Monitoring fracture healing using digital radiographies

Abstract

Non-invasive imaging of fracture healing is a crucial step in making clinical decisions for optimal outcomes and minimizing risks of fixator removal. Although orthogonal routine radiography remains the most cost effective imaging technique to follow all aspects of fracture healing, it is not reliable to predict bony union or the quality or quantity of the regenerating bone, since an estimated 40% increase in radiodensity is needed to visualize a radiological change, and radiographic changes do not always correlate to mechanical stiffness. Supplemental techniques, including digital radiography, mechanical testing for bone strength and stiffness, dual-energy X-ray absorptiometry (DXA) for bone mineral density (BMD), quantitative computed tomography (QCT) for density and cortical continuity, ultrasound for cyst detection and Doppler or angiography for assessing local blood flow and vascularity, have all been used clinically. Among the methods, digital radiography is a useful, cost-effective and relatively accurate means in the evaluation of new bone formation with time during fracture healing. In animal models of fracture healing, histological data, not the mechanical stiffness of the fracture, showed a positive correlation with the digital radiographic assessment data (relative bone density).The advantages of using digital radiography are the minimal expense and dynamic observation of the healing process through sequential radiographies. The bone-healing qualities can be assessed through the estimated relative bone (mineral) density using phantoms. There is a burning need for a quantitative measure of fracture healing in long bone fractures treated by intramedullary nailing. As there is no prospect of a mechanical measure due to the load-sharing design of the fracture/nail construct, radiological imaging has to be the starting point. After normalization, calibration and registration of serial images, a combination of functional images are be used to monitor the changing mineral content of the tissues in and around the fracture; however, due to its 2D nature, the digital radiographies need to be taken in a standard fashion to allow sequential comparison, and it should be used as a complementary, rather than an absolute, measurement for fracture healing. © 2007 Springer-Verlag Berlin Heidelberg.