Minimal femoral cortical thickness necessary to prevent perforation by ultrasonic tools in joint revision surgery

Ultrasonic tools are effective in removing cement in revision surgery and almost eliminate perforation of the femoral shaft, a dangerous complication associated with cement removal using drills, chisels, osteotomes, and other tools. Clinically, the ultrasonic tool used to remove cement could not be passed through a relatively normal femoral cortex; however, a perforation occurred in a patient with a femoral cortex less than 1 mm thick. The purpose of this study was to determine how thin the femoral cortex can be and yet allow the safe use of ultrasonic tools to remove cement without the risk of perforation. A cement mantle was constructed in the intramedullary canal of human cadaver femurs. Each specimen was mounted on a jig, which was then fastened to a Materials Testing System (Minneapolis, MN). The average load generated across the cortex by the ultrasonic tools while removing cement was measured. Loads of varying magnitudes were then applied by the ultrasonic tools to femoral cortices of varying thickness. When the cortex measured 3 mm thick, perforation did not occur. When the cortex measured 2 mm, perforation was possible but required loads three to six times greater than those normally used to remove cement.