I'm currently writing a book where one of my characters falls from about an 80-90 foot drop onto a solid stone surface onto her back.
She's an average 32 female with a healthy diet and weight. She won't survive the fall but I don't quite know what the in-depth extent of the injuries she'd sustain and which one would ultimately kill her.
I of course know she'd suffer broken bones and internal bleeding but I could do with specifics for the 'autopsy' later down the line.
First off, she would be killed instantly. There wouldn't be any question of what might kill her "ultimately" because ultimately would be the moment she hit the ground. Yes, there have been people who survived falls from much greater heights, with the record holder being Vesna Vulović, a Serbian flight attendant who fell 10,160 m (33,330 ft), but those are vanishingly rare incidents and most involved a great deal of luck (hitting things that slowed the fall such as trees and power lines, landing in snow drifts, etc). In general, an 80-90 foot fall onto a hard surface is certain instant death 99.99% of the time.
Since she lands on her back, what will kill her most quickly is the massive head injury. Autopsy will find a crushed skull, massive brain injury, massive spinal cord injury, and possibly a detached brain stem, which would be instantly lethal.
The second thing that will kill her is deceleration. When she hits the ground, her body stops its downward motion instantly, but Newton's First Law of Motion says her internal organs that are free to move will keep going. They'll keep traveling in the same downward direction at the same speed. The result of that will likely be the transection of her aorta, which will cause immediate exsanguination. This is because parts of the aorta are free to move and other parts are anchored in place:
The aorta has some fixed regions, particularly the relatively fixed aortic arch (to the thoracic inlet by the brachiocephalic vessels). The remaining portions of the aorta are relatively free. Ascending and descending aorta are relatively mobile. These can result in an unequal distribution of shear forces on the relatively fixed arch and mobile ascending and descending aorta and stress at the site of attachment of the aorta, particularly the aortic root and the aortic isthmus.
As if the victim isn't dead enough by these two things, there will be a wide ranging assortment of other injuries, many of them lethal in and of themselves. The coroner will most likely find:
In general, even if a full team of trauma surgeons with a fully equipped OR was scrubbed in and ready right at the scene, she would still be dead on impact and nothing they could do would change that.
I agree with @Carey Gregory's answer. I can tell you how a man falling only 30 feet landing on his back on concrete died.
A 30 year old male working on the underside (?) of a bridge, unsecured, fell as above. There were no obvious external injuries. The skull was intact, etc.
He arrived by ambulance unconscious and without a pulse. Advanced Trauma Life Support was carried out, but the injuries were too extensive.
On Xray, he had comminuted fractures of both clavicles, multiple broken ribs, hemothorax on the right and left-sided hemopneumotorax. Otherwise there were no fractures.
He died because the deceleration injuries to his chest caused both pulmonary arteries to shear off were they cross over the mainstem bronchi, and the left mainstem bronchus was shorn through as well. He basically died from massive blood loss into the thorax. He would have been rendered unconscious from the fall, and had he lived, might well ave had significant brain injury.
A fall from almost 3 times that height would have smashed the back of his skull causing massive brain injuries as described above, likely broken his neck and back, broken the pelvis, maybe some long bones depending on the landing, and the internal injuries would be much more serious, although when death is the outcome, how much is much more serious? They would have been much more intensive.
