Patent ID: 8080036

Claim:
A pedicle screw comprising: a fixing unit which comprises a U-shaped housing groove which is formed in a side of the fixing unit to be opened upward so as to house a spinal rod, a fixing screw thread which is formed at an inner surface of the U-shaped housing groove so as to have dents and protrusions with rectangular cross-sections, and a combination groove which is formed in a lower surface of the fixing unit so as to penetrate the lower surface of the fixing unit; a screw bar which comprises a spherical joint which constitutes an upper part of the screw bar and a screw thread which is formed at an outer surface of the screw bar to be inserted into a pedicle through the combination groove of the fixing unit; and a clamp screw which comprises a clamp screw thread which is formed at an outer surface of the clamp screw to have dents and protrusions with right-angled trapezoid cross-sections so as to form a predetermined gap with the fixing screw thread of the fixing unit when the clamp screw is combined with the fixing unit; wherein the right-angled trapezoid cross sections of the clamp screw thread decrease in height from a distal end of the right-angled trapezoid cross sections to a proximal end of the right-angled trapezoid cross sections, wherein said proximal end of the right-angled trapezoid cross sections are adjacent the outer surface of the clamp screw.