The Ulnopisiform Ligament: An Anatomical Study of the Ulnar Wrist

Background The pisiform has traditionally been regarded as a sesamoid bone within the flexor carpi ulnaris (FCU) tendon, with a limited role in carpal stability. Although the ulnar collateral and ulnocarpal ligaments of the wrist are well described, a distinct ligamentous connection between the distal ulna and the pisiform has not been consistently recognized. This study aimed to describe the ulnopisiform ligament (UP) and to define its anatomical relationships with the ulnocarpal complex and the pisotriquetral (PT) joint. Methods Eight fresh-frozen cadaveric wrists were dissected using dorsal and volar approaches. The ulnocarpal region, triangular fibrocartilage complex (TFCC), and PT joint were exposed to identify the presence, course, and insertions of a ligamentous structure connecting the distal ulna to the pisiform. Its topographic relationships with the ulnocarpal ligaments, PT joint capsule, Guyon's canal contents, and the retinacular and subsheath structures of the FCU and extensor carpi ulnaris (ECU) were documented. Manual positioning of the wrist and forearm positioning simulated translational stress across the distal radioulnar joint (DRUJ), allowing qualitative visual assessment of ligament tensioning patterns without quantitative biomechanical measurements. Results In all specimens, a capsuloligamentous structure was consistently identified extending from the ulnar head and adjacent portion of the ulnar styloid to the proximal ulnar surface of the pisiform. The UP ligament formed part of the capsuloligamentous boundary of the PT joint and was consistently observed in association with a volar recess adjacent to the ulnocarpal ligaments. A distinct fibrous connection between the pisiform and the floor of the ECU subsheath (ECU-FPS) was also identified, establishing an indirect anatomical linkage between the pisiform and the TFCC. Conclusion The UP represents an anatomical connection identified in all specimens of this series between the distal ulna and the pisiform and contributes to the ligamentous framework of the PT joint. Together with the ECU-FPS, these findings support a revised anatomical interpretation of the pisiform as a potentially integrated component of the ulnar wrist stabilizing system and provide an anatomical basis for its possible involvement in ulnar-sided wrist disorders.