Introduction: The unilateral external fixator has become a quick and easy application for fracture stabilization of the extremities; the main value for evaluation of mechanical stability of the external fixator is stiffness. The stiffness property of the external fixator affects the local biomechanical environment of fractured bone. Methods: In this study, a theoretical model with changing Young's modulus of the callus is established by using the Castigliano's theory, investigating compression stiffness, torsional stiffness and bending stiffness of the fixator-bone system during the healing process. The effects of pin deviation angle on three stiffness methods are also investigated. In addition, finite element simulation is discussed regarding the stress distribution between the fixator and bone. Results: The results reveal the three stiffness evaluation methods are similar for the fixator-bone system. Finite element simulation shows that with increased healing time, the transmission of the load between the fixator and bone are different. In addition, the finite element analyses verify the conclusions obtained from the theoretical model. Conclusions: This work helps orthopedic doctors to monitor the progression of fracture healing and determine the appropriate time for removal of a fixation device and provide important theoretical methodology.

Introduction: Unilateral external fixators are widely used in orthopedics to stabilize fractured bones and to treat limb deformities. One of the main problems is that it is difficult to detect healing status. In addition, whether load transfer progress between the fixator and bone model are the same under axial, torsional, and bending loads has not been studied. Methods: Therefore the main purpose of this study was to detect the load transfer process between the fixator and a bone model by measuring strains on the fixator-bone system during four healing states using experimental and finite element methods. In the experimental method, 20 strain gauges were used to measure strain on the fixator and bone model under three load conditions. Polyacetal slice models with different material properties were used to simulate the callus model during four growth states. Results:The results indicate that strain on the bone model increased and strain on the fixator parts decreased with maturation of the callus under axial, bending, and torsional loads. Although all curves showed a similar changing trend, they were slightly different under the three loads. Discussion and conclusions:This study provides a useful method to monitor the fracture healing process, and identifies the healing endpoint, detects healing status, and provides useful information for the orthopedist.

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Steel cable plays an important role in modern infrastructure due to its special characteristics. Because most of structure load is transformed to the cable tension in cable stayed structures, it is very important to monitor cable tension. Being a slender element, Fiber Grating Strain Sensor is sensitive to axial strain and is regarded as a most prospective way to monitor the cable tension. The paper reviews a series of problems of FBG when embedded into the cable, and introduced five different embedded FBG strain sensors. Principle, characteristics, and application states of these five sensor has been discussed in details. The prospective of embedded FBG Strain Sensor for cable tension has been forecast.

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