A better knowledge of synovial fluid (SF) ultrastructure is required to further understand normal joint lubrication and metabolism. The aim of the present study was to elucidate SF structural features in healthy joints from three mammalian species of different size compared with features in biomimetic SF. High-resolution structural analysis was performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and environmental SEM/wet scanning transmission electron microscopy mode complemented by TEM and SEM cryogenic methods. Laser-scanning confocal microscopy (LCM) was used to locate the main components of SF with respect to its ultrastructural organization. The present study showed that the ultrastructure of healthy SF is built from a network of vesicles with a size range from 100 to a few hundred nanometers. A multilayered organization of the vesicle membranes was observed with a thickness of about 5 nm. LCM study of biological SF compared with synthetic SF showed that the microvesicles consist of a lipid-based membrane enveloping a glycoprotein gel. Thus, healthy SF has a discontinuous ultrastructure based on a complex network of microvesicles. This finding offers novel perspectives for the diagnosis and treatment of synovial joint diseases.

The problem of the squeezing of a fluid film with a complex rheology is studied. Thefluid is represented by the Phan-Tien and Tanner (PTT) constitutive equation. The goal ofthe paper is to develop an analytical approach which allows one to describe and quantifythis process, which is often present in classical lubrication problems, but particularlyin human joints. The present approach can potentially supplement time-consuming and costlypurely numerical methods which are also susceptible to misleading artifacts. A parametricstudy reveals the effect of fluid elasticity compared to viscous effects and someexplanation is suggested as to their possible links with joint diseases.

The objective of this study was to compare exercise-induced inflammatory responses in horses undergoing three different treadmill exercise tests. Mares completed a graded exercise test (GXT), an interval exercise test (IET) and a repeated sprint exercise test (RSET). Blood and synovial fluid samples were taken 24 h before (PRE) exercise, 20–30 min, 2 and 24 h following exercise (REC). Blood was analysed for total protein, haematocrit and total nitrite concentration. Pro-inflammatory and anti-inflammatory cytokine transcripts were measured in whole blood using quantitative real-time polymerase chain reaction. Synovial fluid was analysed for total nitrite. Mares spent more time at greater than 90% of their maximum heart rate during the RSET than they did for either the GXT or IET. There was an effect of exercise test (P < 0.0001) and exercise test by sample interaction (P = 0.010) for plasma total nitrite. Pro-inflammatory cytokine transcripts and plasma total protein were elevated (P < 0.05) after exercise and there was a higher (P < 0.0001) nitrite concentration in tibiotarsal joints compared with radiocarpal joints. As hypothesised, the higher-intensity exercise test (RSET) resulted in greater nitric oxide responses as well as markers of exercise intensity compared with less intense exercise tests (IET, GXT).