Articular cartilage in synovial joints serves a variety of functions including providing joint congruency, transferring and distributing forces, and allowing joint movement. Healthy cartilage is the prerequisite for proper joint function, and thus for unconfined physical activity. The effects of immobilization on articular cartilage in humans are barely known and cartilage health of the lower limb joints has not been studied in microgravity. Healthy articular cartilage tends to be thickest in joints that experience high forces such as the knee. These data suggest that cartilage thickness in patients is sensitive to unloading.

While in microgravity, the high impact forces are absent, and this potentially could lead to cartilage degeneration or osteoarthritis. The reported changes include decreases in proteoglycan concentration and compressive stiffness, and cartilage softening. To test the effect of unloading on cartilage thickness and volume, magnet resonance imaging of the astronauts’ knees will be performed before and after a stay in microgravity. Blood and urine samples will be taken before, during (if possible) and after a stay in microgravity to investigate the effect of immobilization on biomarkers of cartilage metabolism (COMP, C2C, CPII, C1,2C, CS-846, CTX-II).

Specific Aims:
1. To investigate the effect of microgravity on cartilage morphology.
a. To investigate the effect of microgravity on cartilage biology.
b. To detect possible correlations between cartilage morphology and muscle atrophy.

2. To understand the effects of space flight on articular cartilage health.
a. To assess the risk of cartilage degeneration during medium and long term space missions.
b. To develop effective countermeasures for cartilage degeneration during medium and long-term space missions.

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