Transient-steady state phenomena in microdamage physiology: a proposed algorithm for lamellar bone.

This algorithm suggests that in steady states the momentary burden of unrepaired microdamage (MDx) in lamellar bone equals the rate of creation of new MDx multiplied by the time taken to repair a locus of MDx completely in the biomechanical sense. That "repair period" equals about 0.6 years in healthy human adults. When MDx production suddenly increases, the momentary MDx burden begins to increase too, and does so for a time equal to the repair period and in proportion to the increased MDx production. After the repair period elapses, the momentary MDx would tend to reach and stay at a maximum value as long as increased MDx production continued. Prolonging the repair period, preventing the creation of new remodeling units to repair MDx, or delaying mineralization of the new bone made by those units would also increase MDx burdens. Reducing MDx production or the repair period, or accelerating the creation of new modeling units would have the opposite effects on the momentary MDx burden but would also go through a transient phase before developing the new steady state conditions. Exploiting these relationships quantitatively and experimentally requires expressing them mathematically and using for the terms in any equations things one can define logically and measure practically. Accordingly, the article suggests a special definition of a unit amount of microdamage, how to measure it, and simple algebra and equations for calculating some effects of microdamage on the biologic system.