knee jerk vs patellar reflex

knee jerk and patellar reflex both are nouns.

Word	Noun	Adjective	Verb	Adverb
knee jerk	Yes	No	No	No
patellar reflex	Yes	No	No	No

As nouns, knee jerk and patellar reflex are synonyms defined as:

knee jerk and patellar reflex: a reflex extension of the leg resulting from a sharp tap on the patellar tendon

Other synonyms of knee jerk include knee-jerk reflex.

knee jerk (noun)	patellar reflex (noun)
a reflex extension of the leg resulting from a sharp tap on the patellar tendon	a reflex extension of the leg resulting from a sharp tap on the patellar tendon