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’

Akkadian
kiṣru - joint of the human or animal body (CAD k 436, AHw 488)
The first meaning quoted in both sources is ‘knot’.
Ebla
gi-zi-lu-um - bond, articulation (Fron. Ebl. 178, Kreb. 36)
/ḳiṣrum/ The anatomic meaning ‘joint’ follows from the combination gi-zi-rí bù-tim ‘shoulder joint’ [ibid.]
Phoenician
ḳṣrt - ribs (T 292)
Biblical Aramaic
*ḳəṭar - joint (HALOTg 1773)
pl. ḳiṭrīn Presumably from ‘knot’. In ḳiṭrē ḥarṣēh ‘the joints of his hip’.
Jewish Babylonian Aramaic
ḳiṭrā - joint (Jastrow 1358)
The basic meaning given by Jastrow is ‘knot’, but the meaning ‘joint’ clearly follows from some of the contexts; ḳṭr, pl. ḳyṭryn ‘joint (of fingers)’ [DJPA 488] (the first meaning is ‘knot’, also ‘node of a plant’).
Syriac
ḳəṭartā - articulus (LSyr. 662)
Mandaic
giṭra - ligament (of the body); joint, bond, knot (MD 90)
g-­ < *ḳ-­ by dissimilation of two «emphatic» stops, the process likely inherited by Mnd. from the Akk. substratum
Arabic
kuḏ̣r- - hollow at the top of the chest, between the two collarbones (BK 2 905,)
only with the meaning ‘cushion of fat (of a part of the vulva, of the fat around kidneys)’ [WKAS I 224]
Tigre
ḳäṣir - penis (WTS 264)
Problematic. A meaning shift from ‘joint’?