| 摘要 |
The present invention relates to an orthopedic screw having a torque driving head with spherical surface for multiaxial use, a self starting, self tapping insertion tip and a threaded portion including a modified cancellous thread. The threaded portion has a major diameter defined by a spiraling thread and a minor diameter. The head is joined to the threaded portion by an area of from about 2 to about 6 turns of the thread along the longitudinal axis in which the minor diameter tapers by an angle of from about 4 to about 12° and the major diameter of the screw remaining substantially the same meaning that the major diameter is constant to about +/-0.05 mm along the length of the threaded portion. The screw includes a multilobe torque driving recess joined to a cylindrical recess that corresponds to a cylindrical post on the torque driver so as to form a press fit which acts to self-center the screw, to help avoid stripping of the screw/driver interface and to hold the screw in place on the torque driver prior to implantation. In a further embodiment, the screw includes a variable pitch portion for about half of the length starting from the distil end. The screw can be used be itself, or with a plate. Further a new method of using the screw with a plate is presented in which the screw extends through a cortical section of bone into a cancellous portion but not through the adjacent cortical.
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