Functional strain in bone tissue as an objective, and controlling stimulus for adaptive bone remodelling.

The skeleton consists of a series of elements with a variety of functions. In locations where shape or protection are of prime importance the bone's architecture is achieved during growth under direct genetic control. In locations where resistance to repetitive loading is important only the general form of the bone will be achieved as a result of growth alone, the remaining characteristics result from functional adaptation. This mechanism ensures that bone architecture is modelled and remodelled until prevailing strains match those genetically prescribed for that location. For this match to be established, and subsequently maintained, bone cells must be able to 'assess' feedback derived directly or indirectly from the functional strains produced within the tissue. These strains are therefore the objective of functionally adaptive remodelling, and the stimulus for its control. Evans was the first person to refer to the recording of functional strains from gauges attached to bone in vivo. This technique has allowed quantitative investigations on bone's normal functional strain environment, and its adaptive response to changes in its state of strain. Recent investigations have extended to the immediate effects of dynamic strains on the structure of the bone matrix, and the biochemical behaviour of the resident bone cells. Such studies should reveal the mechanism by which strains within the matrix are transduced into the biochemical signals by which adaptive remodelling is controlled.