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.
(..) There's not a lot of us left. Have to help each other. Maybe I'll see you again. Maybe. Heel-toe, heel-toe out here. Bend at your knees. You want to keep quiet. I heard you from a mile away. Okay. And when this happens, and when we allow freedom to ring... (..)2017 TvShow: The Walking Dead Title: Rock in the Road Season: 7 Episode 9