The human knee: A window on the microvasculature

Abstract

In synovial joints, the lining cells do not have tight junctions with their neighboring cells and they have no underlying basement membrane. Therefore, the synovial fluid within the articular cavity is continuous with the interstitial fluid of the synovial intima. These features, combined with ready access to the space via arthrocentesis, permit quantitative studies of microvascular function in the knees of unanesthetized, volunteer, human subjects both with and without chronic arthritis. This brief article reviews the principal findings of such work over ∼40 years at the University of Washington. Examined variables include bidirectional fenestral diffusion of small solutes, effective blood flow, lymphatic drainage, and endothelial pore size and permeability. The latter work introduced a new method using gel filtration chromatography of paired synovial fluid (SF) and serum (S) to obtain essentially continuous SF/S ratios over a range of radii between 1 and 12 nanometers.

Keywords:

• blood flow
• capillary
• fenestration
• glycocalyx
• lymph flow
• permeability
• pore size
• rheumatoid
• synovium

Abbreviations:

• S, Serum
• SF, Synovial Fluid
• IF, Interstitial Fluid
• P, Plasma
• OA, Osteoarthritis
• BCP, Basic Calcium Phosphate
• RA, Rheumatoid Arthritis
• NSAID, Non-steroidal Anti-inflammatory Drugs
• Cl, Clearance
• C, Concentration
• nm, nanometer

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgements

I am indebted to John Bassett, Wayne Wallis, and many other colleagues who have shared in this work over my many years at the University of Washington.