If you are already suffering from an injury from some other source – another trip and fall, a car accident, or a fall from a horse, and you already have an identified injury to that body part, it could certainly be made worse as a result of a slip, trip, and fall. Your doctor and attorney will analyze the difference between the injuries before the fall and your condition after the fall. There is a qualitative analysis that is necessary to determine how you are today as compared to how you were before the fall.
On the other hand, if you are particularly fragile and susceptible to injury, the law does not hold it against you. If you had no injuries or physical issues prior to the fall, we were “asymptomatic”, and as a result of the fall have injuries that may be more serious than expected because you are particularly fragile, the person responsible for your fall does not get the benefit of the argument that somehow you are more fragile than the rest of society.
If the fall makes a person’s physical “house of cards” to crumble, the people responsible for that happening are responsible for all the damages, not just part of the damages. The fact that you may be more fragile for any reason, isn’t held against you if you had no problems before the fall.