The IOM includes 5 types of ligaments: central band, accessory band, distal oblique bundle, proximal oblique cord, and dorsal oblique accessory cord. The annular ligament is not a part of the IOM.
The IOM bridges the radius and ulna and acts as a hinge for rotation of radius about ulna. The central portion is thickened, and forms the central band which is the most important ligament for IOM load distribution characteristics.
Noda et al, in a cadaver study, identified the precise anatomical insertions and attachment points of each of the 5 IOM components. They found the most distal and proximal ends of the radial origin of the central band were 53% and 64% of total radial length from the tip of the radial styloid, whereas those of the ulnar insertion were 29% and 44% of total ulnar length from the ulnar head.
Pfaeffle et al also performed a cadaveric biomechanical study applying compressive loads to specimens with IOMs that are intact, cut, or cut/reconstructed with flexor carpi radialis allografts. They found that reconstruction of the IOM can restore the normal load transfer chararcteristics and that the central band of the IOM is the most important portion of the IOM to be reconstructed.
Illustration A shows the ligaments of IOM membrane: CB = central band, AB = accessory band, distal oblique bundle, proximal oblique cord, and dorsal oblique accessory cord
The annular ligament is a strong band of fibers, which encircles the head of the radius and keeps the radius in contact with the radial notch of the ulna, but is not a part of the IOM.
Noda K, Goto A, Murase T, Sugamoto K, Yoshikawa H, Moritomo H. Interosseous membrane of the forearm: an anatomical study of ligament attachment locations. J Hand Surg Am. 2009 Mar;34(3):415-22. Epub 2009 Feb 11
PMID:19211201 (Link to Abstract)
Pfaeffle HJ, Stabile KJ, Li ZM, Tomaino MM. Reconstruction of the interosseous ligament restores normal forearm compressive load transfer in cadavers. J Hand Surg Am. 2005 Mar;30(2):319-25.
PMID:15781355 (Link to Abstract)