Reduced energy absorption of healed fracture in the rat

Mechanical testing of closed tibial fractures in rat fixed with a medullary nail was performed after 10-80 days of healing. In the three-point bending test, the maximum load at fracture and maximum stiffness of the fracture gradually increased, reaching 81 and 118 percent, respectively, of intact bone values after 80 days. The fracture failed immediately after the maximum load had been reached in contrast to intact bone, where further bending resulted in gradually decreasing load values until failure occurred at 73-85 percent of the maximum load values. Therefore, the resulting energy absorption until load at fracture and until failure of the healing bone was only 33 and 13 percent, respectively, of intact values after 80 days of healing, and thus markedly reduced even though the maximum stiffness and the load at fracture (maximum load) approximated the values of intact bone.