Development of an in silico hybrid model for scoliosis correction using Ansys Motion

Surgical techniques for correcting scoliotic deformities are continuously evolving, and computer modeling has become a valuable tool to support surgeons in testing and optimizing spinal instrumentation and corrective strategies. This study introduces a novel hybrid model capable of simultaneously computing rigid-body dynamics during surgical correction and estimating mechanical stresses within deformable structures. The model was developed using Ansys Motion, an integrated simulation environment that enables coupled multibody dynamics and finite element analyses to simulate complex interactions between rigid and flexible bodies. As a case study, spinal correction maneuvers were simulated on a simplified scoliotic spine model with vertebral bodies derived from publicly available CT scan data of a female subject. Simplified surgical instrumentation, representing commercially available systems, was applied to the T2-L1 segment and included a concave rod contoured to the desired sagittal profile. Different implant density patterns and corrective maneuver sequences were also investigated. The simulations of rod rotation followed by translation showed a deformity correction of approximately 39%. This correction was less pronounced when the number of instrumented vertebrae was limited to six or three, where a decrease in the estimated maximum pullout forces at the screw-vertebra interface was also observed. The reduction in forces transmitted by the screws during correction led to a decrease in the mechanical stress experienced by the intervertebral disks, as transmitted through the vertebral bodies. This effect may vary slightly depending on how the corrective maneuvers are performed. The preliminary results are promising and highlight the potential of this simulation tool for modeling the mechanical behavior of spinal deformities.