Biomechanical evaluation of early fracture healing in normal and diabetic rats

Diabetes mellitus has been shown to alter the properties of bone and impair fracture healing in both humans and animals. The objective of this study was to document changes in the structural and material properties of intact bone and bone with healed fractures in diabetic rats compared with nondiabetic controls after 3 and 4 weeks of healing. Rods were inserted in the right femurs of control rats and rats with streptozotocin-induced diabetes, and the femurs were fractured in a standardized procedure and then allowed to heal for 3 and 4 weeks. After death, all femurs were mechanically tested to failure in torsion. The degree of healing was quantified for each animal by normalizing mechanical parameters for the femur with a healed fracture with those for the intact contralateral femur. At both time points of healing, diabetic rats exhibited inferior healing compared with that of control animals in terms of failure torque, failure stress, structural stiffness, and material stiffness of the femur with the healed fracture relative to the intact contralateral femur (p < 0.05). Our results demonstrate that the recovery of structural and material strength in femurs with healed fractures in diabetic rats is delayed by at least 1 week compared with that in controls.