Ultrastructure of the human intra-articular disc of the temporomandibular joint.

The ultrastructural appearance of the human intra-articular disc (IAD) was investigated in three discs that had been surgically removed due to disease from three female patients aged 47, 50, and 54 years of age. Regions of the IAD were selected from central areas that appeared to be least affected by disease. Sections were fixed in 2.5 per cent glutaraldehyde in 0.1 M phosphate buffer, pH 7.3 immediately after surgery. The regions examined showed no obvious signs of inflammation. The cells showed moderate amounts of the intracellular organelles associated with protein synthesis and secretion, and possessed considerable amounts of microfilamentous material, thus resembling those described in other mammals. Despite the large number of cells examined, only one cell showed evidence of a chondrocyte-like morphology in that it possessed an incomplete pericellular zone of microfilamentous material separating the cell membrane from the adjacent collagen bundles of the extracellular matrix (ECM). Thus, on morphological grounds, fibrocartilage was virtually non-existent in the specimens examined. The mean collagen fibril diameter was 43.9 nm and the fibril diameter distribution was not unimodal. Although the majority of fibrils had a relatively small diameter, two of the three specimens possessed many fibrils with diameters of over 100 nm, this being consistent with tissue subjected to tension. The mean area of a fibre bundle occupied by collagen (as opposed to the ground substance) was approximately 56 per cent.