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.
I twisted my ankle.
My right ankle hurts a lot.
I sprained my ankle while running away from a feather floating in the air.