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@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)