Cases

Fatal fractures

Head and spinal injuries are important topics in forensic pathology because (maybe obviously) they are often seen in fatal cases: the same trauma applied to another body part is often much less serious, and these areas are prime targets in deliberate attacks.

Skull fractures

It may not seem like it, but all bone is slightly elastic – it can bend a little before it breaks. When you receive a blow to the head, your skull deforms momentarily: bone bends in at the impact site (intrusion) and bulges out around it (extrusion). If the blow is forceful, it may exceed the bone’s elastic limit. The bone can no longer bend, and instead it breaks. It may not necessarily break at the exact site of impact! When a bone bends, one side is compressed and the other side is under traction.

Forcesbone

The structure of bone means that it is strongest under compression, compared to traction. When it bulges, the outer surface of the bone is stretched and can fracture away from them impact site.

Fracture lines won’t cross preexisting fractures, meaning you can tell which impact came first (known as Puppe’s rule).

Puppe

Puppe’s Rule (From: Intersecting fractures of the skull and gunshot wounds. Case report and literature review. Guido Viel, Axel Gehl, Jan P. Sperhake. Forensic Science, Medicine, and Pathology, March 2009, Volume 5, Issue 1, pp 22-27

Skull fractures can be classified as:

  • Linear fractures
    • Straight or curved fracture lines (most common)
    • Hinge fractures are linear fractures along the base of the skull.  The horse below reared-up, fell over backwards and landed on its head.  It died instantly.
    • Diastases are separations of the skull bones along their sutures (joints with adjacent skull bones)
hingefracturedv

Hinge fracture at the base of a horse skull

  • Ring fracture
    • Around the opening of the back of the skull (foramen magnum), where the spinal cord meets the brainstem, when forces are transmitted along the spine to the head e.g. fall from a height.
  • Depressed fractures
    • Bone or bone fragments are pushed into the skull cavity
  • Pond fractures
    • Depressed fractures which leave a concave pond-like cavity
pondfracture

Healed pond fracture

  • Mosaic (also called Spider’s web) fractures
    • Linear fractures which radiate from a depressed fracture

Space inside your head is at a premium, which is why skull fractures are so life-threatening. Anything taking up extra space (like bone bending inward) squashes the brain. Fractures can rip through nearby vessels, and bleeding in the head takes up limited space. The brain also risks injury from loose shards of bone. Finally, the battered brain may swell (oedema) under all this abuse and compromise its space and blood supply further.

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What's this?

What’s this? #8 Spondylosis

What was going on in that strange spine? It’s likely that this poor polar bear had spondylosis (also called spondylosis deformans or ankylosing spondylosis).

He's not letting it ruin his day, though

He’s not letting it ruin his day, though

Spondylosis is the formation of extra bone (osteophytes) between the vertebral bones which make up the spine.  It can look like little projections from the individual vertebrae, or actually form bridges between them.  When joints fuse like this, it is called ankylosis, and is thought to be the body attempting to stabilise the joint (like a bone splint) after damage to the cartilage cushions between the vertebrae.

spondylosis

Projections of bone vs. bridges of bone

Spondylosis is most often seen in dogs, pigs and bulls.  It is particularly important in bulls kept in artificial breeding centres, where repeated mounting of a dummy-cow leads to damage to the lower back.

Your back bone's connected to...uh, all your other back bones (is that how the song goes?)

Your back bone’s connected to…uh, all your other back bones (is that how the song goes?)

In some animals with spondylosis there are no symptoms. However, the bony bridges are more brittle than regular bone, and can sometimes fracture, potentially leading to bleeding and compression of the spinal cord and paralysis.  In most dogs and pigs, spondylosis is often found incidentally and clinical signs can range from nothing to pain and stiffness.

Extra bone around the vertebra. The spinal cord runs through the tunnel at the top of the bone.

Extra bone around the vertebra. The spinal cord runs through the tunnel at the top of the bone (which has been sawn open in this picture).

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Cases

Osteosarcoma

Sad face in the bone surrounded by the bone tumour cells.

Sad face in the bone surrounded by the bone tumour cells.

Last week,  ‘All Creatures Great and Small’ posted an x-ray of the leg of a poor dog with a bone tumour.  Unfortunately, this is quite a common tumour, and we diagnosed one in another dog a couple of days later.  This type of tumour is called an osteosarcoma (osteo = bone, sarcoma = a group of malignant tumours).

You can see the new bone formation in this picture of an x-ray from another dog with osteosarcoma.

You can see the new bone formation in this picture of an x-ray from another dog with osteosarcoma.

They form from the cells that produce bone during life.  There are a few cell types involved in bone formation.  Osteoblasts are cells which divide and mature to form osteocytes.  Osteocytes produce the bone itself.  Osteoclasts are cells which eat bone so that old or damaged bone can be replaced with new bone.  Any of these cells can become tumours.  So some of the tumours will produce lots of bone, whilst others will eat away at the bone.

Tumour cells (blue arrow) invading into a vessel (orange arrow indicates the wall of the vessel).  Black arrow: island of bone formed by the tumour cells.

Tumour cells (blue arrow) invading into a vessel (orange arrow indicates the wall of the vessel). Black arrow: island of bone formed by the tumour cells.

These tumours grow fast and can cause the bone they are growing in to break, known as a ‘pathological fracture’.  They are very painful and spread (metastasise) around the body by first invading vessels.  Osteosarcomas most commonly spread to the lungs where they can cause Marie’s disease.  Due to the painful nature of these tumours, which often occur on the legs, amputation is common to relieve the pain.  Unfortunately the microscopic tumours, which may have already spread around the body, are actually thought to grow faster once the primary tumour is removed…

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What's this?

What is this? #2 Marie’s Disease!

What was that?

It was the tarsal (ankle) and metatarsal (foot) bones of a dog’s leg. But why are they so funky?

The complete set.

The complete set.

These bones are affected by Marie’s disease, or hypertrophic pulmonary osteoarthropathy (people like Marie’s disease because it’s shorter and rhymes).  It is characterised by clubbing of the fingers and toes, and inflammation of the bony surfaces (periostitis) and joints (arthritis).

As you might realise from the name, it is often associated with lung conditions, especially lung tumours. So the whole name breaks down to: hyper = over, trophy = growth, pulmonary = lungs, osteo = bones, artho = joints, and pathy = badness. Phew!

A lung tumour (metastatic melanoma), cut open

A lung tumour cut open (darker red central area)

Aside from lung tumours, other diseases can also cause hypertrophic osteoarthropathy, although for some reason they are mainly problems that affect the chest. No-one is 100% sure how exactly chest problems mess with the bones, but there are several theories.

Longstanding irritation and inflammation to any tissue can cause mineralisation, so it is thought perhaps the blood supply to bone is somehow disrupted which would lead to swelling and inflammation. There is a large nerve running through the chest — the vagus nerve — which has many branches and, among other things, tells the blood vessels how ‘open’ (or dilated) they should be. Perhaps diseases in the chest affect this nerve, in turn causing the blood vessels elsewhere to open up fully and blood to pool, eventually resulting in inflammation and irritation. Another idea is that hormones (or hormone-like substances) might be produced as a by-product of disease, signalling the bones to overgrow.

They may not look it, but these bones are thin and weakened. Though the outer periosteal layer has grown erratic new bone following irritation, the inside of the bone is being reabsorbed.

They may not look it, but these bones are thin and weakened. The outer periosteal layer has grown erratic new bone following irritation, but at the same time the inside of the bone is being reabsorbed.

Pierre Marie and his mate Eugen von Bamberger (probably not actually friends) are credited with first describing the disease. However, about 2500 years ago Hippocrates also recognised clubbed fingers and toes, and signs of hypertrophic pulmonary osteoarthropathy have been found in  human remains from his time.

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