Wolff's law

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.[1] If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.[2][3] The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone,[4] 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.[5] This reduction in bone density (osteopenia) is known as stress shielding 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.

This article is about the medical law. For the album by The Joy Formidable, see Wolf's Law.

Mechanotransduction

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.[6] Mechanotransduction leading to bone remodeling involves the steps of mechanocoupling, biochemical coupling, signal transmission, and cell response.[7] 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.[7] When loaded, fluid flows away from areas of high compressive loading in the bone matrix.[8] Osteocytes are the most abundant cells in bone and are also the most sensitive to such fluid flow caused by mechanical loading.[6] Upon sensing a load, osteocytes regulate bone remodeling by signaling to other cells with signaling molecules or direct contact.[9] Additionally, osteoprogenitor cells, which may differentiate into osteoblasts or osteoclasts, are also mechanosensors and will differentiate depending on the loading condition.[9]

Computational models suggest that mechanical feedback loops can stably regulate bone remodeling by reorienting trabeculae in the direction of the mechanical loads.[10]

Associated laws

Examples
Tennis players often use one arm more than the other
  • The racquet-holding arm bones of tennis 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.[12]
  • Weightlifters often display increases in bone density in response to their training.[13]
  • Astronauts often suffer from the reverse: being in a microgravity environment, they tend to lose bone density. [14]
  • The deforming effects of torticollis on craniofacial development in children.[15]

See also

References
  1. 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.
  2. 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. PMID 8060014.
  3. Ruff, Christopher; Holt, Brigitte; Trinkaus, Erik (April 2006). "Who's afraid of the big bad Wolff?: "Wolff's law" and bone functional adaptation". American Journal of Physical Anthropology. 129 (4): 484–498. doi:10.1002/ajpa.20371. PMID 16425178.
  4. Stedman's Medical Dictionary (Wayback Machine PDF)
  5. Wolff J. "The Law of Bone Remodeling". Berlin Heidelberg New York: Springer, 1986 (translation of the German 1892 edition)
  6. Huang, Chenyu; Rei Ogawa (October 2010). "Mechanotransduction in bone repair and regeneration". FASEB J. 24 (10): 3625–3632. doi:10.1096/fj.10-157370. PMID 20505115. S2CID 3202736.
  7. Duncan, RL; CH Turner (November 1995). "Mechanotransduction and the functional response of bone to mechanical strain". Calcified Tissue International. 57 (5): 344–358. doi:10.1007/bf00302070. PMID 8564797. S2CID 8548195.
  8. Turner, CH; MR Forwood; MW Otter (1994). "Mechanotransduction in bone: do bone cells act as sensors of fluid flow?". FASEB J. 8 (11): 875–878. doi:10.1096/fasebj.8.11.8070637. PMID 8070637. S2CID 13858592.
  9. 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 (1): 108–118. doi:10.1016/j.jbiomech.2009.09.016. PMID 19818443.
  10. Huiskes, Rik; Ruimerman, Ronald; van Lenthe, G. Harry; Janssen, Jan D. (8 June 2000). "Effects of mechanical forces on maintenance and adaptation of form in trabecular bone". Nature. 405 (6787): 704–706. Bibcode:2000Natur.405..704H. doi:10.1038/35015116. PMID 10864330. S2CID 4391634.
  11. 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.
  12. Taylor RE; Zheng c; Jackson RP; Doll JC; Chen JC; Holzbar KR; Besier T; Kuhl E (2009). "The phenomenon of twisted growth: humeral torsion in dominant arms of high performance tennis players". Comput Methods Biomech Biomed Engin. 12 (1): 83–93. doi:10.1080/10255840802178046. PMID 18654877. S2CID 113868949.
  13. Mayo Clinic Staff (2010). "Strength training: Get stronger, leaner, healthier". Mayo Foundation for Education and Medical Research. Archived from the original on September 22, 2012. Retrieved 19 October 2012.
  14. "Preventing Bone Loss in Space Flight with Prophylactic Use of Bisphosphonate: Health Promotion of the Elderly by Space Medicine Technologies". 27 May 2015.
  15. Oppenheimer, AJ; Tong, L; Buchman, SR (Nov 2008). "Craniofacial Bone Grafting: Wolff's Law Revisited". Craniomaxillofacial Trauma & Reconstruction. 1 (1): 49–61. doi:10.1055/s-0028-1098963. PMC 3052728. PMID 22110789.
  • Julius Wolff Institut, Charité - Universitätsmedizin Berlin, main research areas are the regeneration and biomechanics of the musculoskeletal system and the improvement of joint replacement.
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