Experimental testing of a DEXA-derived curved beam model of the proximal femur

This study was designed to test whether, using curved beam theory, a structural model of the proximal femur derived from two-dimensional dual energy x-ray absorptiometry could be used to predict femoral strength in an experimental simulation of a fall on the greater trochanter. A set of 22 fresh cadaveric femoral specimens were scanned with use of two-dimensional dual energy x-ray absorptiometry and then were tested to failure in a materials testing system, under three-point loading, with the ground impact vector aligned within the plane and along the bisector of the femoral neck- shaft angle. Failure locations generally corresponded to stress peak locations predicted by the curved beam model. Predicted failure loads correlated well with measured failure loads for femoral neck fractures (r = 0.89; percent SE of estimate = 23%) and somewhat less well for intertrochanteric fractures (r = 0.83; percent SE of estimate = 29%). Overall predictions for failure load calculated from the maximum stress peak value over both locations corresponded to measured failure loads with an r value of 0.91 (percent SE of estimate = 21%). This kind of structural approach to the analysis of data for hip bone mass has the potential to provide mechanistic interpretations of the statistical associations frequently shown between conventional bone mineral measures and either hip fracture risk in vivo or bone strength in vitro.