Wolff's law is a theory developed by the German anatomist and surgeon Julius Wolff (1836–1902) in the 19th century that states that bone in a healthy person or 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 trabeculae 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 weaker due to turnover, it is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass.
The remodeling of bone in response to loading is achieved via mechanotransduction, a process through which forces or other mechanical signals are converted to biochemical signals in cellular signaling. Mechanotransduction leading to bone remodeling involve the steps of mechanocoupling, biochemical coupling, signal transmission, and cell response. The specific effects on bone structure depends 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 may differentiate one way or another depending on the loading condition.
- In relation to soft tissue, Davis' Law explains how soft tissue remolds itself according to imposed demands.
- Refinement of Wolff's Law: Utah-Paradigm of Bone physiology (Mechanostat Theorem) by Harold Frost.
- The racquet-holding arm bones of tennis players become much 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 result in a twisted bone density profile.
- Surfers who knee-paddle frequently will develop bone bumps, also known as exostoses, on the tibial eminence and the dorsal part of the navicular tarsal bone from the pressure of the surfboard's surface. These are often called surf knots
- Astronauts who spend a long time in space will often return to Earth with weaker bones, since gravity has been greatly diminished and therefore has exerted little force on their bodies.
- Weightlifters often display increases in bone density in response to their training.
- Martial artists who strike objects with increasing intensity (e.g., repeated elbow strikes), display increases in bone density in the striking area. This process is termed cortical remodeling.
- The Humerus bones of old Aleut burials, when uncovered by archeologists, are exceptionally thick and rugose, due to prolonged rowing of Baidarkas.
- Anahad O'Connor (October 18, 2010). "The Claim: After Being Broken, Bones Can Become Even Stronger". New York Times. Retrieved 2010-10-19. "This concept — that bone adapts to pressure, or a lack of it — is known as Wolff’s law. ... there is no evidence that a bone that breaks will heal to be stronger than it was before."
- Frost, HM (1994). "Wolff's Law and bone's structural adaptations to mechanical usage: an overview for clinicians". The Angle Orthodontist 64 (3): 175–188. doi:10.1043/0003-3219(1994)064<0175:WLABSA>2.0.CO;2. PMID 8060014.
- Stedman's Medical Dictionary
- Wolff J. "The Law of Bone Remodeling". Berlin Heidelberg New York: Springer, 1986 (translation of the German 1892 edition)
- Huang, Chenyu; Rei Ogawa (October 2010). "Mechanotransduction in bone repair and regeneration". FASEB J. 24.
- Duncan, RL; CH Turner (November 1995). "Mechanotransduction and the functional response of bone to mechanical strain". Calcified Tissue International 57 (5): 344–358.
- Turner, CH; MR Forwood, MW Otter (1994). "Mechanotransduction in bone: do bone cells act as sensors of fluid flow?". FASEB J. 8 (11).
- Chen, Jan-Hung; Chao Liu, Lidan You, Craig A Simmons (2010). "Boning up on Wolff’s Law: Mechanical regulation of the cells that make and maintain bone". Journal of Biomechanics 43.
- Frost, HM (2003). "Bone's mechanostat: a 2003 update". The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology 275 (2): 1081–1101. doi:10.1002/ar.a.10119. PMID 14613308.
- Taylor RE; Zheng c, Jackson RP, Doll JC, Chen JC, Holzbar KR, Besier T, Kuhl E. "The phenomenon of twisted growth: humeral torsion in dominant arms of high performance tennis players.". Comput Methods Biomech Biomed Engin. Retrieved 27 Feb 13.
- Mayo Clinic Staff (2010). "Strength training: Get stronger, leaner, healthier". Mayo Foundation for Education and Medical Research. Retrieved 19 October 2012.
- Das Gesetz der Transformation der Knochen - 1892. Reprint: Pro Business, Berlin 2010, ISBN 978-3-86805-648-8.
- The Classic: On the Inner Architecture of Bones and its Importance for Bone Growth, Clin Orthop Rel Res. 2010 Apr;468(4):1056-1065
- Julius Wolff Institut, Charité - Universitätsmedizin Berlin, main research areas are the regeneration and biomechanics of the musculoskeletal system and the improvement of joint replacement.