Introduction

The triangular fibrocartilage complex (TFCC) is one of the intrinsic ligaments of the wrist. It is often injured due to a fall on an outstretched hand or in association with distal radius fractures, and central perforations are commonly seen in degenerative processes during aging. It contributes to the stability of the distal radioulnar joint and the ulnocarpal joint. The nomenclature—triangular fibrocartilage complex—is apt because it reflects both structure and anatomical shape. Many recent cadaver and arthroscopic studies have elucidated its exact anatomy and function.1,2 This knowledge clarifies the biomechanical role of the TFCC and guides the arthroscopic management of TFCC tears.2

Histology

The TFCC is composed of two histologically different types of tissues. The central fibrocartilage disk represents 80% of the area of the TFCC. It is avascular and consists of collagen type 1 fibers, which are oriented according to tensile forces and grouped in bundles, with fusiform chondrocytes in the matrix.3 This central disk attaches to the hyaline cartilage that covers the distal radius4 and extends as a meniscus homologue. The peripheral 20% of the disk is vascularized, as are its extensions: the ulnocarpal ligaments (volar), and the sheath of the extensor carpi ulnaris (ECU) (dorsal). These structures are composed of loose vascularized connective tissue, with fibroblasts that secrete proteogly-cans and extracellular matrix. They are interspersed in a gelatinous matrix composed of collagen fibers and elastin fibers. The TFCC is inserted on the fovea of the ulna by Sharpey fibers, which are vertically oriented. At the base of the ulnar styloid, the fibers are oriented horizontally. The ECU tendon subsheath is also firmly attached to the dorsal aspect of the fovea by Sharpey fibers.5 In contrast, the ulnocarpal ligaments do not have any Sharpey fibers.

Thus the TFCC is composed of a vascularized portion and a nonvascularized portion. Vascularization is supplied from branches of the posterior interosseous artery, the ulnar artery, and the medullary arteries of the head of the ulna at the fovea. This histological difference explains the pathophysiology of TFCC lesions. The central disk and its radial insertion are avascular and cannot heal spontaneously. The peripheral portion of the TFCC is well vascularized and has a good healing potential. Macroscopically it is often difficult to distinguish between the fibrocartilaginous and the ligamentous parts.

Anatomy

The TFCC is located between the ulna and the proximal carpal row (opposite the lunate and the triquetrum). It thus supports the distal radioulnar joint (DRUJ) in its proximal portion. The DRUJ is formed by the articulation between the concave sigmoid notch located on the medial aspect of the distal end of the radius and the articular surface of the ulnar head ( Fig. 7.1 ). The DRUJ is stabilized by dorsal and volar radioulnar ligaments, the TFCC, and the joint capsule.

The TFCC consists of five parts:

1. 
   

   The fibrocartilaginous disk and the meniscal homologue

   
   
2. 
   

   The ulnocarpal ligaments on the volar aspect (the ulnolunate and the ulnotriquetral ligaments) ( Fig. 7.2 )

   
   
3. 
   

   The dorsal and volar radioulnar ligaments (each with a superficial and deep part) ( Fig. 7.3a, b )

   
   
4. 
   

   The ulnar collateral ligament

   
   
5. 
   

   The floor of the fibrous fifth and sixth extensor compartments ( Fig. 7.4 )

The central disk is a robust fibrocartilaginous structure extending between the ulna and the radius. The base of the disk is attached to the sigmoid notch of the radius, whereas the apex is attached to the fovea at the base of the ulnar styloid on the head of the ulna. The foveal insertion of the TFCC is not seen during wrist arthroscopy using the standard radiocarpal portals. This important part of the TFCC is best visualized using the DRUJ portals. These fibers are part of the “iceberg” concept propagated by Atzei and Luchetti.2 The central fibrocartilaginous disk continues medially and volarly to merge with the ulnar collateral ligament and the ulnocarpal ligaments, respectively. The ulnocarpal ligaments (the ulnolunate and the ulnotriquetral ligaments) do not insert onto the ulna but are derived from the anterior part of the TFCC, and they connect the carpus (lunate, triquetrum, and capitate3) to the ulna by the palmar portion of the radioulnar ligament at its origin—the fovea.6 The radioulnar ligaments (dorsal and volar) arise from the medial aspect of the distal radius. They insert at different points onto the ulna (the deep fibers insert onto the fovea, whereas the superficial fibers insert onto the styloid process).

Palmer and Werner7 had a two-dimensional view of the TFCC. However, since the work of Nakamura and colleagues,1,4,6 it is interesting to understand the dynamic function and analyze the TFCC in its three-dimensional structure. One can therefore schematically separate the TFCC into three zones: a proximal zone corresponding to the insertion of the triangular foveal ligament, a distal region corresponding to the “hammock,” and an outer area corresponding to the ulnar collateral ligament ( Fig. 7.5 ).