People frequently wash meat out of a sense of cleanliness. This is unnecessary: you can't wash off bacteria, and even if you could, you're going to miss anything that has penetrated the meat. Bacteria will be killed by cooking, not washing. All it does is get bacteria-laden water splashed around your kitchen. There are efforts to get people to stop doing that:
I haven't seen recipes calling for soaking trotters or head. It's possible that this is older advice, since these parts are rarely cooked now. These parts will have more crevices for actual dirt to be retained; it would generally be washed off in processing, but if you're getting it from a non-factory processor, it's possible that they've retained some of the dirt the animal was standing on.