If I can add my two cents and my use case, I think this example about Fracture of femur is a bit misleading.
The fact that Athena and the OMOP vocabularies now contain the SNOMED CT description logic is truly great, but does not solve this question about post-coordination in OMOP CDM.
In my institution we encode all our structured data into SNOMED CT and a significant proportion of our variables (roughly 10 to 20%) cannot be represented by a single SNOMED CT concept. Therefore we rely on post-coordination, following the SNOMED CT Compositional Grammar and the SNOMED CT Machine Readable Concept Model
Concepts such as upper lobe atelectasis are represented in SNOMED CT by
46621007 |Atelectasis (disorder)|:
363698007 |Finding site (attribute)| = 45653009 |Structure of upper lobe of lung (body structure)|
Because there is no such precoordinated concept in SNOMED CT.
The question of how to enter such composed concept into OMOP CDM is not solved for us. There is probably a way of using the FACT_RELATIONSHIP table to do so, but if someone already found a workaround for this I would be very interested.
Sorry if the English is not perfect, not my native language.