also: ひっかがみ
noun
hollow of the knee; popliteal fossa
Anatomical term for the back of the knee; in everyday conversation, 膝の裏 (hiza no ura) is more common.
ひかがみを伸ばすストレッチが、ランナーに勧められることがある。
Stretches that extend the hollow of the knee are sometimes recommended for runners.
ひかがみに痛みを感じたら、無理をしないでください。
If you feel pain in the back of your knee, don't push yourself.
膝の裏 is the common, everyday term for the back of the knee, while ひかがみ is a more technical or literary anatomical term.
The word is of native Japanese origin. The kanji 膕 is a specialized character for this body part, while 引屈 is likely an ateji or historical spelling. The exact derivation is uncertain.