An immunohistochemical study of the triangular fibrocartilage complex of the wrist: regional variations in cartilage phenotype

Abstract

The triangular fibrocartilage complex (TFCC) transmits load from the wrist to the ulna and stabilizes the distal radioulnar joint. Damage to it is a major cause of wrist pain. Although its basic structure is well established, little is known of its molecular composition. We have analysed the immunohistochemical labelling pattern of the extracellular matrix of the articular disc and the meniscal homologue of the TFCC in nine elderly individuals (age range 69-96 years), using a panel of monoclonal antibodies directed against collagens, glycosaminoglycans, proteoglycans and cartilage oligomeric matrix protein (COMP). Although many of the molecules (types I, III and VI collagen, chondroitin 4 sulphate, dermatan sulphate and keratan sulphate, the oversulphated epitope of chondroitin 6 sulphate, versican and COMP) were found in all parts of the TFCC, aggrecan, link protein and type II collagen were restricted to the articular disc and to entheses. They were thus not a feature of the meniscal homologue. The shift in tissue phenotype within the TFCC, from a fibrocartilaginous articular disc to a more fibrous meniscal homologue, correlates with biomechanical data suggesting that the radial region is stiff and subject to considerable stress concentration. The presence of aggrecan, link protein and type II collagen in the articular disc could explain why the TFCC is destroyed in rheumatoid arthritis, given that it has been suggested that autoimmunity to these antigens results in the destruction of articular cartilage. The differential distribution of aggrecan within the TFCC is likely to be reflected by regional differences in water content and mobility on the radial and ulnar side. This needs to be taken into account in the design of improved MRI protocols for visualizing this ulnocarpal complex of the wrist.

Fig. 1

Diagrammatic representation of the articular disc (AD) and meniscal homologue (MH), seen from the carpal side. This shows the location of the sections taken from the palmar (a), central (b) and dorsal (c) regions of the TFCC for immunohistochemistry. Note that the disc and meniscal homologue cover the lower end of the ulna. D, dorsal aspect; P, palmar aspect; R, radius.

Fig. 2

Macroscopic view of a coronal section through the wrist to show the position and components of the TFCC. The section passes through the central portion (‘b’ in Fig. 1) of the articular disc (AD). Note the presence of hyaline cartilage at the radial enthesis (RE) of the disc and the continuity of the disc with the meniscal homologue (MH) on the ulnar side. DRUJ, distal radioulnar joint; ECU, tendon sheath of extensor carpi ulnaris; L, lunate; PSR, prestyloid recess; R, radius; SP, styloid process of the ulna; T, triquetral; U, ulna; UE, ulnar enthesis of the articular disc. Scale bar = 5 mm. Inset: the fibrocartilaginous character of the articular disc. FC, fibrocartilage cells. Scale bar = 50 µm. Both sections are stained with toluidine blue.

Fig. 4

Immunohistochemical labelling for proteoglycans in the articular disc, its radial and ulnar entheses and in the meniscal homologue. (a–c) Strong labelling for aggrecan in (a) the palmar region of the disc – scale bar = 100 µm; (b) the radial enthesis from the central part of the disc – scale bar = 100 µm; (c) the ulnar enthesis (UE) from the palmar region of the disc – scale bar = 200 µm. (d) Versican labelling in the dorsal region of the radial enthesis (RE) of the disc. Note the absence of labelling (*) in the soft tissue immediately adjacent to the tidemark (TM). Scale bar = 100 µm. (e) Tenascin labelling in the central region of the radial enthesis of the disc. HC, hyaline cartilage. Scale bar = 100 µm. (f) COMP labelling in the meniscal homologue. Scale bar = 100 µm. (g) Strong labelling for COMP at the ulnar enthesis (UE) in the central region of the disc. Note the prominent fibrocartilage cells (FC). Scale bar = 20 µm. (h) COMP in the dorsal region of the articular disc, near the radial enthesis. Note the strong labelling in the immediate vicinity of blood vessels (BV). Scale bar = 40 µm. (i) A control section from the palmar side of the radial enthesis of the articular disc, incubated with antibody RT97. No staining was seen at the enthesis. Scale bar = 100 µm.

Fig. 3

Immunohistochemical labelling for collagens and glycosaminoglycans. All figures except ‘i’ were from central sections through the disc (i.e. plane ‘b’ in Fig. 1). (a) Prominent labelling for type I collagen in the articular disc. Scale bar = 100 µm. (b) Prominent labelling for type I collagen in the meniscal homologue. PSR, prestyloid recess; SP, styloid process of the ulna. Scale bar = 1 mm. (c) Type VI collagen in the articular disc. Scale bar = 100 µm. (d) Absence of type II collagen in the meniscal homologue. BV, blood vessels. Scale bar = 200 µm. (e) Type II collagen in the articular disc in the region adjacent to the meniscal homologue. Note that labelling is present on the radial side (RS) of the disc, but absent on the ulnar side (US), i.e. towards the meniscal homologue. Scale bar = 200 µm. (f) Positive labelling for type II collagen at the radial enthesis of the articular disc. R, radius. Scale bar = 200 µm. (g,h) Labelling for chondroitin 6 sulphate (g) and its oversulphated epitope (h) from comparable regions of the articular disc. Scale bar for g = 100 µm and for h = 50 µm. (i) Labelling for chondroitin 4 sulphate at the ulnar enthesis of the articular disc, in a section which passes through its dorsal side (i.e. ‘c’ in Fig. 1). Scale bar = 50 µm.