Shikiji was Kannin who had duties, whereas Sanni (also known as Sani) was Kannin who did not have duties, i.e., who only had the court ranks.
職事（しきじ）とは職務を持つ官人をいい､散位（さんに・さんい）とは職務を持たない官人､つまり位階だけしか持っていない者のこと。