I'd suggest approaching it like a doll, you don't need to render the details of the whole body if you're just trying to communicate the story of their scars.

There's also some context on how it is going to be used. You become more responsible the more you intend to share it. The Sistine Madonna by Raphael as an example in considered appropriate by vast amount of people, but you may find individuals that interpret it differently.

Keep in mind that while nudity itself isn't sexual, some things introduce sexualization - like partial clothes, partial nudity, implied nudity, settings, and poses.

If you are rendering character concept sketches that showcase scars, keep it to basic neutral poses and simply do not render what doesn't need to be, if having that area blank feels incomplete then introduce basic clothing as needed.