A new study from the Henry Ford Hospital has highlighted a potential hazard for future space travelers – bad joints. An examination of the tissues of rodents that orbited the Earth in a Russian spacecraft revealed that the reduced load on their joints caused the breakdown of cartilage and signs of arthritis-like degradation.

One of the depressing facts about spending time in zero gravity is that it is very hard on the human body. Even if protected from the hazards of vacuum, heat, cold, or radiation, the lack of gravity can take a terrible toll. Prolonged space flights, like the Mars missions that will one day take place, can cause all sorts of medical problems, including muscle atrophy, the loss of bone calcium, a weakened cardiopulmonary system, impaired eyesight, and could even affect the immune system.

The recent Henry Ford study raises the possibility that joint cartilage might also be affected, because the body isn't carrying the usual load that it does on Earth. The team led by head of musculoskeletal genetics Jamie Fitzgerald emphasizes that there's no evidence that this is actually happening to humans, but the effects of zero gravity on mice does raise concerns.

Operating under a US$100,000 NASA grant, the research involved sending six male mice into space aboard Russia's unmanned BION-M1 biosatellite, which orbited the Earth from April 19 to May 19, 2013. These pathogen-free lab mice were 19 to 20 weeks old at lift off. Meanwhile, 15 control mice back on Earth were kept in identical conditions, except that they were under full gravity.

Analysis of the tissues and gene expressions of the cartilage after 30 days in space showed signs similar to those of osteoarthritis, indicating that the tissue had broken down. The team believes that this is due to the fact that though the mice could be seen getting exercise as they climbed over one another in the spacecraft, their bodies weren't carrying the weight load that they would have back on Earth. So the cartilage couldn't maintain its integrity.

"We do know that tissues of the musculoskeletal system – bone, muscle, tendon, cartilage and ligament – are constantly subjected to 'loading' everywhere on Earth," says Fitzgerald. "This comes from daily activities like walking and lifting, and the action of gravity pulling down on the musculoskeletal system. When that loading is removed due to weightlessness and near zero gravity in space, these tissues begin to degrade. The most dramatic example is the atrophy of muscle and demineralization of bones that occurs during spaceflight.

"This muscle and bone loss are reversed when the astronauts return to Earth. What is interesting about cartilage is that it's a tissue that repairs very poorly. This raises the important question of whether cartilage also degrades in space. You may have some payload specialists and experienced pilots who already have some degree of pre-symptomatic cartilage damage at the time of their flight. Because cartilage in humans doesn't readily repair, the return to Earth could potentially bring long-term health problems."

The study was published in npg Microgravity.