When an ultrasound reveals that amniotic bands are wrapped around the legs of Sloan's baby, Mark summons Addison to perform the surgery. During surgery, Addison estimates that a complication means there's a 5 percent chance that the procedure can kill Sloan, so Mark orders Addison to stop. Sloan insists that she can't take care of a baby with no legs and Mark tells her he won't let that happen. With a worried-looking Lexie over his shoulder, he tells Sloan to move in with them permanently. We can't blame Lexie for balking at becoming an instant grandmother, but we also understand why Mark chooses his daughter over Lexie. "I think this relationship just ended," Lexie says as she kisses Mark goodbye.