A series of 33 human femoral bones have been subjected to a four point bending test at high strain rates. Two different failure modes were recognized. A Y shaped fracture at the middle region induced by a pure bending moment yielded a zone of non-linearity at the load vs deformation curve and a higher bending force, more deformation of the structure and higher strain energy to fracture compared with the less frequently occurring oblique fracture at the distal third of the structure resulting in a failure without a ‘plastic’ portion at the load-deformation curve.

Estimated values of bending modulus and maximum bending moment based upon a simple uniform beam model showed high correlation coefficients with the experimentally determined values. Scanning electron microscopic examination of the Y fracture showed distortion and void formation of the material at the structural level. This could explain the extensive non-elastic deformation prior to failure.