patellar reflex vs knee jerk

patellar reflex and knee jerk both are nouns.

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

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

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

Other synonyms of patellar reflex include knee-jerk reflex.

patellar reflex (noun)	knee jerk (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