Postmortem radiological case series of acetabular fractures after fatal aviation accidents
Forensic Science, Medicine and Pathology
Postmortem radiological case series of acetabular fractures after fatal aviation accidents
Henri M. de Bakker 0 1 2 3 4
Melanie Tijsterman 0 1 2 3 4
Bela Kubat 0 1 2 3 4
Vidija Soerdjbalie-Maikoe 0 1 2 3 4
Rick R. van Rijn 0 1 2 3 4
Bernadette S. de Bakker 0 1 2 3 4
0 Division of Special Services, Section Forensic Pathology, Netherlands Forensic Institute , The Hague , The Netherlands
1 Department of Medical Biology, Section Clinical Anatomy and Embryology, Academic Medical Center, University of Amsterdam , Meibergdreef 15, 1105 AZ Amsterdam , The Netherlands
2 Bernadette S. de Bakker
3 Department of Radiology, Academic Medical Center, University of Amsterdam , Amsterdam , The Netherlands
4 Department of Pathology, Maastricht University Medical Center, University of Maastricht , Maastricht , The Netherlands
The purpose of this study was to describe radiological fracture patterns of the acetabulum sustained after fatal small aircraft aviation accidents, aiming at facilitating a better understanding of trauma mechanisms in a forensic setting. Postmortem conventional radiographs or CT scans of 29 victims of 20 small aircraft aviation accidents were analyzed for skeletal acetabular trauma. Among the 29 fatalities (27 males and 2 females, median age 55 years (range: 21-76 years)), 20 victims had pelvic fractures (69%), of which 19 victims (66%) had one or more acetabular fractures. Bilateral acetabular fractures occurred in 11 victims. When considering left and right acetabula in each victim as separate entities, 38 of the 58 acetabula included in this case series exhibited one or more fractures. Both the anterior and posterior acetabular columns were fractured in 28 acetabula. Acetabular fractures were frequently encountered in this series of 29 victims of small fatal aircraft accidents. Fractures of the acetabulum occur from ventrally directed impact (i.e. to the knee) or laterally directed impact (i.e. to the greater trochanter of the femur). Radiological descriptions of the fracture patterns can therefore aid in the forensic analysis of the mechanism of trauma in aviation accidents. Postmortem multi-slice CT scan images are preferrable in the assessment of acetabular fractures.
Aviation accidents; Postmortem; Acetabulum; Acetabular fracture; Forensic radiology
In a forensic setting, the use of radiological imaging as an
addition to conventional autopsy has increased in recent
decades. Postmortem computed tomography (PMCT) has
proven to be a helpful tool in the quest for the legal truth, as it
Department of Radiology, Groene Hart Hospital,
Gouda, The Netherlands
contributes to the visualization of skeletal traumatic lesions
and is helpful in the determination of the cause and
reconstruction of the manner of death [
]. For this reason, aviation
accidents are forensically interesting. Various studies have
described injuries obtained during aviation accidents [
was suggested by Kubat et al., the type and severity of injuries
depend on many factors [7, 8], such as the speed of the
aircraft, the type of the aircraft, or the position of the persons in
the plane. Additionally, the degree of injury is influenced by
the forces generated upon impact.
Acetabular fractures are uncommon in the clinical setting
]. Laird and Keating determined the overall incidence
of such fractures as three fractures in 100,000 trauma patients
per year [
]. They included all trauma admissions to the
emergency department. Acetabular fractures mainly occur
after high-energy trauma, e.g. motor vehicle accidents and falls
from height [
]. Such incidents are known to cause
poly-trauma and therefore have a high mortality rate.
Fracture patterns could be indicative for trauma
mechanism(s) . In fatal accidents, this can have forensic
importance, since information obtained from the postmortem
(radiological) investigation of the body can be used for the
detection and documentation of forensic evidence.
Additionally, this information can be useful in the
reconstruction of the incident.
Pelvic fractures or injuries in a forensic setting have been
reported previously, e.g. after falls from height or civil
aviation accidents [3–6]. The acetabulum is a complex three
dimensional (3D) structure, which is a component of the pelvis
(Fig. 1). It is anatomically important because the acetabulum
connects the axial skeleton with the lower appendicular
skeleton; the femoral head articulates with the cup-shaped
acetabulum of the pelvis [
]. An acetabular fracture may
occur when the femoral head transmits a force towards the
acetabulum that was applied on the greater trochanter, knee
or foot [
The purpose of this study was to describe acetabular
fracture patterns after fatal small aircraft accidents and
to investigate the relationship between the presence of
fractures of the spine and/or lower extremities and an
absence of acetabular fractures. We hypothesized that if
there was extensive fracture of the lower extremities or
the spinal column, the acetabulum would remain intact.
Conventional radiographs and PMCT of the subjects in
this retrospective study were obtained from a forensic
radiological database [
Materials and methods
All cases from the Dutch forensic radiological database
relating to fatal aviation accidents, that occurred between 2000 and
2016, were selected [
]. Starting in 2000, per a request of the
pathologist in the Netherlands Forensic Institute (NFI),
bodies (in body bags) were imaged at the Groene Hart
Hospital (GHH) in Gouda, The Netherlands prior to
autopsy. These images were subsequently analyzed by
a forensic radiologist. The images, autopsy report and
radiology report were later used to create the SPSS
database (Armonk, NY, USA) [
]. For this retrospective
study, all aviation accident cases were retrieved from
the SPSS database and re- analyzed. General case
information was obtained from the autopsy reports at the
NFI and/or from the files of the Dutch Safety Board
(Onderzoeksraad voor Veiligheid). Cases concerning
commercial (n = 5) or military aviation accidents (n = 1)
were excluded from the study.
A total of 35 fatalities in 23 aviation accidents were
retrieved from the forensic radiological database [
applying the above mentioned exclusion criteria, 29 victims of
20 small aircraft aviation accidents were included (Table 1).
Among these victims, there were 27 males (93%) and two
females (7%). The median age among the victims was
55 years, in a range from 21 to 76 years. We were unable to
distinguish pilots from passengers, as many passengers were
licensed to fly and therefore can be considered co-pilots who
were actively involved in controlling the airplane.
Conventional radiographs were captured with two
Carestream X-ray systems: recent cases with Carestream
Evolution and older cases from before 2009 with Carestream
7500 (Carestream Health Netherlands B.V., Eemnes,
The Netherlands). Total body PMCT scans were obtained
through scanning with three different scanners: Toshiba
Aquilon 64 slice for cases since 2009 (Toshiba Medical
Systems Europe B.V., Zoetermeer, The Netherlands) and the
Toshiba Aquilon 32 slice and Siemens Somatom 4 (Siemens
Harmony, Siemens, Erlangen, Germany) for older cases. The
imaging protocol for the pelvis (and lower extremities) was
120 kV/363 mA/1 s rotation/0.5 mm slice thickness
/reconstruction 0.5 mm.
Radiographs and CT scans were re-analyzed in
Carestream picture archiving and communication
system (PACS) (Carestream Health Netherlands B.V.,
Eemnes, The Netherlands). Three dimensional
reconstructed images were available in PACS for all PMCT
cases. Fractures of the acetabulum and adjacent
structures (i.e. pelvis, lower extremities and spinal column)
were scored using an in-house developed case report
form. All images were scored by one forensic
radiologist, with 17 years of experience in forensic radiology
(HdB), blinded to the autopsy reports, and an independent
research assistant (MT).
Judet and Letournel set up the first acetabular fracture
classification system in 1964 [
]. Additionally, they explained
the mechanics of acetabular fractures to better understand how
such injuries could be caused and treated . In the decades
that followed other clinicians and researchers like Harris et al.
assessed acetabular fractures [
], with an aim to simplify
their classification. However, the Letournel classification
system is clinically most often used for its application in
conventional radiographs as well as in CT scans [
For this retrospective study, in which we strived to describe
acetabular fracture patterns in victims of aviation accidents, a
distinction has been made between the anatomical acetabulum
and the clinical acetabulum. The anatomical acetabulum was
considered to be composed of the anterior wall, posterior wall,
and roof, i.e. the articulating part of the acetabulum with the
femoral head [
]. The central region where the femoral head
did not articulate with the acetabulum was defined as the
acetabular fossa. This part of the anatomical acetabulum is the
location for ligament attachment (Fig. 2) [
The clinical acetabulum is composed of the anatomical
acetabulum, an anterior column (pubis), and a posterior column
]. In this case series, we distinguished between
fractures in the anatomical acetabulum and fractures in the
clinical acetabulum. As there were no clinical implications in
this study, the classification of fractures was kept simple,
following the Harris classification instead of using the thorough,
though complicated, Judet and Letournel classification system
], because the Judet and Letournel classification system
was created to increase the prognosis of healing of acetabular
fractures, based on different surgical approaches [
case series was solely concerned with postmortem images and
hence treatment of the fractures was out of scope.
Case report forms were used to score and collect the data;
Microsoft Excel 2010 (Microsoft Corporation, Redmond,
WA, USA) was used for the processing of the data. Statistical
analyses were performed with IBM SPSS Statistics 24 and
Microsoft Excel 2010. To test independence between fracture
location and other variables, the Chi- square test was used;
p < 0.05 was considered to be statistically significant.
The pelvis was intact in eight victims; 21 of the 29 victims
showed pelvic injuries. Twelve of 29 victims had a diastasis of
the pubic symphysis or the sacroiliac joint, in combination
with a fracture of the pelvis as can be expected by interruption
of the pelvic ring. This case series showed 19 out of 29 victims
(66%) had fractures of the clinical acetabulum, including the
anterior column (pubis) and posterior column (ischium), as
presented in Table 2. Eleven victims had bilateral acetabular
fractures, whereas eight victims exhibited only unilateral
fractures. Left-sided fractures (16/29) were more prevalent than
right-sided fractures (14/29). When considering the left and
right acetabulum as two separate entities, 40 out of 58 studied
clinical acetabulums and 12 out of 58 anatomical acetabulums
were fractured. The anatomical acetabulum, thus the walls,
roof and acetabular fossa, was fractured in 8 out of 29 victims
(28%). Unilateral fractures of the anatomical acetabulum (n =
6) were more prevalent than bilateral fractures (n = 2).
Acetabular column fractures
Anterior acetabular column fractures occurred in 18 out of 29
victims; 14 sustained a left-sided anterior column fracture, and
14sustained a right-sided fracture. An example of a right-sided
anterior column fracture can be seen in Fig. 3b and d. Ten of
the 18 victims with anterior column fractures exhibited
bilateral anterior column fractures (Fig. 3c and f).
Eighteen of the 29 victims also showed posterior column
fractures, however these 18 victims were not the same 18
victims with anterior column fractures. A total of 15 victims
portrayed left-sided posterior column fractures, whereas 13
portrayed right-sided fractures. Of these 18 victims with
posterior column fractures, there were 10 victims with bilateral
posterior column fractures.
Acetabular wall fractures
The overall frequency of anterior wall fractures in the study
population was 6 out of 29 (Table 2). No isolated left-sided
anterior wall fractures occurred, there was one victim with a
bilateral anterior wall fracture and five victims who showed a
right-sided anterior wall fracture. A right-sided posterior wall
fracture occurred twice, whereas left-sided posterior wall
fractures three times. None of the victims exhibited a bilateral
posterior wall fracture.
Fig. 2 Anatomical definitions depicted on a right hemi pelvis, lateral
view. a Anatomy of the anatomical acetabulum (light pink) and its
acetabular fossa (darker pink). b Anatomy of the clinical acetabulum as
described by Harris including anterior and posterior column (green and
blue respectively). c Anatomy of the clinical acetabulum according to the
Letournel classification system. Note that the anterior column includes
the medial half of the ilium bone for clinical implications. Schematic
drawings by authors
Acetabular roof and acetabular fossa fractures
The acetabular roof was fractured on the right side in 4
out of 29 victims, with penetration of the femoral head
in two victims (Fig. 3a, e and g). The right-sided
acetabular fossa was fractured in two victims. Isolated
leftsided fractures of the acetabular fossa occurred in two
victims. One out of 29 victims had a bilateral acetabular
Fractures in the lower extremities and spinal column
Fractures of the lower extremities occurred in 25 out of 29
victims (Fig. 3h). The number of victims who portrayed one or
more fractured extremities in combination with an acetabular
fracture was 16 out of 29. There were nine victims with
fractures in the lower extremities, without a fracture in the
acetabulum. Statistical analysis did not reveal a significant
dependence of the prevalence of lower extremity fractures on the
absence of acetabular fractures (p = 0.667).
Regarding the spinal column, fractures were encountered
in 21 of the 29 victims. Seven victims had one or more
fractures in the spinal column without the presence of an
acetabular fracture. In 14 victims, a fracture of both the spinal
column and acetabulum occurred. There was no significant
dependence of the prevalence of fractures in the spinal column
on the absence of acetabular fractures (p = 0.833).
We found that two thirds of the victims of fatal aviation
accidents in small aircrafts in our case series had uni- or bilateral
acetabular fractures. The prevalence of acetabular fractures is
still 28% when solely considering the anatomical acetabulum.
The high number of acetabular fractures in this population is
remarkable. However, due to the lack of publications
describing these complex and high energetic trauma mechanisms,
comparison with other studies is not possible.
It would be interesting to see if the 34% of victims who did
not have any fractures of the acetabulum sustained lesions
outside the acetabular region, hence the assessment of fractures in
the lower extremities (femur, tibia and fibula) and spinal
column. Depending on the impact force and direction of the force
transmitting through the bones, some body parts might be
spared while different body parts suffered extensive (skeletal)
injuries. There was no significant dependence between
fractures of the lower extremities and fractures of the acetabulum.
The radiological images did reveal many telescoping fractures
of the lower extremities, meaning that the long bones of the
lower extremities are comminuted and shortened. Additionally,
fractures of the spinal column in relation to acetabular fractures
also did not reveal a significant dependence. Therefore, the
direction of the impact force was substantial enough to cause
fractures in multiple skeletal regions.
Judet and Letournel discussed that fractures of the anterior
column of the acetabulum can occur when the greater
trochanter of the femur experiences a force [
]. This theoretical
explanation means that victims with anterior column fractures
experienced a lateral force to the greater trochanter upon
impact. A fracture of the anterior column could therefore happen
when the aircraft crashes on one of its sides. As for posterior
acetabular fracture with penetration of the femoral head through the
acetabulum (white arrow). f CT transversal view of a bilateral anterior
column fracture (white arrows). g The same case as in f. Additional
CT lateral view of the right hemi pelvis with comminution of the
acetabulum. Note the acetabular roof fracture (white arrow). h
3D–CT reconstruction of the pelvis and lower extremities. The
telescopic fracture pattern of the lower extremities is typical for
aviation accidents [
]. Note also multiple pelvic fractures and
diastasis of the symphysis in contrast to the seemingly intact
pelvic region of the body (Fig. 4e)
Fig. 4 Images of various victims
from small aircraft crashes. a
Picture of a detail of the victim,
taken at the scene of the crash.
The hand and part of the aircraft
are recognizable. b Ventral view
of a bended knee. Note the round
traumatic impression (arrows),
most likely caused by hitting the
dashboard. c Extensive
destruction of the left lower leg
and right upper extremity and
both feet. The toes of the left foot
are recognizable (arrow). d A
large laceration of the right upper
extremity. e Ventral total body
view. Note the destruction of all
four extremities in contrast to the
seemingly intact pelvic region.
Typical telescopic shortening of
the legs [
]. A 3D–CT scan of
this victim is shown in Fig. 3h
column fractures, fracturing can occur when the bended knee
experiences a ventral force and transmits this through the
femur into the pelvis [
], which could suggest that the aircraft
crashed on its nose. However, ranges of flexion or extension
and abduction or adduction can create different fracture
patterns. Any attempt to reconstruct the mechanism of a complex
accident like an aircraft accident requires more than the
analysis of the fracture pattern of a single fracture and no
conclusions should be drawn regarding accident reconstruction
based on the pattern of acetabular fractures alone. Also
important to note is that the biomechanical properties of bone
fracture are complicated and depend on many different factors,
such as age and gender of the victim. Due to the retrospective
nature of the current study, it was not possible to assess the
bone properties of each of the victims.
In fractures with a posterior wall component, the most
common fracture mechanism is trauma to the distal femur or knee
(Fig. 4b) while the hip is abducted, e.g. a knee hitting the
dashboard in a car upon impact [
10, 13, 16
]. In the clinic, fractures
with posterior wall component occur most often [
Interestingly, only five victims sustained a posterior wall fracture.
Small aircrafts also have dashboards and therefore the
mechanism of fracture was expected to be similar to those in cars. The
low number of posterior wall fractures suggests that impact
mechanisms in an aviation accident differ from those in a motor
vehicle accident [
10, 11, 16
]. Additionally, despite the high
impact forces in aviation accidents, we observed a low number
(n = 2) of femoral head penetrations. As already mentioned
above, the direction of forces seems to be more diverse (and
complicated) in aviation accidents compared to motor vehicle
accidents. This idea is also supported by our high number of
bilateral acetabular fractures. Eleven of the 19 victims with
acetabular fractures exhibited bilateral fractures. This observation
could indicate that the impact force and direction was sufficiently
extensive to fracture the acetabulum in both hemi pelvises.
Since Judet and Letournel set up their classification system
in 1964, radiographic technology has improved. The use of
CT scans and their 3D reconstruction possibilities has resulted
in improved interpretation of the anatomical complexity of the
pelvis, which was also pointed out by Geijer and El- Khoury
], and therefore more accurate identification of traumatic
injuries in this region is possible. In our study, the assessment
of acetabular fractures in 16 victims imaged before 2008 was
solely based on conventional radiographs taken in the
anteroposterior direction. Judet and Letournel suggested the
use of two additional oblique views of the affected hemi pelvis
]. But assessment of those conventional radiographs
remained limited compared to the CT scans performed
nowadays. Therefore, assessment should be done solely based on
CT scans to ensure the highest accuracy in clinical or
postmortem settings . The strength of the whole body PMCT
is that it allows for the analysis of whole body fracture
patterns. Following this, a multi-slice PMCT scan has to be
performed prior to autopsy to accurately access all body
fractures and in particular pelvic fractures, since the pelvic region
often appears relatively intact during autopsy, when compared
to other body regions (Fig. 4).
In summary, this is the first detailed assessment of
acetabular fractures in victims of fatal aviation accidents. The results
of this case series show the high prevalence of fractures in
different acetabular locations, with anterior and posterior
column fractures exhibited most often. Fracture of the
acetabulum did not show significant dependence on fracture of the
lower extremities or the spinal column. The use of PMCT
scans for the assessment of skeletal injuries after aviation
accidents is recommended in addition to autopsy, as autopsy
does not give complete insight in skeletal lesions.
1. In victims of small aircraft aviation accidents acetabular
fractures were frequently encountered.
2. Bilateral fractures happened often; 11 of the 19 victims
exhibited bilateral acetabular fractures.
3. The absence of acetabular fractures is statistically
independent from fractures of the leg or spinal column.
4. A postmortem CT scan should be performed prior to
autopsy to accurately access pelvic fractures.
5. Postmortem CT scans are preferred over conventional
radiographs in the assessment of pelvic injuries after
Acknowledgements We would like to thank Dr. JM Ruijter for his help
with the statistical analysis and for critically reviewing this manuscript.
Dr. LFM Beenen is gratefully acknowledged for critically reviewing this
manuscript. Additionally, we thank the pathologists, pathology assistants
and management from the NFI and the radiologists and forensic
radiographers from the GHH for their continuous professional and
Compliance with ethical standards
Conflicts of interest The authors declare that they have no conflict of
Statement of human rights For this type of study formal consent is not
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