title: Spaceflight alters bone mechanics and modeling drifts in growing rats.
abstract: BACKGROUND
  Alterations in bone metabolism may be a particularly serious consequence of spaceflight and a major obstacle to long-term space exploration. The effects of spaceflight on bone mechanics are unclear. This study examined the effects of spaceflight on bone mechanics in a growing rat model during a 17-d mission aboard the space shuttle (STS-78).
  
  
  METHODS
  There were 18 rats that were divided into 3 experimental groups: flight rats (n = 6), ground-based control rats housed in an animal enclosure module (AEM, n = 6), and ground-based control rats housed in standard vivarium caging (n = 6). At the conclusion of the mission, rat femurs were tested in three-point bending followed by static and dynamic bone histomorphometry.
  
  
  RESULTS
  Maximum stress was unaffected by spaceflight, but flexural rigidity was significantly decreased in flight animals. Much of the decrease appeared to be the result of decreases in tissue properties (elastic modulus) rather than structural changes within the bone. No significant differences in cortical bone mass or geometry were observed. In contrast, endocortical resorption was significantly decreased in flight rats accompanied by a nonsignificant decrease in periosteal bone formation, suggesting alterations in bone modeling drifts during spaceflight. For nearly all measured indices, ground-based AEM rats displayed values intermediate to flight and ground-based vivarium rats.
  
  
  CONCLUSIONS
  Spaceflight can impair tissue properties in femoral cortical bone during growth without significant decreases in bone mass or geometry.
authors.affiliation: Department of Veterans Affairs Medical Center, Salt Lake City, UT, USA.
authors.forename: E G
authors.initials: EG
authors.lastname: Vajda
authors.forename: T J
authors.initials: TJ
authors.lastname: Wronski
authors.forename: B P
authors.initials: BP
authors.lastname: Halloran
authors.forename: K N
authors.initials: KN
authors.lastname: Bachus
authors.forename: S C
authors.initials: SC
authors.lastname: Miller
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology; D001842:Bone and Bones / Q000033:anatomy & histology / Q000502:physiology*; D005269:Femur / Q000033:anatomy & histology / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013026:Space Flight; D016474:Weight-Bearing; D014893:Weightlessness / Q000009:adverse effects*