Histologic structure of the articular disk of the human distal radioulnar joint.

A histologic study of the structure of the articular disk of the distal radioulnar joint in humans was performed on 57 disks from 37 fresh cadavers that included fetuses and individuals up to age 65 years. The specimens were stained with hematoxylin and eosin, orcein, and Mallory and Mann-Dominici's methods, and studied with the light microscopy. It was found that the disks of adults were basically formed of the so-called fibrocartilagenous tissue composed of an intercellular substance in which there were interwoven wavelike collagen fiber bundles and between them three specific types of cells: (1) rather sparse fibrocytes mostly situated in dorsal and palmar margins, (2) predominant and constant chondroid cells dispersed throughout the disk, and (3) less-frequent real chondocytes distributed mostly in the central parts. This basic tissue is modified according to the age of the subjects and functional requirements. In fetuses and newborns, it is almost completely fibrous and very cellular, while in adults, it is more cartilaginous with significantly reduced cellularity. The structure of various parts of disks is adapted to the functional stresses exerted on them. In central parts exposed to pressure, the tissue is more cartilaginous, while peripheral, massive margins, subjected mostly to traction, are built in a ligamentlike pattern. The ulnar and carpal surfaces are adapted to the gliding movements of the ulna and carpus. It is concluded that the articular disk in humans, which is basically of fibrocartilagineous nature, is a dynamic structure biomechanically, predetermined and changing with aging.