More on Wolff’s Law
Julius Wolff (1836-1902) was a German surgeon, regarded by many as one of the founding figures of modern orthopaedics. In 1892 he published ‘The Law of Bone Remodeling’* . His theories, although somewhat flawed, were remarkable given the limited knowledge of physiological processes available at the time.
In general terms his theory emphasised that the structure of bone will adapt to super-imposed forces by becoming stronger (or weaker) as necessary. More specifically, he devised a mathematical model to predict how the internal architecture of bone would respond to these forces. It is the assumptions implicit in the specific theory which have been challenged. The general premise of the original theory does however, still hold true.
Over a 40 year period in the late 20th century, an American researcher, Harold Frost, began to add further insight and worked to refine Wolff’s original ideas into what he termed the ‘Mechanostat Theory’ (The Utah Paradigm of Skeletal Physiology)
This refinement states that bone growth and bone loss is stimulated by the dynamic mechano-elastic deformation of bone and not simply by static loading. There appears to be a relationship between muscle cross sectional area and bone cross sectional area. The mechanostat theory seeks to integrate the tissue-level organisation and physiology of bone including. e.g. the dynamic aspects of both osteoblasts and osteoclasts, and their associated feedback loops, with Wolff’s 19th century concept.
The original premise of the Utah Paradigm emphasised the inherent economy of human tissue growth and design:
“The design of healthy, mammalian load-bearing bones would provide only enough strength to keep postnatal voluntary loads from causing spontaneous fractures, whether those loads are chronically small, normal or huge in size”**
However, it should be remembered that our skeletal function is not solely mechanical, and that skeletal structure represents an adaptive compromise between a number of often differing needs. Mechanical integrity is just one part of a set of competing physiological influences including e.g. diet, hormones, pregnancy, bone marrow storage, and absorption of nutrients***.
*Wolff J. “The Law of Bone Remodeling”. Berlin Heidelberg New York: Springer, 1986 (translation of the German 1892 edition)
**Frost HM. A 2003 update of bone physiology and Wolff’s Law for clinicians. Angle Orthodont 2004; 74:3-15.
***Ruff C, Holt B, Trinkaus E. Who’s Afraid of the Big Bad Wolff?: ‘‘Wolff’s Law’’and Bone Functional Adaptation; American Journal of Physical Anthropology 129:484–498 (2006)