Computational Modeling of the Effects of Inflammatory Response and Granulation Tissue Properties on Human Bone Fracture Healing

TL;DR

This study presents a finite-element model to analyze how initial inflammatory and granulation tissue properties influence human bone fracture healing, highlighting key parameters that optimize healing efficiency.

Contribution

The paper introduces a novel finite-element-based simulation of the initial healing phase, including inflammatory response and granulation tissue, which are often neglected in prior models.

Findings

Faster MSC migration enhances healing up to a saturation point.

Stiffer granulation tissue and thicker callus improve healing outcomes.

Close bone segments may heal without callus formation, aligning with primary healing concepts.

Abstract

Bone healing process includes four phases: inflammatory response, soft callus formation, hard callus development, and remodeling. Mechanobiological models have been used to investigate the role of various mechanical and biological factors on the bone healing. However, the initial phase of healing, which includes the inflammatory response, the granulation tissue formation and the initial callus formation during the first few days post-fracture, are generally neglected in such studies. In this study, we developed a finite-element-based model to simulate different levels of diffusion coefficient for mesenchymal stem cell (MSC) migration, Young's modulus of granulation tissue, callus thickness and interfragmentary gap size to understand the modulatory effects of these initial phase parameters on bone healing. The results showed that faster MSC migration, stiffer granulation tissue, thicker callus and smaller interfragmentary gap enhanced healing to some extent. After a certain threshold, a state of saturation was reached for MSC migration rate, granulation tissue stiffness and callus thickness. Therefore, a parametric study was performed to verify that the callus formed at the initial phase, in agreement with experimental observations, has an ideal range of geometry and material properties to have the most efficient healing time. Findings from this paper quantified the effects of the healing initial phase on healing outcome to better understand the biological and mechanobiological mechanisms and their utilization in the design and optimization of treatment strategies. Simulation outcomes also demonstrated that for fractures, where bone segments are in close proximity, callus development is not required. This finding is consistent with the concepts of primary and secondary bone healing.