Hand-Injectable Acrylic Bone Cement Applicator for Skull Base Bone Replacement

Abstract

One of the only existing procedures to remove brain tumors at the skull base is endoscopic endonasal neurosurgery. The most difficult part of this surgery is closing the hole created in the skull, which currently is solved by stuffing fat and biocompatible foam in the hole and sealing it with glue. A better way of sealing this hole would be to use poly methyl methacrylate (PMMA) so that the hole is replaced with a material which more closely resembles bone. In order to better understand the delivery and application of PMMA bone cement into a patient?s skull through the nasal passages by a surgeon, we modeled three-dimensional viscous fluid flow within a surgical device prototype. The model is comprised of a 5-mm diameter tube with a 1-mm diameter wire running through its center. This wire is secured in place with vertical and horizontal supports. We analyzed the effects of the supports and wire on velocity and pressure drop of PMMA material moving through the tube to see if there was any resistance created in the tube that would be unmanageable by an unaided surgeon. To model the fluid flow, we created a three dimensional geometric schematic of the device in COMSOL. We acquired material properties from related literature and ran multiple simulations with several mesh sizes with COMSOL using the 3-D incompressible Navier-Stokes steady state application mode. The overall goal of this project was to determine if a surgeon could push PMMA through the tube without assistance from machines. Using this model we could then determine the manual pressure needed to administer the PMMA into a patient?s skull at an appropriate velocity. Our results indicated that the amount of applied pressure required would be 1.7 lbf, which is much less than the minimal value (~17 lbf) found in the literature regarding thumb strength. From simulations we obtained multiple velocity profiles and plots of pressure drop. Pressure decreases at a constant rate until the tube bends, the wire is introduced, or fluid passes by an obstruction at each point drop in pressure increases. The total amount of pressure drop in the tube was found to be 380 kPa. As we increased inlet velocity, the required applied pressure increased significantly, but not to a magnitude that would be unbearable to a human thumb. The model also gives valuable insight on the effects of obstructions on continuous, viscous fluid flow in a narrow tube