From Wiktionary, the free dictionary
From Ancient Greek ἴσχιον (ískhion, “hip”) + πάγος (págos, “fixed, set”) (from πήγνυμι (pḗgnumi, “fasten, fix, set”)); equivalent to ischio- + -pagus.
ischiopagus (plural ischiopagi)
- (medicine) One of a pair of conjoined twins who are united at the pelvis.