Age and ovariectomy impair both the normalization of mechanical propertiesand the accretion of mineral by the fracture callus in rats

The impact of age and ovariectomy on the healing of femoral fractures was s tudied in three groups of female rats at 8, 32 and 50 weeks of age at fract ure. In the two older groups, the rats had been subjected to ovariectomy or sham surgery at random at 26 weeks of age. At fracture, all rats received unilateral intramedullary pinning of one femur and a middiaphyseal fracture . Rigidity and breaking load of the femora were evaluated at varying times up to 24 weeks after fracture induction by three-point bending to Failure. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry . In the youngest group, 8-week-old female rats regained normal femoral rig idity and breaking load by 4 weeks after fracture. They exceeded normal con tralateral values by 8 weeks after fracture. In the middle group, at 32 wee ks of age, fractures were induced, and the femora were harvested at 6 and 1 2 weeks after fracture. At 6 weeks after fracture there was partial restora tion of rigidity and breaking load. At 12 weeks after fracture, only the sh am-operated rats had regained normal biomechanical values in their fracture d femora, while the fractured femora of the ovariectomized rats remained si gnificantly lower in both rigidity and breaking load. In contrast, for the oldest group of rats, 50 weeks old at fracture, neither sham-operated nor o variectomized rats regained normal rigidity or breaking load in their fract ured femora within the 24 weeks in which they were studied. In all fracture d bones, there was a significant increase in BMD over the contralateral int act femora due to the increased bone tissue and bone mineral in the fractur e callus. Ovariectomy significantly reduced the BMD of the intact femora an d also reduced the gain in BMD by the fractured femora. In conclusion. age and ovariectomy significantly impair the process of fracture healing in fem ale rats as judged by measurements of rigidity and breaking load in three-p oint bending and by accretion of mineral into the fracture callus. (C) 2001 Orthopaedic Research Society. Published by Elsevier Science Ltd. All right s reserved.