[Mechanical borderline indications in the treatment of unreamed tibial nailing].

The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. The goal was to gain a thorough understanding of the load-sharing mechanism between unreamed nail and bone in a fractured tibia, and to identify borderline indications due to biomechanical factors. In finite element analyses of a human tibia, horizontal defects were modeled using unreamed nailing for five different fracture locations, including proximal and distal borderline indications for this treatment method. The findings of this study show that with all muscle and joint contact forces included, nailing leads to considerable unloading of the interlocked bone segments. Unreamed nailing of the distal defect results in an extremely low axial and high shear strain between the fragments. Apart from biological reasons, clinical problems reported for distal fractures may be due to the less favorable mechanical conditions in unreamed nailing. From a biomechanical perspective, the treatment of distal tibial shaft fractures with unreamed nailing without additional fragment contact or without stabilizing the fibula should be carefully reconsidered.