A mechanistic model for internal bone remodeling exhibits different dynamic responses in disuse and overload

Bone is a dynamic tissue which, through the process of bone remodeling in t he mature skeleton, renews itself during normal function and adapts to mech anical loads. It is, therefore, important to understand the effect of remod eling on the mechanical function of bone, as well as the effect of the inhe rent time lag in the remodeling process. In this study, we develop a consti tutive model for bone remodeling which includes a number of relevant mechan ical and biological processes and use this model to address differences in the remodeling behavior as a volume element of bone is placed in disuse or overload. The remodeling parameters exhibited damped oscillatory behavior a s the element was placed in disuse, with the amplitude of the oscillations increasing as the severity of disuse increased. In overload situations, the remodeling parameters exhibited critically sensitive behavior for loads be yond a threshold value. These results bear some correspondence to experimen tal findings, suggesting that the model may be useful when examining the im portance of transient. responses for bone in disuse, and for investigating the role fatigue damage removal plays in preventing or causing stress fract ures. In addition, the constitutive algorithm is currently being employed i n finite element simulations of bone adaptation to predict important featur es of the internal structure of the normal femur, as well as to study bone diseases and their treatment. (C) 2001 Elsevier Science Ltd. All rights res erved.