g- < *ḳ- by dissimilation of two «emphatic» stops, the process likely inherited by Mnd. from the Akk. substratum
PS
*ki/uṯ̣r- - joint (of the ribs, fingers, etc.)
(SED I No. 155)
Though reconstructed as an anatomic term on the PS level, the present root is likely related to, or rather derived from, Sem. *k(ʷ)ṯ̣r ‘to bind, knot, fix’