[Comparative biomechanical studies of conventional and self-tapping cortical bone screws]

In normal cortical screws the thread must be cut by a separate thread-cutter. So a high stability of the connection is achieved. On the other hand thread cutting needs time, which may be assumed to several minutes during a plate osteosynthesis. To avoid thread-cutting, self-tapping screws were used 20 years ago. These old self-tapping screws had a reduced stability and a lower torque at the final screw driving so that they tended to destroy the thread. By a modification of the cutting edges at the tip of the screw the tapping quality is increased decisively. The microscopic examination showed a better cutting of the new screws with little difference to a thread-cutter. In biomechanical tests the final torque and the maximum tension force of the self-tapping screws were at the same level as in usual pre-cut screws. In the practical use the new self-tapping screws have a good handling and save time during operation. In osteoporosis, they should be used carefully in order to meet the opposite corticalis' hole and not to destroy the ipsilateral corticalis' thread.