After nearly 25 years of work in skeletal anatomy, adaptation, and orthopaedics, Julius Wolff published his seminal 1892 work on bone 'transformation' (known today as bone remodeling and modeling). Wolff's work and his general view of how a limb bone's morphology develops has evolved into a nebulous concept known as "Wolff's law", which is essentially the observation that bone changes its external shape and internal (cancellous) architecture in response to stresses acting on it. Although the rationale for the existence of Wolff's law has been challenged on many fronts (e.g., Bertram and Swartz, 1991; Cowin, 1997; Currey, 1997; Cowin, 2001), many contemporary investigators still ascribe to the idea that there is a "Wolff's law" that states that bone models and remodels in response to the mechanical stresses it experiences so as to produce a minimal-weight structure that is 'adapted' to its applied stresses.
For example, should a fracture of a weight-bearing long bone heal with an angulation, each step that the patient subsequently took would result in a bending stress with compression on the concave side at the angulation and tension on the convex side. Rather than progressively weaken the bone structure at this site, such repeated mechanical stress results in a modeling and remodeling, with new bone growth on the concave side and bone resorption on the convex side. If the patient is young enough, the bone will ultimately grow straight. In control-system terms, the applied mechanical stress causes a growth response that negates the applied stress -- a closed-loop negative-feedback control system.
Many authors have made relevant observations regarding the phenomena of bone modeling and remodeling. An orthopaedic surgeon named Harold Frost made the following salient points:
To define some basic terms of bone growth, we have compiled the following list of characteristics in the formation (osteogenesis), modeling and remodeling of bone.