'Knees' in the Bible

Then the king’s face grew pale and his thoughts alarmed him, and his hip joints went slack and his knees began knocking together.

Now when Daniel knew that the document was signed, he entered his house (now in his roof chamber he had windows open toward Jerusalem); and he continued kneeling on his knees three times a day, praying and giving thanks before his God, as he had been doing previously.

Then behold, a hand touched me and set me trembling on my hands and knees.