I-Corps: Integrated Strain Sensor for Dynamic Hip Screws

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The broader impact/commercial potential of this I-Corps project stems from the potential of the technology to address a key clinical gap hip fracture treatment. Intertrochanteric hip fractures are common among elderly patients, affecting their mobility and quality of life. They are routinely treated with a dynamic hip screw (DHS) consisting of a titanium plate and cannulated lag screw that hold the fractured ball of the hip onto the rest of the femur so that the fracture can heal. Like most implants for fracture fixation, the DHS is not designed for long-term load bearing. If a patient's fracture does not heal after surgery, then the DHS or bone will fatigue and fail, requiring revision surgery. This leaves clinicians in a difficult position, as they must carefully monitor their patients for signs of implant failure after surgery. However, by the time signs of failure are apparent, it is often too late to salvage the implant, and a revision surgery is necessary. This device can provide a way to quantitively track fracture healing, enabling physicians and patients to alter rehabilitation protocols and add adjunctive therapies to avoid morbidity and mortality associated with catastrophic implant failure.This I-Corps project focuses on a novel device to help physicians manage hip fracture rehabilitation. The envisioned device is unique in that it can be seamlessly integrated into existing dynamic hip screw (DHS) systems and is read using plain radiography, which is already acquired during follow-up visits but is not quantitative or sensitive enough for tracking fracture stiffness without this sensor. Specifically, the device measures screw bending during weight bearing: immediately after fixation, the screw holds the femur together, carries the full load, and bends significantly under load. However, as the fracture heals and the surrounding bone carries more load, and the screw bends proportionately less. Although the degree of bending is too small to accurately measure from traditional radiographs, this device uses a straight radio-dense tungsten rod through the hollow part of the screw to clearly highlight displacement. Preliminary results have shown proof-of-principle in computer simulations, cadaveric specimens, and a sheep study. Measuring fracture stiffness is important because if the fracture heals too slowly, the implant or bone will fatigue and fail, requiring costly and risky revision surgery.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.