The interosseous membrane of the forearm of 12 fresh cadaver specimens was studied anatomically and mechanically to better understand its role in stabilization of the radius after radial head excision. A central band of ligamentous tissue, approximately twice the thickness of the membrane on either side was identified in all specimens. Mechanical studies determined the relative contribution to longitudinal stiffness of the forearm. The central band was responsible for 71% of the longitudinal stiffness of the interosseous membrane after radial head excision. The contribution of the triangular fibrocartilage complex was 8%. Silicone radial head implants were much less stiff than the intact interosseous membrane. Injury to the central band of the interosseous membrane may be crucial to the development of proximal migration of the radius after radial head excision.