PS

*kVm- - articulation, joint, wrist (SED I No. 143; Kogan 2011: 215)

*-­u-­ may be a secondary development due to the influence of *m-­. As a nominal anatomic term based on Akk. and M. Eth. only.

Akkadian
kimkimmu - wrist (CAD K 373, AHw. 478)
a reduplicated stem
Arabic
kumm- - sleeve (BK 2 927)
possibly related with a meaning shift
Tigre
kəm - joint, articulation (WTS 395)
Zway
kōmä - heel, elbow (EDG 343)
Chaha
ḫumma, ḫuma - heel, elbow (EDG 343)
Ezha
ḫʷəmma - heel, elbow (EDG 343)
Muher
ḫumma - heel, elbow (EDG 343)
Gogot
kumma - heel, elbow (EDG 343)
Soddo
kumma - heel, elbow (EDG 343)
Jibbali
ktum - to sit crosslegged (JL 137)
a possibly related derived verb (-t- infixed ?), with a rather specific meaning shift