Pedicle screw

The invention relates to a pedicle screw having a threaded shank part and a head side receiving part provided on a rod. Such screws are used for mono or multisegmental stabilization of the spine.

Such pedicle screw is known from DE-AS 26 49 042nd The screw has a threaded portion and a rigid so that at the head end provided for receiving part. In each case, screwed several pairs of such screws in a distance from each other on both sides of the spinal column into the vertebral bodies. The respective receiving parts have receiving slots. This receiving slots of the right and left set of screws, a threaded rod is guided in each case. With the help of fixing screws, the rod is then fixed to the respective receiving part. A disadvantage of this solution is that it is very difficult, on the one hand firmly screwing the screws into the vertebral body and the other hand to put the screws in two planes just so that the axes of the receiving slots are aligned in the superimposed located receiving parts so that the threaded rod without distortion of the coil can be passed through the receiving slots. Even the attempt requires a lot of time, which is a big disadvantage in an operation on the spine. In addition to such a precise alignment can hardly reach. The result is that significant shear forces are exerted on the threaded rods, which results in that in the later use after completion of the operation, the rods could even break off and not allow full stabilization.

From FR-A-2499400 is known a pedicle screw in which the threaded shaft portion and the receiving part are pivotably connected about a two ball segments. This arrangement is structurally very bulky and therefore can only be used for an external fixation of long bones, but not for internal stabilization of spinal segments.

The object of the invention is to provide a pedicle screw of the type described above, which facilitates insertion and at the same time also reduces the risks during subsequent use or exclude.

This object is achieved by a pedicle screw Claim 1.

By this solution it is achieved that the screw can be screwed first without regard to the position of the receiving part and the receiving part then easily in a time required for receiving the threaded rod position can be brought. Thereby, the operation time is substantially shortened, and the force acting on the threaded rod forces are substantially reduced.

Further features and advantages of the invention will be apparent from the description of exemplary embodiments with reference to FIGS. Of the figures:<dl id="dl0001"><dt>Fig. 1</dt><dd>a first embodiment of a pedicle screw on average, in an enlarged representation;</dd><dt>FIG. 2</dt><dd>a part of Figure 1 on an enlarged scale; FIG.</dd><dt>Fig. 3</dt><dd>a plan view of the part shown in Fig. 2;</dd><dt>Fig. 4</dt><dd>a portion of Figure 1 in a different scale.</dd><dt>Fig. 5</dt><dd>the part in a position rotated by 90 ° in the display section shown in Fig. 4;</dd><dt>Fig. 6</dt><dd>the part of the back shown in Fig. 4;</dd><dt>Fig. 7</dt><dd>the part of the top shown in Figure 5. and</dd><dt>Fig. 8</dt><dd>a retaining ring from the illustration shown in Fig. 1 in an enlarged scale.</dd></dl>

The pedicle screw shown in the figures 1-8 25 has a threaded shank portion 26 and a receiving part 27th

The threaded shank portion 26 includes a threaded portion 28 for screwing into the vertebral body. At the head end of the threaded part is a spherical segment-shaped head 29 is provided. This has, on its side facing away from the threaded portion on a perpendicular to the axis of the threaded part 28 extending flat surface 30 which is formed by a portion of the ball is cut off. The cut area is roughly equivalent to one half the radius of the spherical body.

As can be seen from Figure 3, is provided coaxially to the threaded portion 28 has a hexagonal bore 31st In this action can be taken with an Allen wrench for screwing the threaded shaft portion 26 into the vertebral body. Instead of the hexagonal hole course also possible to provide other forms for engagement by a screwdriver.

The receiving part 27 comprises two head halves 32, 33 and a retaining ring this cohesive 34th

Each head half has its the other half of the head-facing inside a spherical segment shaped portion 35th The inner radius of the sphere corresponds to the outer radius of the head 29 on the ball segment-shaped section is adjoined by a neck portion 36 at. This has the shape of a segment of a cone section and is formed by the spherical segment shaped section proceeding outwardly divergent. The axis of the neck portion passes through the center of the spherical-segment-shaped portion 35. On the side opposite the neck portion side of the spherical segment-shaped portion 35, a receiving slot extending perpendicular to the axis of symmetry of the neck portion and kugelsegmentförmigem portion 37, facing away from the the other half of the head outside a reduction 38 which is , The width of the receiving slot is selected so that a male threaded rod 39 is loosely guided therethrough, as can be seen from FIG. 1

In the area of ​​the neck portion 36, the head half a extending perpendicularly to the axis of symmetry of the neck portion and kugelsegmentförmigem section shaped recess 40th

The two head halves 32, 33 are identically formed. Their dimensions are chosen so that the center 41 of the spherical segment-shaped portion 35 a fraction of a millimeter outside the side opposite the respective second half-head parting plane 42 is located so as to parallel to each other at joining the two head halves 32, 33 around the head, a gap 43 between the respective two halves arises.

The retaining ring 34 has an inner surface 44 that is substantially the negative of the outer surface of the neck portion 36th In particular, the inner surface 44 at a 40 fitting into the groove-shaped recess projecting bead 45 with each adjoining lateral edge regions 46, 47th The inner diameter of the retaining ring 34, thus in particular of the bead 45 and the edge portions 46, 47 is selected so that the ring 34 such a voltage to the two head halves 32, 33 exerts when used in the manner shown in Figure 4 initially without threaded rod 39 are mounted on the head 29 that it about the longitudinal axis of the threaded shank portion 26 are pivotable within a specified by the taper of the neck portion 36 angle free and 39 sufficiently firmly connected to the insertion of the threaded rod with the head and thus with the threaded shaft portion 26 so are that the two head halves in the area included in the ring portion further together than in the opposite, the region having Aufnähmeschlitz.

As is apparent in particular from Figures 1 and 6, the depth of the receiving slot 37 is selected such that it ends in the assembled state shown in Figure 1 in a distance above the surface 30 so that the free mobility of the receiving part 27 of the about the longitudinal axis threaded shaft portion 26 is not restricted.

To insert the pedicle screw pedicle screw is initially characterized screwed into the respective vertebra that is passed interfered with a key through the receiving slots in the hexagonal hole for screws. After screwing the receiving parts 27, 33 are aligned with the two are held together by the retaining ring 34 halves of the head 32 in its direction, that the threaded rods 39 without the action of shear forces can be used in the receiving slots 37th The threaded rods are then fixed with each seated in the cuts 38 locking screws 48, 49th The fixing screws may become so tight as desired, either, that the receiving part 27 can no longer be pivoted around the head 29 around and thus creates a substantially rigid connection between Aufnähmeteil 27 and threaded shaft portion 26, or the screws only so far attracted that yet a desired damped movement between the two parts is possible.

In the embodiment shown in Figure 1 of the holding ring 34 on its side facing the threaded portion 28 side rounded about a radius, whose center lies on the the threaded part 28 the opposite side. This rounding is achieved that each vertebral body facing surfaces can not cause any injuries.

In one embodiment, the surfaces of the recesses and / or of the spherical segment-shaped head 29 are polished or coated with a lubricant, such as Teflon, so that even when relatively firm screwing a low damped movement of the female part is possible. According to another embodiment, the surfaces can be made rough, so that the ball in the inserted state with a fixed nut tightened quasi seizing and a substantially rigid connection between the receiving part and the threaded shank portion is formed.

With the pedicle screw described above, an unlimited free movement around the symmetry axis and in horizontal and vertical directions a presettable movement, which is preferably at an angle of 10 ° to 30 °, reached. In addition, it is achieved that the structural length of the pedicle screw can be kept particularly short.