The distal radioulnar articulation, triangular fibrocartilage, and its associated ligament complex are the main components of the distal radioulnar joint (DRUJ). The convex distal ulna articulates with the concave surface of the radius at the sigmoid notch. This articulation is not congruent: the radius of curvature of the distal ulna is approximately 10 mm, whereas that of the sigmoid notch approaches 15 mm. This difference in radii of curvature allows both rotational and translational components to motion and is responsible for the inherent instability of the DRUJ. The ridge separating the sigmoid notch from the lunate facet of the radius serves as the point of origin for the triangular fibrocartilage and radioulnar ligaments, important contributors to stability at the DRUJ.