Wolff's law, developed by the German anatomist and surgeon
Julius Wolff (1836–1902) in the 19th century, states that bone in a healthy animal will adapt to the loads under which it is placed. If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The internal architecture of the
trabecula
A trabecula (: trabeculae, from Latin for 'small beam') is a small, often microscopic, biological tissue, tissue element in the form of a small Beam (structure), beam, strut or rod that supports or anchors a framework of parts within a body or ...
e undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone, perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continued
remodeling
Renovation (also called remodeling) is the process of improving broken, damaged, or outdated structures. Renovations are typically done on either commercial or residential buildings. Additionally, renovation can refer to making something new, o ...
.
[Wolff J. "The Law of Bone Remodeling". Berlin Heidelberg New York: Springer, 1986 (translation of the German 1892 edition)] This reduction in bone density (
osteopenia
Osteopenia, known as "low bone mass" or "low bone density", is a condition in which bone mineral density is low. Because their bones are weaker, people with osteopenia may have a higher risk of fractures, and some people may go on to develop o ...
) is known as
stress shielding
Stress shielding is the reduction in bone density ( osteopenia) as a result of removal of typical stress from the bone by an implant (for instance, the femoral component of a hip prosthesis). This is because by Wolff's law
Wolff's law, develop ...
and can occur as a result of a hip replacement (or other prosthesis). The normal stress on a bone is shielded from that bone by being placed on a prosthetic implant.
Mechanotransduction
The remodeling of bone in response to loading is achieved via
mechanotransduction
In cellular biology, mechanotransduction ('' mechano'' + '' transduction'') is any of various mechanisms by which cells convert mechanical stimulus into electrochemical activity. This form of sensory transduction is responsible for a number o ...
, a process through which forces or other mechanical signals are converted to biochemical signals in cellular signaling.
Mechanotransduction leading to bone remodeling involves the steps of mechanocoupling, biochemical coupling, signal transmission, and cell response.
The specific effects on bone structure depend on the duration, magnitude, and rate of loading, and it has been found that only cyclic loading can induce bone formation.
When loaded, fluid flows away from areas of high compressive loading in the bone matrix. Osteocytes are the most abundant cells in bone and are also the most sensitive to such fluid flow caused by mechanical loading.
Upon sensing a load, osteocytes regulate bone remodeling by signaling to other cells with signaling molecules or direct contact.
Additionally, osteoprogenitor cells, which may differentiate into osteoblasts or osteoclasts, are also mechanosensors and will differentiate depending on the loading condition.
Computational models suggest that mechanical feedback loops can stably regulate bone remodeling by reorienting trabeculae in the direction of the mechanical loads.
Associated laws
*In relation to soft tissue,
Davis' law explains how soft tissue remodels itself according to imposed demands.
*Refinement of Wolff's Law:
Utah-Paradigm of Bone physiology (
Mechanostat Theorem) by
Harold Frost
Harold M. Frost (1921 – 19 June 2004) was an American orthopedist and surgeon considered to be one of the most important researchers and theorists in the field of bone biology and bone medicine of his time.Turner C, Burr D, Jee WS, Smith S, Rec ...
.
Examples

* The
racquet
A racket or racquet is an item of sporting equipment used to strike a ball or shuttlecock in a variety of sports. A racket consists of three major components: a widened distal end known as the ''head'', an elongated handle known as the ''grip'' ...
-holding arm bones of
tennis
Tennis is a List of racket sports, racket sport that is played either individually against a single opponent (singles (tennis), singles) or between two teams of two players each (doubles (tennis), doubles). Each player uses a tennis racket st ...
players become stronger than those of the other arm. Their bodies have strengthened the bones in their racquet-holding arm, since it is routinely placed under higher than normal stresses. The most critical loads on a tennis player's arms occur during the serve. There are four main phases of a tennis serve, and the highest loads occur during external shoulder rotation and ball impact. The combination of high load and arm rotation results in a twisted bone density profile.
*
Weightlifter
Weightlifting or weight lifting generally refers to physical exercises and sports in which people lift weights, often in the form of dumbbells, barbells or machines. People engage in weightlifting for a variety of different reasons. These can ...
s often display increases in
bone density
Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although medicine#Clinical practice, clinically it is measured by ...
in response to their training.
* Astronauts often suffer from the reverse: being in a microgravity environment, they tend to lose bone density.
* The deforming effects of
torticollis
Torticollis, also known as wry neck, is an extremely painful, dystonic condition defined by an abnormal, asymmetrical head or neck position, which may be due to a variety of causes. The term ''torticollis'' is derived .
The most common case ha ...
on craniofacial development in children.
See also
*
Functional matrix hypothesis
In the development of vertebrate animals, the functional matrix hypothesis is a phenomenological description of bone growth. It proposes that "the origin, development and maintenance of all skeletal units are secondary, compensatory and mechanica ...
*
Iron Shirt, Wushu/Kungfu bone conditioning
*
Osteogenic loading Osteogenic loading (OL) is a rehabilitative exercise method with the goal of improving bone density and preventing bone fracture. This may be seen as brief, intensive, resistance exercise for bone health.
Osteogenic loading is an outpatient thera ...
References
* ''Das Gesetz der Transformation der Knochen - 1892.'' Reprint: Pro Business, Berlin 2010, .
*
External links
Julius Wolff Institut Charité - Universitätsmedizin Berlin, main research areas are the regeneration and biomechanics of the musculoskeletal system and the improvement of joint replacement.
{{DEFAULTSORT:Wolff's Law
Musculoskeletal system
Biological defense mechanisms