A Novel Method for Determining the Time and Location of Abrupt Fracture Initiation in Bones

Investigation of bone failure is extremely important in orthopaedic biomechanics to reduce the risk of fracture in diseased and operated patients. Identification of the point where fracture starts would be extremely valuable to better understand bone mechanics. However, as abrupt fractures of bones occur in milliseconds, most in vitro studies report the failure load, but cannot localize the point of fracture initiation. Commercially available grid-based or foil crack gauges cannot be applied to the complex double-curvature geometry of bones. In this paper a method is proposed for preparing a fine conductive crack-grid on the bone surface, combined with a dedicated data logger. The proposed system offers a spatial resolution of 0.5—2.0 mm, and a sampling rate of 700 kHz. Suitability of the crack-grid to withstand bone strains prior to failure was checked. A preliminary application on bone specimens confirmed that: (a) preparation of the crack-grid on the bone surface is possible; (b) accurate and consistent results are obtained that enable identification of the fracture initiation point; (c) this method is sensitive to differences in crack propagation rate, depending on alignment with respect to the tissue structure, and on quality of the bone tissue. The applicability and accuracy of this method was finally shown on a real femur, which was tested while a high-speed camera and the proposed crack-grid simultaneously recorded abrupt fracture. The proposed system will provide new insights into fracture mechanics of bone structures (including abrupt fractures).