Smart fracture fixation plate system for measuring callus stiffness in distal lateral femur fractures treated with fracture fixation plates

Abstract

Abstract The purpose of this study was to adapt an off-the-shelf lateral femoral fracture plate into a smart fracture plate by implementing our smart fracture plate add-on that measures changes in callus stiffness. The smart fracture plate add-on is comprised of a novel sensor that measures and transmits load wirelessly and a mechanical amplifier that attaches to the plate and converts the bending of the fracture plate into a transverse load that is then applied to the sensor. The bending of the plate is directly related to callus stiffness which is a biomechanical indicator of fracture healing progress. The sensor can be read wirelessly to determine changes in callus stiffness as an indication of healing progression. In this study, we used analytical and computational models of the fracture plate, mechanical amplifier, and sensor to design and optimize the smart fracture plate system design for improved sensitivity to callus stiffness changes. These models were the corroborated with in vitro experimental testing. The mechanical amplifier design was optimized to maximize its sensitivity to changes in callus stiffness. The optimal combination of parameters was corroborated by an analytical model, computational model, and by experimental testing. The optimization of the force concentrator allowed the smart fracture plate system the ability to distinguish between phases of fracture healing under axial loads as low as 100 N or less than 15% body weight. By measuring callus stiffness, the smart fracture plate add-on has the ability to distinguish between phases of healing and determine progression towards union or non-union. Early detection of progression towards non-union can also help prevent premature weight bearing which often causes catastrophic failure of the fixator. Current clinical methods of assessment are insufficient and other researched systems for measuring callus stiffness are not clinically viable. The smart fracture plate add-on is designed to be clinically viable by being able to adapt off-the-shelf fracture plates into “smart” plates. Throughout the healing process, using the smart fracture plate add-on allows for the collection of unique clinical data to improve the patient’s course of care. Tracking and recognizing the trends of a patient’s healing progress early would allow the surgeon to adjust treatment and therapy and quickly and clearly see the effects in data collected at subsequent visits. The ability to objectively define healing progression has the potential to personalize post-operative care, optimize time to patient return to normal activity, prevent failures due to non-union, reduce healthcare costs, and promote better patient recovery and outcomes.