Bone in middle of leg (7)

I believe the answer is:

kneecap

(Other definitions for kneecap that I've seen before include "one going on bender?" , "Bone" , "Joint protection" , "part of joint" , "The informal patella (7)" .)

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.