94.
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.
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