Spaceflight Results in Formation of Defective Bone

Growing rats were flown on 19 day spaceflights aboard Cosmos 782 and 936 biosatellites. Spaceflight resulted in a prominent skeletal defect at the periosteal surface of the tibia diaphysis. The defect, termed an arrest line, was approximately 3 μm across and separated the bone formed in space from that formed following spaceflight. The bone matrix at the arrest line region was abnormal in that collagen fibers were preferentially orientated parallel to the periosteal surface. In addition, the bone matrix was hypomineralized. The altered bone was inferior to normal bone in resistance to abrasion and may be partially responsible for the decrease in torsiona strength observed after spaceflight.