Fracture Healing Assessment Based on Impact Testing: In Vitro Simulation and Monitoring of the Healing Process of a Tibial Fracture with External Fixator

In clinical practice, bone healing is monitored with X-rays and manipulation. Its assessment is thus subjective, depending on the skills of the operator. Alternative and quantitative approaches have been proposed, generally based on the estimation of bone stiffness, which is known to increase with the healing process. The present study investigates the application of experimental modal analysis to fracture healing assessment focusing on fractures treated with an external fixator. The aim is to ascertain the capability of this approach to detect changes in the bone-callus stiffness as variations in the resonant frequencies despite the presence of the fixator, which might hide the bone response. In vitro tests were performed on a tibia phantom where the healing process was simulated creating three different types of callus surrogates, using glue and resin. The resonant frequencies of the phantom with screwed pins and of the phantom with the complete fixator were estimated. Results confirm an increase in the frequencies as the simulated bone-callus stiffness increases, encouraging the application of experimental modal analysis to fracture healing monitoring. This approach can offer remarkable advantages with respect to the actual standards: being non-invasive and quantitative, it would allow a more frequent healing monitoring