This is the CodeSystem that contains all the codes in NHSN KneeR eplacement (http://terminology.hl7.org/CodeSystem/NHSNKneeReplacement) and NHSN KneeR eplacement (http://terminology.hl7.org/CodeSystem/NHSNKneeReplacement). E.g. what you have to deal with if you get resources containing codes in either of them