Articles techniques et présentations

While prosthetic joints can improve people’s quality of life, there is an unmet need for the treatment of post-surgery infections. A novel technology has been developed that can treat these infections with electromagnetic heating. A series of anatomical models of knees with implants have been developed for simulation of the heat treatment process. These simulations are supporting the ongoing FDA approval process necessary to make the treatment device commercially available to doctors. Initial CAD of a non-surgically repaired knee was used as a baseline for developing a series of CAD models of surgically replaced knees for analysis. Distinct regions in original knee CAD include skin, bone, muscles, ligaments, tendons, bursa, nerves, veins, and arteries. In consultation with surgeons, appropriate femoral and tibial bone cuts, bone drills, and tissue dissections were performed. Commercially available knee implant system CAD was then indexed and placed in the knee with space left for cement. The final, surgically replaced knee geometry was imported into a COMSOL Multiphysics electromagnetic heating simulation model file of the prototype treatment coil. Extensive troubleshooting and tweaking of the geometry finalization operations and meshing was required for a successful mesh of the complicated assembly of tissues and implant domains. Without a CAD representation of the cement paste applied at the time of surgery, cemented digital versions of the knee implant system were generated using custom partial differential equation (PDE) interfaces in COMSOL to solve for the spatial location of cement as a pre-processing step. Transient thermal simulations for heat-up and cool-down cycles of the coil in operation predict spatial distributions of temperature in the digital knees. Uniform high temperatures (75-80°C) in known regions around the metal and cement are desirable as these are regions where infection is common. On the other hand, damage to healthy tissue is a safety concern. To quantify the effect of desirable and undesirable heating, CEM43 damage integration equations are solved within COMSOL based on the transient temperature field. Numerical results are validated against cadaver studies of the treatment without perfusion effects.