elbow joint vs ulna

elbow joint

noun
  • Synonym of elbow. 

ulna

noun
  • The bone of the forearm that extends from the elbow to the wrist on the side opposite to the thumb, corresponding to the fibula of the hind limb. Also, the corresponding bone in the forelimb of any vertebrate. 

How often have the words elbow joint and ulna occurred in a corpus of books? (source: Google Ngram Viewer )