The X-VISUAL (X-ray Visualized Indicator for Screw-strain Under Applied Load)

ABSTRACT We are developing and sensor, the X-VISUAL (X-ray Visualized Indicator for Screw bending Under Applied Load), to track fracture healing in canulated screws used to treat hip fractures. Hip fractures are a major public health concern with high in-hospital mortality rate. Approximately 330,000 hip fixation procedures are performed annually in the US. The average hip fixation hardware failure rate is around 5%, but increases to over 20% in patients with comorbidities such as osteoporosis, unstable fractures and poor initial fracture reduction. When healing is delayed, the screw, other hardware, and bone can fatigue and fail, requiring costly revision surgery with significant risk of morbidity and mortality for these frail patients. For example, the 1-year all-cause mortality rate for patients readmitted within 30 days of surgery is 56%, compared to 19% for those not readmitted. Screws only bend and cutout when they are loaded, and this risk disappears as a fracture callus heals and carries the load. Thus, measuring screw bending under standing load is an ideal way to assess fracture healing and risk failure. This improves communications with the patient and care team, enabling normally healing patients and physical therapists to feel more comfortable with activity, while detecting and avoiding pathologies for slowly healing patients. Innovatively, the X-VISUAL is the first sensor that can detect screw bending (and associated load on the screw), a measurement that is hard to perform in other ways because of the confined geometry. The patent protected device is designed to load into a screw after guidewire removal, and is read using plain radiography which is ubiquitously available in healthcare facilities but is usually insensitive to mechanical strain and usually detects pathologies when they have progressed so far that non-surgical interventions often don’t work. Using previous designs we demonstrated proof of concept for measuring screw bending with X-rays in Sawbones specimens, FEA models, cadaveric specimens, and tracked healing in a sheep. However, the old designs were cumbersome to insert and read, thus this Phase I proposal designs an elegant addon with a gain mechanism and readout on indicator along the pin. We will develop and test the design in FEA computational models, sawbones, and cadaveric specimens. The clinical, industry, and academic partners assembled for this work have a strong history of collaboration in orthopaedic device development and testing. They bring together expertise in measurement systems, mechanical testing, medical device design and orthopaedic surgery. The research is relevant to public health because, it provides a non-invasive means of assessing biomechanical reduction and postop fracture healing to avoid costly and risky revisions.