In Pennsylvania, there is a "leash law" which requires dogs to be under the proper and adequate control of the owner. An investigation would need to be conducted to find out how and why the dog got out.
If the dog escaped from a fenced in front yard of the house on numerous prior occasions, then it can be argued that the dog was not under adequate control because the dog had escaped before. Therefore, the owner needed to take reasonable action by fixing the fence so the dog would not escape.
There could be other ways the dog escaped; therefore, it is important that you talk to a Pennsylvania dog attack/bite injury lawyer to evaluate your case properly.