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

Abstract

Bone is a dynamic tissue which, through the process of bone remodeling in the mature skeleton, renews itself during normal function and adapts to mechanical loads. It is, therefore, important to understand the effect of remodeling on the mechanical function of bone, as well as the effect of the inherent time lag in the remodeling process. In this study, we develop a constitutive model for bone remodeling which includes a number of relevant mechanical 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 as 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 beyond a threshold value. These results bear some correspondence to experimental findings, suggesting that the model may be useful when examining the importance of transient responses for bone in disuse, and for investigating the role fatigue damage removal plays in preventing or causing stress fractures. In addition, the constitutive algorithm is currently being employed in finite element simulations of bone adaptation to predict important features of the internal structure of the normal femur, as well as to study bone diseases and their treatment.

An Investigation of Humeral Stress Fractures in Racing Thoroughbreds using a 3D Finite Element Model in Conjunction with a Bone Remodeling Algorithm

“…Disuse is defined as Φ < Φ 0 and Φ 0 is 1.875E-10 cycles per day (Hazelwood et al, 2001), which is close to the stress fracture sites mechanical stimulus. If an area of bone is in a state of disuse, bone has a faster removal rate than formation rate, so bone density is decreased.…”

“…If an area of bone is in a state of disuse, bone has a faster removal rate than formation rate, so bone density is decreased. Disuse activates remodeling, which adds haversian canals in cortical bone making it difficult to increase bone density (Hazelwood et al, 2001). During equilibrium, the stress fracture site becomes susceptible to a complete fracture due to low bone density and reduced stiffness.…”

“…Both porosity and BMU activation frequency can be increased, in the case of disuse, or they can both be decreased, in a non-disuse state. When the muscle and contact loads were reduced from dirt track to turf and synthetic track loads, it was apparent that the stress fracture site was behaving as an area in disuse, while the caudal diaphysis was a bone not in disuse, but undergoing less (Hazelwood et al, 2001). Decrease in damage at the caudal diaphysis can be explained by lowering the damage formation rate while maintaining the damage removal rate.…”

“…Initial values for state variables used in the bone remodeling algorithm (Hazelwood et al, 2001) ……………………………………………………….. 33…”

“…Schematic of bone remodeling algorithm. This system contains two feedback loops, where the right side results in damage removal and the left side results in increased porosity, strain, and damage formation (Hazelwood et al, 2001) ... 19…”