Connection Member for the Connection of a Resilient Rod With a Bone Screw Which Can Be Anchored in a Vertebra

1. Technical Field

The invention relates to a connection member for the connection of a resilient rod with a bone screw which can be anchored in a vertebra, and further to a device comprising such a connection member for the connection of at least two vertebrae.

2. Description of the Prior Art

It is known in the case of deformed or degenerated spinal columns to operatively clamp a correcting device via connection members to at least two vertebrae of a spinal column in order to thus give the spinal column a greater stability.

From EP 0384001 A1 a correcting device is known which clamps an elongated, resilient rod to a plurality of vertebrae of a spinal column with connection members. This device has a connection member with an opening for the accommodation of a part of an elongated rod. The connection member has a further connection region in order to clamp the connection member to a vertebra via bone screws. In one embodiment, the connection member has a screw with which the elongated rod is clampable within the connection member. This connection member has the disadvantage that when large forces act, a relative movement can result between the connection member and the resilient rod.

The advantages of the invention are that the connection member has a recess for the accommodation of an elongated rod, with the inner surface of the recess being formed such that only partial regions of the inner surface engage with the rod in an operative connection. The rod can have a cross-sectional area such as round, oval, elliptical, triangular or polygonal, so that the recess of the connection member is adapted to the cross-sectional area of the rod, such that only partial regions of the inner surface of the recess engage with the rod in an operative connection. A rod that is clamped in such a way with a screw within the connection member tends not to move relative to the connection member. The inner surface can have groove-shaped recesses for example extending in the longitudinal and/or transverse direction of the inserted rod. Furthermore, the surface of the rod can have groove-shaped recesses. Another embodiment that reduces the contact area between the rod and the inner surface of the recess involves the recess having inner boundary surface comprising a plurality of curved partial surfaces with at least three different radii of curvature. These radii of curvature can be larger or smaller than a radius of curvature of the rod, so that line-shaped contact surfaces result between the recess and the rod. It is particularly advantageous to realize a three-point mounting, wherein the rod is contacted at two line-shaped contact surfaces at the inner boundary surface, and the third point of mounting is provided by a connection means acting on the rod, such as a screw.

A further advantage of the invention is that more than one screw can be arranged in the connection member along the recess for the clamping of the rod, which affords the rod a particularly rigid support.

FIGS. 1a-1c are perspective views of embodiments of a connection member made in accordance with the present invention;

FIG. 1d is a detailed view of the fastener means of a connection member made in accordance with the present invention;

FIG. 2a is a side view of a connection member made in accordance with the present invention;

FIG. 2b is an elevational view illustrating the shape of the inner boundary surface with groove-shaped recesses;

FIG. 2c is an elevational view illustrating the shape of the inner boundary surface;

FIG. 2d is an elevational view with portions in cross-section illustrating a rod which is clamped in the connection member;

FIG. 3 is a cross-sectional view through a vertebra illustrating use of the connection member;

FIG. 4 is a longitudinal sectional view through the connection member illustrated in FIG. 1c; and

FIG. 5 is a perspective view of a portion of a connection member illustrating the inner boundary surface with a plurality of pyramidal elevations.

FIG. 1a shows a connection member 2 comprising an accommodation part 2a and a connection part 2b. The accommodation part 2a has a continuous opening 3 into which a rod 1 can be inserted which is connectable with the accommodation part 2a via connection means 6a, 6b which can be inserted into the recess 5a, 5b. The opening 3 has an inner boundary surface 4. The connection part 2b has an opening 11 through which a bone screw 8 is insertable in order to anchor the connection part 2b to a vertebra 7 of a spinal column.

In FIG. 1b a further embodiment of a connection member 2 is shown which is formed in a similar manner as the embodiment illustrated in FIG. 1a. However, the embodiment illustrated in FIG. 1b only has one recess 5a for the accommodation of a connection means 6a.

Compared to the embodiment illustrated in FIG. 1a, the connection member 2 illustrated in FIG. 1c has an opening 12c in the inner boundary surface 4 which is opposite to the openings of the recess 5a, 5b and which extends in the longitudinal direction of the opening 3. Thus, two contact parts 12a, 12b are formed. FIG. 4 shows a longitudinal section through an accommodation part 2a where the extent of the opening 12c which is bounded on both sides by the contact parts 12a, 12b can be seen. An advantage of the indicated embodiment is that two contact regions A1 result, in particular for a curved rod, 1 when the rod 1 is pressed against the contact parts 12a, 12b by the fastener means 6a, 6b which act on the contact regions A3. The cross-section of the recess 3 is formed in a round manner in FIG. 4 so that the contact regions A1 are opposite to the fastener means 6a, 6b. If the cross-section of the recess 3 were, for example, formed in an oval or in an elliptical manner, then contact regions A1 would result which, as shown in FIG. 2d with A1, A2, could be arranged at the sides. If the curved rod 1 were to be inserted into a connection member of FIG. 1a, but with a round recess, then only one contact region A1 would result approximately in the center of the longitudinal extent of the opening or aperture 3.

FIG. 2a shows a side view of a connection member 2 comprising an accommodation part 2a and a connection part 2b with an opening 11 and a recess 5a. The inner boundary surface 4 of the opening is essentially formed in a round manner, however not in a circular manner. From FIG. 2c it can be seen that the inner boundary surface 4 comprises a plurality of curved partial surfaces 4a, 4b, 4c having three different radii of curvature r1, r2, r3, so that in the present embodiment, an egg-shaped shape of the inner boundary surface 4 results. If the radius of curvature r3 of the partial surface 4c disposed opposite to the outlet opening of the recess 5a is chosen to be smaller than the radius of curvature R1 of the rod 1, then, as shown in FIG. 2d, two contact regions A1, A2 extending in the longitudinal direction of the opening 3 result, and thus a three-point contact of the rod 1 results together with the contact region A3 of the fastener means 6a. The shape of the inner boundary surface 4 of FIG. 2a , can, for example, also be formed in a round, an oval or an elliptical manner.

FIG. 2b shows a further embodiment of a shape of an inner boundary surface 4 comprising curved partial surfaces 4b, 4c, 4d with different radii of curvature. In addition, the partial surface 4d has groove-shaped recesses 9 extending in the longitudinal direction of the opening 3. This arrangement of the boundary surface 4d reduces the contact surface to the rod 1 and thereby a greater force per unit of area results, which allows the transfer of a larger force between the connection member 2 and the rod 1. Every form of an inner boundary surface 4, and thus also a round or elliptically formed boundary surface 4, can have groove-like recesses 9 extending, for example, in the longitudinal direction of the opening 3 and/or in the transverse direction of the opening 3, or in a different direction. An advantageous embodiment of the surface structure of the boundary surface 4 can be achieved by a plurality of pyramidal elevations as illustrated in FIG. 5. In the same way, it can be advantageous to provide the rod 1 with a surface structure, for example with a certain roughness as is achieved by for example sandblasting, or for example with groove-shaped recesses. The inner boundary surface 4 of FIG. 2b can also, however, comprise one or a plurality of partial surfaces 4a, 4b, 4c, 4d which have no curvature, i.e. which are formed in a flat manner. Even with this measure, the contact surface between the rod 1 and the boundary surface 4 can be reduced, wherein a level partial surface 4a, 4b, 4c, 4d can also have recesses such as grooves.

FIG. 3 shows a device for the connection of at least two vertebrae with a resilient rod 1. Fixing elements 8, such as bone screws, are anchored in the vertebra 7 and a connection member 2 is secured to the fixing or anchoring element 8 via a clamp nut 10. The resilient rod 1 is secured to the connection member 2 via a fastener means 6a.