He was forced to ask for their help 'on bended knee'. [=he was forced to beg for their help; he was forced to ask for their help in a very humble way]
If you want to clean the floor properly, you have to 'get down on your (hands and) knees' [=you have to kneel down on the floor] and start scrubbing.
She 'dropped/fell/sank to her knees' [=she knelt down] and begged for forgiveness. = She 'got down on her knees' and begged for forgiveness.
(..) He runs the show. Men. All right, everybody up. Gather around. Now form a circle. Everybody, take a knee. Want you to join hands. We're gonna pray for the death of the man who killed my son. Everybody, bow your heads. You touch her titty? (..)2012 Mud