Time-elapsed synchrotron-light microstructural imaging of femoral neck fracture

Time-elapsed micro-computed-tomography (μCT) imaging allows studying bone micromechanics. However, no study has yet performed time-elapsed μCT imaging of human femoral neck fractures. We developed a protocol for time-elapsed synchrotron μCT imaging of the microstructure in the entire proximal femur, while inducing clinically-relevant femoral neck fractures. Three human cadaver femora (females, age: 75-80 years) were used. The specimen-specific force to be applied at each load step was based on the specimens' strength estimated a priori using finite-element analysis of clinical CT images. A radio-transparent compressive stage was designed for loading the specimens while recording the applied load during synchrotron μCT scanning. The total μCT scanning field of view was 146 mm wide and 131 mm high, at 29.81 µm isotropic pixel size. Specimens were first scanned unloaded, then under incremental load steps, each equal to 25% of the estimated specimens' strength, and ultimately after fracture. Fracture occurred after 4-5 time-elapsed load steps, displaying sub-capital fracturing of the femoral neck, in agreement with finite-element predictions. Time-elapsed μCT images, co-registered to those of the intact specimen, displayed the proximal femur microstructure under progressive deformation up to fracture. The images showed (1) a spatially heterogeneous deformation localized in the proximal femoral head; (2) a predominantly elastic recovery, after load removal, of the diaphyseal and trochanteric regions and; (3) post-fracture residual displacements, mainly localized in the fractured region. The time-elapsed μCT imaging protocol developed and the high resolution images generated, made publicly available, may spur further research into human femur micromechanics and fracture.