Macro-Meso-Micro Biomechanical Analysis of the Lumbar Spine After Pedicle Subtraction Osteotomy for Idiopathic Scoliosis

To investigate the multiscale biomechanical properties and bone tissue osteogenicity at the bone contact surface after pedicle subtraction osteotomy in idiopathic scoliosis, this study constructs a postoperative macroscopic finite element model, a mesoscopic bone unit, and a microscopic lacunar-canalicular system’s finite element model by applying the sub-model approach and based on microstrain. With these models, normal physiological working conditions were simulated, the osteogenicity of bone tissues at the vertebral bone contact surfaces at different scales was analyzed, and the differences in mechanical properties between the mesoscopic and macroscopic models were compared. The results indicated that the bone unit stress and osteocyte synaptic flow velocity and pressure in the end face of the upper vertebra were greater than those in the end face of the lower half of the vertebral body, and the highest values were obtained under the lateral bending condition; the average stress in the end face of the upper half of the vertebral body was ranked from large to small as the right side, the left side, and the rear, while in the lower half of the vertebral body, it was ranked as the left side, the front, and the right side; the stress at the mesoscopic scale in this case was about 1.442–5.217 times higher than that in the macroscopic scale. It can be inferred that there is a difference in osteogenicity of bone tissue at the different end surfaces and around the end surfaces at the bone contact surface; frequent postoperative lateral bending exercises can help the growth of bone tissues, and the stress amplification relationship between the mesoscopic bone unit and the macroscopic cortical bone is revealed. This study demonstrates the importance of multiscale studies for the fusion of bone contact surfaces and provides a theoretical basis for designing and optimizing surgical protocols for idiopathic scoliosis.