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.
- Weightlifters often display increases in bone density in response to their training.
- The deforming effects of torticollis on craniofacial development in children.
- 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."
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- 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.
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- Mayo Clinic Staff (2010). "Strength training: Get stronger, leaner, healthier". Mayo Foundation for Education and Medical Research. Retrieved 19 October 2012.
- Oppenheimer, AJ; Tong, L; Buchman, SR (2008 Nov). "Craniofacial Bone Grafting: Wolff's Law Revisited.". Craniomaxillofacial trauma & reconstruction 1 (1): 49–61. PMID 22110789.
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- Julius Wolff Institut, Charité - Universitätsmedizin Berlin, main research areas are the regeneration and biomechanics of the musculoskeletal system and the improvement of joint replacement.