Q. Dear Rabbi, If there is redness (or any other discoloration) in the area of Tzomet Hagidim in a chicken what should be done with it?
A. Remah (Y.D. 56,9) asserts that a wound that has become inflamed and bloodshot (nifuach venitzrar hadam), in the Tzumas Hagidim area (the base of the drumstick in chickens, where the sixteen tendons that control the movement of the leg, join bone and muscle), requires to be checked. We are to inspect the joint to ascertain that all the tendons are extant, however, since we are not today sufficiently expert in this type of inspection, the fowl is deemed treif.
Shach (ibid, 11) quotes Bach’s opinion that a change in color, be it to blue, brown or yellow, in itself without swelling and bloodshot, does not require any further inspection. He adds that it is preferable to lift the skin and check for decay. If there is decay or rot and decomposition has set in, then we declare it treif.
Kashrus Vetreifois B’of (56, 34) stresses that today in places (Israel and often Europe), where illness of the Tzumas Hagidin is common, any discoloration requires further checking. These illnesses are caused mainly by viral infections, accelerated growth, or a reaction to certain medications or nutrition. (See also Knei Bosem 49, who requires constant inspection and for further elucidation see Chulin Illuminated p.225).
Horav Shlomo Miller's Shlit"a opinion is, that in Canada, a change in color to pinkish that is only superficial and is not inflamed and bloodshot, does not require further inspection.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit"a