Was it ever established how Patti's mother died?
My thought was that it went something like this:
Before Doug moved to Bluffington, Patti's house was invaded by a masked intruder, armed with a gun, who seemed to have a history of stalking women. He broke into the house, killed Patti's mom, shot Chad in the leg, and ran off. The crime was never solved, and the identity of the killer is unknown.
Chad survived, but his injuries left him unable to walk for the rest of his life.
Yeah, I know it sounds crazy, but that was my theory for the longest time.