Hebrew (see on Proverbs 25:11), A broken tooth, and a foot out of joint—confidence in an unfaithful man in time of trouble. A faithless man is as little to be relied on in a time of need as a loose or broken tooth, and a foot unsteady or actually dislocated.
You cannot bite on the one, you cannot walk on the other; so the perfidious man fails you when most wanted. Septuagint, "The way [ ὁδὸς, Vatican, is probably a clerical error for ὀδοὺς, al.] of the wicked, and the foot of the transgressor, shall perish in an evil day."
A Bengal maxim runs, "A loose tooth and a feeble friend are equally bad" (Lane).