Functional adaptation refers to a biologic structure’s unique ability to alter its shape and material properties in response to altered demands. Bone is one such material. This study endeavors to predict the functional adaptation of bone using two different theories of functional adaptation. Each theory is driven by an error signal which represents the difference between the mechanical environment at equilibrium and the same value after the altered loading. The phenomenological theory, based on adaptive elasticity theory uses purely phenomenological constants to modulate the mechanical stimulus signal. The mechanistic theory, a cell-biology based theory of functional adaptation, attempts to define the necessary constants in terms of histomorphometrically measurable parameters.

This work is part of a team study with Dr. David Burr and co-workers from Indiana University. They measured the changes which occurred in a canine radius following ulnar osteotomy, for one, six, and twelve months after the osteotomy. Some of the measured cellular parameters (cell number, cellular activity and the percent of surface covered with cells) define the constants for the cell- biology based theory of functional adaptation.

Five accurate and valid finite element models of the canine radius and ulna were built. Programs and methods to build the models from computed tomography scans were developed Appropriate loading and boundary conditions to yield an equilibrium strain environment for a static forelimb stance were determined. A computational ‘osteotomy’ was performed by removing a small portion of the ulna, thereby overloading the radius. The change in the loading is the driving force in both functional adaptation theories.

Each of the functional adaptation theories was applied to the finite element models. Predictions of the shape of the bones six months after osteotomy were made a priori, and were later compared to the experimental results. The comparisons showed that while the adaptive elasticity predictions overestimated the bone changes in the canine radius, the cell biology based theory was a better predictor, in some cases the simulations were within 10% of the experimental change that occurred although the histomorphometric data did not provide data for including areas of bone resorption.