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.

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
  • 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.[11]

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]
  • The deforming effects of torticollis on craniofacial development in children.[14]
  • Astronauts often suffer from the reverse: being in a microgravity environment, they tend to lose bone density. [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. 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.
  15. "Preventing Bone Loss in Space Flight with Prophylactic Use of Bisphosphonate: Health Promotion of the Elderly by Space Medicine Technologies". 27 May 2015.
  • 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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