knock-knee vs impairment

knock-knee and impairment both are nouns.

Word	Noun	Adjective	Verb	Adverb
knock-knee	Yes	No	No	No
impairment	Yes	No	No	No

As nouns, impairment is a hypernym of knock-knee; that is, impairment is a word with a broader meaning than knock-knee:

knock-knee: an inward slant of the thigh
impairment: the condition of being unable to perform as a consequence of physical or mental unfitness

Other hypernyms of knock-knee include disability, disablement, handicap.

knock-knee (noun)	impairment (noun)
an inward slant of the thigh	damage that results in a reduction of strength or quality
	the act of making something futile and useless (as by routine)
	the occurrence of a change for the worse
	the condition of being unable to perform as a consequence of physical or mental unfitness
	a symptom of reduced quality or strength