**2.10 Wolff's law**

Bone is a dynamic tissue, and the response to internal and external mechanical stimuli can determine bone density and the organization of bone trabeculae and correlate with the magnitude and direction of compressive and tensile stresses of loading. In the late nineteenth century (1892), Wolff's law was proposed by Julius Wolff, a German anatomist and surgeon, as a mathematical law that described the response of bone to mechanical loading. This law described the functional adaptation of bone to mechanical loading and is supported by several experimental and comparative studies over time. Increases in the loading of bone tissue are known to generate the formation of new bone tissue, which increases mechanical rigidity [6]. Similarly, decreases in mechanical loading, particularly associated with prolonged non-weight-bearing lameness, lead to adaptive resorption or osteopenia of bone tissue conducting to a decrease in mechanical rigidity [6]. One of the classic examples of Wolff's law is the femoral trochlear groove formation by the pressure that the patella exerts on the bone. In dogs with congenital medial patellar luxation, with the lack of pressure by the abnormally positioned patella, the trochlea can be shallow or absent. Another practical example of this law is that bone is generally stronger and stiffer in the direction in which the greatest loads are most commonly imposed (e.g., the long axis of the femur).
