Microscopic Pattern of Bone Fractures as an Indicator of Blast Trauma-A Pilot Study

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PAPER

ANTHROPOLOGY

Marketa Pechn ıkov a,1,2 M.Sc., Ph.D.; Debora Mazzarelli,1 M.A.; Pasquale Poppa,1 B.Sc., Ph.D.;

Daniele Gibelli,1 M.D., Ph.D.; Emilio Scossa Baggi,3 Ph.D.; and Cristina Cattaneo,1 M.D., B.Sc., M.A., Ph.D.

Microscopic Pattern of Bone Fractures as anIndicator of Blast Trauma: A Pilot Study

ABSTRACT: The assessment of fractures is a key issue in forensic anthropology; however, very few studies deal with the features of frac-tures due to explosion in comparison with other traumatic injuries. This study focuses on fractures resulting from blast trauma and two types of

blunt force trauma (manual compression and running over), applied to corpses of pigs; 163 osteons were examined within forty fractures by thetransmission light microscopy. Blast lesions showed a higher percentage of fracture lines through the Haversian canal, whereas in other typesof trauma, the fractures went across the inner lamellae. Significant differences between samples hit by blast energy and those runover or manu-ally compressed were observed ( p < 0.05). The frequency of pattern A is significantly higher in exploded bones than in runover and com-pressed. Microscopic analysis of the fracture line may provide information about the type of trauma, especially for what concerns blast trauma.

KEYWORDS: forensic science, forensic anthropology, bone trauma, fracture morphology, osteons, blast trauma

The study of trauma is a crucial topic for forensic anthropol-

ogy. Skeletal trauma is predominantly represented by fractures,

but the mechanism of fracture production as well as the criteria

useful for inferring dynamics from a fracture is not yet well

understood. In addition, a comprehensive description of specific

characteristics of bone injuries caused by various types of forceswould be very useful in reconstructing type of trauma, but a

detailed analysis of macroscopic and microscopic presentations

of fractures is still lacking.

Several studies already exist concerning fracture characteristics

(1 – 6) and morphology of fractures produced by blunt trauma.

Powell et al. (7), for example, studied trauma on porcine crania

inflicted by single blunt impact, Croft and Ferllini (8) tried to

determine whether the trauma inflicted by two different screw-

drivers could be macroscopically assessed, and Hart (9) observed

whether ballistic and blunt force trauma could be diagnosed by

the beveling direction of concentric fractures. Nevertheless, the

studies describing the macroscopic morphology of fractures

caused by different energies and loading rates are still incomplete.

Some studies of fractures at a microscopic level have already

been performed, but they mainly focused on mechanical prop-

erties of bone tissue and its resistance (10 – 13). Several studies

also appeared which examined the microscopic structure of

bone and the role of structural components in the fracture

process (14 – 16); closer attention was paid especially to cement

lines, sometimes assessed as a region which facilitates the

propagation of fractures (17 – 21). The only observation of a

relationship between fracture lines and secondary osteons (here-

after only “osteon”) was observed by a Japanese group (22)

who performed sagittal splitting of the human mandible toobserve the most effective direction for bone chiseling during

osteotomy.

The observation of fracture line direction in fresh and dry

bones was also the topic of a previous study (23), where the

authors inflicted blunt force trauma on fresh and dry long bones

and observed the fracture pattern at a microscopic level. The aim

was to ascertain whether there exists some difference in fracture

propagation in fresh and dry bones. The examination of the

propagation of the fracture line and its relation with secondary

osteons gave similar results in both fresh and dry specimens,

and so an initial hypothesis concerning different propagation

was disclaimed. There seemed to be no possibility to distinguish

fractures which had occurred perimortem on fresh bone from

those which appeared postmortem on dry ones by studying the

course of the fracture line.

However, the study of Piekarski (24) pointed out that the

propagation of the fracture line depends rather upon the velocity

of trauma processing than on the elasticity of bone structure. In

this work, Piekarski (page 223) concluded that “bone is a tough

material at slow strain rates and fractures more like a brittle

material at high strain rates.” According to his investigation “a

crack propagates at slow rates by following weak interfaces of

Haversian lamellae or through interstitial bone, at high strain

rates fracture propagates indiscriminately through all micro

constituents.” It seems that there should be a difference in the

course of a fracture line and its relation to the Haversian systems

in fractures caused by high or slow strain rates, and this maybe useful for distinguishing among lesions due to high- and

1LABANOF, Laboratorio di Antropologia e Odontologia Forense, Sezione

di Medicina Legale, Dipartimento di Scienze Biomediche per la Salute, Uni-versit a degli Studi di Milano, V. Mangiagalli 37, Milano, Italy.

2Laboratory of Biological and Molecular Anthropology, Faculty of Sci-

ence, Institute of Experimental Biology, Masaryk University, Brno 60200,Czech Republic.

3Polizia Scientifica Canton Ticino, Viale Franscini 3, 6500, Bellinzona(CH), Switzerland.

Received 18 Nov. 2013; and in revised form 20 June 2014; accepted 2Sept. 2014.

1140 © 2015 American Academy of Forensic Sciences

J Forensic Sci, September 2015, Vol. 60, No. 5doi: 10.1111/1556-4029.12818

Available online at: onlinelibrary.wiley.com



low-velocity trauma. This has a relevant practical importance,

because in certain conditions, skeletal remains are found with

multiple fractures, and it is not easy to verify what kind of acci-

dent occurred.

A typical example of high-velocity lesion is blast trauma

which causes a complex pattern of bone lesions by a sudden

pressure change and spreading of shrapnel which acts as small

projectiles (25). Very little information is available concerning

the mechanism of production of blast lesions: Christensen et al.

in 2012 published the first experimental study performed on

pigs in four separate series of tests at different distance and

type of explosive (25). Results showed that the severity of

skeletal trauma was found to be directly related to the amount

of explosive and its proximity to the specimen. Fractures usu-

ally showed mixed characteristics of compression, shearing, and

bending, which appear more random than those due to projec-

tile or blunt trauma. In addition, long bones, scapulae, and os

coxae showed extensive comminuted fractures with small bone

fragments, whereas the head, neck, and shaft of ribs were

affected by transverse and oblique lesions. The inclusion of

shrapnel within the explosive showed an even greater fractureseverity (25). The authors stated that the pattern of fractures

due to blast trauma appears distinct from other types of skeletal

trauma in quality and extent, although no comparison is per-

formed with fractures experimentally produced by other man-

ners of lesion: A more recent article by the same authors

focused on the high prevalence in blast lesions of butterfly

fractures in ribs (26). The authors observed that butterfly frac-

tures in these cases began on the visceral surface, on the oppo-

site side than expected in compressive trauma (26). This

pattern was observed in 100% of rib lesions due to blast

trauma and proved that the fractures caused by this specific

modality are due to an extending process of the rib curve. The

same pattern was observed in 93% of ribs manually bent toreproduce the same tensile action. Although the exact mecha-

nism of production of such a fracture profile is unclear, this

article proved once again that from a macroscopic point of

view, blast trauma and compression can be distinguished.

Although the previously cited articles provide relevant data for

what concerns the diagnosis between high- and low-velocity

trauma, all the available information is based on a mere macro-

scopic analysis and no microscopic test was performed on the

specimens, especially for what concerns the interaction with the

osteons and Haversian lamellae.

This article aims at performing a microscopic analysis of

fractures due to blast trauma in order to extrapolate more infor-

mation concerning the differences between high-impulse and

low-impulse trauma, useful in the forensic practice. The study of

Piekarski (24) proves to be essential in fracture analysis at a

microscopic level. This project tried to verify his hypothesis, in

other words ascertaining whether the cracks due to high- and

low-impulse trauma propagate in a different way and whether

some differences in the course of the fracture line in fresh bone,

broken in different manners, can be appreciated.

Material and Methods

The study was performed using pigs. This specific animal

model was chosen for the characteristics of the experiments,

which simulate the real forensic scenario and do not allow the

use of human remains. The porcine model was used becausebone density and mechanical testing proved pig bone structure

to closely approximate human bones (27). In addition, pig bones

have proven to be good models also for human trauma analysis

(28,29).

Corpses of five adult pigs with a weight between 60 and

80 kg were used to reproduce human bodies; in addition, the

limbs of the fifth pig containing long bones were also used. The

pigs all came from the Faculty of Veterinary Medicine of the

University of Milan and had died from causes independent from

this study. Each pig was frozen at

24°C for a maximum of

1 week, and carcasses were allowed to thaw at room temperature

before their use.

The mechanisms of trauma characterized by different velocity

of loading (high and low) were applied to produce the bone

trauma. In detail, blast trauma was chosen as an example of high

velocity, and the compression by a vehicle and a vice as two

low-velocity types, with a different amount of energy (higher in

the compression by vehicle than by the vice).

Two of the pig carcasses were attached to a vertical rod in an

open space within a military camp near Isone (Bellinzona, Swit-

zerland) with a belt full of 600 g of military plastic explosive

(2000 g of gelatine A, detonation velocity: 8000 m/s, explosivity

relative effectiveness factor: 1.34). Each pig wore a belt of explosives and was subjected to an explosion and the pieces col-

lected. Other two pigs were closed into a plastic bag, placed in a

concrete parking area, and run over several times by a vehicle

(Citroen C3©, 1.4, 90 cv diesel) with speed between 10 and

20 km/h when the fractures occurred. Intentional use of very

low speed in the test caused predominantly fractures of the cra-

nium and of the axial skeleton (ribs, vertebrae, and pelvis),

whereas the long bones remained intact. For this reason, as a

third manner of fracturing, slow compression was added. The

entire limbs of the fifth pig were separated from the body by a

knife at the region of the shoulder and hip. They were placed

through a vice and slowly compressed along their long axis until

they fractured.Then an autopsy of the pigs was performed to examine the

long bone fractures. Long bones were chosen for the analysis

because they are well known from a histological point of view.

The broken bones were then macerated and cleaned from soft

tissues manually. The delimited and well-defined margins of

complete fractures were chosen for the analysis. A total of 40

long bone fractures were studied macroscopically and then with

a stereomicroscope (Wild Heerbrugg M650) (using a Eurokam

3.0. camera with BEL View software for the possibility of com-

fortable and a more precise classification of each fracture charac-

teristic).

Various fracture characteristics such as fracture type, outline,

shape of ends, fracture angle, surface morphology and presence

of additional fracture lines were observed and classified accord-

ing to the classification system summarized by Wieberg and

Wescott (2) . The classification of fracture angle was the only

difficult subjective issue because in some rare instances, the

morphology of the fracture did not correspond only to one spe-

cific stage, thus a combination of stages was adopted.

After macroscopic observation, small pieces bordering the

fractures were sampled, mounted perpendicularly to the fracture

surface on a glass slide with Pertex and ground and polished on

a Struers DAP-7 lapping machine (grades 320, 600, 1200, 2400,

and 4000) to create a thin undecalcified section (150 lm) for

light microscopy.

The microscopic examination of fracture lines in relation to

the secondary osteons was performed according to the techniquealready used in a previous study (23). Two different patterns

were distinguished during the observation of the exposed animal

PECHNIKOVA ET AL. . MICROSCOPIC PATTERN OF BONE TRAUMA 1141



bone tissue, composed partly of osteonal bone tissue and partly

of the plexiform one. The course of a fracture line going through

the central canal (Fig. 1) or through the lamellae (Fig. 2) was

called pattern A, whereas cracks traveling around the inner

lamellae (Fig. 3) or along the cement line (Fig. 4), pattern B.

Although the mixed composition of porcine bone did not allow

the operators to perform the examination of all prepared sam-

ples, a number of well-readable fracture lines for the analysis

were still found — 10 lines created by blast trauma and 18 pro-

duced by the two blunt force modalities.

The microscopic examination of these fracture lines thus gave

45 observable osteons for blast trauma and 118 osteons for the

compression modalities. The operators therefore set out to verify

the frequency of pattern A and pattern B in fractures made withdifferent velocity; the independent two-sample t -test and the chi-

square analysis were used for basic statistical analysis.

Results

The explosion led to severe fragmentation of the two pigs,

with predominant fractures the bones of the upper part of the

pigs’ bodies; thus, the fractures of the foreleg were studied.

After running over with a car, only two metatarsal bones of the

first pig were fractured, all other long bones were resistant to the

slow manner of breaking even if it was repeated several times.

On the other hand, limbs manually compressed using a metal

vice allowed the operators to study fractures of all types of long

bones except for the ulna which was never broken.The macroscopic observation of fracture morphology, per-

formed before all other tests, gave very variable results for high

FIG. 1––

Fracture going through the central canal (straight line =

break and arched line = cement line).

FIG. 2––Fracture passing straight through the lamellae (straight

line = break and arched line = cement line).

FIG. 3––Fracture line running around inner lamella (lower line = break

and upper arched line = cement line).

FIG. 4––

The disruption in the area of the cement line (lower line = break and circular line = cement line).

1142 JOURNAL OF FORENSIC SCIENCES



impulse as well as for low-impulse fracture mechanisms

(Table 1). The prevalent fracture type was comminuted, which

occurred in all samples with similar frequency; complete frac-

tures were found only in some of compressed samples, whereas

fissured fractures were noted only in some exploded ones. Both

complete and fissured fracture types had a much lower incidence

than the comminuted ones. The outline was the most variable

characteristic. All types of outlines were observed in high- as

well as low-velocity fracture mechanisms, but for the transverse

one which was represented only when blast trauma was applied.

The shapes of the ends were dependent on fracture outlines,

so they again varied between both high- and low-velocity mech-

anisms; in high-velocity trauma, the variation was even greater.

Some differences in distribution of different forms of fracture

angles were noted between blast trauma and compressions:

There was a great variability in high-velocity trauma, but in the

low-velocity mechanisms, great uniformity was found. Similarly,

the surface morphology was more uniform in low-velocity mech-

anism, whereas when applying high-velocity mechanism, all the

possible forms were detected. Additional fracture lines were

noticed in all three fracture mechanisms.The results show that when the fracture is produced at a fast

rate, the resulting fracture could have various features, and all

types of characteristics were usually found. The fractures result-

ing from slow rate mechanism seem to be more uniform, but the

most frequently occurring characteristics were the same as those

prevailing in the fast rate. No relationship between cause and

frequency in any of the resulting patterns was found; in other

words, there was no rule for fracture formation. It seems that on

the basis of macroscopic fracture morphology, there is no possi-

bility in this case to distinguish fractures produced by blast

(high-velocity mechanism) from those produced from blunt

trauma (low-velocity mechanism).

The microscopic examination of the fracture pattern of a totalof 163 osteons along the fracture lines gave interesting results.

The frequencies of pattern A and pattern B for each bone are

listed in Table 2, and the average frequencies of pattern A and

B for each type of the fracture mechanism are summarized in

Table 3.

The fracture line of run-over bone samples traveled around

the Haversian structure (pattern B, 55% cases on average), rather

than passing straight through the osteons (pattern A, 45% on

average). Almost the same values were found in specimens com-

pressed by the vice, where pattern B again slightly predominated

(54.8% on average) above the pattern A (45.2% on average).

Statistical analysis (t -test) confirmed that there is no statistically

significant difference of frequencies of pattern A between low-

velocity modalities of trauma compression during running over

and compression with a vice (t = 0.157, p < 0.05). In addition,

results seem to suggest that the microscopic profile of fractures

does depend upon the energy content of the trauma, because

there are no appreciable differences between the two types of

compression.

The observation of fractures produced by the explosion gave a

different model. The fracture line crossed through the osteon

(pattern A) much more often (on average in 74% cases) than it respected its structure (pattern B, 26% on average). A statisti-

cally significant difference was found between frequency of pat-

tern A in exploded and run-over samples (t 9 = 3.379, p < 0.05)

as well as between exploded and compressed bones (t 19 = 4.184,

p < 0.05).

A chi-square test in contingency tables was also used to verify

the relative frequency of pattern A and its relation with the type

of trauma. The null hypothesis was that the frequency of pattern

A and pattern B does not depend on the type of trauma. Accord-

ing to counted p values, shown in Table 4, the null hypothesis

TABLE 1––Frequency of individual fracture characteristics (in %) for all

classified marks.

Mark Character Explosion % Compression % Runover %

Fracturetype

Comminuted 71.4 75 100Complete 0 25 0Fissured 28.6 0 0

Outline Helical 14.3 43.8 0Diagonal 19 6.3 0

Transverse 9.5 0 0

Longitudinal 33.3 31.3 50Irregular 23.8 18.8 50End shape Curved 23.1 36.4 0

Curved + step 0 36.4 0V shaped 30.8 27.3 100Columnar 38.5 0 0

Transverse 7.7 0 0Fracture

angleRight 33.3 0 0Acute 6.7 0 50Obtuse 6.7 0 50Acute/obtuse 0 93.8 0Acute/right 40 6.3 0Obtuse/right 13.3 0 0

Surface Rough 13.3 6.3 50

Smooth 6.7 43.8 0Rough/smooth 33.3 50 50Rough/interm 33.3 0 0

Smooth/interm 13.3 0 0Additional

linesPresent 100 81.3 100Absent 0 18.8 0

TABLE 2–– Numbers of observed osteons and relation to course of fracture

line (R: right; L: left).

Pig Bone SideTotal

osteonsPattern

APattern

BPattern

A %Pattern

B %

Car 1 Metatarsal R 11 5 6 45.5 54.5

Car 1 Metatarsal L 27 12 15 44.4 55.6Expl A Humerus R 3 2 1 66.7 33.3Expl A Ulna R 3 3 0 100.0 0.0Expl A Ulna L 7 4 3 57.1 42.9Expl A Radius R 13 9 4 69.2 30.8Expl B Humerus R 5 4 1 80.0 20.0Expl B Humerus L 10 7 3 70.0 30.0Expl B Radius L 4 3 1 75.0 25.0

Compr Humerus R 6 3 3 50.0 50.0Compr Humerus L 11 5 6 45.5 54.5

Compr Radius R 11 3 8 27.3 72.7Compr Radius L 9 5 4 55.6 44.4Compr Femur R 11 5 6 45.5 54.5Compr Femur L 10 4 6 40.0 60.0

Compr Tibia R 4 2 2 50.0 50.0Compr Tibia L 14 6 8 42.9 57.1Compr Fibula R 4 2 2 50.0 50.0

TABLE 3–– Average frequencies of pattern A and B for each mechanism of

fracture processing in bold the most prevent pattern.

Energy MechanismTotal

osteonsPattern

APattern

BPattern

A %Pattern

B %

Low Car run over 38 17 21 44.95 55.05

Low Compression 80 35 45 45.2 54.8

High Explosion 45 32 13 74.01 25.99




that the occurrence of pattern A (or B) is independent ( p

value = 0.0084) between three fracture types (runover, compres-

sion, and explosion) as well as between runover and explosion

( p value = 0.015) or between compression and explosion ( p

value = 0.003) was rejected. Conversely, the hypothesis that the

frequency of pattern A (or B) is independent between runover

and compression ( p value = 0.92) was not rejected. The

frequency of pattern A therefore was significantly higher (and

frequency of pattern B significantly lower) in explosion than in

runover and the compression instance.

Discussion

The aim of this study was to observe macroscopic and micro-

scopic characteristics of fractures produced by high- and low-

impulse mechanisms in order to find some differences in fracture

patterns applicable in the differential diagnosis of bone trauma.

Blast trauma was chosen for its high velocity and facility to

produce fractures of long bones: As a comparison, two types

of compression were chosen as examples of slow rate trauma,

with a different energy content (higher in compression by

vehicle).

The macroscopic observation of fractures showed great vari-

ability in their morphology. The exploded samples gave a widevariation in type of outline, fracture angle, or surface morphol-

ogy. A similar diversity was, however, observed also in the slow

manner of fracture processing — especially in compression. As

the same characteristics were found, with a mixed frequency, in

high velocity as well as in low-velocity mechanisms, differentia-

tion between fast and slow manner of fracture production was

impossible. Powell et al. (7), who studied fracture patterns on

the porcine skulls inflicted by single blunt impact, reveal only

that a rigid interface produces more fractures than a compliant

one when the same high rate impact is used. Croft and Ferllini

(8) performed experimental research on macroscopic characteris-

tics of puncture wounds and fractures caused by two kinds of

screwdrivers. They found that the trauma could be macroscopi-

cally differentiated if studying the macroscopic appearance intandem. The analysis of some differences between ballistic and

blunt force fractures, performed by Hart (9), showed that it is

possible to determine the mechanism of trauma by the beveling

direction of concentric fractures. It seems that observation of

macroscopic characteristics could help in extrapolating the mech-

anism of fracture formation only if some circumstances are

already known.

The present results provide interesting information, especially

for what concerns the specificity of blast trauma which, accord-

ing to previous literature, differs in quality and extent from

lesions due to other fracture mechanisms; however, this evalua-

tion was based on general appearance and distribution of frac-

tures: If one considers the general features of fractures, noappreciable difference is usually observed between high- and

low-impulse trauma. This may have relevant repercussions in the

forensic practice, because, as also pointed out by Christensen

et al. (25), the diagnosis of blast trauma requires a “careful inter-

pretation of the injury distribution over the entire skeleton” and

the main differential features in comparison with other types of

trauma consist in fracture number and distribution; however,

bodies affected by blast lesions are often dismembered and a

complete recovery and survey of the skeleton is not always pos-

sible. In this case, the analysis of isolated fractures shows a sub-

stantial superimposition of morphological characteristics shared

also by all dynamics of lesions.

At the microscopic level, the study of Piekarski (24) proves to

be essential. For that reason, this project tried to verify his

hypothesis, and in detail, whether the cracks due to high- and

low-impulse trauma propagate differentially and whether there

are differences in the course of fracture lines in fresh bone bro-

ken indifferent manners.

The results showed the same pattern in the course of fracture

lines in bones compressed by the car and the vice. The crack

propagated with similar frequency through (pattern A) and

around (pattern B) the osteon structure with slight prevalence of

pattern B (45% vs. 55%). In addition, the two chosen modalitiesof compression do not show a significant difference, and this

suggests that the behavior of fracture lines within a bone struc-

ture depends on the loading velocity rather than on the amount

of energy. In contrast, the difference between frequency of pat-

tern A and B was much more evident in exploded samples (74%

vs. 26%) where pattern A significantly predominated.

Results of the present study confirm Piekarski’s statement that

a crack propagates differentially at high compared to slow rates

(24), as in high rates, it goes rather indiscriminately through all

microstructures, while in slow rates, it respects osteon structure

in more than 50% cases. Secondarily, association of these results

with the conclusions of our previous study indicates that the

course of fracture lines depends rather on the velocity of thefracturing mechanism than on bone elasticity and freshness. This

provides an additional tool for differential diagnosis of blast

trauma, which may add to the general survey of number and dis-

tribution of lesions.

Conclusions

The macroscopic observation of fracture morphology does not

bring sufficient information for a differential diagnosis between

different types of bone trauma, predominantly due to the extreme

variability of the fracture pattern, especially in exploded samples.

Microscopic analysis indicated that the fracture lines propagate

through osteons differentially at high compared to low-impulse

mechanisms. Microscopic observations of fractures on a basic

microstructural level may bring important information concern-

ing the type of trauma, especially its velocity.

Although the present results are only preliminary, this study

does seem to indicate that microscopic analysis of osteon pattern

of breakage may be important in distinguishing blast trauma

from low-velocity modalities of trauma.

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1144 JOURNAL OF FORENSIC SCIENCES



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Additional information and reprint requests:Prof. Cristina Cattaneo, M.D., B.Sc., M.A., Ph.D.LABANOF, Laboratorio di Antropologia e Odontologia ForenseSezione di Medicina LegaleDipartimento di Scienze Biomediche per la SaluteUniversit a degli Studi di MilanoV. Mangiagalli 37MilanItaly

E-mail: [email protected]


Documents

Microscopic Pattern of Bone Fractures as an Indicator of Blast Trauma-A Pilot Study