Refers to the front part of the knee, especially the bony prominence. Often used when talking about hitting or injuring the knee.
I fell and scraped my knee.
I bumped my knee against the corner of the desk.
Standard kanji spelling.
Mixed kanji-kana spelling; less common but still encountered.
Compound of 膝 (hiza, 'knee') + 頭 (kashira, 'head'), literally 'knee head', referring to the prominent bony part of the knee.