A model of cortical window healing in the rabbit

A rabbit femur cortical window model was developed to study the time-dependent mechanical and radiographic changes with various treatments of surgically created windows. In the present experiment the time-dependent differences in torsional whole bone strength between femora treated with window replacement and those treated without replacement were evaluated. The 3.175 mm diameter windows were surgically created with a power trephine at the lateral femoral isthmus unilaterally, with the contralateral femur serving as a paired control. In one group of animals the window was reconstructed by replacement of the excised cortical plug while in the other group the window was left unreplaced. Each group was divided into three subgroups sacrificed at 3, 6, and 9 weeks postoperatively. Lateral radiographs were obtained immediately prior to sacrifice. After sacrifice bilateral femora were harvested and loaded to failure on a torsional testing apparatus to obtain values for ultimate torque, maximum angle of deformation, and energy capacity expressed as percent of paired control. Replacement resulted in significantly greater whole bone strength (P < .041), and strength increased significantly with time (P < .006). Radiographic appearance correlated significantly with both treatment and time, but not strength. The model was sensitive to both treatment-dependent and time-dependent effects, demonstrating potential for evaluation of other cortical window treatments.