Patient-specific finite element analysis of orbital biomechanical responses to malpositioned self-inflating hydrogel implants in congenital microphthalmia.

Purpose: Congenital microphthalmia is characterized by arrested ocular development, resulting in restricted biomechanical stimulation associated with orbital bone growth and craniofacial deformity on the affected side. Self-inflating spherical hydrogel orbital implantation has been clinically used to compensate for orbital volume deficiency and stimulate orbital growth. However, postoperative hydrogel implant malposition occasionally occurs. This study aimed to investigate the biomechanical effects of displaced self-inflating spherical hydrogel implants on biomechanical stimulation associated with orbital bone growth using a three-dimensional finite element model of congenital microphthalmia. Methods: Orbital CT data from a child with congenital microphthalmia were selected from the institutional database. CT images were imported into a simulation platform to reconstruct the geometric structure of the skull. Based on CT measurements of the globe and extraocular muscles, three-dimensional CAD models of the globe, extraocular muscles, and self-inflating spherical hydrogel implant were generated. A three-dimensional finite element model of the orbital bones and intraorbital tissues was then established. A 3-mL self-inflating spherical hydrogel implant was placed at two extraconal retrobulbar positions: inferonasal (Model 1) and inferotemporal (Model 2). The expansion process of the hydrogel implant was simulated, and finite element analysis was performed to obtain stress distribution and radial displacement maps of the orbital bones for biomechanical evaluation. Results: Model 2 showed higher orbital biomechanical response than Model 1. Von Mises stress increased from 10.15-278.15 kPa (Model 1) vs. 200.05-425.36 kPa (Model 2) with hydrogel expansion (3-9×), and displacement reached 0.406 μm vs. 0.703 μm, respectively. Stress and displacement were concentrated near implant-adjacent walls, with inferotemporal dominance in Model 2. Central-point analysis confirmed consistent stress-displacement coupling, with greater overall and regional orbital deformation in Model 2. Conclusion: In children with congenital microphthalmia, displaced hydrogel implants located in the deep inferotemporal orbit may still effectively stimulate biomechanical stimulation associated with orbital bone growth and therefore may support careful clinical observation in selected cases and warrants further validation in larger clinical studies. However, when malposition occurs in the superficial inferotemporal orbit and causes visible cutaneous protrusion, surgical correction should be considered.