How does a prior injury affect the value of my claim?

How does a prior injury affect the value of my claim? Generally, a person who is negligent or careless is responsible only for the harm he or she caused. That means that you have to prove there was negligence and that the negligence caused your injury. So, if you already had an injury, the negligence could not have caused it. But if you can prove that the negligence made the injury worse, you can collect for the degree to which the problem has been aggravated.