The vascularization and structure of the human digital tendon sheath as related to flexor tendon function. An angiographic and histological study.

The gliding surfaces of the flexor tendons and the tendon sheath are delicate structures of the complex digital flexor system. Beside the fibrous parts, the tendon sheath also exhibits membranous synovial components, which represent a dialysing membrane producing a plasma ultrafiltrate--the synovial fluid. In this study, interest was focused on the vascularization of the synovial sheath. By a microangiographic method it was demonstrated that this membrane is richly vascularized and that the vascular plexus is in continuity on the outside of the fibrous pulleys. The friction surfaces of the system--the inside of the pulleys and the surface of the flexor tendons--are devoid of vessels, and here a differentiation into chondrocyte-like cells is observed. It is suggested that these tissue areas, in analogy to joint cartilage, are nourished by diffusion from the synovial fluid, and that the flexor system can be regarded as a specialized joint, sliding longitudinally and exhibiting an extremely large range of motion.