JEFFREY ANKER, Ph.D.
Assistant Professor of Chemistry
Bone healing and maintenance is a consequence of proper fixation and there is a critical need to monitor strain in orthopedic screws in order to detect loosening early. Orthopedic screws apply stress and fix the position of implanted orthopedic devices such as fracture fixators and spinal grafts. Bone healing is accompanied by increased rigidity, while loosening is a major cause of implant failure. Loosening is often an indication of infection on the device surface, which is difficult to eradicate if not treated early and usually requires device removal with risk of mortality and morbidity from surgery and prolonged hospitalization. Approximately half of infections acquired in hospitals are associated with implanted or indwelling devices (one million in 2004) and of the two million fracture fixators implanted annually in the US, 5-10% become infected, and 40% for soldiers due to debris in blast injuries. Loosening is most commonly determined by radiography and is characterized by displacement of the screw in a time series of X-ray images or dark lines surrounding the screw due to bone degradation. However, these results are difficult to quantify, especially at early stages, and the X-ray images are ill-suited for studying dynamic motion. The objective of this pilot project is to provide the preliminary results and instrumentation to demonstrate that in situ changes in strain and spectrum can be monitored noninvasively through tissue. Optical tension-indicating bolts have been described in the patent literature since the 1970s; the novelty of our approach is that we use upconversion and radioluminescence to provide an essentially background-free near infrared signal that can propagate deeply through tissue for orthopedic applications. We will fabricate tension-indicating luminescent screws by modifying existing orthopedic screws. We will then characterize the modified screws both mechanically and optically. We will measure implant loosening after repeated strain cycling in bone mimics and ex vivo bovine bone. This pilot project will enable us to collect data for a future R01 proposal studying implant loosening and biofilm infection in rabbit models. The luminescent tension-indicating screws will enhance our ability to assess mechanical changes in vivo and enable quantitative assessment of implant loosening and bone healing.