The triangular fibrocartilage complex (TFCC) is formed by the triangular fibrocartilage discus (TFC), the radioulnar ligaments (RULs) and the ulnocarpal ligaments (UCLs).
Structure
Triangular fibrocartilage disc The triangular fibrocartilage disc (TFC) is an articular discus that lies on the pole of the distal ulna. It has a triangular shape and a biconcave body; the periphery is thicker than its center. The central portion of the TFC is thin and consists of chondroid fibrocartilage; this type of tissue is often seen in structures that can bear compressive loads. This central area is often so thin that it is translucent and in some cases it is even absent. The peripheral portion of the TFC is well vascularized, while the central portion has no blood supply. This discus is attached by thick tissue to the base of the ulnar styloid and by thinner tissue to the edge of the radius just proximal to the radiocarpal articular surface.
Radioulnar ligaments The radioulnar ligaments (RULs) are the principal stabilizers of the distal radioulnar joint (DRUJ). There are two RULs: the palmar and dorsal radioulnar ligaments. These ligaments arise from the distal radius medial border and insert on the ulna at two separate and distinct sites: the ulna styloid and the fovea (a groove that separates the ulnar styloid from the ulnar head). Each ligament consists of a superficial component and a deep component. The superficial components insert directly onto the ulna styloid. The deep components insert more anterior, into the fovea adjacent to the articular surface of the dome of the distal ulna. The ligaments are composed of longitudinally oriented lamellar collagen to resist tensile loads and have a rich vascular supply to allow healing.
Ulnocarpal ligaments The ulnocarpal ligaments (UCLs) consist of the ulnolunate and the ulnotriquetral ligaments. They originate from the ulnar styloid and insert into the carpal bones of the wrist: the ulnolunate ligament inserts into the lunate bone and the ulnotriquetral ligament into the triquetrum bone. These ligaments prevent dorsal migration of the distal ulna. They are more taut during supination, because in supination ulnar styloid moves away from the carpal bones volar side.
Function The primary functions of the TFCC:
To cover the ulna head by extending the articular surface of the distal radius. Load transmission across the ulnocarpal joint and partially load absorbing Allows forearm rotation by giving a strong but flexible connection between the distal radius and ulna. It also supports the ulnar portion of the carpus.
Load transmission The TFCC is important in load transmission across the ulnar aspect of the wrist. The TFC transmits and absorbs compressive forces. The ulnar variance influences the amount of load that is transmitted through the distal ulna. The load transmission is directly proportional to this ulnar variance. In neutral ulnar variance, approximately 20 percent of the load is transmitted. With negative ulnar variance, the load across the TFC is decreased. This occurs during supination, because the radius moves distally on the ulna and creates a negative ulnar variance. With positive ulnar variance it is reversed. The load that is transmitted across the TFC is then increased. This positive ulnar variance occurs during pronation.
Rotation
The TFCC is a major stabilizer of the DRUJ. To control the forearm rotation the DRUJ acts in concert with the proximal radioulnar joint. The connection between the distal radius and the distal ulna, maintain the congruency of the DRUJ. This attachment is mainly created by the RULs of the TFCC. These ligaments support the joint through its arc of rotation. The role of the TFCC in supination and in pronation is a matter of dispute. Some authors (Schuind et al.) concluded that the dorsal fibers of the TFCC tighten in pronation, and the palmar fibers in supination. These conclusions are opposite of those published by Af Ekenstam and Hagert. Both parties are in fact right, as the RULs consists of two ligaments each made of another two components: the superficial and the deep ligaments. During supination, the superficial palmar and the deep dorsal ligaments are tightened, preventing palmar translation of the ulna. In pronation, this is reversed: the superficial dorsal and the deep palmar ligaments are tightened and prevent dorsal translation of the ulna.
Clinical significance The TFCC has a substantial risk for injury and degeneration because of its anatomic complexity and multiple functions. Application of an extension-pronation force to an axial-load wrist, such as in a fall on an outstretched hand, causes most of the traumatic injuries of the TFCC. Dorsal rotation injury, such as when a drill binds and rotates the wrist instead of the bit, can also cause traumatic injuries. Injury may also occur from a distraction force applied to the volar forearm or wrist. Finally, tears of the TFCC are frequently found by patients with distal radius fractures. Perforations and defects in the TFCC are not all traumatic. There is an age related correlation with lesions in the TFCC, but many of these defects are asymptomatic. These lesions common occur by patients with positive ulnar variance. Chronic and excessive loading through the ulnocarpal joint, causes degenerative TFCC tears. These tears are a component of ulnar impaction syndrome. Even though natural degeneration of the ulnocarpal joint is very common, it is important to recognize. In cadavaric examinations, 30% to 70% of the cases had TFCC perforations and chondromalacia of the ulnar head, lunate, and triquetrum. Cases with ulnar-negative variance had fewer degenerative changes.
Palmer classification of TFCC lesions The Palmer classification is the most recognized scheme; it divides TFCC lesions into these two categories: traumatic and degenerative. This classification provides an anatomic description of tears, it does not guide treatment or indicate prognosis.
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