Synovial Fluid ‐ Its Mass, Macromolecular Content and Pressure in Major Limb Joints of the Rabbit

Abstract

SUMMARYSynovial fluid from rabbit elbow, shoulder, hip and knee was analysed to establish the normal levels of parameters relevant to fluid exchange -viz. fluid mass per joint, hydraulic pressure, temperature, colloid osmotic pressure (COP), protein, albumin and glycosaminoglycan (GAG) concentrations. Fluid mass was greatest in the least congruous joint, the shoulder (43 + 4 mg), cf. 6 + 2 mg in the highly congruous hip. In the knee (24+4 mg) the mean thickness of the fluid layer was calculated to be 30,m. Fluid pressure was subatmospheric in all joints (mean -2-8+0-4cmH20, elbow, to -5-7+0-3cmH20, knee), as in many other interstitial spaces.Colloid osmotic pressure was substantial (mean 114+0-9cmH2O, shoulder, to 131+10 cmH20, elbow), being 40-46 % of serum level. Comparison of synovial fluid results with COP versus concentration curves in vitro indicated that the fluid's COP was primarily generated by its protein content (22-30 g 1-1, 64 % albumin) rather than GAG (4 0-5 8 g 1-1). The GAG was 95 % hyaluronate and 5 % sulphated GAG. Algebraic summation of the hydraulic and colloid osmotic pressures of synovial fluid and serum indicated a net filtration gradient from blood to joint cavity. When serum COP was reduced by intravenous saline infusion, synovial fluid mass increased, in accordance with the ultrafiltration hypothesis of synovial fluid formation. The fluid's colloid concentration declined as volume increased. The relation was not a simple dilution curve, but indicated that the newly formed synovial fluid contained > 8 g protein 1-1 (14-5 % serum concentration); and that hyaluronate was entering the synovial cavity at a rate of > 6 5 ,ug h-' per joint.

Structure and Size-selective Permeability of the Synovial Membrane of the Temporomandibular Joint of the Mouse Measured by MR Imaging at 7T

“…14,23 The reported value of the SF/S ratio (0.48) for the major limb joints of rabbits 24 seems controversial, judging by our results, but this discrepancy is probably due to the difference in the time constant of the exchange. The SF/S ratio reflects a slow exchange with a long time constant between the serum and synovial fluid, whereas the inflow rate of contrast reagents reflects a rapid exchange with a short time constant, in the order of 5 min.…”

Physiology and pathology of the equine joint

“…The synovial fluid is an ultrafiltrate of plasma, containing ions. Most of the molecules present in plasma in the same concentration, with the exception of hyaluronic acid, which is present at a higher concentration in synovial fluid (Knox et al 1988). Synovial fluid cellular content is predominantly mononuclear (synovial lining cells, monocytes, and lymphocytes), the remainder being polymorphonuclear leukocytes (Todhunter 1996).…”

Effect of extravascular plasma protein on pressure‐flow relations across synovium in anaesthetized rabbits.

“…A lagged Hansen electronic membrane osmometer with a 5 mm diameter sample well was fitted with a PM10 membrane (exclusion> 10000 Da; Amicon, Lexington, USA) and calibrated with a water column; for construction details see Knox et al (1988). Readings at room temperature (20)(21)(22)(23) 0C) and osmotic equilibrium (2-3 min) were adjusted to intra-articular temperature (35 TC) by the ratio of absolute temperatures (van't Hoff's law).…”

“…Normal synovial fluid, however, contains plasma protein (23 g 1`in rabbit knee) and hyaluronan (5 5 g I`). Albumin is present at 54 % of the plasma concentration and accounts for most of the oncotic pressure, which is 13 cmH2O (Knox, Levick & McDonald, 1988). The synovial lining is permeable to albumin (Simkin & Benedict, 1990).…”