noun
knee joint
Anatomical term for the joint connecting the thigh and lower leg.
膝関節の痛みで歩くのがつらい。
It's hard to walk because of knee joint pain.
膝関節の手術を受けた。
I had knee joint surgery.
膝 is the general word for 'knee', while 膝関節 specifically refers to the anatomical knee joint.
Compound of 膝 (hiza, 'knee') and 関節 (kansetsu, 'joint').