The ulnocarpal complex is the functional articulation between the distal ulna and the ulnar carpus (lunate and triquetrum), mediated through the triangular fibrocartilage complex rather than a direct bone-to-bone articulation. The articular disc of the TFCC, the ulnolunate and ulnotriquetral ligaments, and the meniscus homologue collectively transmit approximately 20% of axial load across the wrist from the ulnar carpus to the ulna. This load-sharing proportion varies with ulnar variance.
| Origin | Palmar radioulnar ligament of the triangular fibrocartilage complex and the region of the ulnar fovea |
|---|---|
| Insertion | Palmar surfaces of the lunate (ulnolunate ligament) and triquetrum (ulnotriquetral ligament), with the meniscus homologue attaching to the triquetrum |
Suspends the ulnar side of the carpus from the ulna and the TFCC, carries roughly a fifth of axial wrist load across to the ulna, and helps stabilise the distal radioulnar joint.
The ulnocarpal complex is the site of ulnar-sided wrist pain in a broad range of conditions: TFCC tears, ulnocarpal impaction syndrome from positive ulnar variance, ulnolunate ligament injuries, and lunotriquetral instability. In positive ulnar variance, the ulna is longer relative to the radius and bears a disproportionately higher share of carpal load, producing chondral damage to the ulnar side of the lunate and proximal triquetrum. Ulnar shortening osteotomy rebalances load distribution and is the surgical treatment for symptomatic ulnocarpal impaction.
Positive ulnar variance causes the ulnar head and ulnocarpal complex to bear excessive axial load, producing chondromalacia of the lunate ulnar facet, TFCC tears, and lunotriquetral ligament injury, managed with arthroscopic debridement and ulnar shortening osteotomy to offload the ulnar side.
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