The interosseous membrane of the forearm (rarely middle or intermediate radioulnar joint) is a fibrous sheet that connects the radius and the ulna. It is the main part of the radio-ulnar syndesmosis, a fibrous joint between the two bones.
The interosseus membrane divides the forearm into anterior and posterior compartments, serves as a site of attachment for muscles of the forearm, and transfers forces from the radius, to the ulna, to the humerus. As the forearm moves from pronation to supination, the interosseous membrane fibres change from a relaxed state, to a tense state in the neutral position. They once again become relaxed as the forearm enters supination.