Britney Spears says she hurt her knee badly after taking a tumble at her friends house ... but, it's alright now -- 'cause she says it popped back into place???

The singer-songwriter shared another dancing video to her Instagram Sunday ... wearing a low-cut pink dress which ended high on her powerful thighs.

She's wearing white fingerless gloves in the clip ... and, she twirls her hands around -- putting her hands up in prayers at times while seemingly coaxing in the audience with "come hither" movements at others.

In her caption, she wrote her two sons -- Sean and Jayden -- had to return to Maui ... so, she's dancing as way to express herself and even "pray through art."

Spears says she just want to be a better person ... and, she's not putting out her message for pity -- ad

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