*Biomechanical Basis of Bone Fracture and Fracture Osteosynthesis in Small Animals DOI: http://dx.doi.org/10.5772/intechopen.112777*

stress concentration in this example is due to the evidence that the modulus of a material determines its response to an applied force: with high moduli materials, the strain or deformation is inferior to low moduli materials for equal load. As a consequence of that difference in modulus values, the flow of homogenous force is interrupted causing stress concentration. Frequently, clinical cases are reported in bone areas at the limits of the joint prosthesis or stainless-steel bone plating. As the materials are loaded, the bone exhibits greater elastic deformation, creating shear stress at the bone-implant interface [9].

## *3.1.5 Tension*

Tensile loading of bone results when equal and opposite loads are applied away from each other outward from the bone's surface and along its longitudinal axis, as a result of supraphysiological stress, causing the fracture line to be orientated on a plane perpendicular to the axis of loading (**Figure 9**). This mode of loading is primarily due to the contraction of muscles or the effects of ligaments and tendons at bone prominences such as tuberosities, tubercles, and trochanters, where a pure tensile loading is exerted over their cross-sectional area. Clinically, fractures with transverse patterns perpendicular to the applied load are predictably produced and often seen at traction of apophyses such as the olecranon process, tuber calcaneus, and tibial tuberosity (**Figure 9**). Fractures of the patella and avulsion fractures of ligamentous insertion are also exampling where tensile forces predominate and cause a transverse fracture. Because cancellous bone is much weaker under tension than cortical bone, fractures occurring due to tensile loading often occur in regions that have more cancellous than cortical bone, such as bone prominences.

## *3.1.6 Torsion*

When a torsional load is applied to a long bone in such a manner that causes it to twist about an axis (usually the long axis of the bone), that results in the generation of shear, tensile, and compressive forces (**Figure 10**). Specifically, the torsion force causes a shear stress that is distributed throughout the bone. As in bending, there is a gradient in the magnitude of loading, proportional to their distance from the central (long) or neutral axis. Under torsional loading, maximal shear stresses are produced on planes perpendicular and parallel to the central axis. Tensile and compressive stresses are distributed perpendicular to each other and on a diagonal plane to the neutral axis (**Figure 10**). The fracture begins along a plane of maximal shear stress orientated parallel to the neutral axis. The fracture then propagates along the plane of maximal tensile stress creating the typical spiral fracture configuration. Clinically, spiral fractures are commonly seen in the narrow diameters of the distal tibial and distal humeral diaphysis, where the area moment of inertia is relatively small (thus the resultant shear strain from torsional stress is relatively high).
