Strontium is incorporated into the fracture callus but does not influence the mechanical strength of healing rat fractures

Strontium ranelate (SrR) is a new agent used in the treatment of osteoporosis and is suggested to reduce bone resorption and increase bone formation. We investigated whether SrR influences the macro-and nanomechnical properties of healing fractures in rats. A closed tibia fracture model was used to study fracture healing in rats after 3 and 8 weeks of healing. Two groups of rats were treated with SrR (900 mg/kg/day) mixed into the food, while two groups served as control animals. The healing fractures were investigated by three-point bending, dual energy X-ray absorptiometry, energy-dispersive X-ray spectroscopy (EDX), and nanoindentation. There was a 100-fold increase (P< 0.001) in serum Sr after 3 and 8 weeks of SrR treatment. The callus volume was significantly higher in the SrR-treated group than in control animals (P< 0.01) after 3 weeks of healing. This was accompanied by a significant increase in callus bone mineral content (P < 0.05). However, after 8 weeks of healing, no difference was found in either callus volume or bone mineral content. SrR did not influence maximum load or stiffness of the fractures after either 3 or 8 weeks of healing. EDX showed that Sr was incorporated into the callus; however, this did not influence the nanomechanical properties. In conclusion, SrR stimulates callus formation but has no effect on callus remodeling. Sr is incorporated into the newly formed callus tissue, but this has no deteriorating effect on the mechanical properties of rat tibial fractures at either the macroscopic or nanoscopic level after 3 or 8 weeks of healing.