Bramble had one when he was little, only it was concealed in the feathers of his lower leg, just above his stopper pad. He caught it when standing up against the gate (which is covered in chicken wire to stop escapes!) and the first we knew of it was when we saw it bleeding.
He had it removed since it was liable to be a source of infection in that it was open, but he was fine ... He hated wearing his Elizabethan collar though, and we had to tape a plastic bag over his bandage when he wanted to go out into the garden to do business ....