Mechanical boundary conditions of fracture healing: borderline indicationsin the treatment of unreamed tibial nailing

Unreamed nailing favors biology at the expense of the achievable mechanical stability. It is therefore of interest to define the limits of the clinica l indications for this method. The extended usage of unreamed tibial nailin g resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. The goals of this work were to gain a tho rough understanding of the load-sharing mechanism between unreamed nail and bone in a fractured tibia, to identify the mechanical reasons for the unfa vorable clinical results, and to identify borderline indications due to bio mechanical factors. In a three-dimensional finite element model of a human tibial horizontal defects were stabilized by means of unreamed nailing for five different fracture locations, including proximal and distal borderline indications for this treatment method. The loading of the bone, the loadin g of the implant and the interfragmentary strains were computed. The findin gs of this study show that with all muscle and joint contact forces include d, nailing leads to considerable unloading of the interlocked bone segments . Unreamed nailing of the distal defect results in an extremely low axial a nd high shear strain between the fragments. The results suggest that mechan ical conditions are advantageous to unreamed nailing of proximal and mid-di aphyseal defects. Apart from biological reasons, clinical problems reported for distal fractures may be due to the less favorable mechanical condition s in unreamed nailing. From a biomechanical perspective, the treatment of d istal tibial shaft fractures by means of unreamed nailing without additiona l fragment contact or without stabilizing the fibula should be carefully re considered, (C) 2001 Elsevier Science Ltd. All rights reserved.