Is there a mechanical difference between lag screws and double cerclage?

Abstract

Comminuted fractures of the long bones present problems of mechanical instability. We therefore used a plate and six screws as the main osteosynthesis combined with supplementary lag screws or cerclage wire. These two supplementary methods were compared. As a model, we used 60 plastic tibias with standard midshaft butterfly fractures. These models, depending on the osteosynthesis applied for the fixation of the butterfly onto the main fracture, were split into three groups of 20 bones. Group A1 with two lag screws, group A2 with two lag screws and two double cerclages, and group A3 with two double cerclages with no lag screws. The models were tested in torque and axial load. The results were: 1. In torque, group A1 was the most unstable with significant statistical difference from group A2 (P less than 0.01) and from A3 (P less than 0.05). There was no significant statistical difference between groups A2 and A3. 2. In axial load, group A3 was stable with significant statistical difference from A2 (P less than 0.05). There was no difference between A1 and A3. The experiment showed that if the cerclage is used double, anchored at the end of the screws and tensioned, it acts like a spring and is mechanically more stable than lag screws in torque. In axial load, no mechanical difference exists between lag screws and double cerclage.