Intraoperative mechanical characterization of vertebral bone quality during percutaneous kyphoplasty

Osteoporosis (OP) compromises bone strength and markedly increases the risk of vertebral compression fractures (VCFs), which are commonly treated with percutaneous kyphoplasty (PKP). Although bone mineral density (BMD) is widely used to diagnose OP and inform surgical planning, it primarily reflects bone mass rather than mechanical competence. Here, we propose an intraoperative method that derives a bulk-modulus-like mechanical index, κ, from the balloon pressure-volume response during PKP. This method enables direct mechanical assessment of vertebral bone quality without additional surgical trauma or procedural steps. To evaluate its feasibility and robustness, a three-dimensional lumbar vertebral model was reconstructed from computed tomography data, and finite element simulations were performed to characterize the relationship between κ and the elastic modulus of cancellous bone. The effects of balloon geometry, puncture trajectory, material anisotropy and heterogeneity, elastoplasticity, and cortical bone failure were also investigated. The results showed that κ decreased linearly with reductions in cancellous-bone elastic modulus, enabling clear differentiation among the simulated bone-health states. Variations in balloon geometry and puncture trajectory altered κ by less than 5.5%, indicating that the measurement is robust to clinically relevant procedural variations. Moreover, the linear relationship between κ and cancellous-bone modulus was preserved across increasingly realistic constitutive models. These findings establish a mechanically grounded framework for intraoperative assessment of vertebral bone quality and support the potential use of κ to inform PKP procedures, postoperative management, and the acquisition of patient-specific in vivo bone mechanical-property data.