2007 Volume No 13 pages 26-39
Title: A model of synovial fluid lubricant composition
in normal and injured joints |
Author: ME Blewis, GE Nugent-Derfus, TA Schmidt,
BL Schumacher, RL Sah |
Address: Departments of Bioengineering and Whitaker
Institute of Biomedical Engineering, University of California-San
Diego, La Jolla, CA |
E-mail: rsah at ucsd.edu |
Key Words: synovial fluid, proteoglycan 4, hyaluronic
acid, permeability, cartilage, synovium, lavage, HA injection |
Publication date: March 6th 2007 |
Abstract: The synovial fluid (SF) of joints normally
functions as a biological lubricant, providing low-friction
and low-wear properties to articulating cartilage surfaces
through the putative contributions of proteoglycan 4 (PRG4),
hyaluronic acid (HA), and surface active phospholipids (SAPL).
These lubricants are secreted by chondrocytes in articular
cartilage and synoviocytes in synovium, and concentrated in
the synovial space by the semi-permeable synovial lining.
A deficiency in this lubricating system may contribute to
the erosion of articulating cartilage surfaces in conditions
of arthritis. A quantitative intercompartmental model was
developed to predict in vivo SF lubricant concentration
in the human knee joint. The model consists of a SF compartment
that (a) is lined by cells of appropriate types, (b) is bound
by a semi-permeable membrane, and (c) contains factors that
regulate lubricant secretion. Lubricant concentration was
predicted with different chemical regulators of chondrocyte
and synoviocyte secretion, and also with therapeutic interventions
of joint lavage and HA injection. The model predicted steady-state
lubricant concentrations that were within physiologically
observed ranges, and which were markedly altered with chemical
regulation. The model also predicted that when starting from
a zero lubricant concentration after joint lavage, PRG4 reaches
steady-state concentration ~10-40 times faster than HA. Additionally,
analysis of the clearance rate of HA after therapeutic injection
into SF predicted that the majority of HA leaves the joint
after ~1-2 days. This quantitative intercompartmental model
allows integration of biophysical processes to identify both
environmental factors and clinical therapies that affect SF
lubricant composition in whole joints. |
Article download: Pages
26-39 (PDF file) |