My cat has a scab-like lump on its hind leg joint that hurts when touched

A scab-like wound on a cat’s hind joint has a few causes. Long floor lying plus jump weight can wear and break the skin and even cause joint overgrowth; pad the floor and apply antiseptic daily to avoid infection.

Skin infection from fungus, bacteria, or mites causes scaling and crusts needing targeted medicine and a collar. Joint crust or wear may lead to arthritis; if it spreads or the cat moves poorly, see a vet.