Abstract

Ultrasound assessments of lower extremity joint structures from astronauts after 18 days on board the International Space Station

Author(s): Richard T Meehan MD 1*, Smarika Sapkota MD2, Eric D Hoffman MSE 3 , James L Crooks PhD4 ,Elizabeth A Regan MD, PhD5

The purpose of this observational pilot study was to determine how various lower extremity joint structures are affected by space flight and microgravity conditions on board the International Space Station (ISS) where the normal terrestrial cyclic compressive loading is absent.

Methods: This study compared pre- and post-flight mean results obtained from three Axiom-4 Astronauts in 2025 after spending 18 days onboard the International Space Station (ISS). Quantitative musculoskeletal ultrasound measurements were performed using GE LOGIQTM e system with a 12-LRS probe to assess 12 anatomic regions including bilateral hips, knees, and ankles. More specifically, we assessed the amount of synovial fluid in the knees (with and without external pneumatic compression), cartilage depths of hips, femoral condyle and talus cartilage. Infrapatellar ligaments and achilles tendon thicknesses were measured in longitudinal and transverse views. The Radiant DICOM Viewer program linear measurement tool, was used to quantitate measured distances of the identical structures post-flight compared to pre-flight values. Power Doppler Imaging signal (PDI) was used to detect any evidence of joint capsule inflammation suggested by increased blood flow in the hips, knees, and ankles as well as the distal insertion sites of the infrapatellar ligaments and achilles tendons.

Results: No statistically significant differences were observed between pre- and post-flight measurements after this short duration low earth orbital mission. However, each crew member performed between 3 and 4.5 total hours of cycling exercise while on board the ISS. We did not detect any abnormal increases in blood flow signals using PDI and therefore we detected no evidence of active inflammation in the synovium of the hips, knees or ankles or the distal insertion sites of the infrapatellar ligaments or achilles tendons either pre-flight or post-flight.

Conclusions: Statistical differences in ultrasound measured lower extremity joint structures were not observed which may be explained by the short duration of the space mission and/or the effects of ingested NSAIDS and/or the compressive loading exercises all crew members performed while on board the ISS. We believe however, that non-invasive quantitative real-time ultrasound assessments hold promise as a precision medicine instrument to assess cartilage and joint structure health on longer duration missions. This information could hopefully optimize the exercise protocols of compressive loading needed to preserve healthy joints and therefore reduce injury upon returning to Earth or while performing activities on the Lunar or Martian surfaces.