"La" can be used to show possession when it is obvious. I think. Like, one could say "Jen la edzino (here's the wife)" meaning MY ball and chain. But if it's anyone else's edzino, I don't think it's used and via should be used instead.
I don't understand why "la kapo" gets translated as "my head". I understand that from the meaning of the sentence, this is what makes sense and "the head hurts me" sounds super weird, but then why is it no "mia kapo"?