Palmar ulnocarpal ligament

The palmar ulnocarpal ligament is a group of extrinsic wrist ligaments on the volar (palmar) side of the ulnar wrist that connect the distal ulna to the proximal carpal row (lunate and triquetrum), functioning to stabilize the ulnar carpus and the distal radioulnar joint (DRUJ) and to transmit load between the carpus and the ulna. Rather than a single discrete band, it is best understood as the ulnocarpal ligamentous complex, conventionally divided into the ulnolunate, ulnotriquetral, ulnocapitate and ulnopisiform ligaments.

Origin and attachments

• The complex arises from a common origin at the fovea of the ulnar head and the base of the ulnar styloid.

• Importantly, the ulnolunate and ulnotriquetral ligaments attach proximally to the palmar (volar) radioulnar ligament of the triangular fibrocartilage complex (TFCC) rather than directly to the ulna, which allows greater independence between wrist and forearm motion.

• The ulnolunate ligament spans from the palmar cortex of the distal ulna/TFCC to the lunate; the ulnotriquetral ligament runs to the triquetrum (with both palmar and dorsal components); and the ulnocapitate ligament, the most superficial component, passes to the capitate and does not attach directly to the TFCC.

Functional/anatomic relationships

• The ulnolunate and ulnotriquetral ligaments are considered integral components of the TFCC (its ulnocarpal ligamentous portion) and blend with the volar margin of the articular disc.

• Biomechanically they act as passive ulnar-sided stabilizers, becoming taut in supination, ulnar deviation, wrist extension, and radial extension; excessive traction (e.g., fall on an outstretched hand) is one proposed mechanism of TFCC foveal avulsion.