human knee vs knee joint

human knee and knee joint both are nouns.

Word	Noun	Adjective	Verb	Adverb
human knee	Yes	No	No	No
knee joint	Yes	No	No	No

As nouns, human knee and knee joint are synonyms defined as:

human knee and knee joint: hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella

Other synonyms of human knee include articulatio genus, genu, knee.

human knee (noun)	knee joint (noun)
hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella	hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella