Fracture Healing Evaluation of Tibia Treated With External Fixator Based on Vibrational Transmissibility: Experimental Assessment

Bone fractures can be the result of ultimate biomechanical stresses, impact, or pathological conditions such as osteoporosis that cause a disruption of bone continuity. The full recovery of the healing process can vary from a few weeks to several months, depending on the patient’s condition and treatment efficacy. Different osteosynthesis devices can be applied for better bone repair. Among them, the use of external fixators is suitable in the case of open fractures and pathological conditions, especially for long bones. The removal of these devices, once bone mechanical properties have been restored to the original values, should occur at an appropriate time. Nowadays, the gold standard for healing evaluation relies on the use of radiographic imaging [x-rays (Rx)] which conveys a certain quantity of ionizing radiation. This technique provides qualitative information about the bone callus state that is then subjected to a specialist interpretation. This work proposes a novel noninvasive measurement method able to avoid the main drawback caused by the use of Rx imaging. In particular, modal testing and vibrational transmissibility measurements have been performed on different long bone configurations, that is, intact, fractured, and glued tibia. The modal analysis demonstrates that the presence of a fracture implies modification in bone stiffness, thus resulting in different modal parameters compared to the intact bone condition. The transmissibility measurement provides information on the considered configuration and bone state. Results show transmissibility values of 0.05 for the fractured tibia, while the healed tibia shows values of 0.18. The healing curve, represented by the time evolution of the transmissibility, points out the increasing trend during the simulation of bone restoration. The identification and application of a proper filter has then provided a better discrimination among the different bone conditions. These results are significant to furnish an objective evaluation of the healing process, allowing the minimization of ionizing radiation to the patient and supporting the orthopedist’s decision for the fixator removal.