Gemara

48a (Rav Yosef): If a hole in the lung is a Tereifah, even if the lung sticks to the flesh between the ribs, it is Tereifah!

(Beraisa): If a man's Ever was punctured, he is a Petzu'a Daka (he may not marry). If the hole was sealed, he is Kosher. This is a disqualification that can become permitted.

Suggestion: 'This' excludes our case (the sealing does not make the animal Kosher).

Rejection (Ravina): No. It excludes a scab that forms on a hole in the lung. That does not help.

54a: Certain hunters would kill animals by hitting them on the Gid ha'Nasheh, or on the kidney. R. Yehudah ben Beseira and R. Aba ruled that they are not Tereifos, for we cannot add to the Tereifos that Chachamim listed.

Even though we see that the animals die from this, we have a tradition that a salve could enable them to live.

57b (R. Yehoshua ben Levi - Mishnah): A hole in the Kaneh the size of an Italian Isar is Tereifah.

Question (R. Yosi ben Nehhurai): There was a sheep that had a hole in its Kaneh; they sealed it, and it healed!

Counter-question (R. Yehoshua ben Levi): It is known that a detached leg is Tereifah, yet R. Shimon ben Chalifta's chicken leg came off; they covered it with a reed, and it healed!

Answer (to both questions): You must say, even though it healed, the chicken did not live a year. Also the sheep did not survive a year!

59a: A deer whose hind legs were cut was brought in front of the Reish Galusa. Rav checked Tzomes ha'Gidim (the juncture of the sinews) and ruled that it is Kosher.

68b (Rabah): A Treifah never becomes permitted.

76a (Mishnah): If the leg was cut above the (knee) joint, it is Treifah. If Tzomes ha'Gidim was removed, it is Treifah.

Rishonim

Rambam (Hilchos Shechitah 10:12): One may not add to the Tereifos. Anything that happened to an animal or bird other than what the early Chachamim listed and Batei Din of Yisrael agreed upon, it is possible that it will live, even if we know medically that it will not live.

Kesef Mishneh: The Rambam learns from Chulin 54a. He explains that a tradition from Sinai teaches that a salve could enable them to live, even though our medical books say that there is no cure.

Ramban (76a DH u'Posku): If the leg was cut at Tzomes ha'Gidim, or there is a hole in the spleen, the animal can live if we cut the leg higher or remove the spleen! Even so, once it became a Tereifah, it is always forbidden. This requires investigation. If the leg was cut at Tzomes ha'Gidim and one slaughtered it, Vadai it is Tereifah, for it had a mortal injury. It could not live in its present state, even with a salve (unless one cut the leg above). If one cut the leg above and then slaughtered it, it is Kosher. Even if the injury made it start to die, this is merely a dangerously sick animal. We find Tereifos that get cured, e.g. a punctured lung that later became tangled with flesh. Netulas ha'Gidim (they were removed) is Tereifah. If it was cut higher, it is not Netulas ha'Gidim. If one leaves it 12 months, it is Kosher. There are damaged limbs that are Tereifah, even though if they are removed, it is Kosher. This requires investigation.

Rebuttal (Rosh Chulin 4:7): It is difficult to say that a Tereifah becomes Kosher b'Yedei Adam (through man's action). Rather, if it was cut at Tzomes ha'Gidim, it will die. The sickness of Tereifah already entered. We cannot fix it. This is unlike a (punctured) lung that by itself gets tangled with flesh.

Ran (26a DH ul'Inyan): If the leg was cut at Tzomes ha'Gidim, this pains the animal and it becomes Tereifah. It cannot become permitted later. A removed spleen or kidney is Kosher, but if it was punctured or stricken it is Tereifah. Removing it afterwards does not help, for the puncture hurt it more than removal does, and made it Tereifah. Rav checked Tzomes ha'Gidim of the deer brought in front of the Reish Galusa. They did not say to cut it above Tzomes ha'Gidim (and below the knee), to be Machshir it in any case!

Note: perhaps they checked it to avoid unnecessary pain to animals, or to be Machshir the entire remnant of the leg! Perhaps the Gemara connotes that Rav would have declared it Tereifah if it was cut at Tzomes ha'Gidim.

Ha'Emek Davar (Shmos 22:30 (and footnote 1 DH v'Hinei), and ha'Emek She'elah (125 p.33):): The Ramban and Ran hold that if something could be cured, it is not Tereifah. The Shach (57:48) says that if it lives more than 12 months, this is a miracle. The Maharshal says that a tiny minority can live more than 12 months. Both of these are difficult. Rather, a Tereifah cannot live, i.e. by itself. The Rambam says so. Tosfos (Bechoros 38b DH v'Simanech) says that something that does not heal by itself is a fixed Mum, even if we can cure it. If a Safek Tereifah lives 12 months, we assume that it was not Tereifah, for it is very rare that it would chance upon something that heals it. If a Vadai Tereifah lived 12 months, we must say that this happened. This applies to Tereifos of tradition. If we have no tradition for it, it is Tereifah only if there is no cure and it is destined for dogs. We learn from "la'Kelev Tashlichun Oso." This is like the Rambam. Chulin 54a is no proof for the Ramban, for it discusses a potential Tereifah for which there was no tradition. The Mishnah (42a) concludes 'if something like it does not live, it is Tereifah', to forbid even if it lives through a cure.

Toras Kohanim (Shmini Perek 3,10): One might have thought that if an animal ate poison, it is Tereifah. "Neveilah u'Tereifah" equates Tereifah to Neveilah. Just like Neveilah is not Bas Chayim (cannot live), also Tereifah.

Ra'avad: If one would let blood from it, it could live.

Ha'Emek She'elah (125, p.34): A verse equates Tereifos to Tamei animals, to forbid them even if they live through a cure.

Toras ha'Bayis (Beis 2 Sha'ar 3 49b): The Gemara says that a hole in the Beis ha'Kosos the size of a Sela makes a Tereifah. Even though we see people in which a Tefach is open and they live, regarding Tereifos we rely only on what Chachamim said. If not, we would permit a puncture in the intestines or the membrane around the brain, for doctors experimented and say that they can live. We rely on the Ge'onim; their opinion is a Kabalah. Tana'im argue about whether living 12 months is a Siman that it is Kosher. R. Yosi cited a case in which such a woman was cured, and R. Shimon answered that she did not live 12 months. This shows that even a cure will not enable a Tereifah to live 12 months.

Chikrei Lev (YD 26): The Rashba retracted from what he wrote in Teshuvah 1:98 (that a Tereifah cannot live).

Poskim

Shulchan Aruch (YD 55:1): If Tzomes ha'Gidim was removed, it is Treifah.

Gra (3): This is like Toras ha'Bayis and the Rosh, unlike the Ramban.

Pri Chodosh (41:13): A hole in Tarpash ha'Kaved (the boundary between the liver and the lungs) is Tereifah, but if it was sealed with fat or a scab closed it, it is Kosher. The Gemara said that a Tereifah does not become Kosher again, i.e. through man. Naturally, they can become Kosher, e.g. a hole in the lung that became tangled with flesh.

Chazon Ish (YD Tereifos 5:3 DH v'Af): Hash-m created cures even for Tereifos. Bava Basra 74b discusses a stone that can revive the dead! Shmuel could heal someone beheaded, if not for wind. Chizkiyah hid Sefer ha'Refu'os, for it cured people immediately. Not all cures were known in all generations. Some were revealed and forgotten. Hash-m entrusted Chachamim to fix the Tereifos according to the Ru'ach ha'Kodesh that He put on them. Ravina and Rav Ashi are Sof Hora'ah (Bava Metzia 86a). We cannot be Mechadesh Torah after them. Tereifos were determimed according to Hash-m's providence at that time. The illnesses in the arsenal of the angel of death at that time, for which no cure was known, those are the Tereifos that the Torah forbade then and for all future generations.

Igros Moshe (CM 2:73:4): The Rambam knew that nature changed. Traditions for Tereifos are forbidden forever. The Gemara could say that something without a tradition is not Tereifah if they knew a cure for it. The Rashba did not know that nature changed, and this forced him (to refute those who said that Tereifos sometimes live more than 12 months).

Tzitz Eliezer (19:32): In the past, there was no cure if the kidneys were removed. The Rambam permits when the kidneys were removed, and in Perek 10 (Halachah 12,13) he says that we cannot add to or detract from the Tereifos listed. It does not matter if it is medically known that it can or cannot live. We follow the Torah. The Kesef Mishneh explains that this is because it is a tradition from Sinai.