J 2007;22:326–32.

19. Kadioglu HH, Takci E, Levent A, Arik M, Aydin IH. Measurements of the lumbar pedicles in the Eastern Anatolian population. Surg Radiol Anat 2003;25:120–6.

20. Chen W, Wang H, Jiang J, Lyu F, MAX , Xia X. Anatomic study on lumbar cortical bone trajectory of adults. Chin J Orthop 2015;35:1213–21.

21. Torun F, Tuna H, Buyukmumcu M, Caglar S, Baysefer A. The lumbar roots and pedicles: a morphometric analysis and anatomical features. J Clin Neurosci 2008;15:895–9.

22. Kim NH, Lee HM, Chung IH, Kim HJ, Kim SJ. Morphometric study of the pedicles of thoracic and lumbar vertebrae in Koreans. Spine (Phila Pa 1976) 1994;19:1390–4.

23. Zindrick MR, Wiltse LL, Doornik A, et al. Analysis of the morphometric characteristics of the thoracic and lumbar pedicles. Spine (Phila Pa 1976) 1987;12:160–6.

24. Abbas J, Peled N, Hershkovitz I, Hamoud K. Pedicle morphometry variations in individuals with degenerative lumbar spinal stenosis. Biomed Res Int 2020;2020:7125914.

25. Tan SH, Teo EC, Chua HC. Quantitative three-dimensional anatomy of cervical, thoracic and lumbar vertebrae of Chinese Singaporeans. Eur Spine J 2004;13:137–46.

26. Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K. Cortical bone trajectory for lumbosacral fixation: penetrating S-1 endplate screw technique: technical note. J Neurosurg Spine 2014;21:203–9.

27. Feng ZH, Li XB, Tian NF, et al. The technique of cortical bone trajectory screw fixation in spine surgery: a comprehensive literature review. AME Med J 2018;3:8.