Remobilization partially restored the bone mass in a non-growing cancellous bone site following long term immobilization

There is no report in the rat of the effects of remobilization (RM) in an adult bone site. The aim of this study was to determine whether complete recovery from IM-induced bone loss will occur in a non-growing bone site, the distal tibia. Seventy-five 6-month-old virgin Sprague-Dawley female rats were used in this study. Their hindlimbs were immobilized against the abdomen with bandages for 18 weeks, then remobilized for 2, 10 or 20 weeks. Distal tibial sections were analyzed in the former epiphysis, 0.3 mm proximal from the calcified cartilage, and in trabecular bone of the former metaphysis between 0.3 mm and 1.92 mm proximal to the former epiphysis. A significant bone loss occurred in both former epiphyseal and metaphyseal trabeculae at 18 weeks after IM. The lost bone was partially recovered at 10 weeks of RM, but the bone mass was still lower than in aging controls by the end of the study. The partial recovery was characterized by decreasing former epiphyseal bone porosity and thickening of former metaphyseal trabeculae with no effect on trabecular number. We concluded that both distal tibia regions only partially recovered, during 20 weeks of RM from the long time IM.