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.
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.
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).
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)
- 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
- 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.