Patent ID: 8632571

Claim:
A pedicle screw, comprising: a screw shank; a screw head connected to said screw shank, said screw head having a central longitudinal axis extending in one direction, being an X-direction, said screw head further having an upper face, a lower end directed toward said screw shank, a head base disposed at said lower end and having a bottom opening formed therein, and two wall portions disposed on said head base and being integrally formed to extend away from said screw shank in the X-direction and laterally delimit a recess extending in a Y-direction at right angles to the X-direction and opens into said upper face of said screw head for receiving a connection rod with a circular cross-sectional shape, said wall portions each having an inner face with an inner thread; said screw shank having a joint head protruding through said bottom opening in said head base and into said recess and mounted therein such that said screw head is pivotable relative to said screw shank about a single head pivot axis extending parallel to the Y-direction, said screw shank further having a mating cylindrical surface disposed on said joint head; a fixing screw for fixing the connection rod in said screw head being disposed in said recess and engaging, with an outer thread, in said inner thread on said inner face of said wall portions; a clamping device disposed between said fixing screw and said head base being held in said recess so as to be pivotable in said screw head about a pivot axis, said clamping device extending in a Z-direction at right angles to the Y-direction and X-direction and is disposed at a spacing in the X-direction above the single head pivot axis, said clamping device having a hollow space formed therein, through which the connection rod passes in an assembled state, and also a lower spherical surface directed toward said head base and said lower spherical surface having a sphere center lying on the pivot axis of said clamping device; said clamping device, in the assembled state, being subjected by said fixing screw to a force directed toward said head base; and an intermediate element disposed in said head base, said intermediate element having a first side directed toward said clamping device, a mating spherical surface disposed on said first side and cooperating with said lower spherical surface of said clamping device and, on a second side directed toward said screw shank, said intermediate element having a cylindrical surface cooperating with said mating cylindrical surface on said joint head, wherein said cylindrical surface and said mating cylindrical surface having a common axis of curvature coincident with the single head pivot axis of said screw head.