The angioarchitecture of the rat mandibular joint synovium

The synovium (or synovial membrane) lines all intra-articular surfaces of synovial joints except for the articulating surfaces. This study describes the angioarchitecture of the synovium of the adult rat temporomandibular joint using microvascular corrosion casts and scanning electron microscopy. To corroborate findings, India ink-injected, thick-sectioned specimens (200 microns) and haematoxylin and eosin-stained tissue sections (7 microns) were analysed. Rostrally, the synovial membrane was fed by several layers of vessels branching towards the superficial lining of highly convoluted capillary loops. Arterioles were rare, and venules organized in large plexuses. The membrane thinned out in the caudal direction. Villi were present on the surface. They were flat, with a core of two parallel linear feeder vessels, one arteriole and one venule, which were interconnected by capillary loops. At the periphery of the articulating surfaces, the vessels of the synovial layer were flatter. Caudally, the synovial membrane of the richly vascularized retrodiscal pad showed many synovial folds. Feeder vessels were directed rostrally and branched in all directions. The number of subdivisions depended on the size of the synovial fold. Again, venules were organized in plexuses and lining capillaries were convoluted. The densely capillarized synovial membrane with its folds and villi is considered well adapted to serve synovial fluid production and joint dynamics.