Unlike failure in tension, however, the fracture does not always proceed along the theoretic plane perpendicular to maximum stress, but will generally propagate obliquely across osteons. Compression fractures are common in vertebral body fractures, and may occasionally occur in long bones particularly at the growth plates of young dogs. Oblique L6 Fracture in an adult dog caused by compression 3. While tensile and compressive forces act perpendicular to a bone's cross-sectional surface, shear forces act parallel to the surface and tend to cause angular deformity. Deformation or strain under shear stress would cause a rectangle to assume a parallelogram shape rather than elongate or compress.
Bone is strongest when loaded in compression, then tension, and least under shear stress.
This helps explain why compression fractures are relatively uncommon and even when they occur they may propagate along the lines of shear stress generated during loading and failure. It also explains why fractures caused by shear stress often occur with minor trauma. Lateral humeral condylar fracture in a four month old Cocker Spaniel 4. Bending When bending forces are applied to a bone, tensile forces are generated on the convex surface and compressive forces are generated on the concave side. A continuous gradient of stress distribution from tension to compression exists through the bone's cross section.