Bullets and bone fractures


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Odd Job
August 17, 2011, 04:27 PM
This is a side note to do with a discussion brought up in this thread:

http://www.thehighroad.org/showthread.php?t=606797&page=3

As I was saying, in response to 481, there are variables to do with the architecture of different types of bone and the mineralisation along different parts of the same bone.

Here is a CT scan (a type of X-ray imaging from all angles) of an adult male's lower limbs, with the right femur displayed in three anatomical planes:

http://i55.photobucket.com/albums/g154/Odd_Job/Bone1.jpg

In the above image I have triangulated a position within the right femur (all the planar cross-indicators would converge on the same point in the anatomy.
When you look at these scans, you must imagine yourself at the foot of the CT scanner, looking from the foot end of the anatomy as the patient is lying down. That trapezium shape is the scanner table.
Therefore that white ring on your left with the crosshair in it is actually the patient's right femur in cross section. The white is heavy cortical bone and the dark area in the middle is bone marrow. The image has been set up to best view bone, but nonethless you can appreciate different tissue densities. The more white something is, the more dense. So the fat around the edge of the thigh appears darker than the muscle and the bone is the brightest and densest tissue of them all.
If you look at the other two views in that same image, you can see that the bone cortex of the femur is thickest in the middle. You have to look at the coronal (middle) and sagittal (far right) views to make that assessment.

Next I moved the triangulation tool up to the femoral head (the "ball" of the hip joint):

http://i55.photobucket.com/albums/g154/Odd_Job/Bone2.jpg

The cortex is not as thick and there is a greater proportion of trabecular bone (what I call cancellous). It is not as densely packed as the cortical bone of the femur.

Lastly here is the 3rd lumbar vertebra, an irregular bone that does not have a very thick cortex but elements of it are quite hard (the facet joints at the back are quite dense).

http://i55.photobucket.com/albums/g154/Odd_Job/Bone3.jpg

On the last two images you also see part of the ilium: the irregular bones of the pelvis, parts of which are flat. On the iliac crest, the cortex is not very thick (not adequately shown here, but you can guess by the architecture that is seen, that this is the case).

Okay, so what does it all mean?

Well, nothing is ever predictable in gunshot wounds, but some things are common, and some radiological appearances are not unexpected when certain bones are damaged by handgun bullets. After you have seen several hundred to a thousand fractured bones from gunshot injuries, you get a "flavour" for what goes on in many cases.

First, a gunshot pelvis with a fracture up at the crest of the iliac blade:

http://i55.photobucket.com/albums/g154/Odd_Job/Crest.jpg

The yellow arrow points to a lucency (an area of lower density compared to the surrounding tissue). That is a punched out hole in the bone and there is an unremarkable linear fracture seen also (green arrow). Those white specks are pieces of bullet and the triangle is a paperclip for trajectory plotting.

Next is an unusual image of a tibia (the main weight-bearing bone in the lower leg). It is unusual because the bullet has hit the bone, caused it to fracture but not shatter with displaced bone fragments, and the bullet has broken into pieces:

http://i55.photobucket.com/albums/g154/Odd_Job/Tibia.jpg

The red arrow indicates the impact point on the tibia and the yellow arrows indicate fracture lines describing a familiar shape. If you imagine that in 3D it would describe a bowl-shaped fragment, and if you took it out, it would have the bevelled edges that are seen in the shooting of the dry bones. It is very unusual to see the bones undisplaced like this. Probably that bullet didn't have enough oomph to do more damage, and the surrounding tissues aided keeping the fracture undisplaced.

Most of the time when a long bone is hit, the bone fracture fragments are obviously displaced. They often make sharp, pointed fragments. Here is a gunshot forearm, the ulna is shattered:

http://i55.photobucket.com/albums/g154/Odd_Job/Ulna.jpg

You can see that the fragments are not in alignment with the rest of the bone. Don't forget that the overall alignment of the limb bones may have been altered by emergency crews or the patient himself. These X-rays were taken before the orthopaedic surgeon planned treatment.

Here is a lower leg shot just above the ankle joint:

http://i55.photobucket.com/albums/g154/Odd_Job/TibFib.jpg

Both the tibia and fibula are fractured and it is likely that the fractures extend into the joint.
Long bones tend to shatter into obvious fragments and flat bones tend to sustain damage that is less remarkable.

Thanks to supporting tissues and radiological breach markers, it is possible in many cases of long bone fractures to work out the direction of fire even if no other evidence is available,
In flat bones it is much more difficult because the thickness of the bone does not lend itself to the production of fragements that can be easily analysed for that purpose.
In dry bones I imagine the converse is true: it is easier to determine direction of fire through dry flat bones than through long bones, simply because the long bones shatter and you have no fracture patterns to work with.

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481
August 17, 2011, 04:36 PM
Odd Job,

Wow, man! Just wow! :cool:

Oh, yeah, and thank you for the obvious time and effort in producing such an educational demonstration of what happens when bullets hit bone.

This should be a "sticky"! :)

Pyro
August 17, 2011, 05:15 PM
I've heard a few cases where bone fragments actually acted like shrapnel.

2zulu1
August 18, 2011, 01:22 AM
You hit a home run with this post. Great illustrations combined with great explanations. :)

Bob

Double Naught Spy
August 18, 2011, 09:33 AM
The cortex is not as thick and there is a greater proportion of trabecular bone (what I call cancellous).

And, it is also called "spongy" bone because of its sponge-like appearance, although obviously not soft at all.

Nice post. Thank you.

481
August 18, 2011, 04:07 PM
Odd Job,

Stumbled upon this...

http://www.synbone.ch/wEnglish/catalogue/index.php?navanchor=1010043

while surfing the 'net.

Looks like a rigid closed cell PU, but they don't seem to list its hardness (couldn't find a Charpy or Izod notched/unnotched impact test on it) and density seems to be about 55 pounds/cubic foot by my best calculations.

Looks like an analog for cortical bone.

Think it's "valid" (in terms of its physical properties) enough?

ccsniper
August 18, 2011, 04:20 PM
Sticky this. It is nice to see what damage we are capable of, to either ouselves (accidents) or in a defensive situation

Odd Job
August 18, 2011, 04:30 PM
Think it's "valid" (in terms of its physical properties) enough?

I don't know.
I would like to see side-by side tests of the simulant vs a real bone in gel, shot under the same conditions.

forgetitohio
August 18, 2011, 06:12 PM
Odd Job... great post.
This link went around a few months ago. It also deals with bullets, bones, different ammo

For in depth account of what happened please read pg. 6
For their opinion 17-21.


WARNING..... PICS FROM THE MORGUE

http://concealedcarryholsters.org/wp-content/files/FBI-Analysis-on-PA-Police-Shootout.pdf

Odd Job
August 19, 2011, 02:16 AM
I remember seeing that document discussed on M4Carbine. The added difficulty with that case is mutliple shots complicated by mixed handgun and rifle injuries.
Any time you have multiple shots it can be difficult to work out which projectile is associated with which skin breach (if you go by the photographs and radiographs alone).
Also it is better to have two X-ray views at 90 degrees to one another (that is a luxury you have in a post mortem situation, but if the guy made it to the ER with those injuries he might get only the chest X-ray and then straight to theatre).
Can't always get ideal imaging...

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