I didn't know they used pig skin in shoes!
I don't think it is allowed, judging from the following hadith:
May Allah curse the Jews, for when Allah made the swine unlawful for them, they took its fat, melted it and sold it so that the hair might be plaited with it, and ate the price of it. (Al-Bukhari)
I guess that would depend whether it can be made from some other material or not & how much the person needs it. Is the only type available from pig or are there any from other animals that one can use? If it can't be made from other animal or is only available currently from pig, then judging from the part of the verse ...but whosoever is driven by necessity, neither craving for it, nor transgressing (the commands of Allah), for him Allah is Forgiving and Merciful (6:145) I would say it's ok to use it if the patient will die if he/she doesn't get the transplant, but i'm not knowledgeable in this regard, so best to consult a scholar.