Spaceflight leaves astronauts’ joints unchanged after 18 days on ISS, early data suggest

Researchers at National Jewish Health have published new findings demonstrating that short-duration spaceflight may not significantly impact lower extremity joint structures, while also identifying a promising, noninvasive tool to monitor astronaut musculoskeletal health on future long-duration missions.

The study, led by Richard Meehan, MD, and Smarika Sapkota, MD, evaluated three astronauts before and after Axiom Mission 4 (Ax-4), an 18-day mission onboard the International Space Station (ISS). Using advanced musculoskeletal ultrasound imaging, researchers assessed cartilage thickness, synovial fluid levels, and tendon and ligament integrity in the hips, knees, and ankles.

The results, published in the International Journal of Clinical Rheumatology, showed no statistically significant changes in joint structures or evidence of inflammation following the mission. Dr. Sapkota will present the results at the May 2026 Annual Scientific Meeting of the Aerospace Medical Association in Denver.

“This study provides encouraging early evidence that short-duration spaceflight, combined with exercise and medical countermeasures, may help preserve joint health,” said Dr. Meehan, senior author and rheumatologist at National Jewish Health. “Equally important, it demonstrates that ultrasound can serve as a powerful, real-time tool to monitor joint health in space.”

Astronauts in the study engaged in cycling exercise during the mission and used anti-inflammatory medications, both of which may have contributed to maintaining joint health. Researchers observed no significant differences in cartilage thickness across the hips, knees, or ankles, no meaningful overall change in knee synovial fluid levels, and no evidence of inflammation using power Doppler imaging. Tendon and ligament thickness also remained stable before and after spaceflight.

While the findings are reassuring, researchers caution that the study’s short duration and small sample size limit broader conclusions, particularly for longer missions to the moon or Mars, where astronauts may face extended exposure to microgravity.

“Although we did not observe measurable changes after 18 days, longer missions could present very different risks to cartilage and joint structures,” said Dr. Sapkota, co-author and rheumatologist at National Jewish Health. “Our findings highlight the importance of continued research and the potential of ultrasound to guide personalized countermeasures for astronaut health.”

The study is among the first to use quantitative ultrasound immediately following spaceflight to assess multiple joint structures in humans, capturing changes within hours of return to Earth. Researchers believe this approach could play a critical role in future missions by enabling real-time monitoring of joint health, informing personalized exercise protocols, and reducing the risk of injury during and after spaceflight. The implications may extend beyond space exploration, offering potential benefits for patients on Earth, including those recovering from prolonged immobility or facing the risk of joint degeneration.

“This technology has the potential to transform how we monitor and protect joint health, not only for astronauts, but for patients here on Earth,” Dr. Meehan added.

The observational pilot study analyzed pre- and post-flight ultrasound measurements from three astronauts participating in the Ax-4 mission. Imaging was conducted within hours of return to Earth, and the research was supported by National Jewish Health in collaboration with Axiom Space and other partners.

“Leveraging the unique environment of space provides a vital laboratory for developing the next generation of biomedical technologies and medicine for terrestrial use,” explained Emmanuel Hilaire, Ph.D., director of Technology Transfer at National Jewish Health. Dr. Hilaire oversees the commercialization of innovations developed at National Jewish Health and is spearheading a space research initiative to accelerate further biomedical advancements.

Who’s behind this story?

Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

Full profile →