Morphometry of the Ultrastructure of the Blood‐joint Barrier in the Rabbit Knee

Abstract

SUMMARYThe ultrastructure of the barrier to water and solute exchange between blood and a synovial cavity was studied morphometrically in five rabbit knees. The synovial surface consisted of 80 % synoviocytes and 200% interstitium in direct contact with synovial fluid. The surface intercellular gaps were wide (0 1-55 ,um). A rich network of capillaries lay just beneath the surface, the commonest (modal) depth of the capillary perimeter being 5 ,sm at its nearest point. Of these capillaries, 91 % were fenestrated in adipose synovium, 44% in areolar synovium and 210% in posterior synovium; the remainder were continuous capillaries. The number of fenestrae per fenestrated capillary was low (-05,um-1, circumference: -6 ,m-2). The fenestrae (width 52 nm; membrane thickness 3-4 nm) occupied -1 % of the fenestrated endothelial surfacearea. Nuclear segments and intercellular junctions were roughly twice as frequent in continuous capillaries as in fenestrated capillaries of the same circumference, indicating that continuous endothelial cells are of smaller surface area than fenestrated cells. The basement membranes of continuous and fenestrated synovial capillaries were relatively thick (98 and 110 nm respectively), perhaps supporting the synovial endothelium during joint motion. In both fenestrated and continuous capillaries the nuclei were preferentially oriented away from the synovial surface (92 and 670% respectively), which presumably facilitates exchange with the surface.

A Morphometric Study of the Endocrine and Exocrine Capillaries of the Pancreas

“…(The fenestral frequency in these vessels was 2 5 per profile, which is similar to the value of 1 9 found for exocrine capillaries in the present work.) For a recent review of fenestral distribution, see Knight & Levick (1984). In this a n d~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Fig.…”

Microvascular system of anterior cruciate ligament in dogs

“…For example, one function of the joint fluid is to provide a chemical environment for the ACL. In fact, the capillaries of the synovial membrane have been characterized as a fenestrated type, highly permeable to small hydrophilic solutes, 15,44 thus allowing nutrient diffusion. Levick 45 concluded that joint fluid absorption from the joint cavity occurs by two parallel pathways, viz.…”

Cationic PLGA/Eudragit RL nanoparticles for increasing retention time in synovial cavity after intra-articular injection in knee joint

“…1,2 However, the therapeutic outcome following IA injection is considerably lessened by drug delivery issues that include rapid clearance into the systemic circulation from the synovial ultrastructure, which offers little barrier to the diffusion of molecules in and out of a joint. 4,5 Knight and Levick 6 found that the synovial surface consists of a discontinuous layer of synoviocytes (covering 80% of the synovial lining) with wide intercellular gaps measuring 0.1-5.5 μm with no basal membrane. The IA route is even comparable to intramuscular or subcutaneous routes pharmacokinetically with regard to rapid redistribution of drug into the bloodstream.…”