Can radiologic parameters used to detect cervical spinal instability be used in patients with ankylosing spondylitis?

Abstract

Introduction
Cervical spinal instability can be difficult to detect in the shock room setting even with the utilization of computed tomography (CT) scans. This may be especially true in patients with cervical degenerative disease, such as ankylosing spondylitis (AS). The purpose of this study was to investigate the influence AS has on various radiologic parameters used to detect traumatic and degenerative instability of the cervical spine, to assess if CT imaging in the shock room is diagnostically appropriate in this patient population.

Methods
A matched, case–control retrospective analysis of patients with AS and controls without AS admitted at two level-1 trauma centers was performed. All patients were admitted via shock room and received a polytrauma CT. Twenty-four CT parameters of atlanto-occipital dislocation/instability, traumatic and degenerative spondylolisthesis, basilar invagination, and prevertebral soft tissue swelling were assessed. Since the study was assessing normal values, study patients were included if they had no injury to the cervical spine. Study patients were matched by age and sex.

Results
A total of 78 patients were included (AS group, n = 39; control group, n = 39). The evaluated cervical radiologic parameters were largely within normal limits and showed no significant clinical or morphologic differences between the two groups.

Conclusion
In this analysis, CT measurements pertaining to various cervical pathologies were not different between patients with and without AS. Parameters to assess for atlanto-occipital dislocation/instability, spondylolisthesis, or basilar invagination in the trauma setting may reliably be used in patients with AS.

Full text

Teuberetal.
European Journal of Medical Research (2023) 28:97
https://doi.org/10.1186/s40001-023-01052-3
RESEARCH
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Open Access
European Journal
of Medical Research
Can radiologic parameters used todetect
cervical spinal instability be used inpatients
withankylosing spondylitis?
Henrik Teuber1* , Sascha Halvachizadeh1, Melvin Muthirakalayil1, Luxu Yin2, Harry Eisenkrein2,
Frank Hildebrand2, Philipp Kobbe2, Kai Sprengel1, Ladislav Mica1, Hatem Alkadhi3, Hans‑Christoph Pape1 and
Roman Pfeifer1
Abstract
Introduction Cervical spinal instability can be difficult to detect in the shock room setting even with the utilization
of computed tomography (CT) scans. This may be especially true in patients with cervical degenerative disease, such
as ankylosing spondylitis (AS). The purpose of this study was to investigate the influence AS has on various radiologic
parameters used to detect traumatic and degenerative instability of the cervical spine, to assess if CT imaging in the
shock room is diagnostically appropriate in this patient population.
Methods A matched, case–control retrospective analysis of patients with AS and controls without AS admitted at
two level‑1 trauma centers was performed. All patients were admitted via shock room and received a polytrauma CT.
Twenty‑four CT parameters of atlanto‑occipital dislocation/instability, traumatic and degenerative spondylolisthesis,
basilar invagination, and prevertebral soft tissue swelling were assessed. Since the study was assessing normal values,
study patients were included if they had no injury to the cervical spine. Study patients were matched by age and sex.
Results A total of 78 patients were included (AS group, n = 39; control group, n = 39). The evaluated cervical radio‑
logic parameters were largely within normal limits and showed no significant clinical or morphologic differences
between the two groups.
Conclusion In this analysis, CT measurements pertaining to various cervical pathologies were not different between
patients with and without AS. Parameters to assess for atlanto‑occipital dislocation/instability, spondylolisthesis, or
basilar invagination in the trauma setting may reliably be used in patients with AS.
Keywords Ankylosing spondylitis, Cervical spine, Computed tomography, Radiologic parameters
Introduction
Ankylosing spondylitis (AS) is a progressive arthritis that
primarily affects the axial skeleton, which often results in
multi-segmental fusion of the spine. e loss of mobility
in the vertebral column results in a rigid structure that
behaves like a long bone. In association with osteoporosis
often accompanying AS in the elderly, these individuals
are significantly more susceptible to unstable injuries of
the spine. Cervical spinal injuries are common, occurring
in 3% of major trauma patients [1]. Cervical trauma in AS
*Correspondence:
Henrik Teuber
henrik.teuber@gmail.com
1 Department of Trauma Surgery and Harald‑Tscherne Laboratory,
University Hospital Zurich, University of Zurich, Zurich, Switzerland
2 Department of Orthopedics Trauma Surgery, University Hospital
Aachen, RWTH Aachen University, Aachen, Germany
3 Department of Radiology, University Hospital Zurich, University
of Zurich, Zurich, Switzerland
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Teuberetal. European Journal of Medical Research (2023) 28:97
patients requires particular attention in the acute shock
room setting, as the risk of severe neurological complica-
tions due to spinal stenosis is greatly elevated [2, 3].
In the polytraumatized shock room setting, CT is the
imaging modality of choice for assessing cervical spinal
trauma. With sensitivity of 97–100%, it is very sensi-
tive in detecting cervical spinal fractures. However, with
respect to detecting ligamentous instability, sensitivity is
much lower and has not been well documented [1]. To
assess for cervical spinal instability using CT, indirect
parameters primarily looking for subtle subluxations
must be used.
In AS, multiple studies have shown progressive patho-
logic changes to the cervical spine in patients with longer
disease duration [2]. In patients with AS for at least
20years, 19.9% of males and 16.0% of females exhibited
cervical-predominant pathology [4]. After 25 years of
disease, 75% of AS patients had cervical spine involve-
ment [5]. Additionally, patients with early AS exhibit
cervical-predominant pathology in 5.2% of cases. Mor-
phologically, physiologic cervical lordosis may regress
and pathologic cervical kyphosis, due to spondyloar-
thropathy, may develop in AS patients. Patients unload
the inflamed facet joints by assuming a kyphotic posture.
Ultimately, with increasing syndesmophyte formation
and eventual ankylosis, the cervical spine assumes a fixed
kyphotic deformity [6, 7].
To assess if potentially subtle cervical traumatic insta-
bility in patients with AS can be detected in the shock
room setting, it is important to understand if the mor-
phologic changes that can occur in AS affect the measur-
ability of radiologic parameters used in detecting cervical
spinal instability. However, little is known about the effect
AS has on characteristic radiologic changes found in
common traumatic or degenerative soft tissue patholo-
gies of the cervical spine. It is unknown if the normal val-
ues of these parameters are the same in patients with and
without AS. We thus hypothesized that the ankylosis,
spinal degeneration, and deformity commonly found in
AS may affect the normal values of important radiologic
parameters used in detecting cervical instability includ-
ing atlanto-occipital dislocation, spondylolisthesis, and
basilar invagination. To assess this hypothesis, an analysis
of 24 commonly used radiologic parameters were meas-
ured in cervical CTs of non-injured patients with AS and
non-injured controls without AS.
Finally, it is important to note that this study design
was applied in the setting of acute injury diagnostics
in a polytraumatized shock room setting. If CT imag-
ing remains unclear, and cervical spinal instability can-
not be ruled out, prompt additional MRI or functional
conventional imaging to assess for ligamentous injury is
required after the patient has been stabilized, as these
imaging modalities are much more sensitive in detecting
potentially unstable ligamentous injuries of the cervical
spine [1].
Patients andmethods
e study was approved by the respective local ethics
committees of the two level 1 trauma centers. All patients
were treated at two level 1 trauma centers between 2009
and 2019. All patients were admitted via shock room and
received a polytrauma CT. Patients may have had multi-
ple injuries, but were included only if they had no inju-
ries to the cervical spine, since this study was designed to
assess the applicability of normal limits of various radio-
logic parameters used in assessing for potential cervical
spinal instability. In the study group, patients with a con-
firmed diagnosis of AS (fulfillment of the modified New
York criteria for AS or ASAS criteria for axial SPA) were
included. Study group patients were matched 1:1 for age
and gender with patients without AS in whom cervical
spinal injuries were ruled out.
Cervical spine CT examinations
All patients underwent scans by multi-detector row CT
of the cervical spine. Axial images were reconstructed at
a section thickness of 1mm and an increment of 0.7mm.
Axial, coronal, and sagittal reformations were obtained.
Twenty-four radiologic parameters summarized in
Table1 were measured and evaluated by three independ-
ent orthopedic surgeons who were blinded to clinical
data. An example of a sagittal plane CT of the cervical
spine of a patient in the AS group is shown in Fig.1.
Statistics
Data were analyzed using the SPSS software package ver-
sion 20.0 for Windows (SPSS Inc., Chicago, IL, USA).
Descriptive statistics are presented as mean and standard
error of the mean (SEM). Statistical distribution of all the
data was assessed by both the Shapiro–Wilk and Kol-
mogorov–Smirnov tests. An independent t-test was used
to calculate statistical differences between the AS group
and the control group. A p-value less than 0.05 was con-
sidered statistically significant.
Results
Overall, 78 patients were included in the study. e AS
study group consisted of 35 male and 4 female patients
with an average age of 66.2years and was matched on a
1:1 basis with healthy controls. AS patients had a mean
New York criteria sacroiliitis grade of 2.89 (SD 0.76).
Both groups were demographically very similar. However,
steroid use was unsurprisingly significantly higher in the
AS vs. control study group (10.3% vs. 0.0% of patients,
p = 0.044). Study demographics are shown in Table 2.
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Teuberetal. European Journal of Medical Research (2023) 28:97
Overall, the radiologic parameters measured were within
normal limits and showed little variation between the
groups. None of the 24 CT-based parameters meas-
ured were statistically or clinically different between the
groups and are summarized in Table3.
Atlanto‑occipital dislocation/instability parameters
e BDI and BAI were both well within normal limits
(< 8.5mm) and similar in both the AS and control groups
(5.1 vs. 5.3mm, p = 0.544 and 4.9 vs. 5.6mm, p = 0.180,
respectively). Both methods of measuring Powers Ratio
were also similar and within normal limits (< 0.9) in the
AS and control groups (0.87 vs 0.90, p = 0.080 and 0.74
vs 0.78, p = 0.059, respectively). Eleven patients showed
pathological Lee X-Line parameters in both study groups
(28.2%, p = 1.00). Further, we looked at the lengths of
the individual lines used to assess Powers Ratio and Lee
X-Lines as well as measuring a Lee X-Line ratio to see
if we could find any subtle anatomic variation between
the two groups. is analysis, however, also showed no
Table 1 Brief description and method of measurement of the selected radiologic parameters
BAI The distance between the basion and the tangent of the posterior border of the axis
BDI The distance between the basion and the tip of the odontoid process
C2–C3 angle (endplate method) Angle between lines tangent to the inferior endplate of C2 and C3
C2–C3 angle (posterior method) Angle between lines tangent to the posterior vertebral body of C2 and C3
Lee X‑Line Lines of basion to the arch of C2 and opisthion to the postero‑inferior edge of C2. When both lines do not inter‑
sect C2 and C1, respectively, dissociation is suspected
Power ratio 1 The ratio of basis‑arc C1/dens‑opisthion. A ratio greater than 0.9 is considered pathological and suggestive of
atlanto‑occipital instability
Power ratio 2 The ratio of basis‑arc C1/C1 ventral‑opisthion
Chamberlain line The line connects the posterior end of the hard palate and the posterior lip of the foramen magnum
McCrae’s line The line of the opening of the foramen magnum
PADI The posterior interval between atlas and dens
Soft‑tissue shadow of C3 and C6 The distance between the anterior aspect of the vertebral body baseplate to the trachea
Endplate tilt of C4–C5 and C5–C6 Angle of lines drawn along the inferior endplate of C4–C5 and C5–C6
Displacement of C4–C5 and C5–C6 The displacement of the postero‑inferior edge of the superior vertebral body to the posterosuperior edge of the
inferior vertebral body
Fig. 1 Sagittal plane CT of the cervical spine of a patient in the AS
group, an 80‑year‑old male
Table 2 Demographics
Control Ankylosing
spondylitis p
n39 39
Age (yrs, mean (SD)) 66.2 (14.4) 66.4 (14.2) Matched
Female (n, %) 4 (10.3) 4 (10.3) Matched
Height (cm, mean (SD)) 174.5 (6.0) 172.4 (4.7) 0.169
Weight (kg, mean (SD)) 80.7 (11.1) 77.4 (13.8) 0.334
BMI (mean (SD)) 26.5 (3.1) 26.2 (4.5) 0.522
Diabetes mellitus (n, %) 9 (23.1) 12 (30.8) 0.450
Corticosteroid therapy (n, %) 0 (0.0) 4 (10.3) 0.044
Osteoporosis (n, %) 2 (5.1) 3 (7.7) 0.649
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Teuberetal. European Journal of Medical Research (2023) 28:97
differences between the groups. e mean posterior
atlanto-dens interval (PADI) was well within normal lim-
its (> 14mm) and nearly identical in the AS and control
groups (21.0 vs. 21.3mm, p = 0.523).
Basilar invagination parameters
Both Chamberlain’s and McCrae’s lines showed simi-
lar results in both the AS group and healthy controls.
Seven patients in the control group and 8 patients in the
AS group had a pathological Chamberlain line (17.9%
vs. 20.5%, respectively, p = 1.00). ere were no patients
with a pathological McCrae’s line in either group (0%,
p = 1.00). As with the atlanto-occipital parameters above,
line lengths were also compared to observe potentially
subtle anatomic differences, but no differences between
the groups were observed.
Degenerative/traumatic spondylolisthesis parameters
Endplate tilt at C2/3 (1.8° vs 1.9°, p = 0.910), C4/5 (1.6° vs
−1.4°, p = 0.082) and C5/6 (2.6° vs 1.8°, p = 0.597) were
similar and stable (< 11°) between the AS and control
groups. However, a consistent, but subtle trend toward
more kyphotic angulation, especially at the C4/5 level,
was seen in the AS group. Displacement at the level of
C3 and C6 were less than 1mm in both the AS and con-
trol patients. Finally, soft tissue swelling at C3 (4.6 vs
6.1mm, p = 0.070) and C6 (13.8 vs 12.4mm, p = 0.107)
were within normal limits (C3 < 7mm, C6 < 21mm) and
similar in both the AS and control groups, respectively.
Discussion
In this study, despite known morphologic changes to the
cervical spine in the setting of AS, none of the cervical
radiologic parameters measured in patients with AS were
different compared to healthy controls. We could there-
fore not support the study hypothesis that AS may affect
normal values of commonly measured radiologic param-
eters used in diagnosing atlanto-occipital dislocation,
cervical spondylolisthesis and basilar invagination.
Cervical trauma in patients with AS is associated with
a high risk of potentially severe neurologic complications
[8]. Early awareness and recognition of cervical injuries
is, therefore especially important in the setting of AS.
However, the assessment of cervical instability or frac-
tures with conventional imaging in patients with AS is
challenging. Conventional plain radiographs show low
Table 3 Radiologic parameters of various ligamentous injuries
Control Ankylosing spondylitis p‑value
n39 39
BDI (mm, mean (SD)) 5.3 (1.6) 5.1 (2.0) 0.544
BAI (mm, mean (SD)) 5.6 (2.2) 4.9 (2.4) 0.180
Basis–C1 (mm, mean (SD)) 32.8 (2.4) 31.7 (3.0) 0.092
Dens–opisthion (mm, mean (SD)) 36.4 (3.0) 36.7 (3.1) 0.692
Powers ratio 1 (mean (SD)) 0.90 (0.08) 0.87 (0.10) 0.080
C1–opisthion (mm, mean (SD)) 42.5 (3.5) 42.8 (3.4) 0.690
Powers ratio 2 (mean (SD)) 0.78 (0.07) 0.74 (0.07) 0.059
Basis–C2 (mm) 42.05 (3.32) 40.76 (3.39) 0.092
C2–ophistion (mm) 44.49 (5.96) 43.90 (5.34) 0.644
Lee X‑line ratio 0.96 (0.17) 0.94 (0.13) 0.484
Pathological X‑line (n (%)) 11 (28.2) 11 (28.2) 1.000
Chamberlain line length (mean (SD)) 82.07 (3.99) 81.58 (3.75) 0.591
Pathological chamberlain line (n (%)) 7 (17.9) 8 (20.5) 1.000
McCrae’s line length (mean (SD)) 37.60 (2.56) 37.37 (3.57) 0.747
Pathological McCrae’s line (n (%)) 0 (0.0) 0 (0.0) 1.000
PADI (mm, mean (SD)) 21.3 (2.3) 21.0 (2.1) 0.523
C2–C3 angulation (endplate) (°, mean (SD)) 1.9 (5.2) 1.8 (5.6) 0.910
C2–C3 angulation (posterior wall) (°, mean (SD)) 6.3 (6.6) 8.0 (7.0) 0.272
End plate tilt C4–C5 (°, mean (SD)) − 1.4 (5.9) 1.6 (8.6) 0.082
End plate tilt C5–C6 (°, mean (SD)) 1.8 (5.6) 2.6 (7.4) 0.597
Displacement C4–C5 (mm, mean (SD)) 0.6 (1.1) 0.4 (1.2) 0.642
Displacement C5–C6 (mm, mean (SD)) 0.3 (0.9) 0.4 (1.0) 0.651
Soft‑tissue shadow C3 (mm, mean (SD)) 6.1 (4.3) 4.6 (2.6) 0.070
Soft‑tissue shadow C6 (mm, mean (SD)) 12.4 (4.0) 13.8 (3.5) 0.107
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Teuberetal. European Journal of Medical Research (2023) 28:97
efficiency in diagnosing cervical injuries due to diffuse
ossification of cervical spinal ligaments, joints and discs
[9]. In a retrospective review, Anwar etal. showed that
60% of cervical fracture dislocations in patients with AS
were undetectable in initial radiographs [10]. Sensitivity
for detecting cervical injuries is much higher in CT with
an improved sensitivity of up to 98% [11–13]. us, in
the acute trauma setting, the indication for conventional
radiologic imaging of the cervical spine is limited and CT
of the cervical spine is the standard imaging modalityof
choice when cervical trauma is suspected [14, 15]. is is
especially true in the setting of AS.
Parameters assessing atlanto‑occipital stability are
unaltered inASpatients
BAI and BDI are helpful for the diagnosis of atlanto-
occipital dissociation injuries. Normal values should be
less than 12 mm on plain radiographs. An increase in
this distance may indicate instability [16]. Multiple stud-
ies declared that the accepted ranges of normal values
of BDI and BAI on plain radiographs cannot apply to
CT images. Rojas etal. [17] argued that the BAI was dif-
ficult to reproduce on CT images; the value was found
to be highly variable and a number of subjects had BAIs
greater than 12 mm. ey found that the distance of
BDI was < 8.5mm in the vast majority of 200 cases and
the maximum distance recorded was 9.1mm. Gonzalez
etal. [18] also demonstrated a mean BDI of 4.7mm and
a maximum of 9mm in CT images from healthy individ-
uals. In line with the literature, the BDI and BAI in the
control group of our study were well within normal limits
at 5.3 (SD 1.6) and 5.6 (SD 2.2) mm, respectively. Neither
BDI nor BAI differed in the AS group compared to the
control group and were equally well within normal limits.
Changes to the craniovertebral junction in AS with
cervical involvement has been well described and is fre-
quently involved in severe AS [19]. All patients with AS
underwent structural changes of articulation and/or
ligamentous craniocervical structures [19]. e inter-
val of the atlanto-occipital joint and the atlanto-dental
joint were decreased in AS patients, but the BDI and the
Power’s ratio were not changed [19]. Our results confirm
these findings.
Studies of BAI measurements in AS patients are rare.
Robust articular ligaments, such as the cruciform liga-
ment, are important for atlanto-axial joint stability
[20]. In the pathological process of AS, these ligaments
undergo inflammation such as enthesitis, and laxity or
rupture with subsequent atlanto-axial subluxation can
occur [21]. Furthermore, odontoid pannus formation
can lead to atlanto-axial instability [22]. We suspected
that excessive kyphosis might also occur at this level,
potentially altering various parameters, especially BAI.
However, BAI was found within normal limits and not
different to the control group. e only pathological val-
ues we found in the present study were seen with the
Lee’s X-line parameters with pathological findings in 11
(28.2%) patients in both study arms. e hypothesis of
altered atlanto-occipital cervical parameters on account
of AS induced instability, specifically pathologic kypho-
sis, could not be supported in this study.
Parameters assessing basilar invagination andcervical
spondylolisthesis remain stable inASpatients
e endplate and the posterior vertebral body tangent
measurement methods for C2–C3 angulation were first
described by Levine and Edwards [23]. C2–C3 angulation
and translation were usually used to evaluate for trau-
matic spondylolisthesis including Hangman’s fractures
[24, 25]. e physiological cervical spine shows a slight
lordotic curvature at the level C2–C3 of about -1.9 ± 5.20°
[26]. Cervical lordosis in AS patients is decreased and
with increasing severity, even kyphotic deformities may
occur [6]. However, it is unknown if kyphotic changes
in AS are focussed at specific levels, or if the kyphotic
changes are equally distributed throughout the cervical
spine and thus difficult to detect at individual levels. In
this study, the angulation at C2–C3 as well as C4–C5 and
C5–C6 were measured to assess for potential underly-
ing spondylolisthetic changes [27]. Any bony pathologic
changes of the endplate may influence the measurement
of these angles. is is especially true in AS patients,
where the endplate border is altered by the presence of
syndesmophytes characteristic of the disease [28, 29].
In this study, no changes in single-level angulation were
found between the groups. However, a subtle but sta-
tistically insignificant trend toward more kyphosis at all
levels measured was seen in the AS versus control group.
is was most pronounced at the C4/5 level.
Further, results did not differ regardless if measured
using the endplate method or the posterior vertebral
body line method [27]. We do, however, feel that the
posterior vertebral line method may prove more accu-
rate and useful in evaluating the cervical spine in AS, as
it measures the angle of lines drawn perpendicular to
the posterior vertebral body aspect of the two endplates.
e pathological changes of the vertebral edges therefore
have less impact on accurate assessment of possible spon-
dylolisthesis. e results suggest that endplate angula-
tion at single vertebral levels remains largely unchanged,
despite overall loss of cervical lordosis in AS patients.
Additionally, no differences or pathological values in
vertebral displacement (defined as > 3 mm) measured
at C4–C5 and C5–C6 were found between the groups,
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Teuberetal. European Journal of Medical Research (2023) 28:97
further suggesting that spondylolisthetic degeneration
was not present in the AS study group.
Parameters assessing basilar invagination were also
identical between the AS and control group. While
approximately 20% of patients in both the AS (n = 7)
and control (n = 8) groups had a pathological Chamber-
lain line, none of the patients in both the AS and control
group had a pathological McCrae line. While of no clini-
cal or diagnostic significance, the line lengths were also
measured as with the above parameters used to assess
for atlanto-occipital dissociation. Here as well, we saw
no differences between the groups, suggesting that subtle
morphologic changes in the AS group were not present.
While common in other arthopathies, such as rheuma-
toid arthritis, basilar invagination is rare in AS as pannus
formation and degenerative destruction of the craniocer-
vical junction has only been documented in late stage
disease [21, 22, 30]. Our results are therefore in line with
the literature and previous radiologic studies of AS.
It is important to note that with increasing severity
of AS, more osteophytic and syndesmophytic changes
occur, which may have influenced the accuracy of some
of the measured parameters that rely on precise bony
landmarks. e severity of AS was not specifically
assessed for in this study and is an important study limi-
tation, especially considering that cervical changes are
usually found in late stage disease. Since the majority
of the AS patients in this study population were older,
however, it is likely that a significant portion of the study
population was afflicted with more severe disease. Due to
the high patient age, the matched study design was use-
ful in accounting for the potentially confounding effect
of general spinal degeneration. Further study limitations
include the limited size of the study population, and the
fact that the cervical parameters, while carefully meas-
ured by three board certified orthopedic surgeons, were
not evaluated by fellowship-trained musculoskeletal radi-
ologists, potentially affecting the reliability of measured
parameters.
Further research is needed to better rapidly assess
for ligamentous injuries of the cervical spine in older
patients with AS or other pre-existing degenerative dis-
ease processes of the cervical spine in a polytraumatized
shock room setting. A study with a larger population
would be useful to confirm our results. Perhaps one area
of future development could include the identification of
laboratory parameters specific for ligamentous injuries
of the spine as a more rapid adjunct to further imaging
diagnostics, which may not be immediately attainable in
the polytraumatized patient setting.
Conclusion
Our analysis showed that while cervical changes can be
significant in AS, commonly assessed traumatic and
degenerative radiologic cervical spine parameters were
not different in patients with AS compared to matched
controls without AS. is study affirms the applicability
of these radiologic parameters in the acute trauma set-
ting and suggests that their normal values may be used
with confidence in patients with AS. However, further
study is necessary to confirm these results and improve
diagnostic modalities to quickly and accurately assess for
cervical spinal injuries in patients with AS.
Acknowledgements
None.
Author contributions
FH, PK, KS, LM, HP, and RP have made substantial contributions to the concep‑
tion and design of the study. HT, SH, MM, LY, HE, HP and RP have made sub‑
stantial contributions in the acquisition, analysis, and interpretation of data.
HT, SH, MM, LY, HE, HA, LM, HP and RP have drafted the work or substantively
revised it. All authors read and approved the final manuscript.
Funding
No external funding was necessary in completing this retrospective study.
Availability of data and materials
The data generated and analyzed for the current study are not publicly avail‑
able, but are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
The study was approved by the respective local ethics committees of the two
level 1 trauma centers.
Consent for publication
The patient whose CT image is shown in Fig. 1 has signed a general consent
form.
Competing interests
The authors declare that they have no competing interests.
Received: 28 October 2021 Accepted: 7 February 2023
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