[Changes in bone strength during convalescence after immobilization induces bone loss--experiment with adult rats]

The aim of the present study was to evaluate the impact of a hindlimb immobilization on mechanical properties of mature bone, both cancellous and cortical tissue. The effectiveness of bone recovery during free activity after remobilization was also studied. The right hindlimb of mature 24 weeks old male rats was immobilized for three weeks. Femora and proximal tibiae methaphyses as well as the straight muscle of thigh were investigated post mortem just after immobilization period or four weeks after remobilization. Mass of the muscle, mass, density and mineralization of bones as well as mechanical properties in axial compression (tibiae metaphyses) or in three-point bending (femora) were measured. After immobilization all parameters were significantly lower in immobilized tibia than in the left, loaded and in respect to the right tibia in the control group. In femur a decrease of dry mass was observed, without any change of breaking force and work to fracture. After four weeks of convalescence, a significant worsening of mechanical competence of femur, and no recovery in tibia was stated. The results obtained indicate that a restoration of mobility without any additional rehabilitation is not enough to stop the processes of bone deterioration induced by unloading in mature bone.