Research article

Long-term cyclical in vivo loading increases cartilage proteoglycan content in a spatially specific manner: an infrared microspectroscopic imaging and polarized light microscopy study

Ehsan Saadat¹ , Howard Lan¹ , Sharmila Majumdar^1,2 , David M Rempel^1,3 and Karen B King^1,3,4

¹  Department of Bioengineering, University of California, Berkeley, 459 Evans Hall #1762 Berkeley, CA 94720-1762, USA

²  Department of Radiology, University of California, San Francisco, 1700 4^th Street, Suite 203, Box 2520, San Francisco, CA 94107, USA

³  Department of Medicine, Division of Occupational Medicine, University of California, San Francisco, Building 30, 5th floor, San Francisco General Hospital, 1001 Potrero Avenue, San Francisco, CA 94110, USA

⁴  Department of Orthopaedics, Division of Bioengineering, University of Colorado at Denver and Health Sciences Center, 12800 E. 19^th Ave., RC1 N, Room 2103, Mailstop 8343, PO Box 6511, Aurora, CO 80045, USA

author email corresponding author email

Arthritis Research & Therapy 2006, 8:R147doi:10.1186/ar2040

Published:	6 September 2006

Abstract

Understanding the changes in collagen and proteoglycan content of cartilage due to physical forces is necessary for progress in treating joint disorders, including those due to overuse. Physical forces in the chondrocyte environment can affect the cellular processes involved in the biosynthesis of extracellular matrix. In turn, the biomechanical properties of cartilage depend on its collagen and proteoglycan content. To understand changes due to physical forces, this study examined the effect of 80 cumulative hours of in vivo cyclical joint loading on the cartilage content of proteoglycan and collagen in the rabbit metacarpophalangeal joint. The forepaw digits of six anesthetized New Zealand White adult female rabbits were repetitively flexed at 1 Hz with an estimated joint contact pressure of 1 to 2 MPa. Joints were collected from loaded and contralateral control specimens, fixed, decalcified, embedded, and thin-sectioned. Sections were examined under polarized light microscopy to identify and measure superficial and mid zone thicknesses of cartilage. Fourier Transform Infrared microspectroscopy was used to measure proteoglycan and collagen contents in the superficial, mid, and deep zones. Loading led to an increase in proteoglycan in the cartilage of all six rabbits. Specifically, there was a 46% increase in the cartilage deep zone (p = 0.003). The collagen content did not change with loading. Joint loading did not change the superficial and mid zone mean thicknesses. We conclude that long-term (80 cumulative hours) cyclical in vivo joint loading stimulates proteoglycan synthesis. Furthermore, stimulation is localized to cartilage regions of high hydrostatic pressure. These data may be useful in developing interventions to prevent overuse injuries or in developing therapies to improve joint function.