Suppose someone causes you injury in a motor vehicle accident, but you have been involved in prior accidents, or you have a pre-existing medical condition, such as a bad back, or neck. Can you still bring a claim against the other driver for the pain and suffering caused?
The short answer is yes.
There is saying in the law: you take your plaintiff as you find them. So, if someone causes an accident with a 24-year old body builder, who because of his physical condition and age is uninjured as a result of that accident, the wrong doer lucks out. Likewise, if that same person strikes and injures someone who just recovered from back surgery, that person is responsible for the nature and extent of aggravation to that person and their injuries.
The law recognizes the unfortunate, but frankly common, occasions where people are involved in more than a single accident in their lifetime. In cases involving multiple accidents, or prior injuries, the law provides that a person will be responsible for the nature and extent of the injuries/losses caused by the particular accident; no more, and no less.