A simple murine model for immobilization osteopenia.

Reduction of loading force to bone induces osteopenia. Although the tail suspension model is the frequently used osteopenia model, this model burdens the animals with nonphysiologic blood distribution and systemic stress. We developed a new simple animal model for osteopenia under reduced loading. Both hind legs of male ICR mice (8 weeks old) in the experimental group were inserted into plastic tubes, which then were connected with wires of three sizes. This apparatus completely immobilized both femurs while allowing the tibias to move. Animals were pair-fed and sacrificed on Days 3, 7, 10, and 14 after immobilization. Bone mineral density measurement with dual energy xray absorptiometry revealed bone loss in the immobilized femurs. Histomorphometric analysis showed increased bone resorption and decreased bone formation, which started from Day 7 and continued until Day 14, resulting in structural disorders in the cancellous bone. Osteoclast population increase before osteoblast population decrease revealed that osteoclasts initially affect the process of this type of osteopenia. Our immobilization model is simple, easy to use, well-tolerated by the animal, and has potential for evaluating the therapeutic effects of drugs to treat osteopenia caused by reduced loading.