How bones break under different loads
(with examples from the distal radius/ulna):
Types of loading: Structures, i.e. bones, can be loaded to failure in the following 5 ways.
Tension Compression Shear Bending Torsion
Failure with tension: Bone that is loaded in tension fails transversely to the direction the tensile load is applied. This is because the hydroxyapatite is weak in tension and so the collagen (which supplies bone’s tensile strength) ruptures across, much like a rope does. Usually tension failure occurs when bone is “avulsed” by strong ligaments or tendons, as in the example, where the ulnar styloid is pulled off.
Failure with shear: Bone that is loaded in shear fails along a plane parallel to the shear load.