Biomechanical investigation of monolateral external fixator configurations during bone lengthening treatment

The topic below concerns the biomechanical investigation of different configurations of the Rekrea, a monolateral external fixator for bone lengthening treatments developed and commercialized by Citieffe s.r.l. The first part of the paper introduces the clinical scenario, the processes that stimulate bone lengthening, the state of the art of these surgical procedures, the different stages into which they are performed and the complications that can occur. In particular, the present work focuses on tibial lengthening thus the geometry of the bone and the related joints at the extremities are described. It emerged how during this treatment it is particularly important to monitor the inter-fragmentary movement between the two stumps, the global displacement between the ankle and the knee joints as well as the stiffness of the entire system. Several biomechanical tests are done in order to understand how different configurations of the setup affect the values of the parameters of interest: interfragmentary movement, global displacement and stiffness of the entire system. Different angles of insertion of the bone screws respect to the tibial axis, different thickness of the bone callus placed in the fracture site and different number of bone screws through which the fixator is anchored to the bone are investigated. Data collected from the tests are analysed in order to compute the parameters of interests, to do so appropriate Matlab code was written. Later, statistical tests were done to understand if the configurations in each couple of comparison were statistically different from one another. The limits of each setup were analysed. This data will be available for other researches. Finally, the conclusions reveal the salient features of the comparisons between the different configurations; it is also pointed out which ones are efficient in terms of performance and are in agreement with the parameter values reported in the literature.