Wrist-elbow connector (4)
I believe the answer is:
ulna
'wrist-elbow connector' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ulna that I've seen before include "part of anatomy" , "a section of framework" , "Part of body" , "The longer and inner bone in forearm" , "Car document; ticket book" .)