Posterior dislocation for me was about 13 years ago. I had to walk a few km out of the forest and got to a&e about 6 hours later. Yes, very difficult to see on x-ray, apparently because the ligaments etc pull your shoulder back in, albeit not in the socket. Since been told phone Mountain Rescue asap, because of possible trapped veins and nerves causing more damage. anyway, I had long term loss of thumb and forefinger feeling/strength, 18months. but physio is your friend, long elastic band things and an oversized clothes-peg to exercise thumb and forefinger. I still have occasional pain usually after splitting logs with an axe.