Wolff's law

[vôlfs]
n.
  1. The principle that every change in the form and the function of a bone or in the function of the bone alone, leads to changes in its internal architecture and in its external form.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.