Ulnolunate ligament

The ulnolunate ligament (ULL) is one of the extrinsic palmar ulnocarpal ligaments of the wrist, spanning between the distal ulna and the lunate on the volar aspect of the ulnocarpal joint. Along with the ulnotriquetral and ulnocapitate ligaments, it forms the ulnocarpal ligamentous complex.

Origin and insertion: The ULL arises from a common origin at the fovea of the ulna and the base of the ulnar styloid, but it does not attach directly to the ulna itself—instead it originates functionally from the palmar (volar) margin of the triangular fibrocartilage complex (TFCC), specifically the palmar radioulnar ligament. It runs distally to insert on the palmar cortex of the lunate.This attachment to the palmar radioulnar ligament rather than directly to bone allows greater independence between wrist and forearm motion.

Relationship to the TFCC: The ULL is considered an integral component of the TFCC, blending with the volar margin of the articular disc. It is one of the four commonly cited TFCC constituents (dorsal/volar radioulnar ligaments, the ulnocarpal ligaments [ulnolunate and ulnotriquetral], the central articular disc, and the ulnomeniscal homologue).

Function: It acts as a stabilizer between the distal ulna and the carpus, contributing to ulnocarpal stability and constraining wrist motion. Biomechanically, ULL tension is significantly greater in forearm supination than pronation, reflecting its role in stabilizing the ulnocarpal joint during supination. Disruption of the ULL is a recognized (though uncommon) cause of chronic ulnar-sided wrist pain.