Anatomical site

I need a good and clear definition of anatomical site. I have the one for modifier 59 from CMS.gov but it does not explain the limbs. For instance is the lower leg a different anatomical site from the ankle. Is the ankle a different anatomical site from the top of the foot. I know this seems basic but one of my doctors has injected above the ankle and wishes to inject on the foot. Is this a different anatomical site?