Noun
あしくび
足首をひねってしまいました。
I twisted my ankle.
右の足首がすごくいたいんです！
My right ankle hurts a lot.
宙に舞う羽から逃げる途中で、足首を捻挫した。
I sprained my ankle while running away from a feather floating in the air.
What is the neck of your leg? Think about it. It's your ankle.
This word uses the kun'yomi readings from both kanji, probably because it includes body parts. You know the kun'yomi reading of 足 from previous vocab and you know the kun'yomi reading of 首 from learning that kanji. So, you should be able to read this kanji so long as you remember that it's all kun'yomi.