Bending fatigue of cancellous bone screws used in anterior spine surgery.

Abstract

Bending fatigue has been noted in early clinical results of anterior spinal fixation using standard 6.5mm outside diameter (3.2mm inside diameter) cancellous bone screws. Fractography was used to qualify and quantify the failure mode. Fracture mechanics was used to determine the load level from the fractographic findings. These results were used in a test program to reproduce the fatigue failures seen in-vivo. The validity of the experimental model was investigated by varying test coupon parameters, testing the modified specimens and comparing the results to those predicted.