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Landmarks of vertebral artery groove of the first cervical (Atlas) vertebra for
posterior cranio-cervical approach
Gamal Hamed El-Sayed Hassanein
Anatomy Department, Faculty of Medicine –North Jeddah Branch, King Abdulaziz
University
Abstract:
Background & Objectives: The vertebral artery groove on the superior surface
of the atlas vertebra (C1) is an impression of the third part of the vertebral artery. In
the previous location; it is liable to injury during posterior surgical approach in
cranio-cervical region. The aim of this study was to determine relevant anatomical
landmarks of the vertebral artery groove (VAG) on the posterior arch of the atlas
vertebra for identifying a safe zone to avoid the potential injury of the vertebral artery
during these procedures.
Methods: Thirty six dry atlas vertebrae (24 male and 12 female) were used in
this study. The vertebral artery groove (VAG) was identified on the superior surface
of each specimen and five parameters of the groove were measured bilaterally (right
and left) using a Vernier sliding caliper.
Results : Starting from the posterior midline, the distance to the medial most
edge of the VAG on the inner cortex was 12.19 ± 3.0 mm (males) and 11.32 ± 2.88
mm (females) and the distance to the medial most edge of the VAG on the outer
cortex was 16.84 ± 3.58 mm (males) and 15.21 ± 3.66 mm (females). The distance to
the lateral most edge of the VAG on the inner cortex was 17.99 ± 3.81 mm (males)
and 16.78 ± 3.53 mm (females) and the distance to the lateral most edge of the VAG
on the outer cortex was 19.15 ± 3.64 mm (males) and 17.83 ± 3.53 mm (females). The
groove thickness was 4.28 ± 1.14 mm (males) and 3.41 ± 0.86 mm (females).
Conclusion: Dissection of the posterior arch of atlas (C1) vertebra on the
posterior and superior aspects requires a great caution and should remain within about
10 mm and 6mm lateral to the midline respectively. The placement of screws via the
posterior arch of atlas appears unfeasible and carries a great risk of injuring the
vertebral artery.
Introduction
The vertebral artery groove lies on the anterior portion of the cephalad surface
of the posterior ring of atlas. It extends horizontally from the medial border of the
transverse foramen to the medial edge of the posterior ring [1]. Craniovertebral
junction surgery requires knowledge regarding the neurovascular and musculoskeletal
anatomy of this region. The course of vertebral artery on C1 lamina complicates
surgical procedures in this area [2]. The injury to the artery during surgery can lead to
catastrophic intra-operative bleeding and compromise to the blood flow can lead to
unpredictable neurological deficits, which will depend on the adequacy of blood flow
from the contralateral vertebral artery [3]. Moreover, the increasing use of C1 (atlas)
lateral mass screw placements for atlantoaxial fixation requires a detailed anatomy of
the lateral mass and the relation of the entry zone to the vertebral artery [4].
Due to the importance of a detailed anatomical knowledge of vertebral artery
for orthopedicians and neurosurgeons during posterior craniovertebral approaches, the
present study was carried out to determine relevant anatomical landmarks of the
vertebral artery groove on the posterior arch of the atlas vertebra for providing a safe
zone to avoid the potential injury of the vertebral artery during these procedures.
Material and methods
Thirty six dry atlas vertebrae (24 male and 12 female) were used in this study.
The specimens were collected from Departments of Anatomy, Faculties of medicine,
Universities of Zagazig and King AbdulAziz. The selected vertebrae were grossly
normal and did not show any acquired pathology or congenital abnormality.
The vertebral artery groove (VAG) was identified on the superior surface of
each specimen and five parameters of the groove were measured, as previously
described [1]; [5]; [6]. The following 4 linear parameters, starting from the posterior
midline, were measured: (D1) and (D2) extended to the medial most edge of the
VAG on the inner and outer cortexes respectively. (D3) and (D4) extended to the
lateral most edge of the VAG on the inner and outer cortexes respectively (Fig.1).
Figure (1): A photograph of the superior surface of the atlas vertebra showing the linear parameters of
VAG relative to the posterior midline. (D1) & (D2) extend to the medial most edge of the groove on
inner and outer cortexes respectively. (D3) & (D4) extend to the lateral most edge of the groove on
inner and outer cortexes respectively.
The groove thickness (T) was taken as the height between the upper and lower
surfaces of the lateral part of the posterior arch of atlas vertebra in its thinnest part
(Fig.2).
Figure (2): A photograph of the posterior aspect of the atlas vertebra showing the thickness (T) of the
lateral part of its posterior arch at the vertebral artery groove (double-headed arrow).
All measurements were taken bilaterally (right and left) using a Vernier sliding
caliper; accurate to 0.1mm. The range, mean and standard deviation of each parameter
were calculated by the Microsoft office Excel computer program. A student-t test was
used to compare each parameter on right and left sides and between male and female
specimens to determine significant differences (P ≤ 0.05).
Results:
(D1) was 12.19 ± 3.0 mm (males) and 11.32 ± 2.88 mm (females) and (D2) was
16.84 ± 3.58 mm (males) and 15.21 ± 3.66 mm (females). (D3) was 17.99 ± 3.81 mm
(males) and 16.78 ± 3.53 mm (females) and (D4) was 19.15 ± 3.64 mm (males) and
17.83 ± 3.53 mm (females) (table 1).
Table (1): The parameters of VAG relative to posterior midline in the present study ( in mm):
Parameters
D1/R
D1/L
D2/R
D2/L
D3/R
D3/L
D4/R
D4/L
Male
Range
5.9618.25
6.3619.59
10.5622.5
10.9722.89
11.5923.6
12.6524.26
12.7124.11
13.8625.21
Mean ± SD
11.74 ±
2.95
12.64 ±3.06
16.56±3.62
17.11±3.6
17.44± 3.78
18.53±3.86
18.74 ±
3.71
19.58± 3.6
Female
Mean
Range
(Bilateral)
7.5712.19 ±
16.53
3.0
8.2217.85
9.6516.84 ±
20.45
3.58
10.2921.25
10.2617.99 ±
21.31
3.81
11.3721.75
11.4519.15 ±
22.55
3.64
12.3723.26
Mean ± SD
10.85 ±
2.85
11.79±2.94
Mean
(Bilateral)
11.32 ±
2.88
14.97±3.72
15.44±3.74
15.21 ±
3.66
16.37±3.69
16.78 ±
17.18 ±3.48 3.53
17.46±3.67
18.19±3.51
17.83 ±
3.53
The VAG thickness (T) was 4.28 ± 1.14 mm (males) and 3.41 ± 0.86 mm (females)
(table 2).
Table (2): The thickness of VAG in the present study ( in mm):
Parameters
T/R
T/L
Mean
(Bilateral)
Male
Range
2.25-6.86
2.35-6.95
4.28 ± 1.14
Mean ± SD
4.21±1.12
4.36±1.17
Female
Range
1.88-4.85
2.25-4.98
3.41 ± 0.86
Mean ± SD
3.33±0.88
3.49±0.87
Statistical study: The linear parameters & thickness of VAG were higher in
males and on the left side, however, these differences between the right and left sides
and between male and female specimens, based on the student-t test, were not
statistically significant (P ≥ 0.05).
Discussion
The vertebral artery makes a loop after its exit from foramen transversarium of
C1, then occupies a vertebral artery groove over the surface of the posterior arch of
atlas and in this location it is vulnerable to injury during a posterior midline approach
[3]. To define a safe zone from the posterior midline to avoid injuring the vertebral
artery, Ebraheim et al [1] , described a mean distance of 10.4 ± 1.7 mm (males) and
8.9 ± 0.8 mm (females); with a minimum of 8 mm for both genders, from the
posterior midline to the medial most edge of VAG on the inner cortex, and described
a mean distance of 19.2 ± 3.2 mm (males) and 16.5 ± 1.0 (females); with a minimum
of 12 mm for both genders, from the posterior midline to the medial most edge of
VAG on the outer cortex. The previous authors suggested, according to these finding,
that dissection on the posterior aspect of the posterior ring should remain within 12
mm lateral to the midline, and that dissection on the superior aspect of the posterior
ring should remain within 8 mm of the midline. In the present study, the mean
distance from the posterior midline to the medial most edge of VAG on the inner
cortex was 12.19 ± 3.0 mm (males) and 11.32 ± 2.88 mm (females), with a minimum
of 5.96 mm in both genders and on the outer cortex was 16.84 ± 3.58 mm (males)
and 15.21 ± 3.66 mm (females), with a minimum of 9.65 mm in both genders. These
findings, although slightly lower in value, are in line with those of Ebraheim et al [1].
However, higher values were reported for distances from the midline to the medialmost edge of the vertebral artery groove; on the outer cortex 15.03 ± 1.22 mm [2] ,
approximately 12 mm and 16 on the inner and outer and cortexes respectively [5] ;
14.3 mm to 19.7 mm (average 18.2 mm) on the outer cortex [3]. From the findings of
the present study, to avoid injury of vertebral artery , it suggested that dissection of
the posterior aspect of the posterior arch requires a great caution and should remain
within about 10 mm lateral to the midline, and that dissection on the superior aspect
of the posterior ring should remain within about 6 mm of the midline.
Apart from the distances of VAG from the posterior midline, the groove
thickness is another important parameter of the VAG that gains its surgical
importance after the increasing popularity of cranio-vertebral fixation processes via
the posterior arch of the atlas vertebra [7]; [8]; [9]. In the present study, the mean
thickness of VAG was 4.28 mm (males) and 3.41 mm (females). In agreement with
the findings of the present study, Tan et al [7] and Ma et al [8] reported a thickness of
4.25 mm and 4.58 mm respectively. Moreover, Ebraheim et al [1] And Lee et al [9]
described a mean thickness of the vertebral groove of 4.1 mm (males) and 3.5 mm
(females). According to Tan et al [7] the posterior arch at the position of VAG is
regarded as a vertebral pedicle through the screw fixation via the posterior arch of
atlas could be achieved. However, Lee et al [9 ] reported that a minimum thickness of
5mm is required to safely pass a 3.5 mm screw via the posterior lateral arch of atlas,
without violating any of the cortical margins. In the present study, all specimens were
less than 5mm and this indicates that the screw placement via the posterior arch
described by Tan et al [7] to be unfeasible and carries a great risk of injuring the
vertebral artery.
References
[1] Ebraheim NA, Xu R, Ahmad M, Heck B. The quantitative anatomy
of the vertebral artery groove of the atlas and its relation to the
posterior atlantoaxial approach. Spine 1998; 23(3): 320-323.
[2] Naderi S, Çakmakçi H, Acar F,Arman C, Metrol T, Arda MN. Anatomical and
computed tomographic analysis of C1 vertebra. Clinical Neurology and Neurosurgery
2003; 105 (4): 245- 248
[3] Cacciola F, Phalke U, Goel A.Vertebral artery in relationship to C1-C2 vertebrae:
An anatomical study. Neurology India 2004;52(2): 178 - 184
[4] Gupta T. Cadaveric morphometric anatomy of C-1 vertebra in relation to lateral
mass screw placement. Surg Radiol Anat 2008 ; 30 : 589 - 593
[5] Gupta T. Quantitative anatomy of vertebral artery groove on the posterior arch of
atlas in relation to spinal surgical procedures. Surg Radiol Anat 2008; 30: 239–242
[6] Carvalho MF; Rocha RT ; Monteiro JTS; Pereira CU; Leite RF; Defino
HLA.Vertebral artery groove anatomy. Acta Ortop Bras 2009; 17(1): 50-54
[7] Tan M ; Wang H ; Wang W; Zhang G; Yi P; Li Z; Wei H ; Yang F.
Morphometric evaluation of screw fixation in atlas via posterior arch and lateral mass.
Spine 2003 ; 28 (9) : 888-895
[8] Ma X-Y; Yin Q-S; Wu Z-H; Xia H; Lu J-F ; Zhong S-Z .Anatomic considerations
for the pedicle screw placement in the first cervical vertebra. Spine 2005 ; 30 (13) :
1519-1523
[9] Lee MJ; Cassinelli E ; Riew D. The feasibility of inserting atlas lateral mass
screws via the posterior arch. Spine 2006 ; 31 (24) : 2798- 2801
‫الملخص العربي‬
)‫معالم أخدود الشريان الفقاري للفقرة العنقية األولى (األطلس‬
‫للنهج القحفي العنقي الخلفي‬
‫جمال حامد السيد حسانين‬
‫ جامعة الملك عبد العزيز‬,‫ كلية الطب فرع شمال جدة‬, ‫قسم التشريح‬
‫ان أخدود الشريان الفقاري علي السطح العلوي لفقرة األطلس (العنقية األولى) هو بصمة للجزء الثالث من‬
‫ وفي هذا الموضع يكون الشريان الفقاري معرضا ً لإل صابة أثناء النهج الجراحي الخلفي‬, ‫الشريان الفقاري‬
‫ ولقد كان الهدف من هذه الدراسة هو تحديد معالم تشريحية ألخدود الشريان الفقاري علي‬, ‫للمنطقة القحفية العنقية‬
‫القوس الخلفي لفقرة األطلس ذات الصلة بهذا النهج لتعريف منطقة آمنة لتجنب اإلصابة المحتملة للشريان الفقاري‬
.‫أثناء هذه اإلجراءات‬
‫ وتم تحديد موضع‬, ) ‫ مؤنث‬24 ‫ مذكر و‬42 ( ‫استخدم في هذه الدراسة ستة وثالثون فقرة أطلس جافة‬
‫تجويف الشريان الفقاري علي السطح العلوي لكل عينة وتم قياس خمسة معلمات لألخدود علي الجانبين (يمين‬
‫ويسار) باستخدام فرجار فيرنيير المنزلق ‪ ,‬و أظهرت الدراسة أن المسافة من خط المنتصف الخلفي إلي أقصى‬
‫‪ 11.32 ± 2.88‬مم (ذكور) و ‪12.19 ± 3.0‬الحافة األنسية ألخدود الشريان الفقاري علي القشرة الداخلية هي‬
‫مم (إناث) ‪ ,‬والمسافة من خط المنتصف الخلفي إلي أقصى الحافة األنسية ألخدود الشريان الفقاري علي القشرة‬
‫مم (إناث) ‪ ,‬أما المسافة من خط المنتصف ‪ 15.21 ± 3.66‬مم (ذكور) و ‪16.84 ± 3.58‬الخارجية هي‬
‫مم ‪17.99 ± 3.81‬الخلفي إلي أقصى الحافة الوحشية ألخدود الشريان الفقاري علي القشرة الداخلية هي‬
‫مم (إناث) ‪ ,‬والمسافة من خط المنتصف الخلفي إلي أقصى الحافة الوحشية ألخدود ‪(16.78 ± 3.53‬ذكور) و‬
‫مم (إناث) ‪ ,‬بينما ‪ 17.83 ± 3.53‬مم (ذكور) و ‪19.15 ± 3.64‬الشريان الفقاري علي القشرة الخارجية هي‬
‫مم (إناث) ‪ 3.41 ± 0.86.‬مم (ذكور) و ‪4.28 ± 1.14‬كانت سماكة األخدود هي‬
‫االستنتاج ‪ :‬يجب الحذر عند تشريح القوس الخلفي لفقرة األطلس ( العنقية األولى) من الجهتين الخلفية والعلوية‬
‫وأال يتجاوز ذلك ‪ 21‬مم و‪ 6‬مم علي التعاقب من خط المنتصف ‪ ,‬كما أن وضع المسامير عن طريق القوس‬
‫الخلفي لفقرة األطلس يبدو غير مجديا ويحمل خطرا كبيرا نحو اصابة الشريان الفقاري‪.‬‬