Comparison of two different fixation techniques for a segmental defect in a rat femur model.

Studies have attempted to identify the osteogenic effects of bone morphogenetic proteins using a rat femur model, which commonly involves the creation of a critical size defect followed by internal fixation of the femur. Among the most familiar fixation methods are either plating or intramedullary placement of a Kirschner wire (K-wire). There are advantages and disadvantages to each method; however, this study attempts to identify the best method by exploring the histological effects of each technique. The experiment involved two groups with no added treatment: Group P (plate fixation method) and Group K (K-wire fixation method). The animals were allowed a 4-week interval for the femurs to heal, and proximal, distal, and two midshaft cuts were examined under high-power microscopy after the fixation apparatus was removed. Group K exhibited a peculiar fibrotic healing pattern that followed the shaft of the then vacated K-wire and there was minimal new viable bone formation. Group P, however, exhibited a more natural ingrowth of newly formed bone that began at the proximal and distal cuts and proceeded centrally into the core of the defect. Due to the fibrotic tissue in Group K, this study shows that the model is insufficient due to the micromotion created and thus supports plating of critical defects as the fixation method of choice due to the creation of a stable healing environment.