This review summarizes the current literature available on joint cartilage alterations in
long-duration spaceflight. Evidence from spaceflight participants is currently limited to serum
biomarker data in only a few astronauts. Findings from analogue model research, such as bed rest
studies, as well as data from animal and cell research in real microgravity indicate that unloading
and radiation exposure are associated with joint degeneration in terms of cartilage thinning and
changes in cartilage composition. It is currently unknown how much the individual cartilage regions
in the different joints of the human body will be affected on long-term missions beyond the Low
Earth Orbit. Given the fact that, apart from total joint replacement or joint resurfacing, currently no
treatment exists for late-stage osteoarthritis, countermeasures might be needed to avoid cartilage
damage during long-duration missions. To plan countermeasures, it is important to know if and how
joint cartilage and the adjacent structures, such as the subchondral bone, are affected by long-term
unloading, reloading, and radiation. The use of countermeasures that put either load and shear, or
other stimuli on the joints, shields them from radiation or helps by supporting cartilage physiology,
or by removing oxidative stress possibly help to avoid OA in later life following long-duration space
missions. There is a high demand for research on the efficacy of such countermeasures to judge their
suitability for their implementation in long-duration missions