Rib graft or cement to enhance screw fixation in anterior vertebral bodies

This study analyzed the use of a rib graft or cement to enhance the holding power of a screw in a vertebral body. The results were correlated to provide a rationale for surgically enhancing the holding power of a screw when stripping of the bone thread has occurred. Human lumbar vertebral bodies obtained at autopsy were used in this study. The screws were inserted at three different sites of each vertebra and a load necessary to strip the thread was applied. Then costal fixation and cement fixation were tested to determine whether it was possible to restore the ability of the screw to withstand pullout load in the same hole. The main finding was that methacrylate placement or costal fixation restored the ability of the screw to withstand pullout load to within 5% (cement) or 15% (rib graft) of the original value. These results validate the possibility of using a rib graft or cement to enhance screw fixation.