Bones, back-breaking and magical creatures

In the Old Norse literary world, many evil doers (witches, magicians, monsters, etc.) are killed by breaking their backs. Examples are found in sagas, both in prose and skaldic stanzas: see Bárðarsaga, Chap. IV and IX, where respectively Svalr and Kolla are eliminated in such a way, or Friðþjófssaga, Chap.VI, where the two sorceresses Heiði ok Hamgláma suffer the same fate.
Some passages of the Old Testament writings (the terrible curses that Jeremiah proclaimed thrown by the Lord against the idolatrous people of Judah concerning their bones, Jeremiah, VIII, 1,2) would seem to have something to do with the belief that men continued to dwell in their bones. Moreover, saints' bones have been preserved as relics endowed with healing power in churches of nearly all countries. Thus a magic virtue was supposed to reside in bones, in Christian and in pagan times. This article aims to investigate the motif of 'back-breaking' as a means of destroying evil beings – which appears to be rooted also in Scandinavia – by investigating and comparing texts belonging to different genres and traditions (sagas, skaldic verses, charms, folktales), trying to find and reconstruct common elements and patterns in order to discover the possible origin of the motif and how it spread in Nordic literary tradition.