# A Computational Multiscale Framework for Bone Remodeling: Coupling Apparent Density Evolution and Microscale Shape Optimization

## TL;DR

This paper introduces a new framework that combines large-scale and micro-scale models to simulate how bones change over time, using patient-specific data to improve clinical applications.

## Contribution

A novel multiscale framework that integrates mechano-biological remodeling with microscale shape optimization using patient-specific data.

## Key findings

- The framework successfully simulated 9.8% trabecular and 4.9% whole vertebra BMD loss over a spaceflight scenario.
- Vertebral fracture simulations showed reduced peak load and energy absorption due to bone degeneration.
- The model can recover microstructure close to original after simulated bone remodeling.

## Abstract

Bone remodeling models are typically phenomenological or mechano‐biological but often lack mechanisms to incorporate patient‐specific data, limiting clinical use. We present a patient‐specific multiscale framework that couples finite element (FE)‐based shape optimization at the microscale with a mechano‐biological model at the macroscale. The model predicts % bone mineral density (BMD) changes at the macroscale, which in turn drive microscale trabecular adaptation via % bone volume fraction (BV/TV) changes. Micro‐QCT imaging data are used to train a DCGAN‐based ReconGAN for virtual reconstruction of trabecular microstructures, from which FE models are generated. Apparent BMD changes predicted by the macroscale model guide the microscale shape optimization to simulate adaptation. The framework reproduces BMD losses of 9.8% (trabecular) and 4.9% (whole vertebra) over a 215‐day spaceflight scenario, consistent with results from prolonged bed rest and controlled experimental datasets. In vertebral compression fracture simulations, it captures trabecular bone degeneration by reducing peak load from 3.532 to 3.280 kN and energy absorption from 0.243 to 0.218 J, and recovery restores close agreement to the original microstructure. These results demonstrate a path toward patient‐specific simulation of bone remodeling and its mechanical consequences, with strong potential for treatment planning and assessment of skeletal interventions.

This study introduces a multiscale patient‐specific framework that couples mechano‐biological bone remodeling at the macroscale with microscale shape optimization. The framework is validated through literature case studies and demonstrates how remodeling influences vertebral fracture behavior.