A "junction of sinews" are the three sinews that attach the middle leg muscles to the bone of the lower leg. If they are removed, the animal becomes a terefah.
If a bone was fractured and the broken ends pierced the skin, the animal remains kosher, but the limb itself is in question. If the greater part of the flesh remains, the shechitah of the animal makes the limb fit for consumption, but if not, then this is a dangling limb, and it is forbidden for consumption.
Art: George Cochran Lamdin - The Little White Heifer