Apparatus and method for mixing and dispensing bone cement

Abstract

A method and apparatus for mixing bone cement which produces bone cement essentially free of entrained air. The apparatus includes a cartridge having two telescoping cylinders. The outer cylinder receives a cap thereon which hermetically seals the cartridge. The cap includes an outlet port in which a break-away agitator is installed and a port for connection of a vacuum pump. In use, a desired vacuum pressure is drawn on the cartridge and the inner cylinder is allowed to be drawn into the outer cylinder while the vacuum is being drawn, whereupon the inner cylinder automatically stops moving relative to the outer cylinder when the desired vacuum pressure is reached. Mixing of the bone cement is then performed under the partial vacuum thereby created. The agitator paddles provide a scraping action against both inner cylinder walls of the telescoping cylinders thereby improving mixing. After mixing, the agitator is broken away, an appropriate nozzle is attached to the cartridge and the cartridge is inserted into a cement gun. The leading portion of the bone cement develops a convex profile when axially advanced through the cartridge and the piston plug includes a tapered protrusion which generally corresponds to the profile of the bone cement. The cap and paddles are also shaped correspondingly to the convex profile developed by the bone cement, resulting in substantially all of the bone cement being squeezed from the cartridge. An air escape passage is also provided to vent air contained within an annular gap between the agitator shaft and the cap upon initial being essentially free from entrained air.