The ulnar carpal complex is located at the ulnar site of the transition from the forearm to the wrist. It acts as a buffer here, stabilizing the ulna and radius.
As its name suggests, it is a complex structure, and its anatomy and function have only recently been properly understood.
This is also why different classifications exist for describing injuries to this complex. The most commonly used classification to date is Palmer's 1989 classification, which is both anatomically outdated and inconsistent. A significant advance was the 2011 Atzei classification, which identified the ‘deep layer’ (foveal lamina) of the TFCC as the pivot joint's most important stabilizer for the first time. However, this important innovation does not sufficiently consider the central disc as well as the peripheral capsule and other ligament structures.
This motivated us to develop a new classification for TFCC injuries. We have named this the 'CUP' classification, with 'C' standing for 'central', 'U' for 'ulnar' and 'P' for 'peripheral'. Each of these three categories is divided into three degrees of severity, resulting in a total of nine lesion types (the '3x3 rule').
We initially described this in early 2023 in the renowned Journal of Hand Surgery European Volume (R. Schmitt, J.P. Grunz, M. Langer. 'Triangular fibrocartilage complex injuries – limitations of the current classification systems and the proposed new “CUP” classification'. J Hand Surg Eur. 2023;48:60–66). A second publication, with extensive illustrations of the injury types, appeared in 2025 in the German journal ‘Fortschritte auf dem Gebiet der Röntgenstrahlen’ (Schmitt R, Kunz AS, Reidler P, Huflage H, Hesse N. 'Triangular Fibrocartilage Complex (TFCC): Anatomy, Imaging, and Classifications with Special Focus on the CUP Classification'. Fortschr Röntgenstr. 2025; 197: 759–769). Both publications can be obtained in the download area of our website.
Central TFCC lesions of the TFCC (category C)
C1 = thinning and mucoid degeneration; C2 = slit-shaped pinhole lesion; C3 = wide disc perforation.
Ulnar TFCC lesions (category U)
U1 = styloid plate rupture; U2 = foveal plate rupture; U3 = styloid and foveal plate ruptures.
Peripheral TFCC lesions (category P)
P1 = rupture of the meniscus homologue or dorsal capsule; P2 = rupture of the ulnocarpal ligaments (e.g. ligamentum ulnotriquetrum or ligamentum ulnolunatum); P3 = rupture of the ligamentum radioulnare beyond the ulnar insertion.
Ulnar TFCC lesions in fractures of the styloid process of the ulna
U1# = fracture at the tip of the PSU; U2# = fracture through the base of the PSU; U3# = PSU base fracture with ligament ruptures (floating styloid).
Peripheral TFCC lesion in distal radius fracture
P3# lesion: radius fracture at the ulnar notch (here, palmar).
